TM 8-300 
WAR DEPARTMENT 
TECHNICAL MANUAL 
NOTES ON 
EYE, EAR, NOSE, AND THROAT 
IN AVIATION MEDICINE 
V f TM 8-300 
TECHNICAL MANUAL* 
No. 8-300 
WAR DEPARTMENT, 
Washington, November 26, 19^0. 
NOTES ON EYE, EAR, NOSE, AND THROAT IN 
AVIATION MEDICINE 
Prepared under direction of 
The''Surgeon General 
Section I. General 1-8 
II. Nosei 9-15 
III. Maxillo facial injuries 16-20 
IV. External and middle ear 21-25 
V. Effect of flight on middle ear 26-37 
VI. Anatomy and physiology of inner ear or labyrinth__ 38-18 
VII. Vestibular nystagmus 44r-45 
VIII. Vestibular vertigo 46-55 
IX. Vestibular tests 56-60 
X. Blind flying 61-62 
XI. Miscellaneous ear conditions , 63-68 
XII. General methods and equipment for eye examina- 
tion 69-70 
XIII. Visual acuity 71-79 
XIV. Depth perception 80-89 
XV. Ocular movements 90-119 
XVI. Accommodation 120-126 
XVII. Inspection of the eye 127-138 
XVIII. Color vision 139-155 
XIX. Field of vision for form and colors 156-162 
XX. Refraction 163-171 
XXI. Ophthalmoscopic examination 172-180 
Page 
Appendix. Abbreviations and references 270 
Index *-^5 
Paragraphs 
271818*—40 1 
1 TM 8-300 
1 
MEDICAL DEPARTMENT 
Section I 
GENERAL 
Paragraph 
Mouth 1 
Face 2 
Teeth 3 
Tongue 4 
Ranula 5 
Tonsils . 6 
Pharynx 7 
Larynx 8 
1. Mouth.—a. General.—This organ has four main functions: It 
is the entrance of the alimentary canal; it aids in the mastication of 
food; it has an important role in speech; and it is an auxiliary 
entrance and exit for the respiratory system. 
Practically all defects which would be disqualifying are easily 
seen or are distinguished while watching and listening to the indi- 
vidual talk. Applicants with gross defects of the mouth will rarely 
present themselves for examination, and for this reason the inspec- 
tion of the mouth may frequently be neglected. 
h. Disqualifying defects.— (1) Harelip.—This developmental de- 
fect occurs in a variety of forms varying from a simple defect of the 
lip to a bilateral defect involving the lip, the alveolar ridge of the 
maxilla, and the hard and soft palates. Any extensive defect is 
usually accompanied by some defect in speech even when corrected. 
Obviously, applicants with marked defects of this nature will sel- 
dom present themselves for examination. Certain minor cases which 
have had only the lip involved, and which have been satisfactorily 
corrected so that the resulting scar is not ugly, the function is not 
interfered with, and the speech is normal are acceptable for training. 
(2) Loss of whole or large part of either lip or unsightly mutila- 
tions of lips from wounds, hums, or disease.—Such defects require 
little comment. They are so obvious that they will probably never 
be missed, but occasionally an applicant will appear who has a rather 
severe, unsightly scar or deformity of the upper lip camouflaged 
beneath a mustache; so particular attention should be paid to the 
mouths of applicants who have such ornaments. 
(3*) Tumors of lip.—Hemangioma are frequently located in the 
lower lip. If small and nonprogressive, they may be disregarded. 
The larger ones are disqualifying, both from a cosmetic standpoint 
and because of the possibility of severe hemorrhage following 
trauma. 
2 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 1-2 
TM 8-300 
It is to be remembered that the lower lip is a very frequent site 
for the appearance of epitheliomas, especially in males above the 
fourth decade of life. 
The exact cause for this is not known, but overexposure to sunlight 
and chronic irritations are predisposing causes. Aviators, espe- 
cially in this part of the country, have had extreme exposure of the 
lips to the sun, and they are subjected to special trauma in the use 
of oxygen nipples. Particular attention should be paid to the in- 
spection of the lips in the semiannual examination as these cancers 
can be cured in a large percentage of cases if recognized early. 
2. Face.—a. General.—Inspection of the face is done automati- 
cally during the examination of the eyes, nose, mouth, and ears. 
b. Disqualifying factors.— (1) Extreme ugliness. 
(2) Deformities. 
(a) Large birthmarks. 
(b) Large hairy moles. 
(<?) Extensive scars. 
(d) Mutilations due to injuries or operations. 
(e) Tumors. 
(/) Ulcerations. 
(g) Fistulae. 
1. Parotid. 
£. Bronchial. 
3. Dacryocystitis. 
4. Osteomyelitic. 
(A) Atrophy of part of face, if extensive. 
{{) Lack of symmetrical development. Practically no individual 
has a pure symmetry of the two sides of the face and asymmetry occurs 
in many degrees. Only those which are conspicuous enough to be read- 
ily noticed, or in which the condition interferes with function are dis- 
qualifying. Like ugliness, this is entirely a matter of opinion of the 
examiner. 
(3) Persistent neuralgia, tic doloreaux.—The diagnosis of these 
conditions is obtained from the statements of the patient and they will 
seldom be found. Any paralysis of the muscle of the face manifested 
by a ptosis of the lids, a sagging of the mouth, inability to control 
muscles of expression, or a masking of facial expression are disqualify- 
ing. 
(4) Ununited fractures of the maxillary bones or deformities of 
these bones interfering with mastication or speech or any disease of 
these bones such as extensive exostosis, caries, necrosis, osteomyelitis, or 
cysts are disqualifying. 
3 TM 8-300 
2-3 
MEDICAL DEPARTMENT 
(5) The temporomandibular joint must be free from arthritis and 
have normal function. The conditions affecting the bones of the face 
are usually diagnosed during the dental examination. Occasionally 
an exostosis of the hard palate is seen at the site of fusion. Unless these 
are large and interfere with speech or the surface is ulcerated, they may 
be ignored. Applicants who have large tumors of this nature should be 
temporarily disqualified until the tumor has been removed. 
3. Teeth.—a. General.—As a rule, the examination of the teeth is 
made by the dental officer, but there will be times when a dentist is 
not available and in such cases the examiner should know what the 
dental causes of disqualification are. 
The requirements for applicants for flying training are the same as 
for West Point candidates and are covered in AR 40-100, 
b. Disqualifying factors.—(1) Insufficient number of masticating 
teeth.—The regulations require a minimum of six vital masticating 
teeth above, and six below, serviceably opposing. The principal points 
to look for may be teeth which do not occlude and nonvital teeth. 
Doubtful teeth should be X-rayed. In regard to the number of mas- 
ticating teeth, if a case has an insufficient number of teeth, the un- 
erupted third molar may be counted. If a normal third molar, 
properly positioned and developed is shown, it may be assumed that 
it will have a normal eruption and the candidate may be credited 
with possession of this tooth. In such case the report of physical 
examination will carry an appropriate remark such as “X-ray shows 
normally developed and erupting (specify tooth or teeth).” In 
doubtful cases a duplicate of the X-ray films will be forwarded with 
the physical examination form. This authorization, is important 
because a large majority of our applicants are of the age group in 
which a large number of third molars are still unerupted. 
(2) Insufficient number of antenor teeth.—The regulations require 
a minimum of four natural, vital anterior teeth (incisors and cuspids). 
Again attention is called to the word vital. 
(3) Absence of three adjoining masticating teeth in either side of 
upper or lower jaw.—For example, the absence of the first and second 
bicuspids and the first molar, or the second bicuspid and the first 
and second molars, or the first, second, and third molars in either side 
of upper or lower jaw would mean disqualification. - 
(4) Disfiguring spaces between anterior teeth.—This a., ~ matter of 
judgment of the examining officer and, if questionable, casts would 
have to be made and forwarded to The Surgeon General’s Office for 
decision. 
4 TM 8-300 
3-4 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
(5) Marked irregularity of the teeth.—This also depends on the 
judgment of the examining officer and, if doubt exists, casts would 
have to be forwarded. 
(6) Marked malocclusion.—This again is a matter of judgment. 
The applicant is instructed to close his mouth normally and the rela- 
tionship of the opposing teeth is noted. If there is any marked lack 
of uniformity, the applicant should be sent to a dental officer to have 
casts made for forwarding to the office of The Surgeon General. 
Marked malocclusion has been one of the chief causes of rejection 
of applicants who report to the training center for duty. Also a great 
many cadets reporting have defects which place them in class I 
or II. In case minor defects such as caries, gingivitis, heavy deposits 
of calculus, teeth to be extracted, or other conditions which need cor- 
rection are found, the candidate’s papers should be held pending the 
receipt of a certificate from his dentist to the effect that the defects 
have been corrected. An applicant should be an actual class IV case 
and need but little dental work during the flying training course. 
In the semiannual examination of pilots a rigid inspection of the 
teeth is essential. Rapid changes in temperature and the use of oxy- 
gen nipples are deleterious to fillings and inlays. Frequently the first 
sign of nervousness is detected in the unconscious habits of movements 
of the mouth and tongue and these mannerisms are very often cen- 
tered upon a maloccluded or a roughened tooth. Such a case requires 
not only correction of the dental defect, but mental training as well. 
4. Tongue.—The tongue is an important organ in assisting in 
mastication, speech, and swallowing. It is the site of many abnormali- 
ties of development and these must be judged as to how they affect the 
function. Partial loss, hypertrophy or atrophy, split or rigid tongue, 
adhesions of the tongue to the side of the mouth, or shortening of the 
fren-um of the tongue (tongue-tied) are all disqualifying if they inter- 
fere with function. The tongue is frequently the site of relatively 
benign tumors of the hemangioma or lymphangioma type. If these 
are extensive, they are disqualifying. The presence of glossitis is 
usually ihdicative of some other disease, and such a condition should 
suggest the possibility of pellagra, sprue, pernicious anemia, syphilis, 
tuberculosis, diabetes, nephritis, or poisoning with the heavy metals. 
In the Sco.1 ; annual examination care should be taken to notice the 
first signs of leukoplakia. This condition, which begins first as a 
thin whitish plaque and as it progresses becomes a thickened grayish 
fissured mass, is usually considered as being the result of a chronic 
irritation, such as jagged teeth of improperly fitted dentures or smok- 
ing, particularly pipe smoking where the hot draft of smoke is drawn 
against one spot. There is apparently some relationship to syphilis 
5 TM 8-300 
4-6 
MEDICAL DEPARTMENT 
also, as quite a large percentage of people with leukoplakia have a 
positive Wassermann. These patches may appear on the tongue, on 
either side of the gums, or on the lips. The condition is of extreme 
importance because of the relationship between these plaques and 
carcinoma. Even in the early states the condition is very resistant to 
treatment. 
5. Ranula.—Ranula is a term which has been applied to all cystic 
swellings of the floor of the mouth, whatever their form or origin. The 
origin of the word is uncertain and the term may have arisen from the 
resemblance of the smooth tumor to the belly of a frog or because 
people with large ranulae have a croaking voice. 
The tumors may be cystic swellings of the mucous and sublingual 
glands, cysts of Blandin’s gland, congenital ranulae, acute ranulae, 
traumatic ranulae, or large burrowing multilocular ranulae. They 
probably all arise in the floor of the mouth and from there spread or 
burrow through the muscles of the neck. Many are in connection with 
the submaxillary gland and are due to calculi. Whatever their origin 
or type, the treatment is excision and this is frequently a very tedious 
and complicated procedure. The condition must be corrected before 
the applicant is accepted. 
6. Tonsils.—In the past few years more and more applicants have 
their tonsils present. This is due to the fact that the indiscrimi- 
nate removal of tonsils which prevailed years ago has ceased and now 
the tonsils are removed for a definite reason. 
The following are generally accepted as being indications for 
tonsillectomy: 
a. Recurring attacks of tonsillitis or peritonsillitis. 
h. Interference with respiration or glutition. 
c. Chronic infected tonsils which are considered as the focus of 
infection in certain systemic conditions. 
d. Recurring joint symptoms following attacks of acute or sub- 
acute tonsillitis. 
e. Proof that the tonsils are carriers of diphtheria. 
/. Chronic enlargement of the cervical glands, especially those 
situated near the angles of the jaw, 
g. Recurring attacks of otitis media. (In children under 3 years 
adenoidectomy only is usually done.) 
In all cases in which applicants have tonsils or adenoids the ex- 
aminer will decide whether they should be removed prior to his ac- 
ceptance, bearing in mind the intense nature of the flying training 
course. No applicant should be accepted who will possibly be hos- 
pitalized for some condition which can just as well be corrected be- 
6 TM 8-300 
6-8 
NOTES ON EYE, EAK, ETC., IN AVIATION MEDICINE 
fore he arrives here. Cases with tonsils that the examiner believes 
should be enucleated and in which no other defects are found may be 
temporarily disqualified and upon completion of the treatment or 
operation a certificate may be forwarded by the applicant showing 
that the temporary disqualification has been corrected. 
7. Pharynx.—Under this heading is included the postnasal ade- 
noids. If these are hypertrophied sufficiently or if there is a his- 
tory of otitis media they are a cause of rejection. The hypertrophy 
of the adenoids has a greater significance as regards flying personnel 
because of the location of the nasal end of the eustachian tube in 
their vicinity. Moderate inflammation of hypertrophic adenoid tissue 
may be sufficient to interfere with the normal function of this tube 
with a resulting severe involvement of the middle ear. Occasionally 
in the process of development of the nasopharynx there is an incom- 
plete formation of the postnasal space or an atresia, either total or 
partial. This condition, while hardly to be expected in applicants 
for flying training, is of some differential importance in children. 
Probably many children are subjected to adenoidectomy for the cor- 
rection of mouth breathing when the condition is the result of non- 
development of the postnasal space, which in most cases corrects it- 
self with the growth of the skull. If they are operated upon the 
resulting scar tissue makes the stenosis worse rather than better. 
Any perforation, loss of substance, or ulceration of the hard or 
soft palate, or extensive adhesions of the soft palate to the pharynx 
are cause for disqualification. 
The loss of the uvula which occurs rather frequently as a result 
of excision at the time of tonsillectomy is not to be considered dis- 
qualifying unless it is so extensive as to interfere with speech or 
swallowing. A paralysis of the soft palate, which occurs as a result 
of postdiphtheritic neuritis or in association with central nervous sys- 
tem lesions, apoplexy, embolism, or tumors pressing on the bulb or 
from any other cause is disqualifying. This condition can usually 
be rather easily recognized as the patient has a tendency for fluid to 
regurgitate into the nose and has vocalization difficulties and cannot 
pronounce the word “wrong.” A “b” becomes an “m” and the “d” 
an “n.” In saying “egg” he says “eng.” 
8. Larynx.—The larynx is not routinely inspected, but the pres- 
ence of speech defects, husky voice, hoarseness, a persistent desire 
to clear the throat, dysphonia, or scars on the neck in the region of 
the larynx call for such an examination. The most satisfactory ex- 
amination can be made by the direct method. However, with a little 
practice a good view of the larynx may be had by the laryngoscopic 
mirror. 
7 TM 8-300 
8-10 
MEDICAL DEPARTMENT 
Chronic laryngitis, paralysis, partial or total, of the vocal cords, 
tumors, either benign or malignant, of the larynx or adjacent struc- 
tures are disqualifying. 
Section II 
NOSE 
Paragraph 
General 9 
External nose 10 
Cavity 11 
Obstruction 12 
Septum 13 
Polyps 14 
Accessory sinuses 15 
9. General.—This prominent organ is of extreme importance to 
the flyer. Adequate nasal respiration is essential because of rapid 
changes in altitude and prolonged flight at high altitudes. The 
sense of smell is of secondary importance, but an anosmia is a dis- 
qualifying factor. Furthermore, it is of prime importance that the 
structure of the nose permits adequate ventilation and drainage of 
the accessory sinuses, the nasal lacrimal ducts and the eustachian tubes. 
10. External nose.—The loss of the nose, or any deformity of the 
nose which produces an ugly appearance, or ulceration of the ex- 
ternal nose are causes for rejection. While it would be ideal if all 
Air Corps officers had a classic type of nose with a rectilinear dorsum 
and a horizontal inclination of the base that corresponded to the 
individual’s type of face formation, such a Utopian condition is not 
possible. The main concern in this examination is to select normally 
functioning noses. The shape and form of the external nose does 
have an important clinical aspect, however, as this prominent organ 
is frequently grossly mutilated in airplane and auto crashes. In 
these cases the immediate attempt at restoration of the normal con- 
tour is essential. This will be discussed later. 
The external nose is a constant source of irritation to most flying 
trainees during the early period of training. There is a considerable 
blast of air on the face due to the structure of the primary training 
airplane and this, associated with the unaccustomed use of goggles 
which press rather firmly over the infratrochlear, the supratrochlear 
and nasociliary nerves, produces a very annoying itching sensation. 
The prominent position of the nose and the entire lack of protec- 
tion from the sun that the present helmet gives, results in many 
cases of severe sunburn. This especially is true in personnel flying 
long missions in the tropics. A good prophylaxis against this con- 
dition is to paint the nose prior to take-off with a 40 percent solution 
of compound tincture of benzoin in alcohol. 
8 TM 8-300 
11-12 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
11. Cavity.—a. Description.—The nasal cavity is a fairly simple 
inlet and exit for the respiratory system. It consists of a passage- 
way separated, normally into two equal halves by the nasal septum. 
In the anterior portion, just inside the vestibule, we have a filter for 
the removal of gross dust and the prevention of entry of foreign 
objects such as insects. This filter is formed by the cilia of the in- 
ternal epithelial-lined vestibule. Further protection is afforded by a 
backfiring mechanism, a fairly simple reflex nervous action, in which 
foreign particles or irritants excite the act of sneezing. Within the 
nose on the lateral wall of each half we have three baffle plates with 
automatic thermostatic and hygroscopic control, the turbinate bodies. 
They are named from above downward: the superior (very small, 
not visible); the middle (somewhat larger and visible); and the in- 
ferior (the largest and plainly visible on examination). These tur- 
binate bodies are composed of a bony base, the upper two outgrowths 
from the ethmoid bone, while the lower one is an independent osseous 
unit. They are covered with a mucoperiosteum and contain erectile 
tissue. The space below each turbinate is called a meatus and desig- 
nated from above downward as superior, middle, and inferior. The 
superior meatus has the openings of most of the posterior ethmoid 
cells. The middle meatus on its lateral wall has the opening of the 
maxillary sinus, while in the suprabulla fossa the middle ethmoid 
cells have their ostia. In the frontal recess the frontal sinuses and 
the anterior ethmoid cells have their exits. In the inferior meatus 
about 30 to 40 millimeters from the nares is located the ostium of 
the nasolacrimal duct. Posteriorly the nasal passages communicate 
with the nasopharynx. 
b. Functions.— (1) It is the air passageway for the respiratory 
system with the important subsidiary function of warming and 
moistening the inspired air, 
(2) It is the organ of smell, the direction of the inspired air bring- 
ing a fairly large quantity over the end organs of the olfactory nerve. 
(3) It is the drainage area of the nasolacrimal duct and the nasal 
accessory sinuses. These sinuses are integral parts of the nose and 
aid in conditioning the inspired air. 
12. Obstruction.—Clinically the two most common symptoms of 
nasal disorder are— 
a. Nasal obstruction and an undue amount of discharge from the 
nose. 
b. Discharge of pus or other symptoms of empyema of the sinuses. 
The general conditions which cause nasal obstruction are fre- 
quently overlooked. Often it is the result of venous stasis with a 
9 TM 8-300 
12-13 
MEDICAL DEPARTMENT 
resulting congestion and hypertrophy of the mucous membranes and 
turbinates. Common causes are overeating, overdrinking, lack of 
exercise, fear of cold, and the use of too heavy clothing. 
13. Septum.—The septum consists of a partition composed of 
cartilage and bone covered with mucous membrane, which separates the 
two nasal passages. Deformities of the septum result in the most 
frequent cause of rejection of applicants in the nose and throat 
examination. 
The location of the nose makes it particularly liable to trauma and 
these repeated blows from childhood onward result in a variety of 
derangements of the constituent parts of the septum. Naturally devia- 
tions occur more frequently in males than in females and are more 
common in adult life. However, children do fall on their noses, and so 
it is not surprising to find that over 30 percent of children at the age of 
seven have some deviation. The finding of a perfectly normal septum 
in our examination is somewhat of a rarity, and the question of how 
severe the deformity must be to cause rejection must be considered 
from the angle of impairment of function. 
a. Available air space.—To say that the applicant should have four- 
fifths of his natural air space would be a good conservative basis. It 
is to be remembered that what appears to be an adequate space under 
normal conditions will, under the influence of congestion, be practically 
closed, compensatory hypertrophy of the turbinate on the concave side 
of the depression being of very common occurrence. 
h. Location of deviation.—Deviations which occur in the region of 
the drainage areas of the sinuses should be corrected. These occur 
principally high and posterior where they are not so readily seen. 
c. Deviations which impinge on adjacent structures.—The most com- 
mon is a spur formation impinging on the inferior turbinate. Fre- 
quently these result in chronic ulceration of the turbinate, with crust 
formation. A common type of deviation is that in which the anterior 
cartilage and vomer are dislocated from the sulcus of the nasal crest, 
resulting in a long overhanging shelf on one side. In repairing this 
condition it is well to remember that you will have four layers of 
mucous membrane due to its folding. 
d. Deviations which cause ulceration or potential hemorrhage.— 
Very sharp angular deviations, sharp spurs, large spurs, and deviations 
of such an extent that the mucosa is stretched and becomes atrophic are 
frequently the sources of ulcerations and hemorrhages. These must be 
corrected. 
The operations for the correction of these conditions of the septum 
are well known and they do not present a major risk. All defects of 
10 TM 8-300 
13-15 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
this nature to be corrected prior to acceptance and, as in the cases who 
require tonsillectomy, they are disqualified until the correction is made. 
In these cases it is a good idea to make enough of the total examination 
to be fairly certain that the applicant is otherwise qualified, as it is 
very embarrassing to send an applicant to have his nose operated and 
when he returns with a very fine looking nose to find he has a vision 
of, say, 20/50. 
14. Polyps.—Polyps are usually seen in the region of the middle 
turbinate and consist of polypoid degenerations of the turbinate 
body, the result of prolonged irritation by discharges, or as protru- 
sions of polypoid membranes from the ethmoid or maxillary sinuses. 
Most polyps are complications of chronic sinus disease, and unless 
it can be proved to be a benign simple polyp and that the sinuses are 
entirely free from infection, the case is disqualified. 
15. Accessory sinuses.—The nasal sinuses should be considered 
as integral parts of the respiratory system. They are outpouchings 
of the nose, the lining mucous membrane of which is continuous 
with that of the sinuses. In this short outline we cannot attempt a 
discussion of sinus disease and its treatment, but all examiners should 
be familiar with the objective signs of chronic sinus disease, as acute 
or chronic infections of the sinuses are disqualifying. 
Precautions are necessary in considering a positive history of sinus 
disease as many patients have been told that they have sinusitis 
when they have only the normal inflammation of the sinuses that 
accompanies practically all cases of acute rhinitis. For some reason, 
many individuals consider it rather an honor to have a history of 
sinusitis and recall these diagnoses with pride. 
a. Objective signs of chronic maxillary sinusitis.— (1) A dis- 
charge of pus from the nose which may be foul. 
(2) Pus beneath the midturbinate which reappears after removal. 
(3) Boggy appearance of the turbinates with a possible polypoid 
degeneration of the midturbinate or even a blocking of the nose with 
definite polypi. 
(4) Darkness on transillumination. 
b. Objective signs of frontal and ethmoid sinusitis.—Ethmoiditis 
may occur without frontal sinus involvement but frontal sinus in- 
volvement without ethmoiditis is quite rare. 
(1) Discharge of pus from the nose and collections of pus beneath 
the midturbinate. In a typical case the discharge is more apt to be 
constant than in the case of maxillary disease. 
(2) Polypoid degeneration and polyp formation. 
(3) Tenderness over the sinuses. 
(4) Oedema of the lids. 
11 TM 8-300 
15-17 
MEDICAL, DEPARTMENT 
The presence of these symptoms calls for further study such as 
X-ray of the sinuses or a diagnostic puncture. All cases which show 
a polypoid degeneration of the mucous membrane about the middle 
turbinate or the presence of polyps should be considered as probable 
sinus cases unless it can be shown that the sinuses are negative and 
the case is one of a simple benign polyp. 
Section III 
MAXILLO FACIAL INJURIES 
Paragraph 
General 16 
Lacerations 17 
Injuries to nose 18 
Fractures of facial bones 19 
Injuries to orbit 20 
16. General.—The repair of injuries about the face is closely 
associated with ophthalmic and otorhinological surgery. The proper 
understanding of the fundamental therapy in these cases is essential 
to the flight surgeon. 
In airplane crashes, as in auto crashes, injuries to the face and head 
occur in a large percentage of cases. If the trauma is not fatal, it is 
the duty of the flight surgeon to immediately start the repair of these 
defects. It has been stated that “except trauma of vital organs and 
their essential coverings, the final outcome of no injury is so directly 
dependent upon early proper care as injury of the face.” 
The commonest injuries following crashes are— 
a. Lacerations of skin of face varying from small abrasions to 
extensive loss of tissue. 
b. Injuries to the nose. 
c. Fractures of mandible, maxilla, and malar bones. 
d. Injuries to orbit and its contents. 
17. Lacerations.—Immediate suture after debridement naturally 
offers the best chance of a good scar, and extensive lacerations should 
be treated as emergencies. It is of utmost importance in the repair 
of face injuries to preserve all possible tissue and in placing sutures 
those for tension should be placed in the deep structures. The under- 
lying structures must be repaired and returned as near as possible to 
their original position before suturing the overlying skin. 
Lacerations of a scooped nature with beveled edges require imme- 
diate suture. Other types of lacerations which require immediate 
suture are those involving all narrow double-surfaced flaps, such as 
the border of the lips and the ear or eyelids, these to be sutured on 
12 TM 8-300 
17-19 
KOTES OK EYE, EAK, ETC., IK AYIATIOK MEDICIKE 
both sides if possible. Any laceration into or through substance of 
the ear, especially if there is a large flap attached by a narrow pedicle, 
all cuts or tears of the nasal skin and cartilages including the septum. 
18. Injuries to nose.—Injuries to the nose are to be treated as 
emergencies, with replacement and mobilization as soon as possible. 
Neglect of these injuries results in deformities, obstruction to breath- 
ing, and possible involvement of the sinuses. 
Depressed fractures of the nose are usually rather easily replaced 
by pressure from within. Care should be taken to examine the septum 
for evidence of dislocation from the maxillary groove. In replacing 
and remodeling these nasal fractures some form of anesthesia is neces- 
sary. Local intranasal cocain packs with novocain injection of the 
nasal labial angles and the infraorbital nerves are very satisfactory. 
Short inhalation anesthesia is sometimes sufficient. Also, if the patient 
is in good condition, the use of intravenous anesthesias gives excellent 
results. 
Many of these nasal repairs retain their position without support. 
In other cases some form of splinting is advisable. The appliance 
of Straith for the maintenance and correction of severe nasal and labial 
deformities is one of the best. 
In regard to early treatment of nasal injuries, a case of complete 
amputation of the nose by a butcher knife has been reported in which 
the amputated part was resutured and the nose saved. 
19. Fractures of facial bones.—Fractures of the mandible when 
teeth are present are best treated by interdental wiring. This is 
also the method of choice of the neck, the condyles, and the inter- 
muscular part of the ramus. In maxillary fractures which involve 
the alveolar bone the displaced fragments with attached teeth should 
be replaced and held by means of wires or other appliances. A com- 
mon type of maxillary fracture seen after airplane crashes consists 
of a mashed posterior displacement with comminution and compres- 
sion. These are best replaced by prolonged elastic traction between 
an extension bar on a head cap and some form of dental appliance 
attached to the teeth of the maxilla. Malar bone fractures are rather 
common and frequently overlooked. They usually take the form of 
a fracture dislocation of t' e malar from the maxilla, the frontal, and 
the zygomatic arch. The X-ray picture may be frequently misin- 
terpreted. Palpation of the orbital margin will reveal a depressed 
defect of the margin. These fractures require early reduction for 
defects here result in a change in the position of the eyeball which 
is most disfiguring and in which binocular vision is usually impos- 
sible. Several methods for the reduction of this type of fracture 
13 TM 8-300 
19-22 
MEDICAL DEPARTMENT 
are used, namely, the intraoral method, the intramaxillary sinus 
method, the hook method, and the Gillies method. Gillies is usually 
the most satisfactory. A long slender bone elevator is introduced 
through a temporal skin incision and carried downward over the 
temporal muscle and beneath the zygonatic arch and then, by prying, 
the bone is raised into position. Usually no support is necessary to 
maintain position. 
20. Injuries to orbit.—Injuries about the eyes are frequent fol- 
lowing crashes, the most typical being a circular or partial circular 
tearing laceration resulting from the driving inward of the rim of 
the goggle. Particular attention should be paid to the possibility 
of laceration of the levator palpebral and to laceration involving both 
surfaces of the lids. Early suture will prevent the development of 
ptosis, entropion, or ectropion. Injuries involving the eyeball will 
not be discussed in this outline. 
Section IV 
EXTERNAL AND MIDDLE EAR 
General : 21 
Tympanic membrane 22 
Hearing tests 23 
Pitch — 24 
Intensity 25 
Paragraph 
21. General.—The total loss of an external ear, marked hyper- 
trophy or atrophy, or disfiguring deformity of either ear such as 
results from lacerations, burns, or tumors are disqualifying. Atresia 
of the external auditory canal or tumors involving this canal are 
disqualifying. Otitis media, acute, chronic, suppurative, or ca- 
tarrhal is disqualifying. In respect to acute otitis media at least 6 
months must have elapsed without remission or sequelae in order 
to qualify an original applicant. 
A mastoidectomy is disqualifying. In this disease it would seem 
logical to differentiate between a simple posterior drainage of the 
antrum of the mastoid and an extensive destructive cure of an osteo- 
myelitis of the mastoid process. At the jmesent time it is the policy 
to grant waivers in cases of simple mastoidectomies which have nor- 
mal hearing, normal vestibular responses, and in which the scar is 
not disfiguring. 
22. Tympanic membrane.—The appearance of the tympanic 
membrane and the acuity of hearing give the examiner the only ob- 
jective signs of past or present disease of the middle ear. The mem- 
brane in a large majority of cases is readily seen if the cerumen and 
14 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 22-23 
TM 8-300 
debris is cleared from the external auditory canal. Pathology is 
usually very clearly seen, especially with the newer magnifying self- 
illuminated otoscopes. 
In examining the tympanic membrane, the following conditions 
are noted: 
Luster or color. 
Transparency. 
The cone of light. 
Edema. 
Bulging. 
Retraction. 
Thickening. 
Tension. 
Perforations. 
Scars, extent. 
Adhesions. 
Calcium deposits. 
Appearance of the malleus. 
Appearance of Shrapnell’s membrane. 
Movability of the drum. 
Occasionally a cadet appointee lias a chronic otitis media with a 
perforation of the. drum. The failure of the examiner to see this is 
possibly due to failure to clean properly the canal of the discharge 
and debris so that a clear view may be had, and the fact that the con- 
dition may be quiescent and the perforation not recognized. At times 
in very large perforations, when the ear is quiet, the posterior wall of 
the middle ear will give the appearance of a drum membrane if 
examined casually. 
Retractions of the membrane are significant in that they may repre- 
sent the sequelae of old otitis media or the lack of patency of the 
eustachian tube. Cases showing a retraction must have the eusta- 
chian tube catheterized to demonstrate the patency. Obstruction to 
the eustachian tube is a disqualifying defect. 
Scars, thickening, loss of luster, adhesions, and deposits of calcium 
are all indicative of past inflammation. If extensive, they are dis- 
qualifying. Careful examination wull usually show hearing defects 
in these cases. 
23. Hearing- tests.—Regulations state that the hearing in appli- 
cants must be 20/20 in each ear. That is, they must hear at 20 feet the 
whispered voice, this whisper to be made with the residual air, and 
among other symbols the numbers 66, 18, and 23 will be used. This 
is to determine roughly the auditory acuity in different pitches. In 
15 TJVE 8-300 
23-25 
MEDICAL DEPARTMENT 
those already qualified the hearing must be at 8/20 in each ear or 
15/20 in one ear and 5/20 in the other. The regulations further state 
that when an audiometer is available it will be used, and for Class I 
the average hearing loss must not be more than 15 percent. 
The usual examination for hearing is rather crude and nonstandard- 
ized. No two people use the residual air to make whispered tones in 
the same pitch or the same intensity. Proper attention to the use of a 
quiet room is seldom observed, and on the whole hearing tests as such 
give only a rough idea of the auditory sense. 
The hearing sense is actually very discriminative and responds 
through a vast range of pitch and intensity. These two factors are 
the main components in sound, and while actually we seldom experi- 
ence a sound of one pitch it does give a definite point for the recording 
and observation of hearing changes. 
24. Pitch.—By pitch we mean the number of double vibrations 
per second making up the sound. This component is fairly easy of 
measurement. In the human ear the range runs from 20 as the lower 
limit to about 20,000 as the upper limit. Under average conditions, 
except for music, we have very little use for any hearing above 18,000. 
Even 18,000 is seldom heard by people who have reached middle age 
and by the age of 40 the upper limit has dropped to about 15,000; 
between 55 and 65 the upper limit has dropped to approximately 10,000 
to 12,000, and at 75 the upper limit is seldom above 8,000. 
The human ear hears best in the range between 500 and 5,000 vibra- 
tions, and this is also the most important range of the human voice. 
Specifically, for aviation, the tones around 1.024 are important as this 
closely corresponds to the radio beam signal. 
25. Intensity.—a. General.—Unlike pitch, intensity of sound is 
difficult to measure. In all English-speaking countries the decibel 
is the standard unit for the measuring of sound intensities. A decibel 
is a unit which represents a definite pressure upon a definite area of 
drum membrane. The unit is logarithmic. There is a marked varia- 
tion in the amplitude of vibration between sounds which are just barely 
audible and the upper threshold where sound becomes painful. Knud- 
sen and Jones state that for sounds which are just barely audible in 
the range of 1,000 to 4,000 vibrations per second the pulsations of the 
sound waves within the external canal are so small that the amplitude 
of vibration of the drum membrane is only about one-billionth of an 
inch. In response to ordinary conversation the amplitude of vibra- 
tion of the drum membrane is about one-millionth of an inch, or about 
1,000 times greater than that of barely audible sound. In response to 
painfully loud sounds the drum membrane has an amplitude of vibra- 
16 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
25 
tion of about one-thousandth of an inch. That is about 1,000,000 
times the amplitude of a barely audible sound. From the barely 
audible sound to the painfully loud sound, therefore, the amplitude 
of vibration of the drum membrane increases about one millionfold. 
Since the energy of vibration is proportional to the square of the 
amplitude, the intensity of a painfully loud sound is a million times 
the intensity of a barely audible sound, 
1). Hearing tests.—At the present time the audiometer represents the 
most satisfactory method for the testing of hearing. However, it is 
essential that the hearing tests be done in as nearly a soundproof 
room as possible. If an applicant is tested in a noisy room it is not 
the testing of his hearing ability, but the testing of the threshold of 
hearing above the threshold of noise in the room. The findings are 
of little value to the examiner and if disqualifying are unfair to the 
examinee. 
In experienced pilots a practical test of hearing ability is indicated. 
No such test is in use at the present time. Primarily it must be deter- 
mined whether a pilot is able to hear and understand radio messages 
and signals. Experience and practice are important factors in the 
distinguishing of radio messages and many individuals who have very 
definite loss of hearing for ordinary conversation are still very effi- 
cient in using radio. Also the volume of the radio may be easily in- 
creased. Some form of a radio test, using a simulated broadcast under 
adverse weather conditions, would satisfactorily solve the problem of 
the hard-of-hearing pilot. 
c. Range of sound.—The following table shows samples of the 
range of noise expressed in decibels: 
Energy units 
Decibels 
Examples 
10, 000, 000, 000, 000 
130 
Threshold of painful sound. 
1, 000, 000. 000, 000 
120 
Artillery gunfire. 
100, 000, 000, 000 
no 
Airplane cabin (not soundproofed). 
10, 000, 000, 000 
100 
Subway car. 
1, 000. 000, 000 
90 
Auto horn. 
100, 000, 000 
80 
Tabulating machine room. 
10, 000, 000 
70 
Stenographic room. 
1, 000, 000 
60 
Average general office. 
100. 000 
50 
Average quiet office. 
10, 000 
40 
Average residence. 
1, 000 
30 
Quiet farmhouse. 
100 
20 
Underground vault. 
10 
10 
One’s own heart beat. 
1 
0 
Absolute stillness. > 
271818°—40 2 
17 TM 8-300 
2G-27 
MEDICAL DEPARTMENT 
Section V 
EFFECT OF FLIGHT ON MIDDLE EAR 
Paragraph 
General 26 
Anatomy 27 
Physiology I 28 
Terminology 29 
Definition 30 
Etiology 31 
Symptomatology 32 
Diagnosis 33 
Complications : 34 
Treatment 35 
Pathology 36 
Summary 37 
26. General.—Those familiar with aviation medicine are well 
aware that airplane pilots suffer more frequently from disturbances 
of the middle ear than from all other occupational diseases combined. 
The phenomenal growth of commercial air transport, which carried 
approximately one million passengers in 1936, makes this problem 
of interest and importance to the general medical profession, for 
airplane passengers are exposed to the same influences as the pilots 
during flight and in most instances are much more adversely affected. 
Since the. deleterious effects of flight on the middle ear depend 
entirely on the peculiar structure and functioning of the eustachian 
tube, a brief anatomic, normal physiologic, and special physiologic 
review of the latter structure will be presented first, followed by a 
discussion of the new clinical entity “aero-otitis media.” 
27, Anatomy.—a. General.—The eustachian tube is a slitlike, 
potential tube extending from the middle ear to the nasopharynx. 
It is formed of bone, cartilage, and fibrous tissue. 
h. Bony 'portion.—The bony portion begins at the upper part of 
the anterior wall of the tympanic cavity and. gradually narrowing, 
passes downward, forward, and mediad. for about 12 millimeters, 
ending at the angle of the junction of the squamous and petrous por- 
tions of the temporal bone, 
c. Cartilaginous portion.—The cartilaginous portion of the tube 
extends from the bony portion to the nasopharynx. This section is 
about 24 millimeters in length and is formed of a triangular plate 
of elastic fibrocartilage with its apex attached to the bony portion 
and its base placed directly under the mucous membrance of the naso- 
pharynx, where it forms a prominence, the torus tubarius. The upper 
edge of the cartilage is bent laterally and takes the form of a hook 
18 TM 8-300 
27 
KOTES OK EYE, EAR, ETC., IK AVIATIOK MEDICIKE 
on cross section, open below and laterally. These walls of the canal 
are completed by fibrous tissue. 
(1. Lumen.—The lumen of the eustachian tube, is narrowest at the 
junction of the bony and cartilaginous portions, the isthmus, and 
expanding rapidly in both directions reaches its largest diameter at 
the pharyngeal orifice. At rest, the lumen of the cartilaginous por- 
tion of the tube is a vertical slit with its walls opposed. 
e. Tissue.—The mucous membrane of the eustachian tube is a 
direct extension of that of the nasopharynx and continues backward 
to line the middle ear completely. The mucous membrane of the 
bony portion of the tube is thin, but in the cartilaginous portion it 
is thick and very vascular, contains numerous mucous glands and is 
composed of ciliated columnar cells. Near the mouth of the eusta- 
chian tube is a variable amount of adenoid tissue known as Gerlach’s 
or tubal tonsil. The pharyngeal ostium of the eustachian tube is 
located high up on the lateral wall of the nasopharynx. This opening 
is triangular, bounded behind by the torus tubarius and in front by 
the nasal cavity. 
/. Musculatum.—The muscles that are attached to the eustachian 
tube and their actions are as follows: 
(1) Levator veil palatine.— (a) Origin.—Inferior aspect of the 
pyramidis ossis temporalis and from the lateral end of the medial 
lamina of the eustachian tube. 
(6) Insertion.—Downward medially and forward parallel to the 
inferior margin of the medial lamina of the eustachian tube, uniting 
in the soft palate with the corresponding muscle of the opposite side. 
(c) Action.—Elevates the soft palate, narrows the eustachian 
ostium, and dilates the isthmus. 
(2) Tensor veli palatini.— (a) Origin.—Scaphoid fossa of the 
sphenoid bone, lateral and membranous lamina of the eustachian tube, 
and angular spine of the sphenoid bone. 
(h) Insertion.—The fibers run downward and forward around the 
sulcus of the pterygoid hamulus and, radiating mediad into the soft 
palate, attach to the hard palate and to the corresponding muscle of 
the opposite side. 
(c) Action.—Tenses the soft palate and opens the eustachian tube. 
(3) Salpingopharyng&us.— (a) Origin.—Inferior part of the os- 
tium of the eustachian tube. 
(h) Insertion.—Blends with the posterior fasciculus of the pharyn- 
gopalatinus muscle. 
(c) Action.—Raises the upper and lateral parts of the pharynx; 
opens the ostium of the eustachian tube. 
19 TM 8-300 
28 
MEDICAL DEPARTMENT 
28. Physiology.—a. Normal.—The eustachian tube drains the 
middle ear and ventilates it. The motion of the cilia and the flutter- 
valve like action of the tube favors the motion of material from the 
ear to the nasopharynx and opposes motion in the opposite direction. 
The tube, while normally closed, is opened by contraction of its dilator 
muscles, and at such times any air pressure differential existing between 
the middle ear and the atmosphere is equalized. This contraction may 
occur during swallowing, yawning, and other similar physiologic acts. 
b. /Special.— (1) Altitude-pressure relationship.—Aircraft flights 
involve changes in altitude, and this in turn involves changes in atmos- 
pheric pressure, the relationship between the two being shown in figure 
1. It is to be noted that, with ascent, equal changes of pressure in- 
Figure 1.—Altitude-pressure curve. 
volve increasing intervals of altitude. The rates and degrees of atmos- 
pheric pressure changes during flight depend on the rates and degrees 
of ascent or descent, and these factors become important when it is 
remembered that the ear is an air-filled, closed cavity with pressure 
equalization possible only when the eustachian tube is opened. 
(2) Results of laboratory investigations.—Laboratory investiga- 
tions of the physiology of the eustachian tube under marked variations 
of atmospheric pressure were carried out on five healthy men, pressure 
variation rates being from 5.4 to 27 millimeters of mercury per minute 
(200 to 1,000 feet per minute) through pressure ranges of from 760 
to 141 millimeters of mercury (0 to 40,000 feet altitude). The results 
of this study were briefly as follows ; 
20 TM 8-300 
28 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
Beginning at sea level pressure and decreasing the pressure at a 
constant rate, a pressure change of from 3 to 5 millimeters of mercury 
(110 to 180 feet altitude) was required before any effect was perceptible 
in consciousness. At this point there appeared a slight sensation of 
fulness in the middle ears and examinations showed the tympanic 
membranes to be slightly bulged. This bulging and the sensation of 
fulness increased with the decreasing of pressure until at 15 milli- 
meters of mercury (500 feet altitude) differential there was a sudden 
annoying “click” heard and felt in the middle ear, the drum snapped 
back to, or almost to, normal position, and the sensation of fulness 
disappeared. The eustachian tube had been forced open by the excess 
pressure in the tympanic cavity and the ear pressure relieved by a sud- 
den rush of air from the ear to the nasopharynx. 
During the remainder of the pressure decrease this cycle was repeated 
except that all succeeding “clicks” occurred at intervals of only 11.4 
millimeters of mercury (435 feet altitude) pressure change. This in- 
dicated that it requires 15 millimeters of mercury excess pressure in 
the middle ear at sea level conditions to force the eustachian tube open, 
and that it remains open until the pressure is reduced to about 3.6 milli- 
meters of mercury, when it again closes, leaving 3.6 millimeters of mer- 
cury (130 feet altitude) excess pressure in the ear. It had been as- 
sumed that, since the pressure altitude curve is not a straight line (fig. 
1), the eustachian tube would open at equal intervals of pressure but at 
increasing intervals of altitude during ascent. Actually the reverse 
was found to be true, the tubes opening at 425-foot intervals (except 
the first), which amounts to 11.4 millimeters of mercury pressure at sea 
level but only 3.5 millimeters at 40,000 feet. The explanation of this 
phenomenon is probably based on the fact that air of the higher alti- 
tudes, being less dense, passes more readily through the eustachian 
tubes. These figures are averages based on repeated tests. Actually 
there was considerable variation between individuals and in the same 
individual. These variations ranged from 5 to 30 millimeters at sea- 
level conditions, but the averages for individuals were remarkably 
constant. 
When the atmospheric pressure was increased instead of decreased, a 
totally different effect was obtained. Here the eustachian tube, acting 
like a flutter-valve, remained closed under all degrees of pressure (one 
subject tested to —470 millimeters of mercury pressure) and the tym- 
panic membrane finally ruptured. 
In the course of these studies, swallowing and other voluntary ef- 
forts to open the eustachian tubes were suppressed. However, in a 
subsequent series of tests it was found that opening the eutachian tubes 
21 TM 8-300 
28-31 
MEDICAL DEPARTMENT 
by voluntary effort immediately equalized the ear pressure completely 
except that, after a negative pressure of from 80 to 90 millimeters of 
mercury or more had developed in the tympanic cavity, it was then 
impossible for the eustachian muscles to overcome the negative pressure 
which held the fibrocartilaginous portion of the eustachian tube tightly 
collapsed, and it was then necessary to decrease the atmospheric pres- 
sure below that point before the eustachian tubes could again be volun- 
tarily opened. 
29. Terminology.—Since the condition being discussed is already 
a recognized occupational disease and seems destined to become of 
general professional concern, it seems logical to suggest a proper 
terminology. 
In the United States the term “aviator’s or aviation ear” has be- 
gun to appear in the literature, while in Germany the terms “baro- 
trauma” and “tonetrauma” have been suggested. The former are 
obviously unsuitable and the latter may be criticized as not being 
descriptive of the disease. We therefore suggest “aero-otitis media” 
(aero, combining form from the Greek app, akpos, air, + otic, Greek 
utlkos, pertaining to the ear, + itis, Greek -ms, inflammation of) as 
suitable descriptive term for the new clinical entity about to be 
described, and that term will be used throughout the remainder of 
this paper. 
30. Definition.—Aero-otitis media is an acute or chronic, trau- 
matic inflammation of the middle ear caused by a pressure differ- 
ence between the air in the tympanic cavity and that of the surround- 
ing atmosphere, commonly occurring during changes of altitude in 
airplane flights and characterized by inflammation, discomfort, pain, 
tinnitus, and deafness. 
31. Etiology.—Aero-otitis media is due to the lack of ventilation 
of the middle ear during changes of atmospheric pressure to the extent 
that the tympanic cavity is traumatized. There are two principal 
causes of improper middle ear ventilation: one a failure to open the 
eustachian tube voluntarily when necessary, the other the inability to 
open it. 
Failure to open the eustachian tubes during changes in altitude in 
aircraft flights is most often due to ignorance of the necessity to do so 
but may be due to carelessness or to being asleep or may arise from 
the influence of analgesics or anesthetics or from coma. The first two 
of these instances usually occur among inexperienced pilots and pas- 
sengers. the third in sleeper airplanes, and the last group on ambu- 
lance planes. 
22 TM 8-300 
31-32 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
Inability to ventilate the middle ear voluntarily is much more 
prevalent than is generally recognized. Some of the most frequent 
causes of eustachian stenosis are acute and chronic infections of the 
upper respiratory tract, nasal obstructions, sinusitis, tonsillitis, tumors 
and growths of the nose and nasopharynx, paralysis of the soft palate 
or superior pharyngeal muscles, enlargement of the pharyngeal or 
tubal tonsil, inflammatory conditions of the eustachian tube or middle 
ear, scar tissue about the ostium of the eustachian tube following 
adenectomy, and malposition of the jaws. 
The latter two conditions have but recently been recognized. Con- 
siderable scar tissue about the pharyngeal ostium of the eustachian 
tube sometimes occurs as the result of adenectomy when the adenotome 
had been allowed to pass too far laterally, causing trauma or lacera- 
tion to the torus tubarius. 
The effect of malposition of the mandible in relation to stenosis of 
the eustachian tube was first reported by Costen1 and later applied 
to aviation by Willhelmy.2 They showed that in individuals with 
edentulous mouths, ill-fitting dental plates, marked overbite, malocclu- 
sion, worn or lack of molar teeth either unilateral or bilateral or with 
any other condition in which there was a shortening of the vertical 
position of the lower jaw a compression-stenosis of the eustachian 
tube was likely to occur from a relaxation of the surrounding soft 
tissues. 
33. Symptomatology.—The symptoms of aero-otitis media de- 
pend on the duration, frequency, and severity of the trauma sustained. 
a. Aero-otitis media, acute.— (1) Subjective symptoms.—Positive 
pressures of from 3 to 5 millimeters of mercury in the middle ear are 
perceptible in consciousness to most individuals as a feeling of fullness 
in the middle ear. At about 10 to 15 millimeters of mercury pressure 
the feeling of fulness is distinct and somewhat annoying and affects 
the hearing by imparting a distant sound and a lessened intensity. 
Pressures between 15 and 30 millimeters of mercury usually increase 
the discomfort and may be accompanied by tinnitus. The latter is 
of a steady hissing or roaring character or crackling and snapping. 
In some individuals there may be actual pain and vertigo of a mild 
nature. Above 30 millimeters of mercury pressure in the middle ear 
there is increasing pain, tinnitus and vertigo, which finally becomes 
unbearable. 
1J. B. Costen, “A Syndrome of Ear and Sinus Symptoms Dependent upon Disturbed 
Function of the Temporomandibular Joint,” Annals of Otology, Rhinology, and Laryngol- 
ogy, 43 : 1 (March), 1934. 
2 G. E. Willhelmy, “Ear Symptoms Incidental to Sudden Altitude Changes and the 
Factor of Overclosure of the Mandible : Preliminary Report,” United States Naval Medi- 
cal Bulletin, 34 : 533-541 (Oct.), 1936. 
23 TM 8-300 
32 
MEDICAL. DEPARTMENT 
In normal cases about 15 millimeters of pressure is sufficient to force 
air out through the eustachian tube, which relieves the pressure in the 
tympanic cavity and consequently the accompanying symptoms. 
However, this relief is initiated by an annoying “click,” which is 
both felt and heard as the drum snaps back to normal position. In 
stenosis of the tube the pressure required to force it open varies with 
the degree of stenosis. In these cases the pressure may be relieved 
gradually over a period of time instead of instantaneously, and a 
greater amount of pressure remains in the middle ear after the tube 
has again closed. 
In descent, in which the atmospheric pressure is increasing and 
the pressure in the ear becomes negative, the symptoms are the same 
as already described except that the pressure is never relieved through 
its own force acting on the eustachian tube because of the flapper- 
valve like action of the latter. For this reason the greatest difficulty 
usually occurs during descent in aircraft, and the highest pressure 
differentials have been seen and studied experimentally under this 
condition. At about 60 millimeters of mercury negative pressure the 
pain in the ear is severe and resembles that of acute otitis media. The 
tinnitus is marked and there is usually vertigo with beginning nausea. 
At from 60 to 80 millimeters of mercury negative pressure the pain 
is very severe and radiates from the ear to the temporal region, the 
parotid gland, and the cheek. Still higher pressures produce agoniz- 
ing pain, which seems to localize not in the ear but deep in the sub- 
stance of the parotid gland. Deafness is marked and vertigo and 
tinnitus usually increase, but the latter may disappear. At between 
100 and 500 millimeters of mercury pressure the tympanic membrane 
ruptures. 
This occurrence is a dramatic episode in which the patient feels “as 
though hit along the side of the head with a plank,” a loud explosive 
report is felt and heard in the affected ear, there is a sharp piercing 
pain on the affected side, vertigo and nausea become marked, and col- 
lapse or generalized shock follows. With rupture of the tympanic 
membrane the acute pain quickly subsides, but a dull ache persists 
for from 12 to 48 hours. Hearing is distinctly diminished and vertigo 
and nausea may persist for from 6 to 24 hours. 
With both positive and negative pressures, voluntarily opening 
the eustachian tube will immediately relieve all acute symptoms; but 
it is to be remembered that with a negative pressure in excess of about 
80 or 90 millimeters it becomes impossible to overcome this by muscular 
action, and relief is obtained only by a return to a higher altitude 
and a pressure difference of less than from 80 to 90 millimeters of 
mercury. In cases in which the pressure has already produced 
24 TM 8-300 
32 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
trauma, opening the eustachian tube will not relieve the symptoms 
of that trauma, and they persist until recovery has taken place. The 
symptoms following trauma to the middle ear depend on the extent 
and duration of the trauma. Pressures that may be only uncom- 
fortable at first finally become painful. Moderate trauma to the ear 
is followed by a sense of soreness in the ears and deafness lasting 
from 1 to 12 hours. Severe trauma is followed by pain, deafness, 
vertigo, and tinnitus for from 4 to 48 hours. The pain is similar to 
that of suppurative otitis media, the tinnitus usually of a hissing or 
roaring character, the deafness of the conduction type, and qualitative 
as well as quantitative. 
(2) Objective symptoms.—The objective signs depend on the 
amount of trauma sustained. In mild cases the drum may appear 
normal except for a moderate degree of bulging or retraction when a 
small amount of pressure differential still persists. An increased 
pressure in the tympanic cavity is denoted by a bulging of the tym- 
panic membrane with a decrease or loss of the light reflex. 
A negative pressure in the tympanic cavity is denoted by a 
retraction of the tympanic membrane with a decrease in size and 
brilliance of the light reflex and an increased prominence of the short 
process of the malleus with a foreshortened and more horizontal 
handle. 
Following more severe trauma, the drum may be retracted or 
bulging as already described, and in addition there is also an inflam- 
mation, which in appearance varies from a slight pink tinge to an 
angry red. In all cases the inflammation is most marked along the 
larger vessels that follow the malleus handle and around the drum 
periphery. When the inflammation is severe it cannot be distin- 
guished from acute infectious otitis media and has frequently been 
mistaken for it. 
Traumatic ruptures of the tympanic membrane are usually linear 
and quite extensive and may involve any portion of it. The margins 
of fresh ruptures are red and the whole drum is highly inflamed. 
There is usually a small amount of blood in the external auditory 
canal. If the labyrinthic wall is visible through the freshly ruptured 
drum membrane, it is seen to be red, congested, and swollen. 
Audiometer tests shown a variable diminution of hearing, depend- 
ing on the severity of the injury. 
b. Aero-otitis media, chronic.—(1) Subjective symptoms.—In these 
cases there is a “full and stuffy” feeling in the ears and difficulty in 
“clearing” them. There is a partial loss of hearing, which is either 
unilateral or more pronounced on one side and in some instances may 
vary from day to day. Head noises may be present, but rarely ver- 
25 TM 8-300 
33-35 
MEDICAL DEPARTMENT 
tigo or pain. The condition is worse after flights, during acute infec- 
tions of the upper respiratory tract, during changes of weather, and 
during fatigue or debilitated states. 
(2) Objective symptoms.—The eardrums are bulging or retracted, 
usually the latter. The drum membrane is dull, lusterless, and 
slightly thickened and the light reflex is diminished or absent. Hear- 
ing acuity is diminished either unilaterally or bilaterally, and in the 
latter case there is usually a considerable difference between the two 
sides. This deafness is of the conduction type, the lower tones of the 
scale being lost first. Rinne’s test is negative. Weber’s test is posi- 
tive and bone conduction is prolonged beyond the normal. Exami- 
nation of the ostium of the eustachian tube shows the presence of a 
chronic inflammatory process or a mechanical obstruction. 
33. Diagnosis.—The diagnosis of aero-otitis media is simple only 
if the history is known. The different traumatic inflammatory stages 
closely resemble the various stages of infectious otitis media and, as 
previously stated, have frequently been mistaken for it. Likewise, 
chronic aero-otitis media may be easily mistaken for a chronic infec- 
tious middle ear process unless a history of exposure to repeated 
changes of altitude is obtained. 
34. Complications.—While trained pilots usually try to avoid 
flying during periods when they have an acute infection of the upper 
respiratory tract, because of the discomfort and pain in the ears which 
almost invariably occurs, nevertheless a considerable amount of such 
flying has been done. It might naturally be expected in these cases 
that during descent the intermittent blasts of air from the pharynx to 
the tympanic cavity would carry with it septic material to the mechan- 
ically irritated tympanum and readily set up an acute inflammatory 
process. While it is possible or even probable that this septic mate- 
rial is carried into the tympanus there are no reports of such cases, 
35. Treatment.—a. Prophylaxis.—Those who take up aviation as 
a profession are, and should continue to be, carefully tested for patency 
of the eustachian tubes. This may readily be done by means of the 
Politzer bag. Those who have a stenosis of the tube should be exam- 
ined for chronic infection of the ear, sinuses, nose, and pharynx, the 
mouth of the tube inspected for mechanical obstructions, and the 
eustachian tube catheterized, if necessary. When any of these condi- 
tions are found and corrected, it is likely that the tube will become nor- 
mal. Persons examined during periods of an acute infection of the 
upper respiratory tract should be reexamined after the infection has 
subsided before a final decision is made. 
26 TM 8-300 
35 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
Probably the most useful prophylactic measure in all cases is proper 
instruction of the individual concerned. As long as the patency of the 
eustachian tube is under voluntary control there is no reason why any 
person in command of his faculties need experience difficulty at any 
rate of ascent or descent possible in present commercial aircraft. A 
simple explanation of the functioning of the eustachian tube followed 
by instructions as to how to ventilate the tympanus, when to ventilate 
it, and how frequently this is necessary should suffice. Probably the 
simplest maneuver to actuate the normal eustachian tube is to swallow. 
It may also be accomplished by yawning, by singing, by shouting, by 
autoinflation, and by contracting the salpingopharyngeal muscles. The 
last named defies description and can be learned only by practicing the 
suppression of a simulated yawn, at which time a roaring in the ears 
will indicate when the effort is successful. 
Since the average person swallows involuntarily about every 60 to 
75 seconds, it can be seen that a rate of climb or descent of 200 feet per 
minute will usually cause no discomfort, 500 feet per minute slight dis- 
comfort, and 1,000 feet per minute moderate discomfort even though no 
effort is made to ventilate the tympanum artificially. Descents above 
4.000 feet per minute may catch an individual unaware and create a 
tympanic vacuum which it is impossible to relieve by any method 
except a return to higher altitudes. 
Chewfing gum, eating, drinking, or inhaling oxygen reduces swallow- 
ing to intervals of from 1 to 30 seconds. Sleeping and comatose indi- 
viduals swallow at increased intervals and present a serious problem. 
The allowable rate of ascent and descent of commercial air lines is 
set by the Department of Commerce at 300 feet per minute, and some 
such companies limit themselves to 200 feet per minute, although 
unusual conditions such as weather may require that both of these rates 
be exceeded to insure the safety of the flight. Those who are suffering 
from either temporary or permanent stenosis of the eustachian tube 
should be enjoined from flying except under controlled conditions of 
gradual changes of altitude through a maximum range not to exceed 
2.000 feet. Those with an acute infection of the upper respiratory tract 
who insist on aerial flights should be prepared by gargling hot physio- 
logic solution of sodium chloride or by having a detergent spray di- 
rected well back into the nasopharnyx followed by the instillation or 
inhalation of atrophine, ephedrine, or benzedrine compounds. 
h. Active treatment.—Relief of pain is the first consideration in 
acute cases. The tympanum should be gently inflated by Politzer’s 
method if the drum indicates the existence of either positive or nega- 
tive pressure. Heat, dry or wet, is very effective. The installation 
27 TM 8-300 
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MEDICAL DEPARTMENT 
of copious quantities of water into the external auditory canal at 
from 110° to 115° F., followed by dry heat is the method of choice. 
Inflammation of the ostium of the eustachian tube requires treat- 
ment, and hot saline gargles followed by the instilling or mopping 
of astringents over that area will shorten the period of discomfort. 
In severe cases analgesics and even the injection of morphine, from 
one-eighth to one-fourth grain (0.008 to 0.016 gm.), may be neces- 
sary for the first 24 hours, 
c. After-treatment.—The after-treatment consists of the applica- 
tion of dry heat to the ear and the inhalation or instillation of as- 
tringents into the nasopharynx every 4 hours. A plug of cotton 
in the external canal seems to add to the comfort, especially during 
cold weather. 
If the condition does not subside materially in 24 hours, acute 
infectious disease of the middle ear should be suspected or a stenosis 
of the eustachian tube looked for and corrected. 
Ruptures of the tympanic membrane should be left alone and 
treated expectantly. 
In chronic aero-otitis media, stenosis of the eustachian tube should 
be looked for and treatment directed to its relief. Chronic infec- 
tions of the ear, tonsils, sinuses, nose, and pharynx should be con- 
sidered as possible causative factors and corrected. Mechanical ob- 
struction of the eustachian ostium or tube should be removed. If 
there is no apparent infection and no obvious obstruction of the 
tube, a malposition of the lower jaw with compression of the tube 
may be assumed and the jaw temporarily repositioned by the technic 
of Willhelmy 3 for clinical test and, if successful, permanent meas- 
ures applied. 
The eustachian stenosis having been relieved, the chronic inflam- 
matory process in the tube and middle ear usually subsides spon- 
taneously, but this may be hastened by gentle inflation of the ear 
or, if the congestion is marked, by the application of heat to the 
external ear and nasopharynx. Until the condition is entirely re- 
lieved, flying should be avoided as a potential source of irritation. 
36. Pathology.—In acute cases the first change is a passive 
hyperemia of the mucous membrane of the middle ear and eustachian 
tube from negative pressures or an ischemia from positive pressures. 
On relief of the pressure in either case there follows a period of 
active hyperemia, the degree and duration depending on the severity 
,and duration of the trauma. With high pressures actual traumatic 
inflammation takes place accompanied by a serous exudate. The 
8 ma. 
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NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
mucous membrane becomes congested and swollen, the eustachian 
tube blocked, and the tympanic cavity a closed cavity. The epidermal 
layer of the tympanic membrane takes part in the reaction and 
becomes inflamed and may rupture. 
Chronic aero-otitis media depends on frequently repeated insults 
to the tympanic cavity in which the tympanic membrane and the 
mucous membrane of the middle ear and of the eustachian tube be- 
come chronically congested and thickened. 
The pain in aero-otitis media is not merely local. In severe cases 
it may reflexly or directly affect the facial nerve and its branches and 
thus produce a neuralgic-like pain which radiates over the distribu- 
tion of that nerve. 
37. Summary.—A new clinical entity is presented which consists 
of a traumatic inflammation of the middle ear caused by a pressure 
difference between the air in the tympanic cavity and that of the 
surrounding atmosphere, commonly occurring during changes of 
altitude in airplane flights and characterized by inflammation, dis- 
comfort, pain, tinnitus, and deafness. 
Section VI 
ANATOMY AND PHYSIOLOGY OF INNER EAK OR 
LABYRINTH 
Osseous labyrinth 38 
Membranous labyrinth 39 
Cochlear and vestibular branches of auditory nerve 40 
Special sense organs of inner ear 41 
Physiology of vestibule and semicircular canals 42 
Cochlea 43 
Paragraph 
38. Osseous labyrinth.—Two distinct mechanisms are to be con- 
sidered as comprising the inner ear or labyrinth. 
a. The cochlea, the essential organ of hearing. 
b. The vestibular apparatus, a contributory organ of equilibrium or 
orientation consisting of the saccule, utricle, and three semicircular 
canals. 
These structures are contained within a series of little communicat- 
ing cavities located within the petrous portion of the temporal bone 
and known as the osseous labyrinth. Within the cavities of the bony 
labyrinth and surrounded by a supporting fluid, the perilymph, is the 
essential structure known as the membranous labyrinth, the cavity of 
which is filled with endolymph. 
c. Anatomically the osseous labyrinth is divided into three main 
portions, a central cavity, the vestibule; an anterior portion, the 
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MEDICAL DEPARTMENT 
cochlea; and a posterior portion, the semicircular canals. The vesti- 
bule lies internal to the middle ear and but for the foot plate of the 
stapes would communicate with it by means of the oval window. 
Anteriorly it communicates with the cochlea and posteriorly with the 
semicircular canals. 
(1) Vestibule.—The oval window of the middle ear opens into the 
vestibule and marks the center of its outer wall. It measures 5 or 6 
millimeters from before backward and approximately 4 millimeters 
each in width and height. On the inner vestibular wall, nearer the 
anterior than the posterior wall, is a slight ridge, approximately ver- 
tical, the crista vestihuli. In front of this is the recessus sphericus, 
which lodges the saccule, while behind is the recessus ellipticus, which 
lodges the upper part of the utricle. There are eight openings into 
the vestibule, as follows: 
(a) Five openings for the three semicircular canals. The ampullar 
ends of the horizontal and anterior vertical enter the vestibule through 
the roof, above the oval window. The ampulla of the posterior vertical 
canal is in the floor. Behind this, that is, in the posterior wall near the 
roof, is the opening of the small end of the horizontal canal. The 
common opening of the anterior and posterior canals is near the angle 
formed by the inner and posterior walls with the roof. 
(b) Opening of the scala vestihuli of the cochlea in the anterior and 
outer corner. 
(c) Aqueductus vestihuli. On the inner wall. 
(d) Maculae cribosae. Small openings in the crista vestihuli, reces- 
sus sphericus, and recessus ellipticus. These give passage to sacular 
and utricular branches of the vestibular nerve. 
(2) Cochlea.—The cochlea is a bony tube about 1 y2 inches in length 
having two and one-half coils about a central core, the modiolus, the 
coils resembling a snail. The diameter of the tube near the vestibular 
end is about 2 millimeters, this calibre rapidly diminishing after the 
first turn to about 1 millimeter. From the center of the base to the 
apex, its axis lies in a horizontal plane and is directed forward and 
outward. The lamina spiralis, a bony projection, passes outward from 
the modiolus into the lumen of the spiral canal and extends about half- 
way across the cochlear tube. The basilar extends from the 
outer edge of the lamina spiralis to the outer edge of the cochlear tube, 
dividing it into two channels, an inner, communicating with the middle 
ear through the round window, and known as the scala tympani, and 
an outer, opening into the vestibule, known as the scala vestihuli. 
These two cavities communicate with each other at the apex of the 
pyramid, the helicotrema. On the floor of the scala tympani near its 
beginning at the round window is the aquaductus cochleae, a small, 
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NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
short canal, leading to the basal surface of the skull near the jugular- 
foramen. The membranous canal, however, is continued inward and 
perforates the dura to communicate directly with the subarachnoid 
space. 
The cochlear branches of the auditory nerve pass through the core 
of the modiolus to reach by minute openings the osseous lamina spiralis 
and thence to the basilar membrane and organ of Corti. 
(3) Semicircular canals—(a) Number.—The semicircular canals 
are three in number, horizontal, anterior vertical, and posterior 
vertical. 
(b) Description.—Each semicircular canal comprises about two- 
thirds of the circumference of a circle, the diameter of which is 7 
to 8 millimeters. They are elliptical on cross section and each canal 
has a slight enlargement at one end, called the ampulla. The canals 
are a little over 1 millimeter in diameter, except at the ampullae 
where they are millimeters in diameter. Both ends of each 
semicircular canal open into the vestibule. The narrow ends of the 
anterior vertical and posterior vertical join before they reach the 
vestibule into which tl*ey open by means of a common limb. The 
ampulla of the anterior canal lies at its outer end. The ampulla of 
the horizontal canal lies at its anterior end. The ampulla of the 
posterior canal lies at its lower end. The ampullated ends of all 
three canals lie nearer to the middle ear than do the small ends, also 
all are the more anterior ends. 
The middle portion of the horizontal canal lies exposed in the attic 
and aditus. It forms a prominence on the inner wall of the attic 
and aditus, lying just above and behind the facial nerve, and here 
suppurative processes in the middle ear frequently cause erosions and, 
as a matter of fact, this is the most common situation for a laby- 
rinthine fistula. The horizontal canal is a guide in the simple mas- 
toid operation, exposure of same indicating that the aditus has been 
reached. In the radical mastoid it indicates the limit to which the 
posterior wall of the external auditory meatus may be taken down 
fVithout injury to the facial nerve. 
(c) Position.—With head erect and chin drawn inward, the hori- 
zontal or external lies very nearly in a horizontal plane. The other 
two are both vertical, the anterior vertical lying in a vertical plane 
directed from within outward and forward, and the posterior vertical 
occupying a vertical plane at right angles with that of the anterior 
vertical, that is, outward and backward. It is obvious that each canal 
lies in a plane at right angles to the other two. The posterior verti- 
cal is on a much lower plane than the anterior vertical. 
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MEDICAL. DEPARTMENT 
It has been noted from a large number of corrosion specimens that 
the planes of the canals, as well as the angles between them, are very 
inconstant. The horizontal canal is rarely horizontal. Its plane is 
tilted downward and backward and forms with the horizontal plane 
an angle varying from 0° to 30°. This fact is important in inter- 
preting the results of functional examination of the static labyrinth. 
The angle which the plan© of the anterior vertical canal makes with 
the medial plane, varies between 30° and 65°. There may be a differ- 
ence of 20° between the right and left sides. The angle between 
the anterior vertical and horizontal canals varies between 65° and 
90°. The angle between the horizontal and inferior vertical canals 
is most constant, varying from 90° to 100° and being usually 90°. 
The anterior vertical canal of the right side is parallel to the pos- 
terior vertical of the left side, and the anterior vertical of the left 
side is parallel to the posterior vertical of the right side. 
39. Membranous labyrinth.—a. General.—The membranous 
labyrinth consists of— 
(1) The membranous vestibule, which is divided into the saccule 
and the utricle. 
(2) Three membranous semicircular canals, namely, horizontal, 
anterior vertical, and posterior vertical. 
(3) The membranous cochlea. 
The membranous labyrinth is partly surrounded by a supporting 
fluid, the Perilymph, partly because in most regions it is connected 
at some points with the endosteum lining the walls of the osseous 
labyrinth. On account of the perilymph separating it, in many 
places, from the osseous canal, it is necessarily smaller than the 
osseous portion. Wherever the labyrinth filaments of the auditory 
nerve perforate the bony capsule to reach the membranous labyrinth, 
the membranous parts so supplied are attached to the bony surface 
thus perforated, for example, cristae acusticae of the ampullae and 
the maculae acusticae of the utricle and saccule. 
The perilymph space communicates with the subarachnoid space 
of the skull through the aquaductus cochleae, which opens on the 
basilar surface of the petrous portion of the temporal bone, internal 
to the jugular fossa. The cavities and canals of the membranous 
labyrinth are filled with endolymph. The endolymph space does not 
communicate with the subarachnoid space of the skull as is the case 
with the perilymph space. 
b. Membranous vestibule.—The membranous vestibule consists of 
the saccule, in the recessus sphericus, and the utricle, in recessus 
ellipticus. 
32 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
39 
(1) Saccule.—The saccule communicates with the scala vestibulae 
and scala media (ductus cochlearis) of the cochlea through the canalis 
reuniens and only indirectly with the utricle. It lies in front of the 
crista vestihuli, being partly separated from the utricle by this ridge. 
The recessus sphericus and the anterior surface of the crista ves- 
tibuli present numerous small perforations through which the sac- 
cular branches of the vestibular nerve pass. Penetrating the con- 
tiguous surface of the saccule, they present a circumscribed bulging 
of the inner wall known as the macula acustica. The canal reuniens, 
a membranous canal, passes downward from the lower part to enter 
the ductus cochlearis of the cochlea. Another small canal from the 
posterior part passes downward and backward to unite with a similar 
canal from the utricle, aquaductus vestibuli, or aqueduct of the endo- 
lymph. This is the only communication between the saccule and 
utricle. 
(2) Utricle.—The utricle, about 5 millimeters in length, is attached 
to the posterior part of the inner wall of the bony vestibule. Its 
upper half is lodged in the recessus ellipticus, behind the crista vesti- 
buli, The portion resting against the recessus ellipticus, the recessus 
utriculi, is perforated by numerous small foramina for the passage 
of the utricular branches of the vestibular nerve forming on its inner 
wall a circumscribed bulging which is the highly specialized neuro- 
epithelial end-organ, the macula acustica. 
The cavity of the utricle communicates by five openings with the 
three semicircular canals. The ampullar ends of the horizontal and 
anterior vertical open on its roof, the ampullar end of the posterior 
vertical perforates its floor, and the opening of the small end of the 
horizontal canal and the common opening of the two vertical canals 
enter the posterior wall. From the lower end of the utricle a small 
membranous tube passes forward, inward, and downward. This 
unites with a similar tube from the saccule to form the aquaductus 
vestibuli. The aquaductus vestibuli enters a small bony opening on 
the inner wall of the bony vestibule and traverses the bone in a curved 
direction inward and somewhat backward to emerge by a slit-like 
opening upon the posterior surface of the petrous portion of the tem- 
poral bone, seven-eights millimeter behind the internal auditory 
meatus. It here expands into a closed sac, the saccus endolym- 
phoaticus, with no direct communication with the cerebrospinal chan- 
nels or subarachnoid space. The perilymph, as previously stated, 
escapes through the aquaductus cochlea to mingle directly with the 
cerebrospinal fluid. 
c. Membranous semicircular canals.—(1) Membranous semicircular 
canals are elliptical’ on transverse section and are attached to the 
271818°—40 3 
33 TM 8-300 
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MEDICAL DEPARTMENT 
greater circumference of the bony tubes. The peripheral portion of 
the ellipse is fixed to the periosteal lining of the bony canal, while the 
opposite part is free, except that it is connected by irregular bands, 
the ligament labyrinthi canaliculorum, which pass through the peri- 
lymph space to the bony wall. Like the bony canals, each mem- 
branous canal is dilated at one extremity into an ampulla, which is 
especially developed toward the concave aspect of the tube. While 
the membranous ampullae nearly fill the corresponding portions of 
the bony tubes, the calibre of the remaining parts of the membranous 
canals is equal to only about one-fourth of that of the osseous canals. 
(2) Histology.—Histologically there is a great similarity in the 
membranous semicircular canals, the utricle, and the saccule. They 
are composed of three layers, an outer fibrous layer, a delicate basal 
membrane, and a single layer of squamous epithelial cells. The 
fibrous layer is similar to the periosteum lining the bony canals and 
vestibule with which it is continuous, at the points where the mem- 
branous canals are attached to the bone. The basal membrane is 
homogeneous and very thin. This as well as the connective tissue 
layer becomes thicker at the maculae and cristae. As we approach 
the maculae and cristae the squamous epithelium becomes columnar 
and in the end organs changes into ciliated neuro-epithelium. 
(3) Overhanging the ciliated neuro-epithelial cells is a structure 
containing a mass of minute crystalline grains of carbonate of lime 
imbedded in a gelatinous substance. This structure is known as the 
otolith membrane where it overhangs the maculae acusticae in the 
vestibule and as the cupula where it overhangs the cristae acusticae in 
the semicircular canals. It is claimed by some authors that the otolith 
membrane and the cupula are attached to, or are a part of, the walls 
of the vestibule and semicircular canals, opposite the neuro-epithelial 
cells and is not a free membrane. 
d. Membranous cochlea.— (1) The membranous cochlea consists 
of— 
{a) Basilar membrane. 
(b) Reissner’s membrane. 
(<?) Spiral organ of Corti, 
(d) Membrana tectoria. 
(2) These structures divided the cochlear tube into four lesser tubes 
or canals as follows: 
(«) Scala tympani. 
(h) Scala vestibuli. 
(c) Scala media or ductus cochlearis. 
(c?) Canal of Corti. 
34 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
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39-40 
(3) As previously stated, the basilar membrane extends from the 
apex of the lamina spiralis to the opposite wall of the cochlear tube, 
thereby dividing this tube into two main canals, the scala tympani 
and scala vestibuli. Reissner’s membrane originates near the apex of 
the lamina spiralis on the vestibular side, and extends upward and 
outward to become attached to the opposite cochlear wall. This mem- 
brane forms an additional canal within the scala vestibuli, the scala 
media or ductus cochlearis, and it is in this canal that the essential 
organ of hearing, the spiral organ of Corti, is located. The scala 
media and the scala vestibulae communicate with the saccule through 
the ductus reuniens. The scala tympani extends to the round window 
in the inner wall of the middle ear with which it would communicate 
except for a thin membrane which covers this opening. 
(4) Spiral organ of Corti.—The spiral organ of Corti is the essen- 
tial end-organ of hearing and is located in the scala media and extends 
the entire length of this canal. It is composed of a series of epithelial 
structures and appears as a small elevation upon the basilar membrane. 
The more central of these epithelial structures are two rows of rod- 
like bodies, the inner and outer rods of Corti. The bases of these 
rods rest upon the basilar membrane, and the two rows are some dis- 
tance apart. The rods are inclined toward each other and the free 
ends come in contact above, thus forming a minute tunnel, the canal 
or tunnel of Corti. On the medial side of the inner rods is a single 
row of short columnar epithelial cells, the inner hair cells, the upper 
ends of which are on a level with the upper extremities of the rods 
and extend about halfway down to the basilar membrane. Each 
columnar cell is surmounted by twenty to thirty hair-like processes, 
arranged in the form of a descent. These hair cells are supported 
by two or three rowTs of columnar epithelial cells. 
On the lateral side of the outer rods of Corti are two to three rows 
of columnar cells, similar to the inner hair cells, but somewhat longer 
and surmounted in the same manner by hair-like processes, the outer 
hair cells. Between the outer hair cells are rows of supporting cells 
with expanded bases terminating in phalangeal-like processes, known 
as the cells of Dieters. Overhanging the inner and outer hair cells, 
but not touching them while in a position of rest, is a membrane of 
irregular thickness attached to the vestibular side of the lamina 
spiralis, near the origin of Reissner’s membrane, known as the mem- 
brana tectoria. This membrane is composed of a multitude of delicate 
fibers imbedded in a transparent matrix of marked adhesiveness. 
40. Cochlear and vestibular branches of auditory nerve.— 
The cochlear branches of the auditory nerve enter the cochlea by 
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MEDICAL DEPARTMENT 
minute perforations in a circular depression at the base of the mo- 
diolus. They traverse this to reach the base or outer margin of the 
lamina spiralis, where they form bipolar ganglion cells, the spiral 
ganglion or ganglion of Gorti. From this ganglion the fibers radiate 
outward between the plates of the lamina spiralis and perforate its 
outer plate to reach the basilar membrane and the organ of Corti, 
where they arborize around the hair cells. 
The distribution of the vestibular branch of the auditory nerve has 
been mentioned in the description of the membranous vestibule. In 
the internal auditory meatus the vestibular portion of the nerve divides 
into an upper branch which supplies the utricle and ampullae of the 
horizontal and anterior vertical canals and a lower which supplies the 
saccule and ampulla of the posterior vertical canal. 
Within the auditory meatus the cochlear and the vestibular branches 
are traced to their common trunk which passes inward across the 
subarachnoid space to the restiform body in the medulla. The nerve, 
according to Dana, enters the medulla by two roots, a lateral or a 
posterior root composed chiefly of auditory fibers and a median root 
composed chiefly of vestibular fibers. These roots communicate with 
three nuclei, namely— 
a. A central, the acustic tubercle on the floor of the fourth ventrical. 
I). The ventral or accessory nucleus, springing from the lateral root 
and lying between it and the median root. 
c. A large-celled nucleus (Defiers’ nucleus) which lies external to 
and below the central nucleus. 
The lateral or auditory root communicates chiefly with the acces- 
sory nucleus, but also with the other nuclei. From the central and 
accessory nuclei auditory fibers are sent to the temporal lobes of both 
hemispheres, but more to the opposite than to the corresponding side. 
The cortical centers for hearing are in the first and second convolu- 
tions of the temporal lobes. Owing to the above distribution of the 
auditory nerve fibers, destruction of the cortical center on one side will 
result in impairment of function of both ears, but the impairment will 
be greater in the ear opposite to the side on which the destruction 
occurs. 
The median root is composed chiefly of vestibular fibers and connects 
principally with Deiters’ nucleus and through this to the cerebellum. 
41. Special sense organs of inner ear.—a. The following three 
types of special sense organs are located within the inner ear; 
Macula acustica (two in number). 
Christa acustica (three in number). 
Spiral organ of Corti. 
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(1) One of the maculae acusticae is located in the saccule on the 
anterior surface of the christa vestibuli and recessus sphericus, the 
other in the utricle behind the crista vestibuli in the recessus elipticus. 
Both maculae occur as irregularly round or oval elevations which pro- 
ject from the inner walls into the cavities of the saccule and utricle, 
(2) The cristae acusticae are located one in each of the ampullar 
ends of the semicircular canals and are similar in appearance to the 
maculae. 
(3) The spiral organ of Corti is located in the scala media (ductus 
cochlearis) of the cochlea. It rests upon the basilar membrane and 
appears as a small elevation extending the entire length of the cochlear 
tube. 
b. These three types of end-organs appear superficially quite differ- 
ent, but when examined closely are found to be fundamentally alike in 
many respects. In each end-organ the important physiological element 
is a peculiar hair-bearing cell which receives the terminal filaments of 
the eighth nerve, and in which the transference of a physical to a nerv- 
ous impulse takes place. In each end-organ, moreover, there is a 
peculiar structure of epithelial origin which overhangs the hair cells 
and with the under surface of which in each instance the hairs of 
the hair cells come in contact. In the maculae acusticae this structure 
is known as the otolith membrane, in the cristae acusticae it is known 
as the cupula, and in the spiral organ of Corti it is known as membrana 
tectoria. 
42. Physiology of vestibule and semicircular canals.—That 
the vestibular apparatus is not an organ essential to equilibrium has 
been definitely shown, in that after complete ablation of the organs, 
equilibrium is soon reestablished. 
It is highly probable that the vestibular mechanisms are in one sense 
organs of orientation, in that they enable man under all conditions 
(on the ground), that is, in light or darkness and in whatever position 
the body may be placed, subconsciously and without effort to determine 
the position of the different parts of his body. It is the sudden with- 
drawal of this power which places the individual, after removal of the 
labyrinths, in some danger of serious accident, even after he has re- 
covered from the first vestibular disturbances incident to the operation. 
That he soon learns to guard against such mishaps under all or any 
conditions does not disprove the value of these organs in health. It 
proves simply that certain other faculties, for example, the so-called 
muscle, arthrodial, and tactile senses and the sense of sight, have so 
enlarged their scope as to compensate for that which he has lost. 
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MEDICAL DEPARTMENT 
Whatever the exact function may be, it is fairly certain that the 
essential structures are the end-organs in the cochlea, vestibule, and 
semicircular canals. Both histologically and physiologically they are 
similar. Thus, both the organ of Corti and the cristae and maculae 
acusticae are covered by a highly organized neuro-epithelium, of which 
the surface strata are composed of cells from which hair-processes 
project. On each of these organs the hair-processes project into an 
important superimposed structure, friction or impact against which is 
essential to its proper performance of function. Thus the hair cells of 
the cristae acusticae do not project directly into the endolymph of the 
ampullae, but into the soft cupula overhanging them. The hair cells 
of the maculae acusticae are in contact with the otolith membrane, 
while the hair cells of Corti’s organ project toward the under surface 
of the tectorial membrane. According to one authority, the relation of 
the free surface of the organ of Corti and tectorial membrane is one of 
actual contact, impact of the hair processes with the membrane is 
brought about through the agency of the sound waves propagated 
through the labyrinthine fluids. In the case of the cristae and maculae 
acusticae, interaction is brought about by sudden changes in the posi- 
tion of the head. 
In health, it is probable that the various parts of the vestibular 
apparatus act in concert, injury to any one canal causes subjective and 
objective symptoms similar to those following injury of the other two, 
or to the parts resting within the bony vestibule. 
One theory considers a threefold function: 
a. Acoustic.—Located in the cochlea. 
h. Static.—Located in the saccule and utricle. 
c. Kinetic.—Located in the semicircular canals and the utricle and 
saccule. 
It is believed that wave impulses in the external ear cause a move- 
ment of the drumhead; those impulses are carried mainly by the chain 
of ossicles through the footplate of the stapes, which vibrates in the 
oval window, causing similar movements in the endolymph; these in 
turn impinge upon the hairs of the organ of Corti. In bone conduction, 
the stimulation is more directly through the endolymph, both produc- 
ing the appreciation of sound, originating in the external world. In 
contrast to this, the hair cells of the kinetic labyrinth are usually set in 
motion by movements of the body itself. 
When the body is at rest the otoliths by their pressure on the 
maculae of the saccule and utricle give information as to the position 
of the body; this is the static function. The kinetic function is de- 
pendent upon the entire equilibratory portion of the ear; the three 
38 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
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42 
semicircular canals take cognizance of rotary movements of the body 
in all conceivable planes. Movements in a linear direction, anterior- 
posteriorly, are probably detected by the macula of the utricle; linear 
movements in a lateral direction are detected by the macula of the 
saccule; and linear movements in a vertical direction, up and down, 
are detected by both utricle and saccule. 
If the body moves forward in a linear direction there results a 
lagging behind of the otoliths above the macula of the utricle. If 
sideways there is a lagging behind of the otoliths above the macula 
of the saccule. If there is a rotary movement there results a move- 
ment of the endolymph in one or more of the semicircular canals, 
thereby affecting certain of the hairs in the corresponding crista or 
cristae. When the current is toward the ampulla, the hairs of that 
side are put upon the stretch; if the current is away from the am- 
pulla the hairs of the opposite side are put upon the stretch. The 
hair cells of the two sides of the crista are connected by separate 
nerve fibers with different central nuclei and because of this arrange- 
ment it is possible for the cells of one side of the crista to produce 
diametrically opposite phenomenon. A current toward the ampulla 
in the horizontal canal -produces twice as strong a reaction as a cur- 
rent away from it, while in the vertical canals the current away 
from the ampullae produces twice as strong a reaction as a current 
toward the ampulla and here the two canals act together. 
The entire labyrinthine cavity is considered by some authorities as 
an irregularly shaped vessel containing fluid, the perilymph, and 
within the membranous labyrinth the endolymph, all having the 
temperature of the blood. In douching test the hot or cold water 
in contact with a part of the wall causes either a rise or fall in the 
temperature at that point and a consequent rise or fall in the fluid. 
Since the anterior half of the horizontal canal and the anterior or 
outer third and ampulla of the anterior vertical canals are nearest 
the tympanic surface, these parts are first influenced by rise or fall in 
temperature. In rotation experiments, there is at first a lagging 
behind of the endolymph, then the endolymph moves as rapidly as 
the subject being rotated and when rotation suddenly ceases, the 
endolymph continues moving in the direction toward which the sub- 
ject has been turned. 
That an endolymph movement takes place is clearly shown by 
the following: Incline the head backward 60°; this puts the hori- 
zontal canal in the vertical position. Douching the right ear with 
cold water then produces— 
Horizontal nystagmus to left. 
Sensation of rolling to left. 
39 TM 8-300 
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MEDICAL DEPARTMENT 
Past-pointing to the right. 
A rolling or falling to right. 
Kow without further douching tilt the head forward 120°, which 
puts the horizontal canal in the vertical plane, but exactly upside 
down from the previous position; there immediately appears— 
Horizontal nystagmus to right. 
Sensation of rolling to right. 
Past-pointing to the left. 
A rolling or falling to left. 
43. Cochlea.—a. If the three structures present in the scala media, 
that is, the organ of Corti, the supporting basilar membrane, and 
the superimposed membrana tectoria are regarded as constituent 
parts of one mechanism, and it is assumed that sound waves trans- 
mitted through the cochlear perilymph will impress certain fibers in 
this mechanism and thereby induce auditory impressions of tone vary- 
ing with the vibration rapidity, the common belief of otologists 
shall have stated. 
h. One authority believes the basilar membrane to be the essential 
structure. A later view holds that the different tones in the scale 
affect certain definite parts of the tectorial membrane by vibration, 
accomplishing in this way a stimulation of a different group of hair 
cells for each particular tone. The impulse is transmitted directly 
from the scala vestibuli through Reissners membrane to the tec- 
torial membrane and as this lies directly over the hair cells, the 
movement is imparted to the hairs. This theory brings the action 
of the end-organ in the cochlea into harmony with the action of the 
end-organs in the vestibule and semicircular canals. The otolith 
membrane in the vestibule, the cupula in the ampullae of the semi- 
circular canals, and the tectorial membrane in the organ of Corti all 
overlie hair cells. 
c. Telephone theory.—In this it is assumed that the entire basilar 
membrane vibrates with every tone as the receiver of a telephone; 
analysis of the sound takes place in the brain. 
d. In an article “HowDoes the Organ of Corti Distinguish Pitch?” 
the following conclusions are drawn: 
(1) That neuro-anatomic and physiologic evidence is in favor of 
the resonance theory. 
(2) Pitch perception is definitely placed on the basilar membrane 
of the cochlea. 
(3) There is apparently a difference in sensitivity between inter- 
nal and external hair cells. The external are responsible for the 
detection of very faint sounds. The internal hair cells are concerned 
with the fine discrimination of pitch. 
40 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
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43-44 
(4) The external hair cells are more liable to degeneration than 
the internal hair cells. 
(5) The chief cause of perception deafness is probably a degenera- 
tion of the external hair cells. 
Section VII 
VESTIBULAR NYSTAGMUS 
Paragraph 
General 44 
Differentiation between ocular, vestibular, and physiological nystagmus 45 
44. General.—a. Definition.—Vestibular nystagmus may be de- 
fined as a rhythmic to-and-fro motion of the eyes, consisting of two 
components, a slow movement in one direction, which is followed at 
once by a rapid movement in the opposite direction. The slow move- 
ment is the vestibular reflex, yet the reaction has been named accord- 
ing to the direction of the rapid component. It has been shown that 
nystagmus always occurs in the plane of that semicircular canal in 
which the impulse calling forth the nystagmus arises and further that 
the slow component always takes the same direction as the endo- 
lymph movement, or that the rapid component takes a direction 
opposite to that of the endolymph movement. 
The differentiation of the vestibular from the cerebral compo- 
nent of vestibular nystagmus has been demonstrated in certain cases 
in which the caloric experiment has been employed on patients under 
narcosis. In these cases the eyes remain fixed in the direction of 
the slow component until either the patient recovers from the anaes- 
thesia or the muscles of the eyes tire, then the eyes assume their nor- 
mal position. 
b. Planes.—There are three main planes of vestibular nystagmus: 
Horizontal, frontal, and sagittal. 
(1) Nystagmus in a horizontal plane consists of a movement of the 
eyes toward the right or toward the left, 
(2) Nystagmus in a frontal plane consists of a rotary movement 
of the eyes on their antero-posterior axes, either toward the right 
or toward the left. 
(3) Nystagmus in a sagittal plane consists of a vertical move- 
ment of the eyes either upward or downward. 
The eyes are always drawn in a direction of the endolymph move- 
ment, this being the vestibular component, while the so-called direc- 
tion of nystagmus, being that movement of restitution, is opposite 
to that of the endolymph movement. 
41 TM 8-300 
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MEDICAL DEPARTMENT 
c. Cause.—Nystagmus in the horizontal plane is due to stimulation 
of the horizontal canals and is quite simple, the fibers from the 
horizontal canals being distributed exclusively to the internal and 
external recti muscles. It has been demonstrated that the flow of 
endolymph toward the ampulla in the horizontal canal induces a 
stimulus twice as strong as when the endolymph flow is away from 
the ampulla. In turning, therefore, to the right the after nystag- 
mus is to the left and is due two-thirds to endolymph movement to- 
ward the ampulla in the left canal, and one-third to an endolymph 
movement away from the ampulla in the right canal. In turning 
to the left the conditions are reversed. In turning, the endolymph 
at first lags, then catches up about the seventh turn and the move- 
ment continues in the direction of rotation for about 26 seconds after 
rotation has ceased. A great shortening in the after-nystagmus in 
one direction as compared with that in the opposite points to a non- 
functioning labyrinth on the side toward which the shortening is 
directed, for example, turning 10 times to the left equals a nystag- 
mus to the right of 30 seconds; 10 times to the right equals a nystag- 
mus of 15 seconds to the left. This would indicate that the left 
vestibule is either destroyed or its function abolished. 
As previously stated the anterior or ampullar end of the horizontal 
canal is nearest to the tympanic cavity and is therefore most influ- 
enced by changes in temperature. With head inclined 60° backward 
the horizontal canals assume the vertical position. Douching the 
ear with cold water induces endolymph flow away from the ampulla. 
This causes a vestibular pull of the eyes toward the same side in 
the horizontal plane, hence a nystagmus in the horizontal plane to 
the opposite side. Hot water induces in the same position, endolymph 
flow toward the ampulla, and a vestibular pull toward the opposite 
side, hence a nystagmus in the horizontal plane to the same side 
as the ear douched. Similarly if the head is inclined 120° forward 
and the ear is douched with cold water the endolymph current is 
toward the ampulla, giving a vestibular pull of the eyes toward the 
opposite side, and a nystagmus toward the same side. 
Nystagmus produced by the vertical canals is more complicated. 
The nystagmus produced is explained as follows: The anterior 
vertical canal lies in a plane halfway between the frontal and the 
sagittal and viewed from the outside of the head it runs from a for- 
ward position backward. The posterior vertical likewise lies in a 
plane halfway between the frontal and the sagittal, only it runs 
forward. The anterior canal is not placed in the frontal plane, nor 
is the posterior placed in the sagittal plane; the essential feature is 
42 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
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44-45 
that the two vertical canals act together. This has been shown ex- 
perimentally, either by douching with the head upright or turning 
with the head forward or backward. The plane of the resulting 
vertigo is the resultant of the planes of the vertical canals. Anatom- 
ically, at their innermost point, they unite in a common crus. 
With the head 120° forward, on turning, the plane of movement 
of the head is frontal, and in this the frontal plane bisects the 
planes of the two vertical canals, causing a rotary nystagmus in the 
frontal plane. With the head inclined 90° toward the shoulder and 
turning in that position the plane of turning is sagittal and the re- 
sulting nystagmus is a nystagmus in the sagittal plane, that is, a 
vertical-nystagmus upward or downward. 
Turning to the right with the head G0° backward produces a rotary 
nystagmus to the left. Turning to the right with the head 90° for- 
ward produces a rotary nystagmus to the left. Turning to the right 
with the head inclined toward the right shoulder produces a vertical 
n3Tstagmus downward. Turning to the right with the head inclined 
toward the left shoulder produces a vertical nystagmus upward. The 
exact opposite direction of nystagmus is produced if the turning is to 
the left with the position of the head as here indicated. 
To stimulate the vertical canals for the production of nystagmus 
it is necessary to recall that the outer or anterior third and ampulla 
of the anterior vertical canal is nearest to the tympanic cavity and 
hence most influenced by temperature changes in the ear. Also that 
a current away from the ampullae here is twice as strong as a cur- 
rent toward the ampullae, the exact opposite to the horizontal canal. 
With the head in the upright position, douching influences both 
vertical canals causing a nystagmus in the frontal plane. Cold water 
causes a flow of endolymph downward toward the ampullae, causing 
a vestibular pull of the upper meridian of the eyes toward the same 
side; in other 'words, a nystagmus toward the opposite side. Hot 
water gives the opposite effect. 
The directions for carrying out the turning and douching experi- 
ments are given in section IX. 
45. Differentiation between ocular, vestibular, and physio- 
logical nystagmus.—a. Ocular.—If the oscillations of the eyeball 
are a simple to-and-fro roll, like the swing of a pendulum, then it 
is not of the vestibular type but may be due to cerebellar lesions, cer- 
tain ocular diseases, hereditary syphilis, neurasthenia, etc. Ocular 
nystagmus may be due to opacities in the media, etc., the patient 
attempting to look around the opacity as it were. Another cause 
of ocular nystagmus may result from an interference with the proper 
43 TM 8-300 
45 
MEDICAL DEPARTMENT 
action of light rays on the macula, provided that the lesion occurred 
before central fixation was established. 
b. Vestibular.—The nystagmus due to vestibular stimulation or ir- 
ritation exhibits a definite rhythm, a slow movement in one direction 
followed by a quick recoil in the opposite direction, and is due to 
a disturbance in the ocular nerve mechanism and not to a lesion 
in the eyes themselves. It can be produced by a lesion affecting 
any of the pathways between the ear and the eye muscle nuclei. 
Such a nystagmus is not due to an attempt to accomplish fixation. 
When the eyes are thus drawn to one side, impulses from the cereb- 
rum to the eye muscle nuclei quickly bring the eyes back in the op- 
posite direction. The slow component is caused by an irritation, 
impairment, or destruction of the pathways from the ear to the eye 
muscle nuclei, whereas the quick component results from the attempt 
of the cerebrum to correct the altered position of the eyes. 
Vestibular nystagmus has the following characteristics: 
(1) A quick movement in one direction and a slow movement in 
the opposite direction. 
(2) It is increased, usually in rapidity and always in the length of 
excursion, when the eyes are turned voluntarily in the direction of 
the quick movement. 
(3) It becomes weak, or may disappear wholly, when the eyes are 
turned in the direction of the slow movement. 
This applies to vestibular nystagmus whether produced by experi- 
mental irritation or in the course of acute labyrinthine disease. 
Since irritation of a single canal can produce nystagmus only in its 
own plane, and since the nystagmus accompaning acute labyrinthine 
disease rarely corresponds exactly to the plane of any single canal, 
we may assume that suppurative invasion of the labyrinth almost 
invariably involves all, and always more than one of the three canals. 
Rotary nystagmus can be followed with ease if we fix our atten- 
tion upon some dilated vessel near the cornea and note carefully its 
changing relation to the border of the lower lid. 
c. Physiological.—The term physiological nystagmus has been ap- 
plied to the nystagmus which is seen in many normal persons when 
the eyes are voluntarily placed in the extreme lateral position in either 
direction. It is differentiated from nystagmus due to labyrinthine 
disease or irritation by the following points: 
(1) Spontaneous vestibular nystagmus in its most active stage is 
constant, but is exaggerated when the eyes are voluntarily directed in 
the direction of the quick movement. Physiological nystagmus is 
44 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
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45-46 
present only when the eyes are turned strongly in one or the other 
lateral directions, and then usually lasts but a few’ seconds. 
(2) Vestibular nystagmus in its active stage is present wdiatever the 
position of the eyes. Later, however, as the strength of the nystagmus 
is gradually reduced, it may be wholly absent when the eyes are 
turned in the direction of the slow7 movement. Physiological nystag- 
mus changes direction according to the position of the eyes, the quick 
movement corresponding to the lateral direction in wdiich the eyes 
are voluntarily turned. 
(3) Vestibular nystagmus in its most active stage is almost in- 
variably accompanied by vertigo and ataxia and these symptoms, even 
after the nystagmic movements have grown weaker, can usually be 
reinduced by sudden movements of the head. Physiological nystag- 
mus is unaccompanied by any subjective symptoms. 
Section VIII 
VESTIBULAR VERTIGO 
Paragraph 
General „ f 46 
Vertigo after douching 47 
Seasickness 48 
Past-pointing 49 
Past-pointing after douching 50 
Past-pointing cerebral function 51 
Falling 52 
Falling after turning , 53 
Falling after douching 54 
Summary 55 
46. General.—a. Definition.—Vertigo from whatever cause is a 
subjective sensation of a disturbed relationship to objects in space. 
As with nystagmus, so may vertigo and ataxia result from many 
functional and organic disorders. 
h. Planes.—Vestibular vertigo is always rotary in character, that 
is, is always accompanied by a subjective impression of the rotation 
of surrounding objects, and this subjective rotation is always in a 
plane corresponding to the plane of the nystagmus. As there are 
three planes of nystagmus, so there are three planes of vertigo. 
(1) Sensation of turning in the horizontal plane, either from right 
to left or from left to right.—Sensation of turning in the horizontal 
plane originates in the horizontal canals by rotation of the patient 
with head upright or inclined forward 30°. It is not unpleasant. 
(2) Sensation of turning in the frontal plane, consisting of falling 
to the right or the left.—Turning in the frontal plane originates in 
45 TM 8-300 
46 
MEDICAL DEPARTMENT 
the vertical canals by rotation of the patient with the head forward 
or backward, and with the head in this position the plane of rotation 
is parallel to the floor and is not unpleasant, the sensation being the 
same as turning a patient with the head upright, namely, a move- 
ment about one’s own axis either to the right or left. As it is a 
sensation of turning parallel to the plane of the floor it is not un- 
pleasant; if, however, the patient’s head is raised the frontal plane 
then becomes at right angles to the plane of the floor and the sensa- 
tion is that of falling in the frontal plane either to the right or to 
the left. 
(3) /Sensation of turning in the sagittal plane, consisting of a 
falling forward or backward.—The sensation of turning in the sagit- 
tal plane originates when the vertical canals are stimulated in the 
sagittal plane, that is, with the head well inclined toward the shoul- 
der while rotating. Here again with the head kept in this position 
the sense of rotation is parallel to the plane of the floor consisting of 
a sense of movement about one’s own axis and is not unpleasant. If, 
however, the head is raised to the upright position, the plane of rota- 
tion is at right angles to the plane of the floor, and is decidedly un- 
pleasant and causes a falling in the sagittal plane, either forward or 
backward. 
c. Sensation.— (1) The essential feature of the subjective sensation 
of vertigo after turning is that after turning to the right the in- 
dividual feels he is turning to the left, regardless of the position of 
the head. Vertigo being a cerebral phenomenon, in determining the 
interpretation of the sensation of movement, the cerebrum takes into 
consideration the head and in this way properly interprets the sig- 
nificance of the endolymph movement with the head in any given 
position. In the discussion on nystagmus it is found that since it 
is a simple reflex depending directly on the direction of the en- 
dolymph movement, the direction of nystagmus is influenced by the 
position of the head. 
(2) As vertigo is always in the direction opposite to the endolymph 
movement the following subjective sensations of vertigo are produced 
by turning: 
(a) Turning to right. 
1. Head upright.—Sensation of turning to left. 
2. Head 120° forward. 
(a) Sensation of turning to left in horizontal plane. 
(b) With head brought upright, sensation of falling to left 
in frontal plane. 
3. Head back 60°. 
(a) Sensation of turning to left in horizontal plane. 
46 NOTES ON EYE, EAE, ETC., IN AVIATION MEDICINE 
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46-49 
(b) With head brought upright, sensation of falling to 
right in frontal plane. 
(5) Turning to the left gives exactly the opposite sensation of 
vertigo and falling. 
47. Vertigo after douching.—a. Wafer at 68°.—(1) Douching 
right ear, head upright, produces sensation of falling to left in frontal 
plane. 
(2) Douching left ear, head upright, produces sensation of falling to 
right in frontal plane. 
(3) Douching right ear, head back, 60°, produces sensation of fall- 
ing to the left. 
(4) Douching left ear, head 60° back, produces sensation of falling 
to the right. 
(5) Douching right ear, head 120° forward, produces sensation of 
falling to the right. 
(6) Douching left ear, head 120° forward, produces sensation of 
falling to the left. 
b. Hot water gives the opposite results. 
48. Seasickness.—In speaking of the unpleasantness resulting 
from endolymph movements in the vertical plane, seasickness may be 
referred to as an illustration, A ship at sea tosses in various planes; 
stimulation of the horizontal or vertical canals results, depending on 
the position of the body in relation to the plane of the ship. 
a. Horizontal plane.—From right to left. This is, however, very 
slight and is the only plane of movement that is not unpleasant. 
b. Frontal plane.—A rolling from side to side. Facing the bow of 
the ship, the vertical canals are affected in the frontal plane, and this 
is unpleasant. By lying down with head or feet toward the bow, the 
rolling movement then affects the horizontal canals and the unpleas- 
antness disappears. 
- c. Sagittal plane.—A pitching of the snip fore and aft. By stand- 
ing and facing the bow, the vertical canals are affected in the sagittal 
plane, which is unpleasant. Lying down with the body extending 
across the ship from starboard to port, the pitching movement then 
affects the horizontal canals and the'unpleasantness disappears. 
d. The up and down movement of the ship, rising and sinking, in a 
similar way affects the vertical canals with the individual in the up- 
right position. This unpleasantness is also relieved when the indi- 
vidual lies down, as then the up and down movement affects the hori- 
zontal canals, the stimulation of which is so much less unpleasant. 
49. Past-pointing.—a. Orientation and equilibration.—It is nec- 
essary here first to consider the functions of orientation and equilib- 
47 TM 8-300 
49 
MEDICAL DEPARTMENT 
ration. By orientation is meant the determining of the relation of 
the body in space. Equilibration means the maintenance of position 
whether walking, standing, or sitting. Pointing may be considered 
a cerebral act of orientation. Past-pointing after turning or douch- 
ing is not due to the misplaced position of the eyes or to the dis- 
turbance of vision, but is due to the stimulation of the ears. The 
normal person is always aware of the location of his hand or finger 
in space. Furthermore, with his eyes closed he is aware of the exact 
position in space of objects previously located. 
h. Examinations.—The various examinations can be carried out 
with the shoulders either from above or from below; shoulder from 
the side and shoulder to the side, elbow from above and elbow 
from below; wrist from below; hip from below; neck from below; 
trunk from below. In this study of past-pointing will be consid- 
ered only shoulder from above and shoulder from below, the patient 
in the latter touching the examiner’s finger above, behind the sub- 
ject’s head, and to the side of the patient’s head. In all of these 
methods of examination, the normal patient can with great accu- 
racy and with eyes closed touch the finger of the examiner. After 
ear stimulation, however, with the production of a systematized 
vertigo, he is no longer able to touch the examiner’s finger but past- 
points. If he feels he is turning to the left, he will past-point to 
the right; if he feels he is turning to the right he will past-point 
to the left. 
c. Planes.—The plane of past-pointing is always in the plane of 
the vertigo producing it; the direction of the past-pointing is nat- 
urally opposite to the direction of the vertigo producing it. Here 
again are the same three planes. After an individual is turned with 
the head upright the horizontal canals produce a sensation of turning 
in the horizontal plane. Past-pointing, therefore, occurs in the hori- 
zontal plane to the right or left in the direction opposite to the 
subjective sensation of turning. 
d. Sensations.—Turning sensations following rotation with the head 
inclined 120° forward are in the frontal plane and with the head in 
this position the frontal plane is parallel to the plane of the floor; in 
other words, the same as turning with the head upright. If the patient 
has been turned to the right he feels that he is turning to the left and 
past-points to the right. Now if after turning the head is raised, the 
frontal plane then assumes a position at a right angle with the floor 
giving a sensation of falling to the left in the frontal plane. As he 
feels that he is falling to the left he past-points to the right. Note that 
the result is the same after turning with the head forward; he will 
48 TM 8-300 
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NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
past-point to the right whether the head is kept in the forward 
position or brought upright after turning. 
Turning the individual with head 60° backward, the turning sensa- 
tion is also in the frontal plane and with head kept in this position, the 
frontal plane is parallel to the plane of the floor, hence the sensation is 
the same as turning with the head upright. If he has been turned to 
the right he feels, therefore, that he is going to the left and past-points 
to the right. If the head is now brought to the upright, the frontal 
plane assumes a position at right angles to the floor. Immediately the 
previous sensation of turning to the left is changed to a sensation of 
falling to the right and he past-points to the left. This gives a com- 
plete reversal of the past-pointing and yet the explanation is simple 
and according to rule, that is, the past-pointing is in the direction 
opposite to the vertigo. We always consider vertigo in terms of our 
relation to what is in front of us or below us. After the turning to the 
right with the head back, the endolymph movement is to the right in 
relation to objects in front of us. When, however, the head is brought 
upright, this same endolymph movement is to the left in relation to 
objects above him. His sensation of vertigo is therefore immediately 
reversed when the head is brought upright. 
With the head inclined toward the shoulder, turning produces the 
subjective sensation of turning in the sagittal plane of the head and as 
this plane is parallel in this position with the plane of the floor, the 
individual past-points in a horizontal plane either right or left. If the 
head is now brought upright, the plane of subjective vertigo becomes a 
right angle to the floor, producing a sensation of falling in the sagittal 
plane forward or backward and a past-pointing in the sagittal plane 
either above or below. Turning to the right with the head inclined 
toward the right shoulder, and then bringing head upright produces 
past-pointing upward. Turning to the left with the head inclined to- 
ward the right shoulder produces past-pointing downward when the 
head is brought in the upright position. 
50. Past-pointing’ after douching’.—a. Water at 68°.—(1) 
Douching right ear with head upright produces past-pointing to 
right. 
(2) Douching left ear with head upright produces past-pointing to 
left. 
(3) Douching right ear, head back 60°, produces past-pointing to 
right. 
(4) Douching left ear, head back 60°, produces past-pointing to 
left. 
(5) Douching right ear, head forward 120°, produces past-point- 
ing to left. 
271818°—40 4 
49 TM 8-300 
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MEDICAL DEPARTMENT 
Douching left ear, head forward 120°, produces past-pointing 
to right. 
b. Hot water gives diametrically opposite reactions. 
51. Past-pointing cerebral function.—a. Past-pointing is not 
an ear reaction. Ear stimulation produces only two reactions, nystag- 
mus and vertigo. Ear stimulation causes a pulling of the eyes, this 
being a simple reflex as explained. Vertigo is not a reflex, but is a 
subjective disturbance of the cerebral cortex due to sensory impulses 
received directly from the ear. Pointing, on the other hand, is a 
cerebral act. Neither turning nor douching causes one to past-point. 
The subject is asked to raise his arm and then bring it back to find the 
finger. Before ear stimulation he can do so; after stimulation he is 
unable to find the finger because of the vertigo. Therefore, the law 
of ear tests: where there is no vertigo there is no past-pointing. Ver- 
tigo is the primary reaction; past-pointing the secondary manifesta- 
tion. One conception of past-pointing is that it is due to a cerebellar 
pull of the arm to one side, in the same way that the eyes are drawn to 
one side by the stimulus from the labyrinth. Past-pointing, however,, 
is not a cerebellar function; it is cerebral. Spontaneously, the cerebral 
mandate is to find the finger at the exact point where it is; after ear 
stimulation the cerebral mandate is to find the finger where the cere- 
brum now conceives it to be. In either case the cerebellum carries 
out the cerebral command with accuracy. 
b. Proofs of the above are supplied by the following: 
(1) Successive greater past-pointing if the examiner catches the 
finger each time after a given rotation or douche. 
(2) Compensation, that is, if an intelligent subject knows that he 
usually past-points say 12 inches in a given direction, he can deliber- 
ately over-correct or correct. 
(3) Duration of vertigo and duration of past-pointing are equal. 
(4) Moving finger up and down after turning is accomplished in a 
vertical plane, deviation or past-pointing only occurring if he touches 
some external object and then tries to touch same again. Here the 
sensation is one of leaving the object touched behind him and thus: 
past-pointing to touch same. 
(5) The results of turning with the head back 60° being the same 
as rotating with the head forward 120° in the same direction. This 
has been previously stated and need not be repeated here. 
c. The tracts for pointing and for past-pointing are one and the 
same. The paths of the sensory impulses from the ear to the cerebral 
cortex producing vertigo have been explained. The pointing paths 
are purely motor. They begin in the motor area of the cerebral 
50 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
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51-53 
cortox and end in the peripheral distribution to those particular mus- 
cles which are employed in the pointing tests. These paths are two: 
(1) Pyramided tract.—The power tract, which supplies the motor 
force for pointing. 
(2) Cerebro-s pinal tract.—The accuracy tract. 
Through this tract the cerebellum is able to exercise its synergic or 
inhibitory influence. The pyramidal tract alone would be able to 
supply the necessary energy for the movement, but it is the cerebellum 
that enables the arm to point accurately. Jones explains this ac- 
complishment as follows: In the cerebellar cortex are separate cen- 
ters, one for the outward pointing and one for the inward pointing 
of different joints. As the arm descends to find the finger, if it 
tends to point outward, the inward pointing center restrains this 
aberrant movement and draws it back to its proper course and vice 
versa. 
53. Falling1.—Falling after ear stimulation may be considered as 
a past-pointing of the whole body. The patient falls because of the 
vertigo. Falling is not in evidence when the subjective sensation of 
rotation is in the horizontal plane; in this the individual feels that 
he is being rotated on his own vertical axis and there is no tendency to 
fall. If the vertigo is in a frontal or sagittal plane he tends to fall 
either to one side or the other, or forward or backward. Under all 
circumstances both the past-pointing and the falling are always in 
the direction of the endolymph movements. 
Vertigo being always in the direction opposite the endolymph move- 
ment, falling and past-pointing, being dependent on the vertigo, are 
in a direction directly opposite to the subjective sensation of move- 
ment. Falling reactions, as the past-pointing, are cerebral. The 
patient, having a sensation of falling to the right, throws his body to 
the left and falls to the left, and vice versa. 
After turning to the right with head forward the patient raises his 
head and falls directly to the right. With the head in the upright 
position the endolymph movement is to the right, and therefore falling 
is in the frontal plane to the right, the vertical canals having been 
stimulated in the frontal plane in the turning with the head forward. 
Falling in the sagittal plane is produced when the vertical canals 
are stimulated in the sagittal plane, as with the head inclined toward 
either shoulder. 
53. Falling1 after turning1.—a. Rotating to right.—(1) Turning 
to right, head 120°, and sitting upright, produces falling to right. 
(2) Turning to right, head back 60°, and sitting upright, produces 
falling to left. 
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MEDICAL DEPARTMENT 
(3) Turning to right, head inclined toward right shoulder, and 
then bringing head to upright position, produces falling backward. 
(4) Turning to right, head inclined toward left shoulder, and then 
bringing head upright produces falling forward. 
b. Exactly the opposite results are obtained by rotating to the left. 
54. Falling after douching.—a. Water at 68°.—(1) Douching 
right ear, head upright, produces falling to right. 
(2) Douching right ear, head back 60°, produces falling to left. 
(3) Douching left ear, head upright, produces falling to left. 
(4) Douching left ear, head back 60°, produces falling to right. 
b. Hot water gives directly opposite results. 
55. Summary.—The entire physiology of the ear tests may be 
summed up in four sentences, as follows: 
The eyes are always drawn in the direction of the endolymph 
movement. 
b. The vertigo is always in the direction opposite to the endolymph 
movement. 
(1) Past-pointing is always in a direction opposite to the vertigo. 
(2) Falling is always in a direction opposite to the vertigo. 
Section IX 
VESTIBULAR TESTS 
General 56 
Nystagmus 57 
Pointing T 58 
Falling — 59 
Caloric douche test 60 
Paragraph 
56. General.—a. To whom given.—For many years the vestibular 
tests were required on all original examinations. This was a hold-over 
from the early days of aviation when undue stress was placed upon the 
labyrinth. It was believed that to be a good pilot one must possess an 
unusually refined type of labyrinth in order to imitate the birds. With 
increased experience the “sense of equilibrium” has now been giten its 
proper evaluation in the examination and vestibular tests are given in 
the following types of cases: 
(1) Those who give a history of trainsickness, seasickness, swing- 
sickness, or airsickness. 
(2) Unsteadiness on the self-balancing test. 
(3) Cases showing marked tremor of lids and fingers. 
(4) Unsteadiness on Romberg and gait tests. 
(5) Cases who have a sitting pulse of over 90. 
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NOTES OX EYE, EAR, ETC., IX AVIATION MEDICINE 
b. Equipment.—All tests are given in a turning chair equipped with 
an adjustable headrest, a foot support, and a stop pedal. 
c. Reactions tested. 
(1) Nystagmus, to the right and left. 
(2) Pointing (past-pointing), to the right and left. 
(3) Falling, to the right and left. 
d. Technique.—The technique for making the above tests is given in 
the following paragraphs. 
57. Nystagmus.—With head 30° forward, so that the tragus of 
the ear is on a horizontal line with the external canthus of the eye, 
the examinee is asked to fix his eyes on a distant point and the chair 
is turned slowly from side to side in order to note whether or not a 
spontaneous nystagmus is present. Then turn examinee to the right, 
eyes closed, ten times in exactly 20 seconds. The instant the chair is 
stopped click the watch; examinee opens his eyes and looks straight 
ahead at some distant point. There should occur a horizontal nys- 
tagmus to the left of 26 seconds’ duration. Examinee then closes his 
eyes and is turned to the left; there should occur a horizontal nystag- 
mus to the right of 26 seconds’ duration. 
For all three classes a nystagmus of 10 to 34 seconds is qualifying, 
provided it is approximately of the same duration in the two direc- 
tions. Any variation in the twm directions of more than 5 seconds 
should arouse suspicion of labyrinthine or brain disturbances and 
should call for the caloric douche test. 
58. Pointing.—a. Examinee closes eyes, sitting in chair facing 
examiner; touches the examiner’s finger held in front of him; raises 
his arm to perpendicular position; lowers the arm and attempts to 
find the examiner’s finger. First the right arm, then the left arm. 
The normal is always able to find the finger. 
b. The pointing test is again repeated after turning to the right ten 
times in 10 seconds. During the last turn the stop pedal is released, 
and as the chair comes into position it becomes locked, care being 
taken to ease the chair into the slot so as not to throw the examinee out. 
The right arm is tested; then the left; then the right; then the left, 
until he ceases to past-point The alternating of arms is kept up even 
after he ceases to past-point with one arm. The examinee should 
watch the arm at the top of the swing. Experienced flyers often 
correct their past-pointing before the arm is brought down. If there 
is no past-pointing at the bottom of the swing, have the candidate past- 
point from below up. The normal will past-point to the right three 
times with each arm. If he past-points once in each direction with 
each arm, the test is satisfactory for all classes of examination. If 
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MEDICAL, DEPARTMENT 
he past-points more than six times, he will be disqualified. This 
applies to all three classes of examination. 
c. Repeat pointing test after turning to the left, 
59. Falling.—Examinee inclines head 90° forward, resting his 
forehead on his upper fist, his fists being placed one above the other 
on his knees, which are brought close together, or the headrest may be 
used. Turn to the right five times in 10 seconds. On stopping, ex- 
aminee raises his head and should fall to the right. This tests the 
vertical semicircular canals. Turn to the left, head forward 90°; on 
stopping, the examinee raises his head and should fall to the left. The 
examiner should place his hand in readiness to press on the back of the 
neck of the examinee as he starts to sit up. When it is clear that he is 
falling properly, force his head down again, as this will avoid many of 
the disagreeable sensations. If this test is unsatisfactory, give him the 
caloric douche test. Unless each test is normal, it is a cause for rejec- 
tion for any class. 
60. Caloric douche test.—So-called borderline cases can be tested 
by-the caloric test, each ear separately. Water at 68° F. is allowed to 
run into the external auditory canal from a height of about 3 feet 
through a stop nozzle with the head tilted 30° forward, until the eyes 
are seen to jerk and the individual becomes dizzy. This should be ac- 
curately measured by a stop watch. The type of nystagmus is then 
noted. With head in upright position it should be rotary and the 
direction of the jerk should be to the side opposite the ear douched. 
The length of the douching shown by the stop watch in the normal is 
40 seconds. The eyes are then closed and the past-pointing is taken. 
The head is then immediately inclined backward 60° from the perpen- 
dicular; there should appear a horizontal nystagmus to the side oppo- 
site the ear douched. The eyes are then closed, and the past-pointing 
is taken with the head in this position. The left ear is then douched, 
and the same procedure is carried out. If instead of 40 seconds of 
douching there was required not more than 90 seconds, the examinee is 
not rejected. Care should be taken that the cold water reaches the 
drumhead, as wax or other obstruction in the external canal would 
interfere with the responses in a perfectly normal individual. 
Section X 
BLIND FLYING 
General 61 
Medical contribution 62 
Paragraph 
61. General.—a. Essentials.—To master blind flying the pilot 
needs just two things—a knowledge of his instruments and a knowl- 
54 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
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edge of his ears. Unless he understands the sensations from his ears, 
he is at least bound to pass through a disturbing period, which is en- 
tirely unnecessary. More than this, his lack of knowledge about his 
ears may lead to disaster. 
h. Popular conception.—In the popular mind blind flying has an 
element of mystery. Not so long ago certain of the transport com- 
panies in their publicity gave the impression that “their pilots were 
able to flv in any kind of weather.” This sort of thing only adds 
to the impression that there is only some particular and remarkable 
type of pilot that is able to do this mysterious thing, and that if one 
Figure 2.—Instrument board equipped for blind flying. 
flies in bad weather and arrives safely, he ought to congratulate 
himself and feel that he is very fortunate to get through. So far 
as the special senses of the pilot himself are concerned the human 
side of this problem was thoroughly understood in 1918.* Today if 
there is anything in the world mastered, known thoroughly, it is the 
principles of blind flying. 
c. Improvement.—“Blind flying” is also termed “instrument flying.” 
There will be improvements in the instruments of precision, and every 
♦Isaac H. Jones, M. D., Equilibrium and Vertigo, J. B. Lippincott Company, 1918. 
55 TM 8-300 
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MEDICAL DEPARTMENT 
little improvement will, of course, be welcomed. But one should know 
that the present instruments are first-rate. They work. One should 
think not only of the future, but should realize wdiat is being done 
right now. 
d. Blind landing.—“Blind landing” is the next step. The first 
blind landing was made in 1928. Soon after this a blind landing was 
done in a covered cockpit. The pilot could see nothing except his 
instruments. He flew west for 15 miles, then back until the “radio 
beam” told him he was directly over the landing field, then east for 
2 miles, turned and headed back for a beautiful three-point landing; 
then he got out and took a look around for the first time since he had 
started on the flight. In the past 2 years so much has been done in 
blind landings that soon this also will become commonplace. It 
will then be taken for granted, just as today blind flying is taken for 
granted. 
e. Safety.—It used to be very dangerous to fly “blind.” But it need 
not be so today. With the necessary instruments, any good pilot who 
understands his own ears and is taught to fly blind can now do so 
with complete safety. 
/. Ear—instrument discrepancy.—All that is known today about 
the ears and how they work was known back in the beginning, but 
the instruments were not available. These precision instruments are 
accurate and dependable. They give the pilot definite information, 
but his ears may give him contradictory information when he is fly- 
ing blind. The instruments tell him one thing, but he feels another 
thing. Therefore, the pilot’s difficulty today lies in his attempt to 
reconcile what the instruments tell him with what he feels. It is a 
very simple problem with a simple answer. Any pilot can under- 
stand the essentials of his vestibular sense after y2 hour’s instruction 
by a flight surgeon. Every pilot, either military or commercial, 
should be required to receive this instruction. It is so simple, but 
so important. The earlier the pilot receives this instruction, the 
better. The ideal would be for every student pilot to be taught to 
fly blind as soon as he has learned the mere rudiments of flying. 
The beginner has no difficulty in learning blind flying; the veteran 
pilot has great difficulty. He has to unlearn so much. Such in- 
struction in the vestibular sense by a flight surgeon is the very basis 
for training in flying blind. 
g. Origin of studies.'—Studies of blind flying were begun in May 
1917 by a pilot and a flight surgeon. At the beginning of the World 
War, at Essington, Pennsylvania, there were two little 1915 Curtiss 
Pusher seaplanes and 20 cadets. There was a similar little organiza- 
56 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
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61 
tion at Mineola, Long Island, and another at North Island, San 
Diego. That was about all there was to the air service at that time. 
The investigators could only speculate about the problem. It was 
known that flying, more than any other activity, would make the 
most exacting demands upon the eyes, the nervous system, and the 
heart. But even in the beginning it was sensed that the brand new 
problems in aviation were those of the vestibular sense (whirling, 
airsickness, and blind flying) and the problems of oxygen want. 
h. Ear 'problem.—Considerable was already known about the oxy- 
gen problem. For many years this had been studied, on high moun- 
tains and in balloon ascensions. But in the problem of whirling and 
blind flying there was nothing whatever to guide. No one knew any- 
thing about rotating in the air and its results. It was known that 
it is an ear problem; that the ears of the aviator should not be “dead” 
or too active; and it w~as realized that the vestibular sense had a 
greater importance in aviation than in any other human activity. 
But it was not known until later how vital it is for the aviator him- 
self to understand these little organs which even to this day so few 
pilots realize are hidden away in their skulls. 
i. Weather.—At that time nobody actually went into a cloud if 
he could possibly avoid it. In fact, he always waited until the 
wind died down before going up, usually about 5 P. M. or about 
sunup. Pusher airplanes were barely able to maintain flying speed. 
They were unsafe except under the best weather conditions—and 
not safe even then. It never occurred to anyone to fly in bad weather. 
So at first there was no chance to study the problem of flying blind. 
At that time all that was known was that an earnest study of the 
“ear and aviation” must be made. 
j. Ear senses change in motion.—Before there was actual experi- 
ence, it was wondered whether the ear might enable the pilot in a 
fog to tell whether he was right side up or upside down. This was 
a forlorn hope. It was soon found out that neither the ear nor any 
other organ can keep one straight wdien he is flying blind. The ear 
cannot tell position in space. When a plane takes off, the ear 
senses the sudden change of speed; when it is flying at a constant 
speed the ear senses nothing; each change of speed gives a new sen- 
sation; but in a well executed banked turn the ear is not affected in 
the least, since the pull of centrifugal force neutralizes the pull of 
gravity. The ear is not affected because it senses only a change of 
motion. So the senses cannot tell one where he is. 
h. Importance of ear studies.—For a while too many came to think 
that if the ear could not do everything as hoped, there was no need 
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MEDICAL DEPARTMENT 
to pay much attention to the ear or to ear studies. The ear went 
under a cloud of disapproval. But as time went on it was found 
out that a good foundation had been laid in creating studies of the 
ear, which organ it is far more important for the pilot to understand 
than was dreamed back in the beginning. 
l. Information from ear.—Like the eye, the ear can give correct 
information and it can also give incorrect information—illusions. 
What correct information the ear gives to the pilot should be con- 
sidered before illusions. 
m. Source of sense of motion,—How is motion sensed, anyhow? 
Where does the information come from so that one is able to detect 
whether moving or not ? One cannot tell much by the senses of touch, 
smell, or taste. Practically all information comes from three 
sources—the eye, the ear, and the “general” sense. It is known that 
the eye and the ear can detect motion, but what is meant by the 
general sense? The brain receives information from the muscles, 
joints, the intestines—and in fact from all parts of the body. This 
is what is meant by the general sense. From different parts of the 
body nerves go into the spinal cord, which carries the impulses to 
the brain. If one has, for example, locomotor ataxia, these impulses 
are interrupted. Such a person has a poor general sense. 
n. Motion in vertical line.—Experiments were performed during 
the World War to find out what information the pilot gets from the 
eye, the ear, and the general sense. The detection of motion in a ver- 
tical line was studied in elevators that made a trip of 40 stories, a 
height of 400 feet. The elevator shafts and the men were in the dark 
so that no information could come from the eyes. The elevator car 
was lined with thick blankets so that no information could come from 
the sense of touch. The individual could learn nothing except for 
his general sense and from his ears. Three groups of men were se- 
lected—-normals, deaf-mutes with no vestibular function, and patients 
with locomotor ataxia who lacked the normal general sense. These 
studies showed that the general sense could inform the individual 
when his movement was changing. The direction of the motion was 
chiefly determined by the ear. The ear was not accurate in telling 
that the elevator had stopped because the wave impulses in the ear 
still affected the ear, even though there was no motion. This is the 
illusion. It is the same thing that happens after turning to the right 
in the turning-chair and stopping—one feels he is turning to the left, 
although he is actually sitting still. 
o. Feel of ship.—The next study, on the “feel of the ship,” was made 
in actual flight. The pilot sat in the rear cockpit and the one to be 
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tested in the front cockpit. When about to change from the straight 
line, the pilot would reach forward and tap the man on the shoulder. 
The man would then write down what he thought the airplane had 
done. Those with normal ears were compared with seven deaf-mutes 
that had no vestibular function. All were blindfolded. Those with 
normal ears were fairly accurate in their detection of motion during 
these flights. The deaf-mutes were not. 
p. Air—chair relationship.—As a result of these studies it was con- 
cluded that one who shows good responses in the turning-chair shows 
good detection of motion in the air. JOne who shows poor responses 
in the turning-chair shows poor detection of motion in the air. It was 
expressed, “There is a direct relation between the chair and the air, 
and the air and the chair.” 
q. Contributions of psychologists and physiologists.—Earnest work 
was also conducted by a group of eminent psychologists and physiol- 
ogists. Before, it was thought that the nystagmus could not be altered 
by experiences in turning; they showed that if a man is turned, over 
and over again day after day, the duration of the nystagmus would 
become shorter and shorter. Also, it had been thought that the fluid 
in the ears actually moved; their experiments suggested that it does 
not move. A scientific storm raged for years on this subject. Otologists 
said it did move and the psychologists said it didn’t. Of course, so far 
as tests of the ears are concerned, it makes no difference whether there 
is an actual movement or a wave impulse. The latest work on this 
subject was done by injecting india ink, and then one drop of oil, into 
a semicircular canal of a fish. It was shown that, after turning, the 
drop of oil follows the movement of the fluid in the canal; that the 
eyes jerk only when the hairs are displaced; and that, although the 
movement acts for only a short time, the displaced hairs do not regain 
their normal position for 20 seconds. Regardless of different opinions 
it was known that either an actual movement or a wave impulse does 
occur and that this results in a displacement of the hairs.. 
r. Education of senses.—To this day most aviators still think it is 
a weakness if they have dizziness, nausea, or any other vestibular 
response, either in the turning-chair or in the air. There were also 
some doctors who thought that the safest aviators would be those 
whose ears do not work—because they do not have the illusion which 
normal persons have after spinning nose dives and other whirling 
maneuvers. This sounds plausible until a little thought is given to 
it. All normal sense organs can give illusions. Surely the aviator 
needs all the information that he can get from all of his senses. First 
of all he needs normal senses, including the vestibular sense. He then 
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MEDICAL DEPARTMENT 
needs the education of all of his senses, including the vestibular sense. 
In mastering seasickness, or whirling dances, or acrobatics, the brain 
must learn to interpret the unusual impulses from the ears. A whirl- 
ing dance may be well performed by a beginner, but the expert dancer 
can suddenly stop still without falling. The beginner falls down 
simply because he has not had experience. The difference between 
the artist and the beginner is that the artist has come to understand 
the impulses from his ears. 
s. Cat question..—After the World War, work was done to settle the 
problem of how much each of the senses contributes to the detection 
of motion. Although it was not recognized at the time, a way to do 
it was found. It seemed that one of the most remarkable feats is 
performed by the cat when he falls in the air. He always rights 
himself and always lands on his feet. The question was, “Why and 
how does a cat turn over?” It was felt that if this could be discovered, 
exactly how much each of the senses contributes to the detection of 
motion would be known. 
t. Experiment.—Cats and dogs were dropped and their movements 
from the moment they were dropped until they landed on a soft mat 
were analyzed by means of slow-motion photography. The animals 
were held upside down and then dropped. First normal cats and 
dogs were studied; then a number of the cats were operated upon. 
Of course the operations were done under ether and the cats were 
nursed until they had fully recovered. Then the pictures were taken 
all over again. 
u. Results.—By watching the slow-motion pictures every detail of 
the movements of the animals can be seen. 
(1) Normal cats, kittens, dogs, and puppies.—Immediately after 
they are dropped, all cats and kittens turn right side up—extend all 
legs downward with back humped upward, float downward, and land 
perfectly. The dogs do the same, only the dogs do not turn so 
promptly and do not hump the back so much. 
(2) Same normal animals blindfolded.—The cats and kittens turn 
over just as promptly as with the eyes open; hump the back just the 
same and land as well, but crawl away with bellies close to the mat. 
(3) Cats and kittens whose internal ears had- both been operated, on, 
and were not working—eyes open.—Do not turn over. On descending, 
roll over and over until earth is struck. 
(4) Same cats and kittens blindfolded.—Same result, except that on 
landing, crawl off with bellies close to the mat. 
(5) Gats and kittens with one internal ear not working.—Better per- 
formance than those with both ears not working, but not so good as 
the normal. 
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(6) Cat with one ear not working plus absent cerebellar hemisphere 
of opposite side.—(The “cerebellum” is the “small brain”; it coordi- 
nates movements.) Indefinite but generally poor, both in delayed 
turnings and variable landings. 
(7) Cat with one ear not working plus absent cerebellar hemisphere 
of same side.—Same result, 
(8) Cats with removal of one cerebellar hemisphere without oper- 
ation on either ear.—Turn over very well, both with eyes open and 
blindfolded. Performance almost as exact as that of normal cats. 
v. Conclusion.-—When these studies were started it was known 
that the ear played a part; when they were completed it was found 
that the ear is really the answer. When the cats were actually 
dropped very little could be told. It all went too fast. But the 
slow-motion pictures were so beautifully taken that each animal 
could be seen to turn over and then slowly drift to the mat. The 
normal animals, blindfolded, turn over just as promptly as when 
their eyes are open and then float downward until they make a 
perfect landing. But these same cats, after their ears are operated 
upon, do not turn over at all, even when their eyes are open. On 
descending they roll over and over and make no attempt to right 
themselves. So the importance of the ear in sensing motion was 
realized. The complete “feel of the ship,” which is the “sense com- 
plex” that makes for a first-class pilot, requires internal ears that 
are working. 
w. Vestibular sense.—From the pilot’s standpoint it is all very 
interesting for him to know how important his ears are in his detec- 
tion of motion. He realizes that he is constantly receiving im- 
portant information from his ears (without being in the least con- 
scious of it). But it is so much more important for him to under- 
stand his vestibular sense because of the illusions. These illusions 
have disturbed every man or woman who has ever gone up into the 
air. All pilots have come to disregard them so long as they can see. 
The serious thing is for the pilot not to understand these illusions 
when he can’t see. But while one studies “how the ear can fool one” 
he must always keep in mind that it is the normal ear that is capable 
of giving the illusions. But the eye or ear is not merely an organ 
that may at times give illusions. They are both constantly giving 
good and helpful information, invaluable in seeing, in hearing, and 
in sensing motion. 
x. Conception of airplane.—It was originally thought that the air- 
plane was an automobile with wings, that this contrivance simply 
went up in the air instead of running along on the ground, and 
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MEDICAL DEPARTMENT 
that, relying upon senses, one could drive it just as he was accustome'd 
to drive an automobile. The change in the attitude of flight sur- 
geons as well as pilots during the succeeding months and years came 
with experience. They came to realize that the airplane is not an 
automobile, but a ship—a ship navigating the ocean of the air. One 
of the great reasons for advancement and safety in flying is this 
change in mental attitude toward it. 
y. Birds and Mind flying.—Any overconfident pilot who still feels 
that he can rely upon himself and his own senses in meeting all 
the conditions in the air is in danger. He is apt to come to grief. 
Through all the ages the bird has been meeting the conditions in 
the air. He has internal ears of tremendous size and he has used 
these and the parts of the brain that are connected with the ear 
through countless experiences from the time when the first bird took 
to the air. Yet a bird always avoids a fog or a cloud. A bird is 
not found flying in the clear air above the clouds—no doubt because 
he did not wish to fly up through them. In short, even the bird is 
not at his ease when he is flying blind. 
z. History of 'precision instruments.—(1) The answer to the prob- 
lem of blind flying is instruments of precision. Much time passed 
before instruments of precision were available for the airplane. 
Through all the early years most aviators felt that their natural 
instincts were better guides for operating their craft than the best 
instruments available. Years were required to convince the majority 
of fliers that their old belief was wrong and the cause of so many 
fatal crashes. Wilbur and Orville Wright were conspicuous excep- 
tions. They designed the first instrument ever used. It was a string 
about 8 inches long. This cord was fastened in front of the pilot 
with one end swinging free. So long as this string pointed directly 
at the pilot’s nose the ship was flying without slipping or skidding. 
This was in 1912. In 1814 they brought out a pendulum bank-indi- 
cator, and also an accurate rate-of-climb indicator. These two were 
used in conjunction with the earlier string. But they found it diffi- 
cult to get even their own student pilots to use these instruments 
because of the humiliation when other aviators would say that the 
sudents of the Wright Brothers found it necessary to use instruments 
in flying. In other words, for many years instruments were not 
popular. Fliers took pride in scorning them. 
(2) Until the World War began in 1914, airplanes carried few 
instruments. These as a rule were crude; and air activity ceased dur- 
ing foggy weather. The reverse will probably be true in future wars, 
and most of the flying will purposely be done in bad weather. 
62 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
61 
(3) Blind flying had its real beginning for our country in 1917 
when a “turn indicator” was produced. That year, with the aid of 
this instrument, a fog flight over the Allegheny Mountains from 
Washington, D. C., to Ohio was made. This turn indicator was 
described by its inventors as a “crutch” for the magnetic compass. 
(4) The modern instruments include the Sperry gyro-horizon, the 
directional gyro, the turn-and-bank indicator, the rate-of-climb, the 
rate-of-speed, the sensitive altimeter, and the flight integrator, now 
being perfected. It is the combined use of all these instruments that 
stabilizes the mind of the pilot. Each instrument makes its own con- 
tribution. The end result is. that the pilot has a definite conception 
of his position in relation to the external world. In other words, 
all of the precision instruments combine to tell the pilot his position 
and his relation to the horizon. 
(5) These instruments are so reliable that one would think it a 
simple matter for anyone to rely upon them and fly safely in any 
kind of weather. To this day, however, many a pilot is sending his 
instruments back to the manufacturer to have them corrected—only 
to have the instruments returned with the information that they are 
in perfect condition. In brief, such a pilot does not trust his instru- 
ments, because his own sensations conflict with what the instruments 
tell him. All his anxiety is unnecessary. 
aa. Ear deaths.—If one analyzes the disasters of modern aviation, 
he cannot fail to be impressed with what has come to be an old story: 
“bad weather,” “fog,” “storm”—in brief, blind flying. During the 
World War each crash was investigated by a committee consisting 
of the commanding officer, the officer in charge of flying, and the 
flight surgeon. The results of all of these crash reports were studied 
and tabulated. Many of the accidents were caused by weakness of the 
airplane and motor failure. Certain airplanes burned in the air and 
in those days there were no parachutes. In addition many crashes 
were due to what was even then termed “ear deaths.” There is a great 
contrast today. Structural defects and motor failures are practically 
unknown. The “ear deaths” still occur. 
db. Illusions.— (1) In the railroad station one is sitting at the win- 
dow of the car looking out. Suddenly his train starts to go forward. 
He rushes out to the platform to wave good-bye to friends, but the 
friends are still there and so is the platform. He was not moving; 
it was another train that was coming toward him. Immediately he is 
at his ease. He thoroughly understands the situation. He knows 
where he is and why. 
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MEDICAL DEPARTMENT 
(2) Now consider the illusions that may come from the ears, par- 
ticularly in blind flying. In a fog, after the pilot has rotated in the 
air and the ship straightens out, his own head is no longer actually 
turning. But anyone who knows the first thing about the ear knows 
why he feels that he is rotating in the opposite direction. In other 
words, in the railroad station one has an illusion from his eyes, and 
now one has an illusion from his ears. He feels that he is going in 
the opposite direction when he is not. He has “vertigo”—a sensation 
of movement contrary to fact. All he needs to do is to look at the 
instruments in front of him and believe in them. Immediately he dis- 
regards the feeling that he is turning. He pays no attention to his 
feelings. He understands them. The sensation in the head of the 
pilot is exactly the same as when one comes out of the railroad train 
and looks at the platform. The illusion is gone. He knows the facts 
of his position. 
ac. Buggies orientator.—In 1918 the Buggies orientator was a 
great step in advance. It is, so to speak, a turning-chair that re- 
volves in every direction. The pilot sits in a cockpit and rotates it in 
every possible direction. This was, and is, a great help, because it 
enables the pilot to get used to these queer sensations while he is 
safely on the ground. 
ad. Training.—The pilot should be trained to understand his ears. 
First he taught with the “instrument box on the turning-chair.” 
Then he is instructed in actual flight “under the hood.” * 
(1) Instrument hox on turning-chair.— (a) The “instrument box 
on the turning-chair” is the key to blind flying. The principle is to 
show the pilot how to understand his ears and his instruments at the 
same time. The procedure is simple. The pilot is rotated—prefer- 
ably in the presence of other pilots. He is turned to the right and 
then the chair is stopped. He calls out, “I am turning left, to the 
left.” He is then turned very rapidly to the right, and then slowly 
to the right. He may say, “I am not moving,” or “I am turning to 
the left,” whereas all the observers assure him he is turning to the 
right. 
(h) The pilot is then told to look into the instrument box. A 
flashlight in the box shows a turn-and-bank indicator and a compass. 
As he looks at the instruments he is again rotated. He watches the 
instruments while he is being rotated. He says, “I am turning right; 
the indicator also shows I am turning right.” When the speed of the 
chair is slightly reduced, he will say, “The indicator shows I am turn- 
*Blind Flight, by Lt. Col. William C. Ocker and Capt. Carl J. Crane, published in 1932 
by the Naylor Company, San Antonio, Texas. 
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NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
ing right; my senses tell me that I have stopped,” or “The indicator 
says that I am turning to the right, but I feel that I am turning to 
the left.” 
(c) It frequently happens that the pilot who has just had this dem- 
onstration will argue that his sensations are correct, in spite of what 
the instruments tell him. In that case it is helpful to have him stand 
by and watch someone else go through the same performance. As a 
rule a few such experiences in the turning-chair will convince the 
pilot that he can rely upon the instruments. His thought then is 
“Oh, yes, I have that feeling of turning, but I am not actually turn- 
ing.” From that moment his problem is solved. 
(2) Hood.—(a) The next step is actual flight under the hood. 
Such instruction requires more time, largely because of the element 
of fear. But after the pilot has mastered flying under the hood he 
no longer has any fear or apprehension when he suddenly enters a 
cloud. The most difficult fliers to train are the old veterans. Blind 
flying should be taught early—the sooner the better. As soon as a 
pilot is at his ease in flying blind he has then mastered the situation. 
When he suddenly enters a cloud he feels at home. When he is able 
to see, so much the better. 
(5) To teach the pilot to interpret his instruments and respond 
automatically to what the instruments tell him, a hood was put over 
the cockpit in the Buggies orientator, which can be “flown” by 
either the pilot inside or his instructor outside. The orientator ro- 
tates the pilot in every conceivable manner; the more recent Link 
trainer has more limited movements, but it duplicates many of the 
motions of the airplane—the turns, banks, glides, and climbs. After 
he gets out of the orientator or the trainer, the pilot can see how 
well he responded to his instruments, because his performance is 
recorded on a chart. In addition to becoming familiar with the in- 
struments the pilot is also receiving messages through his earphones 
and learns to interpret the direction signals by radio. This not only 
helps him to fly blind but instructs him in “avigation,” which means 
the navigation of the air. When flying blind, the pilot must not 
only be able to keep the plane in proper position but must be able, by 
avigation, to arrive at his destination. This is best accomplished by 
radio messages which guide him to the proper place. 
ae. Sperry gyro pilot.—There is one motion-sensing device that is 
perfect. It detects changes of motion accurately. It has absolutely 
no illusions. This device is the Sperry gyro pilot. It is now in use 
on most of the air lines everywhere. The attractive feature of the 
gyro pilot is that it is automatic. The human element is eliminated. 
The gyro pilot not only detects motion—it actually operates the 
271818°—40 6 
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MEDICAL DEPARTMENT 
controls and holds the airplane in correct flying attitude. About 75 
percent of all air-line flying in the United States is now done by the 
gyro pilot. 
af. Ignorance of 'pilots concerning ear.—A thorough knowledge of 
the ear has been available to the pilot since 1918. Of course, fliers 
would not see, or understand, the medical books; but it is hard to 
understand why, in some way, they have not become acquainted with 
at least the simple facts that have been known for such a long time. 
To this day, out of one thousand pilots there is perhaps only one who 
knows that he has a vestibular part of the ear. Any intelligent pilot 
simply needs to be told the following: Remember that just because the 
eye can fool one, it does not mean that one does not need his eyes. 
And just because the ear can fool one, it does not mean that one does 
not need his ears. It is highly desirable to have good eyes; and in 
flying more than in any other occupation one will be helped by nor- 
mal motion-sensing impulses from the ears. With all one’s organs 
and senses, the nearer one is to a full normal the better it is for him. 
One must simply come-to understand his ears, not only for the correct 
information which they give, but for the incorrect information which 
they may give, when flying blind. In clear weather the ear helps to 
give the “feel of the ship.” In a fog, after one comes out of a spin 
and the ship straightens out, he feels that he is spinning in the op- 
posite direction. If the pilot simply looks at his instruments and 
believes in them, he will know the facts of his position. He will 
realize that his sensations are contrary to fact. In brief, just as the 
eyes can fool one, so the ears can fool one. But the difficulty is that 
although one knows perfectly well what the eyes are for he does not 
understand his ears. The ear is thought of as the motion-sensing 
organ that receives impulses from without—what is called hearing. 
But it is the other part of the internal ear, the part that senses the 
motion of the airplane and the pilot, that is far more important to 
understand. Knowledge of this little organ may make all the differ- 
ence between safety and disaster. A pilot will be much better and 
safer if he studies and understands this little motion-detector in his 
internal ear. 
62. Medical contribution.—a. Conception of term.—Many avia- 
tors and most laymen have no proper conception of the term “blind 
flying.” To the vast majority it simply means flying when the pilot 
cannot see things clearly. To the properly trained aviator, the ability 
to do blind flying, and to understand the basic underlying human 
reactions governing the same, means the difference between life and 
death. 
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NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
b. Popular education,—The pioneer medical research work accom- 
plished during 1926 firmly established the basic principles from the 
human standpoint on which the art of blind flying is founded. A re- 
port of this research and the conclusions arrived at were placed on file 
in the office, Chief of the Air Corps, War Department, in 1926. Fol- 
lowing the filing of this report, articles began to appear in many 
popular and technical magazines, newspapers, etc., on “blind flying.” 
These articles were prepared by “feature writers”, usually after an 
interview, and were released for the purpose of bringing this new dis- 
covery in aviation to the attention of the public and to create an in- 
terest in the matter by aviators in general. Naturally, the dramatic 
side was emphasized. Many lectures and demonstrations before civic 
bodies, clubs, and technical societies were given. In all of the articles 
published and the lectures and demonstrations given, the basic prin- 
ciples discovered were freely discussed and explained, resulting in a 
more or less general understanding by the public of the underlying 
physiological reactions experienced in blind flying. 
c. Definitions.— (1) Blind flying.—Research work attains value of 
importance only when its results can be directly applied to either 
clinical findings or practically used in some one of the vocations 
of life. In order that the relationship between blind flying and the 
research accomplished may be understood, it is essential to know 
what blind flying is. Blind flying is that flying accomplished in 
which any visible reference to the earth for the purpose of recog- 
nition of position is impossible by reason of fog, storms, dust, com- 
plete darkness, thick clouds, etc. 
(2) Simulated blind flying,—Simulated blind flying is that flying 
in which visual reference to the earth for the purpose of recogni- 
tion of spatial position is limited to the pilot’s cockpit and its 
equipment by means of proper coverage of the cockpit. Simulated 
blind flying is that flying accomplished by visual reference to the 
instruments installed in the airplane; therefore, the proper term is 
“instrument flying” or, as it is expressed by airmen, “flying under 
the hood,” 
d. Efforts to fly.—Since the beginning of time and until recent 
years mankind has traveled almost entirely on the surface of the 
earth or the oceans. Man’s invasion of the air began when small 
animals attached to balloon? were sent into the air to ascertain if 
life were possible above the earth’s surface. They all returned 
safely to earth, with the exception that one suffered a broken leg, 
thus establishing the fact that this contemplated flying era would 
produce its category of ills and problems for the doctors to treat 
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MEDICAL DEPARTMENT 
and solve. From this time to the epoch-making flight of the 
Wrights at Kitty Hawk mankind continued his efforts to fly. From 
the Wrights at Kitty Hawk to the present space-annihilating air- 
plane is a long way in terms of transportation. It has been a much 
longer way in terms of adapting the human body to the changes 
and the solution of the medical problems presented. 
e. Special senses.—The present generation is the first to move freely 
in three dimensions asi do the birds and fishes. The evolution of 
mankind had reached a more or less fixed stage when aviation was) 
born, and, as flying was not concerned in this evolution, mankind 
developed into an “earthbound” entity. Every human being, in 
arriving at his present state, has had one common factor in his de- 
velopment—contact with mother earth. Individually each is noth- 
ing more than the sum total of his experience stored up in the 
brain, plus the body he lives in. These experiences are obtained 
for storage as the result of the action of our special senses: sight, 
hearing, smell, taste, and touch. Two more, vitally important to 
the aviator, are muscle sense and vestibular or kinetic-static sense. 
/. Fwnction of senses.—Stimulation of any of these senses arouses 
action, and action eventually results in consciousness, a knowledge 
of environment, and a perception of the physical facts constituting 
that environment. It is apparent that all stored up experience has 
had a common stimulator, contact with the earth and its material 
objects. Experience, based on special senses, has taught one how to 
adjust himself to various environments. The lessons learned from 
experience are indelibly impressed in the consciousness. One of the 
earliest lessons learned is how to maintain equilibrium. Undoubt- 
edly equilibrium is a bodily function maintained by the action of all 
of the special senses. Some of these senses enter very little into 
this maintenance; taste, smell, and hearing have little, if any, effect; 
tactile sense or touch, used in connection with muscle sense, has a 
little more effect. Chiefly, if not entirely, our equilibrium is main- 
tained by means of a coordinated cooperation of sight, muscle sense, 
and vestibular sense. By the use of this “trinity sense” one is able 
to maintain and realize position, rate, and direction of motion, and 
generally orient himself in relation to the earth, 
g. Equilibrium..—(1) Man’s equilibrium on the grovmd consists of 
the ability to maintain his body in any position it is possible or desir- 
able to put it. Man’s equilibrium in the air consists of the ability 
to maintain an airplane, which he has become a part of, in any posi- 
tion it is possible or desirable to put it, plus the added factor that all 
contact with the earth is entirely lost except for two things, sight 
68 TM 8-300 
62 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
and the column of air the plane is flying in. Human sensations, reac- 
tions, and consciousness having developed after countless years of con- 
tact with the earth, it is not possible for man to invade the air and 
safely function using the prior experiences stored up in his brain by a 
set of special senses evoluted in contact with the earth. 
(2) Stabilized equilibrium, either in the air or on the ground, is 
maintained only when each of the trinity of senses—sight, muscle 
sense, and vestibular sense—functions correctly, and their stimulations 
are correctly interpreted by the. brain. Some equilibrium and orienta- 
tion may be present with all three imperfectly acting. Adjustment 
to environment will take place if two remain unimpaired. The com- 
binations of impairment, function, and adjustment are many.- All 
compensatory equilibrium or adjustment to environment, however, has 
been developed on the ground, and in taking to the air we separate 
ourselves from the universal common factor, earth contact, and attempt 
to function with a set of senses and stored up experience developed for 
earthbound use only. 
h. Interpretation of senses.—Since time began human beings have 
been receiving sensations in their brains and storing them away for 
future use and guidance when the same situation again arises. In the 
process of storing away these sensations the brain has accomplished 
many seemingly weird things. The image of objects on the retina 
is upside down; yet the brain properly interprets, and we actually 
see right side up. That portion of our equilibrium sense having 
its origin in the vestibular apparatus is stimulated into action by 
body motion. This may be accomplished by motion of the body itself 
or motion of any object with which the body is in contact. This mov- 
ing body need not be in contact with the earth to have this sense stim- 
ulated into action. One walks, runs, rides a merry-go-round, rides in 
an airplane, and by use of equilibrium sense is able to maintain any 
possible or desirable position. Although the three senses—sight, 
muscle sense, and vestibular sense—are bound into one combination 
sense (the equilibrium triplets), each of them may be brought into 
separate action, and send its messages to the brain. One can “muscle 
sense” his position without sight. He can “sight” his position with- 
out the aid of the others.. Acting alone, the “vestibular sense” will 
give the brain information regarding motion, rate of motion, and di- 
rection of motion. 
i. Reliability of equilibrium triplets.—(1) Sight is the reliable 
one of the “triplets.” “Muscle sense” is an alert, variably acting 
“triplet.” The bad actor of the three is the vestibular sense. This 
sense, constantly alert, delicately sensitive, and easily stimulated 
69 TM 8-300 
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MEDICAL DEPARTMENT 
into action, must be continually checked up on and kept under con- 
trol by the other two of the combination if proper and continuous 
equilibrium is maintained. If the body on the ground or the body 
and an airplane in the air be turned, as in a spin, all three of these 
senses, acting in coordination, will give reliable information regard- 
ing body motion and position both on the ground and in space. 
Ground equilibrium and spatial orientation will be complete. 
(2) Sight is the same in the air as on the ground. Muscle sense 
(the so-called seat sense of the airman) cannot be as good in the 
air as on the ground, having been developed by years of contact 
with the earth and its material objects. Automatically on taking 
to the air one is robbed of a great portion of his muscle sense. All 
airmen have developed “seat sense”—some to a high degree, and 
most of them have that essential thing, “the feel of the ship.” No 
false impressions are received from sight and muscle sense. They 
may be much lessened in case of lack of proper vision or poorly 
developed muscle sense. Their messages to the brain, "whether jointly 
or separately, are reliable. This is not true of the messages re- 
ceived from the vestibular sense. If your body is rotated in any 
dimension of space, certain definite and fixed messages will be sent 
the brain by the vestibular sense acting in coordination with 
sight and muscle sense. Provided this body motion is not so violent 
or long-continued as to produce loss of perception, the brain will 
receive reliable information from this trinity of senses and one will 
maintain his equilibrium and know accurately at all times what 
position his body occupies with relation to the earth’s surface and 
in what direction, if any, it is moving. If, during this rotation, 
the body is stopped or retarded, one will have a momentary sensa- 
tion of giddiness, but will immediately, by the use of sight, adjust 
himself to the earth (gravity) and maintain equilibrium. 
(3) Whenever the human body is rotated in any dimension of 
space, with the eyes closed, thus removing vision from the trinity 
of sight, muscle sense, and vestibular sense, and this rotation is re- 
tarded, stopped, reversed, or continued until rotating body motion 
is coincident with the motion of the fluid in the vestibular (semi- 
circular) canals, just as definite and fixed messages will be sent 
the brain as if the eyes were open and vision intact, but each and 
every one of these messages will be false. One will be able to cor- 
rectly interpret the original starting motion only. He will recall 
that the vestibular apparatus is primarily composed of three tiny 
sets of fluid-filled canals placed at right angles to each other in the 
70 TM 8-300 
63 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINI 
labyrinth, in the sagittal, coronal, and horizontal planes, thus pro- 
viding motion-sensing in any dimension of space. 
j. Experiment.—Now consider a practical experiment in order to 
visualize what happens when vision is absent and the body is ro- 
tated. Any smoothly running revolving mechanism will do. A 
barber chair is ideal. Flight surgeons use the Jones-Barany chair. 
In such a mechanism only right or left rotation is possible; there- 
fore only the action of the horizontal motion sensing vestibular 
canals can be demonstrated in this chair. In an orientator any of 
the spatial positions may be assumed, and the corresponding canals 
tested. The results are the same in any case. If there is such a 
thing as acquiring immunity, the horizontal canals, being the ones 
in constant daily use, should be less sensitive than the others. It 
was found that there was no difference- and that constant use did 
not affect the sensitivity. With the eyes covered, rotation at any 
average speed is started. One will immediately and correctly inter- 
pret right or left rotation Having always experienced this same 
sensation during prior experience of body motion to the right or left, 
one will be positive as to what is happening. The number of rota- 
tions should be limited in order that too violent reactions will not 
be produced. If on the sixth to eighth rotation the motion of the 
chair is now retarded to a slow speed, one will have an immediate 
sensation of turning in the opposite direction, and a message will be 
sent the brain to that effect by the vestibular apparatus, which is now 
acting without its “control coordinator,” sight. One will be positive 
his body is now turning in the opposite direction of prior motion. 
If the rotating chair is now stopped, the s&nsation of opposite turn- 
ing will be much intensified. This sensation of opposite turn- 
ing will last from 5 seconds to as high as 25 seconds in some indi- 
viduals. The average is about 23 seconds. This average was estab- 
lished after examining hundreds in the Jones-Baraiiy revolving 
chair during the research conducted. Every human being has his 
own individual threshhold of vestibular stimulation and reaction. 
If the rotation of the body is continued (usually 8 to 10 turns) 
until the motion of the body and the motion of the fluid in the semi- 
circular canal being stimulated is the same speed, the vestibular 
sense will apparently be put out of action and the brain will receive 
an immediate message that all motion has ceased and that the body 
is sitting still. 
Tc. Vertigo.—[Repeated reversal of rotation, without stopping, 
creates an utter confusion of motion sensing. What has happened? 
Vertigo (to turn or turning) has been produced. Vertigo consists 
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MEDICAL DEPARTMENT 
of two things, a sensation of turning in the opposite direction to 
prior motion, and a sensation of falling in the same direction as 
prior motion. 
Vertigo is medically defined as “the subjective sensation of a dis- 
turbed relationship in space.” 
l. Effect on flying.—It will now be realized that the pioneer avia- 
tor dependent on messages sent to his brain by his vestibular sense, 
acting without the “control coordinator, vertigo stopper” sense of 
sight was in a dangerous predicament. 
The above is exactly what happens in blind flying. All visual ref- 
erence to the earth or any object the prior position of which in 
relation to the earth’s surface is part of the consciousness is absent, 
and only muscle sense and vestibular sense remain. As a matter of 
fact, a real blind man would function better in this predicament, 
because after all there is no difference in not being able to see cmy- 
thing and not being able to see, except that the real blind would 
have usually developed compensatory equilibrium to a high degree. 
m. Immunity.—All of the published literature and the research 
work accomplished prior to 1926 concentrated on one idea, the find- 
ing of a way of producing immunity against vertigo by means of 
placing pilots in a freely movable, revolving apparatus, and turn- 
ing their bodies through the various spatial positions in the belief 
that constant repetition of motion would establish an immunity. 
Every old-time pilot has had “a ride” in the Jones-Barany chair 
and most of them have spent hours in some type of revolving orien- 
tators. Nothing came of all this except to establish the fact that 
pilots who could expertly handle an orientator were possessed of 
a high degree of muscle sense and a keen sense of perception. No 
immunity was obtained against the reactions experienced in that 
deadly enemy of the airman—the spin. No immunity was possible 
from a physiological or a technical standpoint because no research 
or experiment conducted had arrived at a solution of the problems 
involved. There was no scientific basis established on which to build 
instructions to airmen in the practical application of these perfectly 
normal physiological reactions experienced when doing blind flying. 
n. Vertigo as an entity.—Vertigo is one of the oldest symptoms 
found in medical literature and when clinically present is believed 
to have a pathological basis. No study of vertigo as a purely phys- 
iological entity, to establish it as a causative factor in the behavior 
of human beings in their adjustments to their environment, has been 
found in the medical literature prior to 1926, and none is believed 
to exist. Induced physiological vertigo (that is, vertigo without 
72 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-3UU 
62 
pathological basis) may be a common causative factor in human 
behavior in vocations other than flying. The automobile, swiftly 
and freely movable in any horizontal plane, subjects the occupants 
to many of the factors that tend to produce “induced vertigo.” 
o. Universality of reactions.—All vertigo reactions follow certain 
definite and fixed lines and all humans are subject to the same reac- 
tions varying only in intensity. A human being in whom these re- 
actions are absent or distorted is abnormal and has either met with 
a physical disaster or was bom without properly functioning sense 
apparatus. In such cases some of the normally acting senses must 
compensate for this lack in order that the individual may avert dis- 
aster and simulate normal control in following the ordinary rou- 
tines of life. 
p. Aviation history.—In order to understand how and why this 
research was started it is necessary to digress into aviation history. 
From the beginning of man’s invasion of the air, fog, the universal 
menace to travel of all kinds, has taken a great toll of human life. Old- 
time pilots learned to fly without artificial instrumental aids of any 
kind, and developed to a remarkable degree what -was called “flying 
sense.” Until long after the War flying for any length of time without 
sight of earth or sky was impossible. 
About 1918 a “turn” indicator was invented. Since that time many 
artificial aids to spatial orientation have appeared. Bank-and-turn 
indicators, artificial horizons of various types, flight integrators, etc. 
All of these instruments are gyro-controlled to overcome the pull of 
gravity and allow their “indicators” to show ship movement and 
spatial position. Two of the common ones in use are illustrated in 
figure 3. 
The Sperry artificial horizon consists of a miniature gyro-controlled 
airplane which will assume the position of the carrying plane -while in 
flight. The pilot controls the position of his airplane by visualizing 
wdiat the miniature plane is doing, and correcting his position 
accordingly. 
The bank-and-turn indicator mounted at bottom has a pointing 
arrow which indicates all turns of the plane, and a small ball, seen in 
the runway at the tip of the arrow, which moves from side to side 
when the plane is banked up in a turn to right or left. Every artificial 
aid to spatial orientation lets the pilot “mentally” keep one foot on the 
ground. » 
The original intent of these instruments was to improve technical 
flying ability by showing pilots when smooth turns and banks were 
being made and to function as a crutch to the magnetic compass. All 
73 tm y-aoo 
63 
MEDICAL DEPARTMENT 
Figure 3,—Spatial orientation indicators. 
74 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TjVE 8-300 
62 
of the old-timers were, however, taught to fly by instinct, and the 
terms “inherent flying ability,” “seat sense,” and “flying sense” came 
into use. Artificial aids showing them when their ships were turning 
or banking were considered as entirely useless, as all they had to do 
was look at the earth and see what their plane was doing. So, although 
all planes were later equipped with indicators, they went unserviced 
and unused. Unfortunately for many, the visibility did not always 
stay good on every flight, so that pilots could look overboard at God’s 
horizon and see what their ships were doing. When visual contact 
with the earth was obliterated they discovered that it was impossible 
to maintain their planes in the air. If the fog was not completely on 
the ground, they would come down under it and “hedge hop” over 
trees and houses in a desperate attempt to keep visual contact with the 
earth until they could find a place to land. Only extreme skill and 
good luck brought many of them through. If the fog was completely 
on the ground, the only alternative was to climb high above possible 
danger. This was little comfort, for there is the disturbing knowledge 
that when the ceiling is reached the fuel may be gone and the plane 
must come down. Flying in fog without proper navigation instru- 
ments, the pilot will become hopelessly lost from a directional stand- 
point. 
q. Flying in jog without instruments.—Flying in fog without a 
visual reference to gravity (the earth), such as a bank-and-turn indi- 
cator, or some form of artificial horizon, the pilot will be unable to 
sense the position of his ship with relation to the earth’s surface, unable 
to sense the speed and direction of motion and will eventually go into 
circular motion, experience the vertigo described, and crash unless he 
takes to his chute before volitional control is lost. 
r. Instrument jlying.—Blind flying is the grim specter of aviation. 
The remedy for all this is to practice simulated blind flying under the 
hood until instrument flying is as easy as flying under clear skies and 
with perfect visibility. About 1919 the Air Corps advocated the use 
of any instruments that would add to the safety of flying, and there 
was a revived interest in various flying instruments. However, no 
progress was made until 1926. 
A report made by Donald E. Key hoe in 1929 follows: 
* * * Full credit must be given these men (pilots) who have tested the vari- 
ous instruments and methods suggested by scientists. The invention of the bank- 
and-turn indicator was the first step. But the pilots who first used it tried differ- 
ent methods without instruction, so few became expert. Those who succeeded 
were able to go through fog or snow for 20 or 30 minutes and at the end of that 
time their strained nerves would stand no more. Sight of ground or sky became 
vitally necessary to clear away the confusion that was swiftly taking control. 
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MEDICAL DEPARTMENT 
Two men were mainly responsible for progress beyond this stage. Ocker and 
Myers proved that this strain was caused by the pilot’s disbelief in his instruments 
and a strong tendency to trust his own senses, which are alway misleading. The 
Ocker-Myers method takes into account the three elements which give balance: 
muscle sense, sight, and restibular sense. * * * 
s. Overconfidence.—There is a tendency in an occasional young 
aviator to become so cocky over his flying ability that it becomes 
necessary to partially deflate it for his own safety. For many years 
the following plan was used in such cases: they were placed in the 
Jones-Barany revolving chair and turned right or left and asked 
which way they were turning. Their replies were naturally correct. 
Their eyes were then covered and the rotation repeated. After a 
few turns the chair was gently stopped and they were asked which 
direction they were turning. Vertigo having been induced, their 
replies were invariably that they had started to turn in the oppo- 
site direction of prior motion. The eyes were uncovered and to 
their amazement the chair was not turning at all. If this did not 
quite satisfy them, the rotation was continued until they experienced 
the sensation that the body was not moving. On being uncovered and 
finding they actually were turning right or left their chagrin was. 
very evident. For an aviator to suddenly discover his inability to. 
tell which way his body is turning, if at all, is, to say the least,, 
disconcerting. 
t. Origin of research.—In January 1926 this induced vertigo test 
was given to an old-time pilot. Following the test he disappeared 
without comment of any kind but soon returned with the view box 
(fig. 4) in his hand. The test was repeated in all combinations of 
rotation, using the unlighted box to cut out the light and thus; 
remove sight from the trinity of equilibrium senses. There was the 
usual induced vertigo with the usual inability to correctly tell which, 
way his body was turning, etc. The gyroscope was then started and 
the bank-and-turn indicator put in action. The flash was lighted and. 
the tests repeated. This time every answer was correct as to direc- 
tion of motion, stopping, and starting. Even the confusion of re- 
versals was absent. The sensations were felt the same as before;: 
but by giving the answer shown by the pointer on the bank-and-turn 
indicator, instead of the answer prompted by his senses, it was found 
impossible to confuse him. This demonstration started the research 
into blind flying. It was immediately recognized that here was the 
answer to pilot’s inability to do blind flying without a visual refer- 
ence to gravity. 
u. Bank-and-turn indicator.—By lighting the box the equilibrium 
trinity senses was restored to a coordinated action. Merely restoring 
76 KOTES OK EYE, EAR, ETC., IK AVIATIOK MEDICIKE 
TJYL S-aUU 
62 
Figukb 4.—View box. 
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MEDICAL DEPARTMENT 
sight to the equilibrium sense, however, is not enough. There must 
be something within the pilot’s range of vision that will act as a 
vertigo stopper and tell him what position his ship is in with relation 
to the earth. In other words, allow the pilot to mentally visualize 
“where the ground is.” The hand on the bank-and-turn indicator 
will accurately show motion in either direction, right or left, and will 
come to a dead center and remain there when there is no rotation. 
There will be the same false impressions of reversal of movement and 
falling received by the brain following the rotation; but by means of 
sight one will be able to correct these false impressions of movement 
and vertigo will be almost immediately overcome, 'provided one 
believes the instrument. 
v. Importance of discovery.—That there was any connection between 
the normal physiological reactions of a pilot and his lack of ability 
to do blind flying had not been considered until experience with, and 
belief in, the action of the bank-and-turn indicator crashed head-on 
into the knowledge of induced vertigo and the physiological reactions 
involved in the special senses concerned. Out of the wreck emerged 
several things of vital importance to aviation. 
w. Fovmdation sense.—The foundation sense of all spatial orienta- 
tion is vision. There is no substitute for visual reference. It makes 
no difference what the pilot sees so long as it gives him that vital in- 
formation, “Where is the ground and what is the position of the air- 
plane with reference to it.” Many accidents have resulted from ig- 
norance of this vital fundamental factor. Many have resulted because 
there were pilots who knew they could do blind flying by using their 
“flying sense.” There is no longer any excuse for ignorance regarding 
blind flying. Without exception the present day pilot who can do 
so obtains training in instrument flying. This is a far different reac- 
tion than the general attitude of most aviators when it was an- 
nounced, in 1926, that “no one could do blind flying without artificial 
aids” and that it had been “discovered how to do it.” The idea was 
promptly labeled as being enthusiastically crazy. 
x. Flying sense.—In the past those pilots who had discovered they 
could not fly blind did so through bitter experience. They, however, 
had nothing of value to report as an aid to their fellow pilots. They 
merely labeled themselves as better fliers than the average. However, 
it was noted they avoided fog flying. Having been taught to fly- by 
instinct it was hard to convince the average pilot that his flying sense 
would not bring him back from every flight. 
A knowledge of the uses of any one of the special senses and the 
care of and our reactions under all conditions toward these special 
78 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
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62 
senses become of vital importance and value only to the individual 
making special and expert use of that special sense. 
The airman being vitally concerned in his ability to sense his posi- 
tion, change of position, and relation to the earth’s surface, has called 
all his special senses into play and has developed “flying sense.” 
What is flying sense ? It is not an inherent sense. It is an acquired 
sense. It is something the airman has that others do not. In its 
entirety it is composed of the special senses of sight, hearing, taste, 
smell, touch or tactile sense, muscle sense, and vestibular or inner ear 
sense. 
Just as there are degrees of “doctor sense,” there are airmen with 
varying degrees of “flying sense.” Being an acquired sense and de- 
pendent for its development on the ability, adaptability, aptitude, 
and knowledge of the person, it is evident that, everything else being 
equal, the airman who correctly understands and interprets the sensa- 
tions received from his various senses will have the most “flying 
sense.” 
y. Reactions in air.—Constant repetition of demonstrations with 
the “vertigo stopper box” finally convinced pilots that it was a real 
lie detector and that, on the ground at least, they could not tell 
which way they were turning if they could not see. Many con- 
tinued to fly by instinct in the stubborn belief that these “reverse” 
reactions could not happen in the air. In answer to this a covered 
cockpit ship with one exposed control pilot seat was devised and 
many hours were spent testing out the various reactions of pilots. It 
was proven beyond a doubt that these reactions do take place in the 
air and, in addition, are much intensified. 
Later the findings were communicated to the National Advisory 
Committee for Aeronautics and elaborate flight tests were made 
with a covered hood and a control pilot. Their findings verified 
the theory that circular movement invariably resulted during flights 
made by a pilot flying in a totally dark cockpit. These findings veri- 
fied our original contention regarding movement and the production 
of induced vertigo. Carroll and McAvoy published the following 
conclusions: 
Many pilots have felt that the flying sense was largely one of muscular 
balance and that visual reference played a more or less insignificant part. 
These experiments should serve to remove this idea and develop the apprecia- 
tion of the fact that muscular balance plays an extremely small part in flying, 
excepting in correlation with visual reference in the development of a polished 
technique. Visual reference of some sort must be provided, either by the 
horizon, by the reflection of the sun or moon while in dense fog or clouds, 
or by proper instrumental equipment. 
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MEDICAL. DEPARTMENT 
The fact should not be neglected that the use of proper navigational instru- 
ments provides an artificial horizon, if not in a single instrument, then in the 
correlation of several instruments, such as a turn-and-bank indicator and an 
air-speed meter. 
It can be recommended to all pilots that a careful self training in the use 
of and reliance on navigational instruments of this character will provide them 
not only with definite mechanical assistance, but likewise will go far to remove 
the psychological hazard of blind flying. 
z. Spiral movement.—Many years ago experiments were conducted 
with blindfolded individuals and proved conclusively that spiral 
movement always resulted when running, walking, swimming, driv- 
ing a car, etc. Continuing the experiments on the lower forms of life 
it was concluded that any forward-moving organism (including 
man) would move in a spiral path provided no orientating sense, 
such as sight, touch, etc., guided it. 
aa. Value of viem box.—The value of the Ocker-Myers view box 
became generally recognized as the only available means of instructing 
pilots and prospective pilots while on the ground in the sensations they 
would experience and the reactions they would have if they attempted 
to do blind flying without an artificial horizon. 
db. Artificial horizon.—The term “artificial horizon” was originated 
and given the folloAving definition in the original report: 
Any instrument or combination of instruments that will quickly, easily, and 
reliably give the pilot information that he may mentally visualize in terms of 
where is the ground. 
ac. Reference.—In the United States Air Service magazine, issue of 
April 1928, there appeared an article, “The Artificial Horizon Seeks 
Recognition,” by Frederick R. Neely, in which the research conducted 
was fully explained. 
ad. Results of research.—Instrument flying and simulated blind fly- 
ing were the logical outcome of this research work, because there had 
been established the physiological foundation on which to build the 
technical superstructure. The device (except chair) illustrated in fig- 
ure 4 was originated and a course of ground instruction in blind flying 
was formulated which was adopted by the Air Corps as routine in 
May 1934. In addition, a routine course in actual instrument flying 
follows the ground instruction. 
ae. Function of demonstration box.—The Ocker-Myers demonstra- 
tion box is based on sound physiological fundamentals and its value as 
a preliminary to actual instrument flying in an airplane is essential 
because only in this way can the student be actually shown that he 
cannot depend on his own sensations when God’s horizon is not 
available. 
80 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
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af. Developments.—The problem of how to keep the pilot in the 
air when he did not have a horizon to look at having been solved, it 
became necessary to solve the problem of guiding him to his intended 
destination and safely landing him on an airport he could not see. The 
development of blind take-off, blind navigation, and blind landings 
was much stimulated by the discovery of the basic fundamental fac- 
tors underlying blind flying. Today they are accomplished facts. 
Figure 5.—Instrument board of blind flying ship. 
ag. Key to problem.—If this type of flying is participated in for a 
length of time sufficient to train the pilot in automatic control he will 
finally become as proficient as if he were flying in ideal weather. The 
successful blind flier must correlate his senses to his instruments. 
Section XI 
MISCELLANEOUS EAR CONDITIONS 
Paragraph 
Costen’s syndrome 63 
Tinnitus aurium 64 
Meniere’s symptom complex 65 
Labyrinthitis 66 
Deafness in aviators 67 
The “leans” 68 
63. Costen’s syndrome.—a. History.—These neuralgias and 
ear symptoms associated with disturbed function of the temporoman- 
dibular joint were first proposed as a symptom complex in 1933. At 
271818°—40 6 
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MEDICAL DEPARTMENT 
that time, it was considered to be of infrequent occurrence, but since 
then a rather large number of cases have been observed and the condi- 
tion may now be considered quite common. 
b. Cmse.—The chief function of the jaw is mastication, and.it is 
equipped with powerful muscles, the masseter, the temporalis, and the 
pterygoid internus, which act to close the jaw. Most of the action of 
closure is brought against the posterior third of the jaw and so, when 
the molar teeth are missing or the grinding teeth are reduced in size, 
the mandibular joint is liable to destruction. Anatomically, the symp- 
toms resulting may be explained by— 
(1) Erosion of the bone of the glenoid or mandibular fossa and im- 
paction of the condyle against the thin bones separating them from the 
dura. 
(2) Irritation by the uncontrolled movements of the condyles back- 
ward or mesially, of the auriculo-temporal nerve. 
(3) Production of reflex pain and sensory disturbances in the various 
connections of the chorda tympani nerve, the condyle irritating it 
where it emerges from the tympanic plate at the mesial edge of the 
glenoid fossa through the petrotympanic fissure. 
(4) Compression of the eustachian tubes; in overclosure of the 
joint, the tensor veli palatini muscle bordering the membranous ante- 
rior edge of the tube and the adjacent spheno-meniscus muscle are 
seen to wrinkle and crowd the eustachian tube, closing it firmly. 
Normally, during the act of swallowing the tensor palatini muscle 
should be tensed and effect a temporary opening of the tube. 
c. Symptoms.—The following symptoms either singly or in com- 
bination are found in this condition: 
(1) Ear symptoms. 
(a) Intermittent or continuously impaired hearing. 
(b) Stopping or “stuffy” sensation in the ears, marked about 
mealtime. 
(c) Tinnitus usually low buzz in type, less often a snapping noise 
while chewing. 
(d) Dull or drawing pain within the ears. 
{e) Dizziness, with nystagmus. 
(2) Pain and irritative symptoms. 
(a) Headache about the vertex and occiput and behind the ears, 
increasing toward the end of the day. 
(b) Burning sensation in the throat, tongue, and side of the nose. 
(c) Dry mouth with almost total absence of saliva; rarely, exces- 
sive saliva. 
82 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
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63-65 
(d) Occasional herpes of the external ear canal and buccal mucosa, 
most marked on the edentulous side. 
d. Treatment.—The treatment of these cases is reposition of the 
mandible by opening the bit, increasing the vertical dimension, and 
correcting the malocclusion. 
64. Tinnitus aurium.—a. Description.—Tinnitus aurium is a 
subjective sensation of sound in one or both ears. It is a common 
symptom of aural disease. It is sometimes divided into two types: 
external, produced in the middle ear by actual stimulation of the 
tympanic membrane; internal, beginning in the labyrinth and cre- 
ated by some upset of metabolic equilibrium or disease of the nerves, 
cerebrum, or associated organs. 
Tinnitus may or may not be associated with deafness. The sounds 
may be constant or intermittent and the severity may increase or 
diminish. It may precede or follow the onset of deafness and 
may be associated with dizziness or staggering. 
The noises may be simple or complex and vary in character and 
intensity. They are described as hissing, whistling, humming, rus- 
tling, burring, blowing, ringing, clicking, shrieking, jangling, roar- 
ing, rumbling, and rasping. Occasionally they may have the form 
of a specific tune. 
b. Classification.—Tinnitus is sometimes classified according to the 
underlying lesion or disorder; 
(1) Obstruction sounds—Noises due to occlusion or impaired 
motility of some portion of the sound-conducting apparatus. 
(2) Labyrinth sounds.—Noises due either to structural changes 
in the cochlea or to alterations, either increase or diminution of 
the intralabyrinthine pressure. 
(3) Neurotic sounds.—Noises due to abnormal instability of the 
auditory nerve. 
(4) Cerebral sounds.—Noises due to abnormal conditions acting 
upon the auditory centers in the cerebral cortex (auditory hallucina- 
tions). 
(5) Blood sou7\ds.—Noises produced by the blood currents in ves- 
sels in or near the ear and due either to disturbances in the local 
or general circulation or to abnormalities in the size, shape or posi- 
tion of the vessels. 
The first four types will cause,a subjective tinnitus, while the fifth 
type may be both objective and subjective. 
65. Meniere's symptom complex.—a. History.—In 1860 Meniere 
reported a case of spontaneous hemorrhage into the labyrinth. In 
his report he gave a clear picture of the symptoms which accompany 
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MEDICAL DEPARTMENT 
recurrent aural vertigo. There has been some confusion as to the 
terminology and it is generally conceded that the term “Meniere’s 
disease” be used to define true cases of the rare labyrinthian hemor- 
rhage and “Meniere’s symptom complex” or “Meniere’s syndrome” 
be used in cases of recurrent aural vertigo. 
h. Symptoms and characteristics.—This condition is characterized 
by the following symptoms: 
(1) A sudden onset in a previously healthy auditory apparatus. 
(2) Vertigo, uncertain gait, rotations, and falling associated with 
nausea and vomiting. 
(3) Tinnitus, continuous or intermittent. 
(4) Deafness, unilateral and progressive. Occasionally hearing 
may be suddenly completely abolished. 
In a few cases there occurs in the attacks a transitory loss of vision 
and diplopia, and cases in which loss of consciousness occurs have 
been noted. 
These attacks are recurrent, the period between the attacks varying 
from weeks to years. These attacks are so distressing that even the 
symptomless intervals are marred by the dread of their recurrence. 
The disease is one of middle life and affects males more frequently 
than females. There is a tendency for the process, whatever it may 
be, to progress for several years until the function of the ear is lost. 
c. Cause.—The cause of the condition is unknown; the following 
causes having been suggested by various authors: 
(1) Local infection. 
(2) Allergy. 
(3) Lesions of the auditory nerve. 
(4) Cyclic changes, either chemical or physical, in the endolymph. 
d. Treatment.—There have been many types of treatments advo- 
cated, and the following have met with some success: 
(1) Surgical. 
(a) Section of the vestibular fibers of the VIII nerve. 
(h) Alcoholic injection of the labyrinth. 
(2) Dietary.—The use of a salt-free diet with addition of massive 
doses of ammonium chloride. 
66. Labyrinthitis.—a. Recognition.—The symptoms are so severe 
and the findings so positive that the question of labyrinthitis in the 
examination of applicants for flying training presents no difficulties. 
Also, it is most unusual to have a case of involvement of the labyrinth 
without an accompanying deafness of the involved ear. 
Labyrinthian disorders will occasionally occur in the active per- 
sonnel, and a brief description of types, causes, and symptoms is 
indicated. 
84 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
66 
h. Sources of infection.—True infection of the labyrinth with pyo- 
genic organisms occurs from three sources: metastitic, meningeal, and 
tympanic. The meningeal source is usually associated with cerebro- 
spinal meningitis. The tympanic cases are usually by direct extension 
from acute or chronic suppurative otitis media, or mastoiditis. Laby- 
rinthitis is said to occur in about 1 percent of cases of middle ear 
suppuration. The end results may vary from recovery with normal 
function to complete destruction of the labyrinth. 
c. Symptoms.—The symptoms consist of— (1) Vestibular nystagmus 
(slow movement in one direction and a quick movement in the oppo- 
site direction).—This nystagmus varies from the mild type, in whicli 
the movement only occurs when the eyes are directed in the direction 
of the quick movement, to the type in which the nystagmus persists 
no matter where the eyes are turned. 
(2) Vertigo.—Rotary in character with the subjective impression 
that the surrounding objects are rotating in the plane of the nystag- 
mus. There is a tendency of the body to fall in the direction of the 
slow component. 
(3) Nausea and vomiting. 
(4) Tinnitus and deafness. 
Cases show great variations in the types and severity of the symp- 
toms, One recent case showed only nystagmus when looking to- 
ward the direction of the quick movement, and complained only of 
a feeling of “lightness” in the head and a tendency to fall to the left. 
d. Tests.—Vestibular tests should not be made during the acute 
stage of the disease, but on subsidence of the acute attack, the ves- 
tibular reaction will usually be absent. 
e. Other cases with similar symptoms—Labyrinthian symptoms are 
seen in cases other than those with suppurative labyrinthitis and 
many causes are given. All may produce typical findings: 
(1) Cold, heat, and sunstroke. 
(2) Hyperemia or hemorrhage into the labyrinth. 
(3) Sudden changes in pressure in the middle ear, seen in divers 
and aviators. 
(4) Mechanical disturbances produced by movements, airsickness, 
trainsickness, seasickness, and swingsickness. 
(5) Drugs: alcohol, quinine, tobacco, morphine, and salicylates. 
(6) Detonations and shock, probably by sudden changes of pres- 
sure in the middle ear. 
(7) Repeated loud noises. 
(8) Mental disturbances, such as fright. 
(9) Injuries to the labyrinth, such as may occur while doing a 
paracentesis or from penetrating wounds which strike the labyrinth. 
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MEDICAL DEPARTMENT 
(10) Focal infection, toxemia, circulatory disturbances. 
(11) Associated with other diseases such as syphilis, exanthemata, 
nephritis, mumps, leukemia, and others. 
/. Airsickness.—Airsickness is a major problem, as many cadets 
are unable to continue training because of the severity of the attacks. 
So far it has been impossible to tell which men will be airsick. 
Labyrinth tests usually do not give any reliable findings. Probably 
a truthful history of train or swingsickness would be indicative, but 
such histories are difficulut to obtain, as young men are as a rule some- 
what ashamed to admit these defects. Most probably airsickness is 
a complex reaction to the consciousness of disordered orientation of 
the body in space and results from a combination of causes, ocular, 
vestibular, cerebellar, cerebral, and psychogenic, particularly the 
feeling of anxiety, combined with an overactivity of the sympathetic 
nervous system. 
67. Deafness in aviators.—a. Terminology.—It has been noticed 
for many years that the older pilots have a diminished auditory 
acuity. This condition has sometimes been called aviator’s deafness. 
Liberty Motor deafness, flying deafness, and aero otosclerosis. It is 
doubtful that this condition warrants a specific name. 
b. Causes.—The diminished hearing is due to a number of causes; 
(1) Repeated exposure to noise of high decibel rating of fairly 
constant pitch over prolonged periods of time. After riding in an 
open airplane for any great period of time, one is more or less deaf 
for a subsequent variable period of time. Repeated exposures tend 
to cause this temporary condition to become permanent. Several 
theories as to the cause of this type of deafness have been given, but 
it is probable that it results from derangement or injury to the 
external hair cells of the organ of Corti. 
(2) In addition to this cause, the factors mentioned in section V 
must be added, and, of course, these factors are variable in different 
individuals. 
(3) Of late years the widespread use of radio has added still 
another insult to the auditory apparatus, and it is still too early to 
say what the final result of this additional factor will be. 
c. Incidence.— (1) Past.—It is noted clinically that the deafness in 
any marked degree has occurred in the older pilots, particularly 
some of the wartime pilots, one of the reasons for this being the 
general reduction in auditory acuity that occurs in age. However, 
other conditions must be considered. These pilots flew in ships with 
cockpits which were very little protected from the slipstream. The 
engines with open stacks were either directly in front or directly to 
86 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
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67-68 
the side and very close. Furthermore, they did not know or did not 
use prophylactic measures such as plugging the external auditory 
canals with cotton or other material and the maintenance of middle 
ear pressure equilibrium during ascent and descent. 
(2) Present.—At the present time we find many younger pilots 
who have more air hours than the older pilots who show little or no 
decrease in auditory acuity. This is due to the better construction 
and protection of the cockpit, change in type of engines used, greater 
distance from engine to pilot, streamlining with decrease in struc- 
tural noises, decreased vibration, and a better knowledge of prophy- 
lactic measures. 
(3) Future.—With increasing refinements in engineering and noise 
control, it is to be expected that the deafness of aviators will grad- 
ually decrease so that their auditory acuity will be but little below 
that of other males of the same age group. In the meantime, it is 
essential to select only those with good hearing as applicants. 
d. Mixed type.—As a rule the deafness noted in the pilots is of a 
mixed type—diminished reception of the low tones with a marked 
decrease or even total loss of the notes above 2048 D. V. This type 
of hearing curve is to be expected for a condition resulting from 
both a conduction and a perception deafness. It is interesting to 
note that the right ear is usually more involved than the left. 
68. The “leans.”—This is a term used by some pilots to describe 
an interesting reaction to a disordered orientation of the body in space. 
The phenomenon occurs following prolonged flights by instruments, 
and is described as being a feeling that the ship is flying in a banked 
position. The degree of lean is variable in different individuals and at 
different times, the length of time varying from a few seconds to 1 or 2 
minutes. Either the right or the left wing may seem to be down. Some 
pilots describe the condition as being merely a momentary disturbance 
following a turning movement, while others describe the sensation as 
being very definite, with a strong urge to right the ship. In practically 
all cases where this occurs the pilots are experienced instrument flyers, 
and a glance at the instruments, which show level flight, corrects the 
false sensation. 
The condition is important in that if an inexperienced pilot should 
neglect his instruments and attempt to correct his impression by the 
use of his ailerons, disaster could easily follow. Most pilots of this 
day have had instrument-flying experience and have confidence in the 
accuracy of their instruments. There is, however, a period of transi- 
tion—that is, in changing from flying contact to flying instruments— 
when our false physiological conceptions of our position in space are 
confusing even to some of the best instrument flyers. 
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MEDICAL DEPARTMENT 
Section XII 
GENERAL METHODS AND EQUIPMENT FOR EYE 
EXAMINATION 
Paragraph 
General 69 
Purpose 70 
69. General.—a. Importance.—There is no vocation as yet under- 
taken by man that is so dependent upon “vision” as that of flying. 
“Reduced to its simplest terms the function of the eye is the light 
sense. This is the discrimination between light and darkness, and 
various degrees thereof” (Adler), Going a little further it may be 
said that “vision” is the proper appreciation of light, of form, of 
color, and of distance, and we see how all of these are of vital im- 
portance to the aviator; and a defect, which may be considered as 
minor or insignificant in the ordinary walks of life may be serious 
indeed for the pilot of aircraft. 
h. Equipment.—In order that a thorough and intelligent examina- 
tion of the eye and its adnexa may be conducted, it is essential that 
adequate and proper equipment is used, and that ample floor space 
and lighting facilities are available. For certain phases of the sub- 
jective examination a dark room of sufficient length to permit a dis- 
tance of 6 meters between the examinee and certain test objects em- 
ployed is necessary, and in addition there should be a well-lighted 
room, particularly for the objective parts of the examination. In the 
dark room there should be a convenient lamp situated over or near 
the chair of the examinee, controlled by a switch which is accessible 
to the examiner. It should be remembered that a conclusion may be 
arrived at in some instances by two or more methods, and where 
possible the examiner should verify his findings by two or more 
methods before making a final interpretation. 
c. Accuracy.—In all probability there is no other type of physical 
examination where the time element is so important and where the 
adage “make haste slowly” applies more forcibly." A complete ocular 
examination is at best a tedious procedure and requires an infinite 
amount of patience on the part of both the examiner and examinee, 
and where “short cuts” are employed, or decisions made hastily, the 
accuracy of the findings is at best questionable. 
d. Type.—In the examination of applicants for appointment or 
detail to the Air Corps for flying training, it should be borne in the 
mind of the examiner that such an examination differs materially 
from the examination of patients reporting to a clinic for treatment 
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of some condition that they themselves perhaps have recognized. It 
is to be presumed that all applicants for flying training are anxious to 
qualify physically, and in some instances may attempt to conceal or to 
minimize some ocular defect, provided they are aware of its existence. 
Therefore, it is not infrequently the problem of the examiner to 
uncover and recognize defects without the assistance and cooperation 
of the examinee. For this reason, all phases of the examination 
should be so conducted that, where possible, findings are based upon 
objective methods of examination. Obviously, this is not altogether 
possible. In many instances, however, subjective findings may be 
checked by objective methods. 
e. Phases.—In the examination of the eyes of applicants for flying 
training in the Air Corps, there are 14 phases or steps toward its 
completion, and where each phase is carefully and painstakingly 
accomplished there is little that may be overlooked. It will be noted, 
and will be explained later, how some of these phases may overlap 
or be very closely associated with one another. Below are listed 
these various steps of the ocular examination and the equipment 
employed. In some instances more than one method may be em- 
ployed to arrive at one finding, and in such cases those pieces of 
equipment as are called for in All 40—110 are mentioned first. 
(1) Visual acuity {right and left).—Apparatus Required: Il- 
luminated Snellen test types at 6 meters, or various modifications of 
test types incorporated with electrically lighted cabinet or projection 
device. 
(2) Depth perception.—Apparatus required: Howard-Dolman 
depth perception apparatus with proper illumination. 
(3) Maddox rod screen, test at 6 meters.—Apparatus required: 
Phorometer trial frame equipped with multiple Maddox rods, right 
and left, Risley rotary prisms, right and left; or prisms, Maddox rod 
and trial frame from trial lens case; and in either case, whether 
or not the phorometer trial frame is used, a spotlight 1 centimeter 
in diameter placed at 6 meters in front of examinee’s chair. 
(4) Red lens test.—Apparatus required: Red piano lens, trial 
frame, flat surface such as a blackboard, and meter rule. 
(5) Prism divergence.—Apparatus required: Risley rotary prism 
in phorometer trial frame, or prisms from trial lens case. 
(6) Associated parallel movements {and tangent curtain).—Ap- 
paratus required: Small test object, as white-headed pin, Bjerrum 
tangent screen, or blackboard in conjunction with tangent rule, and 
spotlight as used in Maddox rod test at 33 centimeters. 
(7) Inspection.—Apparatus required: Adequate illumination, con- 
densing lenses as required for oblique, illumination (from trial 
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MEDICAL DEPARTMENT 
lens case), and, where available, binocular loupe (Beebe), hand slit 
lamp, ophthalmic lamp, slit lamp with binocular corneal microscope, 
and electric ophthalmoscope. 
(8) Pupils.—Apparatus required: Same as for inspection. 
(9) Accommodation.—Apparatus required: Prince rule with card, 
or Thorne rule. 
(10) Angle of convergence.—Apparatus required: Prince rule, or 
small millimeter rule and small test object, as white-headed pin, and 
table for computing angle of convergence. 
(11) Central color vision.—Apparatus required: The Ishihara test, 
and the Stillings’ pseudoisochromatic test and three sets of Holm- 
gren’s wools. 
(12) Field of vision.—Apparatus required: Perimeter with test 
objects, Bjerrum tangent curtain or blackboard with tangent rule, 
campimeter if available. 
(13) Refraction.—Apparatus required: Cycloplegic, retinoscope, 
trial lens case, and Snellen test types. 
(14) Ophthalmoscopic examination.—Apparatus required: Oph- 
thalmoscope, preferably electric. 
Each of these phases of the examination will be discussed in turn. 
In many instances references will be made to physiologic optics, 
physiology, histology, anatomy, and pathology of the eye in ex- 
planation of the procedure of the examination. It is suggested that 
the student familiarize himself particularly with the physiology 
of the eye. 
70. Purpose.—The purpose in the preparation of the following 
part of the manual is primarily to enable the officers to conduct 
the required examination of Air Corps personnel in a thorough 
manner and to be able to interpret intelligently the findings of such 
examinations when he is assigned to duty as flight surgeon. The 
flight surgeon’s responsibility does not cease with routine, original, 
annual, and semiannual examinations of flying personnel under his 
care. While he is not expected to become an ophthalmologist (nor 
by any means will his practice be limited to ophthalmology) he 
should be able to arrive at an intelligent conclusion regarding the 
diagnosis of an ocular defect, disease, or injury, and within limita- 
tions, to treat such conditions where treatment is indicated. In 
some instances he may be able to detect an abnormality in its in- 
cipiency and by proper measures prevent its development to the ex- 
tent that the services of a capable pilot are lost. He should re- 
member that he is the “engineering officer” of flying personnel and 
is as much concerned with “maintenance” as with “selection” of the 
aviator. 
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Section XIII 
VISUAL ACUITY 
Physiological and psychological factors concerned 71 
Formation of retinal image 72 
Resolving power of eye 73 
Acuity of retina 74 
Alining power of eye 75 
Conditions that interfere with normal visual acuity 76 
Snellen test letters 77 
Metric system 78 
Readability of various letters 79 
Paragraph 
71. Physiological and psychological factors concerned.—It 
should be remembered that in asking an individual to read certain 
test letters on a chart some distance away there are various phycho- 
logical as well as physiological factors that enter into the examination 
These are the power of attention, the willingness and ability of the 
examinee to exert an effort to cooperate, and the power of concen- 
tration. There is another factor which, in some instances, may af- 
fect the findings obtained, namely, the ability to accurately and 
precisely control the extrinsic ocular muscles so that the retinal im- 
age of the test letters falls exactly upon the fovea, the most sensitive 
portion of the retina when the definition of form is concerned. 
Accuracy of fixation is a factor that should be given consideration, 
particularly in the examination of children. 
72. Formation of retinal image.—Before going further into the 
determination of visual acuity or the appreciation of form, optics 
may be reviewed to the extent of how an image is formed upon the 
retina. Consider first a single point seen in the distance, or at in- 
finity ; from this point, which may be lighter or darker than its sur- 
roundings, rays of light radiate in every direction until interrupted 
or interfered with in some manner. Of these rays of light there 
will be a certain number, forming a cone, that will strike the cornea 
of the eye of the observer. Of the cone of rays of light striking the 
cornea there will be a certain number of rays that will pass through 
the pupil, and of these there will be one ray, the axial ray, that will 
pass through the optical center (nodal point) of the dioptric sys- 
tem of the eye. This ray will not be refracted and eventually will 
strike the retina at a point where one cone will be stimulated. If the 
eye be emmetropic, all other rays of light emanating from the point 
and passing through the pupil will be refracted and will converge 
upon the point on the retina as stimulated by the axial ray, and the 
result will be the stimulation of a single cone on the retina. Con- 
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MEDICAL DEPARTMENT 
sider a line as being made up of a series of points immediately 
adjacent to one another, and follow the formation of a retinal im- 
age as by points forming the line. The end result will be the forma- 
tion of an inverted retinal image greatly reduced in size, of the 
line being observed. The observation of two lines crossing one an- 
other explains the retinal picture in two dimensions. 
73. Resolving power of eye.—?n determining visual acuity the 
visual angle is utilized, and this angle is the guide by which test 
objects have been constructed. By the visual angle is meant the 
minimal angle formed by the intersection of the two (axial) rays 
crossing at the nodal point of the eye when two points are seen as 
separate and distinct points. It is thought that in order to distin- 
guish two points as separate and distinct points, separate cones of 
the retina must be stimulated and there must exist at least one un- 
stimulated. It is believed that in order to perceive two points as 
separate and distinct points, the angle formed by the crossing of the 
two axial rays must be not less than 1 minute, and it is upon this 
assumption that the Snellen test types are designed. More re- 
cently it has been determined that the minimal angle is considerably 
less, probably around 50 seconds. “The discrimination of two points 
as separate has been sometimes spoken of as the optical resolving 
power of the eye” (Adler). There are two other factors which may 
influence the “visual angle” even in emmetropic eyes, these being 
aberrations, spherical and chromatic, and irradiation, the latter caus- 
ing an intensely bright object to appear larger than one of the same 
size but darker. Quoting Adler directly— 
A good example of this is seen in light from the stars. The visual angle of 
light coming from the stars is infinitesimal. The rays of light are practically 
parallel. In spite of this they are visible to us. * * * The factor which 
determines the visibility of a point of light has nothing to do with the visual 
angle it subtends, therefore, but depends upon the amount of light energy falling 
on the visual receptors. The brighter the star the larger it appears. 
74. Acuity of retina.—Furthermore, various portions of the 
retina differ as to degree of sensitivity in perception of form, or 
acuity, the most acute area being the region of the fovea, and visual 
acuity rapidly diminishes as the retinal image approaches the periph- 
ery of the retina. This is considered as being due to two factors, 
that the macular area is made up of cones, packed very closely to- 
gether as it were; and that each of these cones has its own fiber 
leading back to the brain. In the periphery of the retina there are 
both rods and cones; these are widely separated, and several of them 
may be connected with the same fiber so that when one is stimulated 
the same sensation is produced as when another or several in the 
92 NOTES ON EYE. EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
74-76 
same group are stimulated. A comparison may be made as to the 
sense of touch upon the skin surface of various parts of the body. 
For example, one can distinguish two separate points of contact, as 
pin points, on the finger tip very readily even though they be quite 
close together, while on the skin of the back the two points must be 
fairly widely separated in order to be recognized as separate points. 
The difference in the ability of varying portions of the retina to 
recognize detail of form may be easily demonstrated by the use of a 
perimeter with an ordinary Jaeger near vision card. The acuity will 
be found to decrease rapidly as the card is moved away from the points 
of fixation. 
75. Alining power of eye.—In the recognition of test letters, 
such as are used with the Snellen test charts, there is a factor in- 
volved in addition to the resolving power of the eye. This may be 
described as the “alining power of the retina” by which is meant the 
ability to perceive changes in position or a break in a line. “Although 
the minimum angle which the eye can resolve is nearly 60 seconds of 
arc, the alining power of the eye is much more sensitive than this. 
It is probably the most acute of the human senses. The precision of 
the eye in adjusting a mark on a vernier scale is extraordinarily deli 
cate. Under the best conditions a skilled observer will make read- 
ings on the scale with an average error of not more than 3 seconds 
of arc. Thus, the alining power can be 20 times as delicate as the 
resolving power” (Adler). 
76. Conditions that interfere with normal visual acuity.— 
In the testing of visual acuity (central or foveal) there are some factors 
to be considered as influencing the findings. These are, in probable 
order of importance: 
a. Errors of refraction or ametropia, in all its varieties, in which the 
retina is “out of focus” with the dioptric system of the eye, and 
consequently the retinal image appears poorly defined. 
h. The size of the pupil. This may have two effects upon the find- 
ings. An increase in the diameter of the pupil naturally allows more 
light to enter the eye, and with low degrees of illumination will 
improve visual acuity. Still, a dilated pupil permits an intensification 
of spherical and chromatic aberrations, which do interfere with a 
retinal image having sharply defined borders. Where an error of 
refraction exists, a reduction in the diameter of the pupil will result in 
an improvement in acuity. This can be easily demonstrated. Granted 
that the individual is emmetropic, or nearly so, render him myopic by 
placing before his eye a plus sphere lens of 4 diopters and determine 
his acuity, which will probably be approximately 10/200. Now place 
a pinhole disc before the lens and the acuity will be markedly improved, 
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MEDICAL DEPARTMENT 
probably to 20/40 or even better. When an individual is moderately 
myopic his acuity will be improved by a contracted pupil. Conse- 
quently an examinee may present altogether different findings as to 
acuity when examined with a brilliant light before him (causing a con- 
traction of the pupil) and when examined in a dark room with only 
the test letters illuminated. Cobb has shown that the pupil should be 
between 1 and 5 millimeters for optimal visual acuity when the test 
object is under ordinary illumination. 
c. The amount of illumination upon the test objects will affect the 
findings in an estimate of acuity. The effect of irradiation has already 
been mentioned. Above a certain point of illumination of test objects 
acuity will become less and below a certain degree of illumination it 
will decrease also. These are factors that vary with individuals and 
are problems necessitating further experimentation before definite con- 
clusions may be reached. In the use of the ordinary electrically lighted 
test cabinets, it is probable that too much illumination is made use of, 
rather than too little. It has been found that the most acute vision is 
obtained when the test letters are illuminated by about 9-foot candles. 
Recent researches have determined that the maximum amount of illu- 
mination before reduction in visual acuity (with test objects) is approx- 
imately 300-foot candles for normal individuals. This may be 
considered as the “glare point.” 
d. Test objects when illuminated by monochromatic light are seen 
with sharper definition of borders, therefore with increased visual 
acuity, due to the fact that the factor of chromatic aberration is 
eliminated, 
e. Pathological changes in the eye itself, or optic nerve, chiasm, 
optic tracts, visual pathways, and higher centers can cause a reduction 
in visual acuity. For example, choroidoretinitis, retinal hemorrhage, 
optic atrophy, retrobulbar neuritis, intracranial tumors, etc. 
77. Snellen test letters.—The acuity of vision is determined 
clinically by the use of test letters. These are so designed that each 
component part, or stroke of the letter, subtends an angle of 1 minute 
and the letter as a whole subtends an angle of 5 minutes, these dimen- 
sions being based on test letters being used at a distance of 20 feet 
from the examinee. The Snellen test letters, constructed on this prin- 
ciple, are in universal use. Each Snellen test letter is of such shape 
that it can be placed in a square, which is in turn divided into 25 
smaller squares of equal size. Therefore the entire letter subtends 
an angle of 5 minutes, and each stroke of the letter subtends an angle 
of 1 minute. It will be noted that on the Snellen test charts there are 
rows of letters of different sizes, there being usually a row of small- 
94 TM 8-300 
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NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
sized letters of the alphabet, and above or below this row a row of 
somewhat larger letters, and above still larger, etc. The size of the 
letters in the different rows is determined as follows: For the smaller 
row each individual letter subtends an angle of 5 minutes at 10 feet, 
or approximately 3 meters’ distance; in the next row, above or below 
as the case may be, each letter subtends an angle of 5 minutes at 15 
feet; the next, 20 feet, and so on. If an individual being examined, 
seated 20 feet away from the test types, is able to read readily the row 
of letters, each of which subtends an angle of 5 minutes at this dis- 
tance, his vision is recorded as being 20/20, the numerator being the 
distance from the examinee to the test charts, and the denominator 
being the size of the letters in the row which is read. If at 20 feet 
he can read the letters in the row, each of which subtends an angle 
of 5 minutes at 15 feet, his vision is recorded as being 20/15. Thus we 
have the findings 20/20, 20/30, 20/40, and so on. The acuity of each 
eye is tested separately; the eye not being tested is screened by an 
opaque card or disc. Where an examinee can read all of the 20/30 
row of letters, and only three of the letters in the 20/20 row, his vision 
is recorded as 20/30 plus 3 for the eye being tested. 
78. Metric system.—Some examiners use the metric system. 
In such instances the acuity is recorded as being 6/6, 6/12, etc. These 
1. Axial rays from extreme points of object (a) passing, unrefracted, through nodal 
point (n), forming inverted image (6) upon retina. Associated rays from extreme points 
of object are divergent and refracted upon entering eye and come to focus on axial rays 
at retina. 
lb. Axial rays forming angle of 5 minutes. Test letters are constructed under this 
angle. Distance from eye determines size of letters. 
Figure 6.—Diagrammatic illustration of visual angle and method of constructing visual 
test letters. 
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MEDICAL DEPARTMENT 
fractions may be reduced, and an acuity of 6/6 (20/20) may be re- 
corded as 1; an acuity of 6/12 (20/40) being recorded as 1/2 or 0.5. 
But a visual acuity of 0.5 does not mean that the examinee has only 
one-half normal vision from a practical viewpoint. These “fractions” 
do not signify a percentage of “vision” in that form, being strictly 
empirical units. 
In explanation of repeated references to the use of Snellen test 
charts at a distance of 20 feet (6 meters), it may be said that this 
distance is chosen as a mean because at this distance, or distances 
greater than 20 feet, accommodation plays a very insignificant part in 
visual acuity of the emmetropic eye. At any distance less than 20 
feet accommodation is brought into play, particularly at near dis- 
tances. Hence, 20 feet is selected as being the minimum as far as 
convenience and accommodation are concerned. As a matter of 
fact, the emmetropic eye must accommodate to a certain extent at 
this distance, presumably one-sixth of a diopter, this strength of 
lens having a focal distance of 6 meters. The use of a mirror at 10 
feet distance with reverse Snellen charts alongside or above the 
examinee (the mirror may be used at any distance, provided the dis- 
tance from the chart to the mirror plus the distance from the mirror 
to examinee is exactly 20 feet) is a great convenience, but care must 
be taken that the mirror is silvered on the front surface in order 
that accurate findings are obtained. Otherwise the two reflecting 
surfaces may cause a blurring of the reflected letters. 
79. Readability of various letters.—It is to be remembered that 
all letters of the alphabet do not possess the same “readability.” For 
example, consider the capital letter “L,” which in block form repre- 
sents a right angle, the apex of which is down and at the left. If 
visual acuity is defective to such an extent that the outline of the two 
strokes of the letter is blurred, the letter may be still recognized by* 
the fact that a right angle is formed. The letter “A” may be recog- 
nized as A when acuity is below normal because it is the only letter 
which is characterized by an acute angle apex up, and the examinee 
may be unable to distinguish the cross bar. The same conditions 
apply to the letters “T,” “V,” and even “F”; the latter may be recog- 
nized as a right angle apex up and to the left, and the cross bar of 
the upward stroke not seen. Sheard has concluded after extensive 
investigation that the letter “B” is the most difficult to distinguish 
and has prepared a table of comparison of the letters of the alphabet,, 
as follows, using the letter “B” as the unit of measurement 1.00. 
L 0. 71 C 0. 79 
T 0. 74 O 0. 80 
V 0.78 Y 0.81 
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NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
P 0. 81 R 0. 88 
F 0. 81 S 0. 89 
D 0. 82 G 0. 92 
Z 0. 84 H 0. 92 
N 0.85 B 1.00 
E 0. 85 
The usual Snellen test charts are so arranged that in each row of 
letters there are an equal number of those that are distinguished 
readily and those that are more difficult to recognize. 
Theoretically, the Snellen test types at 20 feet (6 meters) leave 
much to be desired as an accurate test of visual acuity, but from a 
practical viewpoint in conducting a clinical examination they have 
proven satisfactory. While 20/20 (6/6 or 1) may not be the maxi- 
mum acuity for the optically normal eye, it serves as a working basis. 
As a matter of fact, there are many instances of an acuity of 20/15 
and better, without hesitation, encountered. Evidence seems to indi- 
cate that actually an acuity of 20/15 or better is much more near thei 
normal standard. The examiner should consider a defect in visual 
acuity as a symptom rather than a disease entity. 
In the examination of Air Corps personnel, the examiner should 
have accessible as great a variety of rows of test types as possible, 
particularly of the 20/20 size, as the probability of memorizing a 
row of letters, in many instances seen repeatedly on different occa- 
sions by the examinee, is not infrequently encountered. It is sug- 
gested that' where several rows of the 20/20 types are on hand, one 
or more be kept in reserve for use in questionable cases. In addi- 
tion, all letters except one at a time may be screened, which may 
elicit the fact that an examinee is repeating the letters in sequence 
from memory when he is permitted to see the entire row at once. 
If such is the case he will show some confusion where only one letter 
is exposed and all others screened. 
Section XIV 
DEPTH PERCEPTION 
General 80 
Basic and adjunctive factors 81 
Monocular and binocular factors 82 
Size of retinal image , 83 
Physiological diplopia 84 
Binocular parallax 85 
Adjunctive group of factors 86 
Measuring parallactic angle 87 
Etiology of defective depth perception 88 
Summary 80 
Paragraph 
271S180—40 7 
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MEDICAL, DEPARTMENT 
80. General.—By depth perception is meant the ability to judge 
distance, or the power to appreciate the third dimension. It is this 
power that materially aids in rendering an individual capable of cor- 
rectly orientating himself in relation to surrounding objects. It can 
be appreciated readily that this is an extremely important factor in 
aviation. It is this factor that enables the pilot to level off his air- 
plane at the proper distance from the ground in landing, to take off 
with a safe margin over obstacles, to be proficient in gunnery, and 
maintain his position in formation flights. 
81. Basic and adjunctive factors.—a. Basic.—The factors 
composing the basic group constitute a part of the physical functions 
of the individual; they are constant, and when considered together 
may be termed his “inherent ability” to judge distance. 
These factors consist of— 
(1) Physiological diplopia. 
(2) Accommodation. 
(3) Convergence. 
(4) Binocular parallax. 
b. Adjvmctive.—The factors composing the adjunctive group may 
function independent of the individual; they are inconstant, and are 
common to all persons. They may be termed as factors which assist 
or enhance the basic group. 
These factors consist of— 
(1) Size of retinal image. 
(2) Motion parallax (movements of head or object). 
(3) Terrestrial association. 
(a) Linear perspective. 
(b) Overlapping of contours. 
(c) Light, reflections, and shadows. 
(4) Aerial perspective, that is, the changes with respect to color, 
brightness, and contrast which different objects undergo on account 
of variation in the clarity of the intervening atmosphere. 
82. Monocular and binocular factors.—a. Some of the factors 
operating to constitute depth perception are common to monocular 
and binocular single vision alike, while others pertain to binocular 
single vision only. 
b. yactors common to monocular and binocular single vision are— 
(1) Size of retinal image. 
(2) Accommodation. 
(3) Motion parallax. 
(4) Terrestrial association, 
(6) Aerial perspective. 
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NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
c. Factors which operate with binocular single vision only are— 
(1) Physiological diplopia. 
(2) Binocular parallax. 
(3) Convergence. 
d. In employing a test for the purpose of determining an individ- 
ual’s ability to judge distances, it is necessary to utilize only those 
factors which operate to make for an individual difference in ability; 
that is, it is necessary to measure an individual’s inherent or acquired 
ability. 
In order to do this, the method employed must eliminate all exter- 
nal assistance that experience has taught us to employ. For instance, 
motion parallax is produced either by movement of the observer or 
by objects within his field of vision. For that reason it may be con- 
sidered as an artificial factor employed to enhance the already exist- 
ing facility. It should, therefore, be eliminated as a factor not 
related either to inherent or acquired ability. 
Factors external to ourselves which assist all of us equally, such as 
terrestrial association and aerial perspective, should be eliminated 
for the same reason. 
Factors which normally operate only at distances of less than 6 
meters, such as accommodation, do not need to be considered when 
examining prospective aviators. Fliers are not, as a rule, called upon 
to form judgments at a distance of less than 6 meters. 
e. When all external factors and those operating at a distance of 
less than 6 meters are eliminated, there remains to be considered— 
(1) Size of the retinal image. 
(2) Physiological diplopia. 
(3) Binocular parallax. 
(4) Convergence. 
83. Size of retinal image.—As the size of the retinal image oper- 
ates with monocular as with binocular single vision, the relative value 
of this factor can be obtained with the same testing apparatus by 
examining first both eyes and then one eye, the other being covered. 
With the test described herein it has been demonstrated that the 
ability to judge distances is many times more accurate with binocular 
single vision than with monocular vision. 
In monocular vision, there are eliminated the binocular parallax, 
convergence, and physiological diplopia. Therefore, judgment must 
depend upon the size of the retinal image alone. 
Since judgment of distance is many times less,accurate when the 
decision depends upon the size of the retinal image alone it follows 
that the important factors to be considered are physiological diplopia, 
binocular parallax, and convergence. 
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MEDICAL, DEPARTMENT 
84. Physiological diplopia.—The faculty of recognizing differ- 
ences in distance between objects, which are located in space within 
our visual fields, is founded upon physiological diplopia, although 
we do not recognize it as diplopia. 
When the eyes fix an object (binocular fixation), the image of 
that object falls upon the maculae of both retinae. This image is 
projected outward and we see the object at the point where the visual 
lines cross, which is the place where the object is actually located. 
The image of another object within the field of vision, at a greater 
or lesser distance than the object fixed, falls upon the retinae at points 
outside of the maculae. 
If the second image falls upon the nasal side of the macula of the 
right eye, it is projected to the temporal field and the object is located 
to the right of the point actually occupied by the real object, and 
at a distance equal to the distance between its point of contact on the 
retina and the macula. If the imago falls upon the temporal side 
of the macula, it is projected to the nasal field and is located in the 
same manner. The same applies to the left eye. These two images 
are not focused by the cerebral fusion center and diplopia occurs. 
If the image falls upon symmetrical points of the retinae, that is, 
exact points on the nasal side of one and the temporal side of the 
other, the images are fused and are projected to the same point in 
space and diplopia does not occur. Two objects are located in the 
field of vision and but two objects are seen. However, if the image 
of the second object falls upon different points of the nasal and tem- 
poral portions of the retinae, the two images are not fused and two 
objects will be seen. The image or images of the second object are 
not to be confused with the object fixed. The object fixed appears 
as one and in its proper position. 
Figure 7 0 illustrates two objects (a) and (b) located at dif- 
ferent distances in space but within the visual field. The eyes have 
fixed (a), the far object. The image of (a) falls upon the macula 
of both eyes, and appears as one object at the place it actually occu- 
pies. The image (&), the near object, falls upon the temporal side 
of the macula of both eyes at (£, t). Therefore, the image (b) seen 
by the right eye is projected to the left at (V) and the same image 
seen by the left eye is projected to the right at (&"), giving rise 
thereby to bilateral crossed diplopia. 
In figure 7 (D the eyes have fixed (a), the near object. The 
image of (b), the far object, falls upon the nasal side of the macula 
of both eyes at (n, n). The image of (5) seen by the right eye is pro- 
jected to the right at (&"), and the same image seen by the left eye 
100 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
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84-86 
is projected to the left at (b') giving rise thereby to bilateral ho- 
monymous diplopia. 
Therefore objects located nearer than the object fixed give rise to* 
crossed diplopia, and those more remote than the object fixed give 
rise to homonymous diplopia. It is because of this homonymous and 
crossed diplopia that we receive the impression that objects are 
nearer or farther away in relation to other objects. 
In figure 7 ® the objects (a) and (b) are located in space in posi- 
tions similar to those occupied by the objects in the Ho ward-Dolman 
testing apparatus. The eyes have fixed the near object (a). It will 
be noted that the image of the far object (b), falls upon the temporal 
side of the macula of the right eye and upon the nasal side of the 
left eye, but at a greater distance from the macula of the left eye 
than the right. These points not being identical, the images are 
therefore not used but are projected into space as two objects (b') 
and (b"). 
85. Binocular Parallax.—While we perceive, through physio- 
logical diplopia, the existence of difference in distance between objects, 
the binocular parallax augments this perception by giving rise to the 
impression of relief and solidity. 
When we fix an object the right and left eye obtain somewhat dif- 
ferent views of that object. The right eye sees a little farther around 
the object to the right, and the left a little farther around to the left. 
This gives rise to two retinal images which are not exactly alike. 
When these images are fused the disparity is responded to by percep- 
tion of relief and solidity. 
When we perceive a difference in distance between objects our 
conception of the amount of difference may be accurate or it may be 
decidedly inaccurate. It is, therefore, desirable to determine the 
degree of acuracy and this is accomplished by utilizing the binocular 
parallactic angle. 
Figure 8 (T) is a representation of two objects (o) and (o') located 
at unequal distances from the eyes (a) and (b). The two distances 
may be represented by two imaginary lines, one from (o), the near 
object, and the other from (o'), the far object, to a point midway 
between the two eyes, that is, an imaginary Cyclopean eye (an eye 
occupying the center of the forehead). 
These differences may be compared with less difficulty by using a 
more diagrammatic illustration. Let us therefore consider one eye 
(b) and the two objects (0) and (O') in a straight line as illustrated 
in figure 8 ®. 
86. Adjunctive group of factors.—The adjunctive factors, with 
the exception of motion parallax, exist and operate independent of 
101 TAE 8-300 
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MEDICAL, DEPARTMENT 
the individual, but they are probably of as much value in judging 
distances as are the basic factors. 
We are primarily equipped with the essentials for forming judg- 
ments and we soon learn, through experience, to utilize all other 
assistance that comes to hand. However, if these essentials do not 
function properly, then the value of all external assistance that is 
available is proportionally reduced because we do not know how to 
employ it. Because of this it is necessary to determine whether or 
not the prospective flier possesses all the basic factors of depth per- 
ception, and if these factors are functioning properly. 
With a normal foundation for judging distances the student soon 
learns, in his new environment in the air, to utilize all external assist- 
ance that is available. 
After one becomes experienced in flying he may be deprived of all 
basic factors, with the exception of the size of the retinal image, and 
still be able to judge distances sufficiently accurately to fly a ship. 
This is especially true if he is familiar with the ship, the terrain, etc. 
This fact is demonstrated with experienced fliers who have lost an 
eye. At first they experience some difficulty, but this is soon over- 
come. Their ability to continue flying is due to the fact that flying, 
landing, etc., have become partially mechanical and subconscious and 
they have learned from experience how to utilize all external assist- 
® Eyes fixing far object. 
a. Far object, 
ft. Near object. 
m-m. Maculae. 
t— t. Temporal side of retinae. 
Eyes are fixing far object »• Image falls upon maculae at m-m. Image of ft, near ob- 
ject, falls upon temporal side of maculae at t-t and is projected to 6' witli right eye and 
to ft" with left eye, inducing thereby increased diplopia. 
Figukh 7.—Physiological diplopia. 
102 KOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
86 
a. Near object. 
b. Far object. 
© Eyes fixing near object. 
m—m. Maculae. 
n—n. Nasal side of maculae. 
Eyes are fixing near object a. Image falls upon maculae at m—m. Image of b, far 
object, falls upon nasal side of maculae at n—n and is projected to b” with right eye and 
to b' with left eye, inducing thereby homonymous diplopia. 
® Objects arranged similar to those in testing apparatus, 
a. Near rod. * m—m. Maculae. 
5. Far rod. t. Temporal side of retina. 
n. Nasal side of retina. 
Eyes have fixed near rod a. Image falls upon maculae at m—m. Image of far rod & 
falls upon temporal side of right macula and upon nasal side of left, but image falls 
upon retina of left eye at greater distance from macula than in right eye. Therefore 
image of b is projected to b' with right eye and to b" with left, inducing thereby homony- 
mous diplopia with left eye and crossed diplopia with right eye. 
Figure 7.—Physiological diplopia—Continued. 
103 TM 8-300 
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MEDICAL DEPARTMENT 
ance to the utmost. However, when these individuals are deprived 
of all external assistance, and their judgment must depend upon the 
size of the retinal image alone, as with the testing apparatus, they 
are many times less accurate than when both eyes are functioning. 
87. Measuring parallactic angle.—The Howard-Dolman appa- 
ratus employed to measure the parallactic angle is designed to utilize 
only those factors belonging to the basic group. All external factors 
d Distance to near object 0. 
P Interpupillary distance Or~b. 
D Distance to far object O'. 
D minus d = difference in distance, or depth difference. 
Angle 1 minus angle 2 equals angle of binocular parallactic angle. 
P Interpupillary distance a-b. 
d Shorter distance h—O. 
D Longer distance b—O'. 
D minus d = depth difference. 
Let angle 1 equal aOh, angle of convergence upon near object, angle 2 equal aO'b, 
angle of convergence upon far object, and angle 3 equal angle OaO'. Then angle 1 
minus angle 2 equals angle 8, which is the binocular parallactic angle represented by 
depth difference D—d. 
Figure 8.—Binocular parallax. 
104 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
87-88 
which usually operate to assist in judging distances are eliminated. 
The examinee is given two objects at unequal distances from him. 
His physiological diplopia, binocular parallax, and convergence tell 
him that a depth difference exists between the two objects. It is his 
task to eliminate this difference, that is, to place the objects at equal 
distances from him. The accuracy with which he accomplishes this 
determines his inherent degree of ability to judge distances. 
The testing apparatus consists of two upright rods, 64 millimeters 
apart, laterally, viewed through an aperture in a screen at a distance of 
6 meters. All that is visible to the examinee is an illuminated white 
background crossed vertically by two black rods. One rod is stationary 
and the other can be moved backward and forward in a groove along 
the margin of a millimeter scale by means of cords. The examinee en- 
deavors to place the adjustable rod beside the stationary one so that 
both are at equal distances from him. When the rod is accurately 
placed the reading on the millimeter scale is zero, and the parallactic 
angle and physiological diplopia cease to exist. 
The abolition of diplopia and the parallactic angle can be demon- 
strated with the figures 7 (D and 8 @. If the object (&), figure 7 
(a), is placed at the same distance from the eyes as (a), then the image 
of (h) will fall upon symmetrical points of the retinae, become fused, 
and be projected to the left of (&), as a single object. In figure 8 (2), 
if (O') the far object, is placed beside (O) the near object, the 
binocular parallactic angle (3) will be eliminated. 
The testing apparatus is so constructed that the size of the binocular 
angle will equal 10.3 seconds when the interpupillary distance is 64 
millimeters, the stationary rod is located at 6 meters distance and a 
depth difference of 30 millimeters exists between this and the adjustable 
rod. 
Among Americans, interpupillary distances range from to 74 
millimeters with an average of 64. In conducting tests it is impracti- 
cable to compute the size of the parallactic angle of every individual 
whose interpupillary distance is greater or less than 64. Therefore, a 
depth difference of 30 millimeters is taken as the outside limit and those 
who persistently exceed this limit are considered as defective in judg- 
ing distances. 
It has been demonstrated that an individual who persistently pro- 
jects the adjustable rod more than 30 millimeters from zero, and pos- 
sesses an ocular defect, experiences great difficulty in learning to fly. 
88. Etiology of defective depth perception.—a. Occurrence of 
defective perception.—Ninety-nine and one-half percent of persons 
who are free from nervous, ocular, and general defects exhibit a per- 
105 TM 8-300 
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MEDICAL DEPARTMENT 
sistent parallactic angle average 10.3 seconds or less, that is, they will 
persistently project the adjustable rod an average of not more than 30 
millimeters from zero. The remaining one-half percent of this class 
of individuals will project the adjustable rod more than 30 milli- 
meters from zero for a large number of trials, but will eventually 
project it less than 30. Just why this occurs has not been definitely 
determined, but the cause seems to point to nervousness, poor com- 
prehension, and particularly to carelessness in performing the test. 
These men usually project the rod between 30 and 50 millimeters 
from zero. If they persist in this indefinitely they are considered 
as defective in judgment, but if they correct this error, after two or 
three series of trials, they are considered normal. Observation has 
taught us that these men experience no difficulty in flying, that is, 
insofar as judgment is concerned. Furthermore, practice on the 
testing apparatus will not reduce the average error when an ocular 
defect exists. 
5. Known factors operating for poor depth perception. 
(1) Inequality of vision. 
(2) Refractive errors resulting in accumulative ocular fatigue 
and manifested by— 
(a) Accommodative asthenopia. 
(h) Heterophoria. 
(c) Insufficiency of convergence. 
All individuals, with the exception of the small number mentioned 
above, who are inaccurate in their judgment of distances are found 
to have one or more of the above defects. These individuals will 
project the adjustable rod 75 millimeters from zero in one direction, 
in the next trial will project it 150 millimeters in the opposite direc- 
tion, and in still another trial may place it at zero. In other words, 
they have no conception of the relative or actual positions of the 
rods. 
However, it must be remembered that some individuals may have 
all the defects enumerated above, with the exception of inequality of 
vision and still possess a very accurate estimation of distances, but 
in general, it may be stated that when any of the defects mentioned 
are severe enough to cause symptoms, for example, muscular fatigue, 
blurring of vision, diplopia, etc., judgment of distances is inaccurate, 
and the degree of inaccuracy is in proportion to the degree of symp- 
toms manifested. 
c. Inequality of vision or anisometropia.—Given a case with a 
visual acuity of 20/20 in one eye and 20/50 in the other, and assum- 
ing that there is no strain of accommodation in the defective eye, 
106 TJVE 8-300 
88 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
the defective judgment is due, under these conditions, to an inability 
to utilize fully the assistance alforded by ohysiological diplopia 
and binocular parallax. The cerebral interpretation of this diplopia 
FLOOR 
SIDE ELEVATION 
A-SLIDE. C-C- RODS 2" APART. 
B-CORD FOR MOVING SLIDE. 
Figure 9.—Depth perception apparatus. 
107 TM 8-300 
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MEDICAL DEPARTMENT 
into distances is partially lost because of the diminished vision, also 
the impression of relief is not as marked as normal. Therefore the 
individual is utilizing monocular judgment in his estimation to a 
greater or less extent and the greater the reduction in vision the 
nearer will binocular approach monocular vision. 
d. Hyperopic refractive errors.—The existence of refractive errors 
creates a defect in the ocular mechanism and when accumulative 
fatigue ensues as a result of work, nervous strain, infection, etc., it 
is the existing defective structure that is first to become impaired in 
function. 
When hyperopic refractive errors exist, the individual must at all 
times accommodate to bring far as well as near objects into focus. 
Therefore, in order to do this the ciliary muscles must receive a 
greater amount of enervation than is required by a normal eye, and 
the increased amount is interpreted into distance by the cerebrum. 
Consequently the amount of nervous force employed gives rise to the 
sensation of a proportional amount of distance. Usually this ap- 
parent distance is less than that which actually exists. 
When the refractive error is equal in both eyes and is fully com- 
pensated for by accommodation, the defective judgment resulting 
therefrom frequently can be corrected. The increase of nervous 
impulse required to correct the defect is equal in both eyes. If the 
object upon which the eyes fix appears nearer or at a greater distance 
than it really is, the other objects or object will be falsely projected 
in proportion, and the relation between the two will remain un- 
changed. This type of defect gives rise to faulty landings. The 
student will persistently level off too high or too low until he has 
learned to compensate for his error. 
When the refractive errors are unequal in the two eyes, for ex- 
ample, one-half of a diopter in one and one diopter in the other, 
the higher error will require the greater amount of nervous impulse 
to accommodate. The unequal nervous strain will alter the apparent 
relative position of objects, and defective and erratic judgment 
results. 
e. Accommodative asthenopia.—When accumulative ocular fatigue 
is present, there are usually errors in refraction responsible for it. 
As it is necessary to accommodate constantly for distant objects, 
the eyes become tired as a result of the nervous and physical strain, 
accommodation relaxes, and objects are seen out of focus. Because 
of the indistinct vision an accurate estimation of distance is im- 
possible. This condition is particularly noticeable in some individuals 
who are undergoing flying training. One day they can judge dis- 
108 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
88-89 
tances very accurately and experience no difficulty in landing their 
ships, while on the following day they cannot level off and land 
consistently or accurately. These cases have latent hyperopic errors, 
and because of the mental and physical strain incident to training, 
their accommodative powers become reduced and objects are not 
brought into focus. The wearing of correcting lenses usually im- 
proves the faulty judgment. 
/. Heterophoria.—Heterophoria may be considered as fatigue of 
one or more of the extrinsic ocular muscles due to refractive errors, 
to a deficiency in the normal amount of enervation from some cause, 
or to an actual defect in the muscle structure itself. In order to fix 
both eyes upon an object the defective muscle must receive a greater 
amount of enervation than its fellows. This increased amount of 
enervation is interpreted into distance by the cerebrum just as it is 
in refractive errors, therefore the relative position of objects is in- 
accurately judged. If the defective muscle becomes sufficiently 
fatigued, or the required amount of nervous impulse cannot be sup- 
plied, the visual line of the eye concerned will deviate and objects 
will become blurred or pathological diplopia will ensue. When 
diplopia occurs all objects within the field of vision appear double, 
the true objects appearing more distinct than the false objects. 
g. Insufficiency of convergence.—Convergence must occur at all 
times in order to fix both eyes upon an object, no matter how remote, 
but the degrees of convergence required for distant objects are 
necessarily less than those for near objects. When the eyes become 
fatigued, convergence relaxes and objects are blurred or pathological 
diplopia results. This condition is usually associated with refractive 
errors, as is the condition of heterophoria. 
h. Myopic refractive errors.—Myopic errors have little or no effect 
upon depth perception, until the errors are sufficient to cause indis- 
tinct images and a strain upon convergence. When the errors are 
sufficient to cause these symptoms, depth perception becomes defec- 
tive as in insufficiency of convergence and inequality of vision. 
89. Summary.—Accurate judgment of distances is important to 
the aviator because, if this sense or function is impaired, it is im- 
possible for him to learn to fly an airplane safely unless he is given 
an enormous amount of flying training. He may under these condi- 
tions become sufficiently prpficient to fly with comparative safety, 
but he will never attain even an average degree of proficiency. 
Inherent depth perception for objects located in infinity is de- 
pendent upon physiological diplopia and augmenting this diplopia 
are binocular parallax, size of the retinal image, and convergence. 
109 TM 8-300 
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MEDICAL, DEPARTMENT 
Physiological diplopia is interpreted into distance by the cerebrum 
and the binocular parallax gives rise to the impression of relief and 
solidity. 
An adjunctive group of factors assist inherent depth perception. 
These factors are common to all persons; they are inconstant but 
they play a very important part in accurate judgment. 
The degree of accuracy of judgment is determined by the size of 
the binocular parallactic angle. The testing apparatus is so con- 
structed that with an interpupillary distance of 64 millimeters, the 
stationary rod at 6 meters distance, and a depth difference between 
this and the adjustable rod of 30 millimeters, the binocular paral- 
lactic angle thus formed subtends an angle of 10.3 seconds. 
In determining the degree of accuracy in judging distances only 
the basic group of factors is considered, because if these are not 
functioning properly the adjunctive factors cannot be utilized fully. 
An experienced flier who has been deprived of some of the basic 
factors may be able to fly a ship with reasonable safety because he 
has learned from his flying experience to utilize to a marked degree 
the adjunctive factors. However, he is not as safe or reliable as 
the normal person. 
Ninety-nine and one-half percent of persons who are inaccurate in 
judgment have a defective ocular mechanism. These defects may 
be reduction of vision in one or both eyes or refractive errors result- 
ing in ocular fatigue and manifested by accommodative asthenopia, 
heterophoria, or insufficiency of convergence. 
A persistent parallactic angle of more than 10,3 seconds, that is, 
a depth difference of more than 30 millimeters, is considered as 
defective provided an ocular defect is present. 
Any hyperopic error in refraction may cause inaccurate judgment. 
Myopic errors have little effect upon judgment unless the error is 
sufficient to cause diminished acuity of vision and insufficiency of 
convergence. 
If in the first series of trials the candidate makes an average error 
of over 30 millimeters, for example, between 30 and 60, and no 
ocular or general physical defect can be found to account for it, it 
is advisable to recheck him every day for at least 3 days. Invari- 
ably these candidates will eventually attain an average error of 30 
millimeters or less. Experience has taught us that these individuals 
experience no difficulty in flying, insofar as judgment of distances 
is concerned. 
110 TM 8-300 
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NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
Section XV 
OCULAR MOVEMENTS 
’Monocular and binocular projection 90 
Field of fixation 91 
Orthophoria and heterophoria 92 
Review of physiology of extrinsic ocular muscles 93 
Binocular movements 94 
Prisms 95 
Numbering of prisms 96 
Rotary prism 97 
Maddox rod 98 
Phorometer trial frame 99 
Sighting eye 100 
Technique of determining imbalance : 101 
Optical principles involved in horizontal deviations 102 
Vertical deviations 103 
Heterophoria at 33 centimeters 194 
Etiology of heterophoria 105 
Incidence of heterophoria 106 
Other methods of detecting heterophoria 107 
Associated factors 108 
Power of abduction 109 
Optical principles involved 110 
Power of adduction 111 
Prism convergence 112 
Angie of convergence 113 
Near point of convergence 114 
Interpupillary distance 115 
Meter angle 116 
Associated parallel movements 117 
Squint 118 
Complete oculomotor paralysis 119 
Paragraph 
90. Monocular and binocular projection.—a. General.—After 
the estimation of visual acuity and ability to judge differences in 
depth or distance, there is to be determined whether or not there 
exists any abnormality in the motility of the eye. Under this 
heading there are to be considered, in the examination of flying per- 
sonnel, the Maddox rod screen test at 6 meters, the power of diver- 
gence, power of convergence, and associated parallel movements. 
Before taking these up in order, it is worth while to discuss briefly 
orientation of objects, binocular vision, the field of binocular fixation, 
the action of the extrinsic ocular muscles, defects in ocular move- 
ments, and the methods used in arriving at a conclusion in this 
phase of the examination. 
h. Monocular vision.—First, consider monocular vision, using the 
right eye alone. When a point {A) (fig. 10 ©) upon the horizon or at 
111 TM 8-300 
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MEDICAL, DEPARTMENT 
infinity fixed upon, the extrinsic ocular muscles of the eye are brought 
into play so that it is rotated to such a position that the retinal image 
of that point is formed on the fovea of the retina, where it is most 
clearly defined. Now suppose there is another point (B) to the right 
of point or the point of fixation, and it is located 10° to the 
right of point {A). The image of point (B) will be formed on the 
retina 10° away from the fovea on the nasal side of the right eye. 
If there is a third point (G) located 20° to the left of point (A) 
its image will be formed on the temporal side of the right retina 
20° away from the fovea. The position of objects in space is deter- 
mined by their relation to the nodal point of the eye. If an image 
of an object is formed on the retina a number of degrees away from 
the fovea, this image will be projected in space the same number 
of degrees to the opposite side of the point of fixation, that is, if 
an image is formed on the retina at 10° to the nasal side of the 
fovea, it will be projected in space 10° from the point of fixation 
in the temporal field of vision. Or if an image is formed 10° above 
the fovea the object in space is projected 10° below the point of 
fixation. 
c. Binocular vision.—Now let us suppose both eyes are brought into 
use, and both eyes are fixed on point (.4) (fig. 10 (2)), point (B) (to 
the right of point will have its image formed at a point 10° 
medial to the fovea of the right retina, and 10° lateral to the left fovea. 
Point (C) (to the left of point (J.)) will have its retinal image 
formed 20° away from the right fovea on the temporal side, and, 20° 
from the left fovea on the nasal side. However, point (B) seen 
with both eyes will be seen as a single point, the images on the 
right and left retinae being fused into one. The same is true, of 
course, with point (C). When fusion occurs we may conclude that 
it is because images are formed on the two retinae at corresponding 
points. The two foveae are corresponding points; 10° to the nasal 
side of the right fovea and 10° to the temporal side of the left fovea 
are corresponding points; and so on. However, 10° immediately 
above the right fovea has a corresponding point 10° above the left 
fovea. When we fix upon an object in the distance, images of ob- 
jects to the right and left of the point of fixation will be formed on 
corresponding points of the retinae and binocular single vision re- 
sults. Points of the two retinae which are not corresponding are 
known as disparate points. When retinal images of the same object 
are formed on disparate points diplopia results. 
d. Convergence.—When an object nearer than infinity is the point 
of fixation there is necessarily a certain amount of convergence, or 
adduction, accomplished in order that the visual lines (visual line 
112 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM S-C30 
90-91 
being a line from point of fixation through nodal point to fovea) 
intersect at the point of fixation, and the image of this point is 
formed upon the fovea of each retina. 
® Monocular. 
A ig point of fixation. The image of B, A Is point of fixation. The Image of S 
to the right of A, would fall on the retina would fall on corresponding points on the 
at B' on the nasal side of the fovea, F. right and left retinae. 
The image of 0 would fall on O’ on the 
temporal side of the fovea. 
® Binocular. 
Figueb 10.—Projection, 
91. Field of fixation.—a. Definition.—“The field of fixation may 
be defined as the base of a cone, the apex of which is the center of 
rotation of the eyeball as the eye is rotated to its extreme limits in 
all directions, foveal vision at all times marking or defining the 
base of the cone” (Peter), Thus, foveal or central vision is limited 
to within the field of fixation, is limited by the possible amount of 
rotation of the globe about its center. The average field of fixation 
extends upward 33°, up and in 47°, inward 50°, in and down 47°, 
downward 57°, downward and outward 47°, and outward 45°. The 
field of fixation, like the visual field for form, is limited on the 
medial side by the contour of the nose, so that a proper determina- 
tion of the maximum degree of adduction of the eye is difficult to 
determine. 
271818°—40 8 
113 TM 8-300 
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MEDICAL DEPARTMENT 
6. Binocular fixation.—The field of binocular fixation may be con- 
sidered as consisting of the overlapping portions of the right and 
left fields of fixation. It is only within the binocular field of fixa- 
tion that binocular single vision is possible, and it is only within this 
area that the factors which operate with binocular single vision in 
depth perception (physiological diplopia, binocular parallax, and con- 
Ftgttrh 11.—Composite field of binocular vision of 50 men, showing concentric constric- 
tion when flying goggle B-6 is worn (outer line normal field ; shaded area field with 
goggie worn). 
vergence) can be employed. Therefore accuracy in depth percep- 
tion is limited to the field of binocular fixation. We may say that 
the field of binocular fixation is limited by the nasal field of fixation 
of each eye. This fact should be remembered and given considera- 
tion in aviation goggle design. 
114 TM 8-300 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
91-92 
c. Normal 'position.—Normally, the eyes are held in their proper 
position in the orbits by the combined action of the extrinsic ocular 
muscles and are so acted upon by these muscles that the visual lines 
are held practically parallel. 
d. Diplopia.—While the extrinsic ocular muscles hold the eyes in 
their proper positions, these muscles in turn are directed to their 
action by nervous impulses originating in the fusion centers. These 
fusion centers operate to maintain binocular single vision under all 
normal conditions. In order to maintain such vision, the lines must 
be held in their proper relation to each other. When visual lines 
fail in this respect, diplopia or double vision results. 
92. Orthophoria and heterophoria.—When toe action of the 
fusion centers is weakened or abolished, normally balanced eyes will 
maintain parallel visual lines (orthophoria). If the visual lines 
deviate from the parallel under these conditions, heterophoria exists, 
that is, a deviation becoming manifest only when fusion control is 
weakened or abolished. If the visual lines deviate from the parallel 
while the fusion centers are presumably functioning, and fixation is 
maintained with one eye only, heterotropia or squint exists, that is, 
a manifest or obvious deviation of the visual lines occurring inde- 
pendent of the action of the fusion center. The term heterophoria 
includes all varieties of latent tendencies to deviation from parallel 
positions of the visual axes. In heterotropia the deviations are mani- 
fest and do not have to be uncovered by weakening the fusion con- 
trol. The following table of nomenclature is generally accepted: 
a. Orthophoria.—Normal binocular balance. 
b. Heterophoria.—A latent imbalance, or tendency toward devia- 
tion of the two visual lines from parallel. It includes the following: 
(1) Esophoria.—A latent deviation of the visual lines inward. 
(2) Exophoria.—A latent deviation of the visual lines outward. 
(3) Hyperphoria.—-A latent deviation of the visual lines of one 
eye above that of the other. It is designated as right or left. 
(4) Hypophoria.—A latent deviation of the visual lines of one eye 
below that of the other. Designated as right or left, 
(5) Double hyperphoria.—A latent elevation of both visual lines. 
Also termed anaphoria. 
(6) Double hypophoria.—A latent lowering of both visual lines. 
Also termed kataphoria. 
(7) Cyclophoria.—A latent deviation of the globe about its antero- 
posterior axis, that is, an intorsion (rotation of the upper portion of 
the cornea about the antero-posterior axis of the globe nasally or 
115 TM 8-300 
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MEDICAL DEPARTMENT 
inward) or an extorsion (outward rotation), necessarily designated 
as right or left. 
c. Heterotropia.—A manifest deviation of the visual lines (as de- 
fined previously). 
(1) Esotropia.—A manifest deviation of the visual lines inward; 
a convergent squint. 
(2) Exotropia.—A manifest deviation of the visual lines outward; 
a divergent squint. 
(3) Hypertropia.—A manifest deviation of one visual line above 
the other—right or left. 
(4) Eypotropia.—A manifest deviation of one visual line below 
the other—right or left. Also termed catatropia. 
(5) Cyclotropia.—A manifest deviation about the antero-posterior 
axis. 
d. Other diagnostic terms used in connection with defective ocular 
movements are: 
(1) Hyperkinesis.—Excessive action of an individual muscle. 
(2) Hypokinesis.—Deficient action of an individual muscle. 
93. Review of physiology of extrinsic ocular muscles.—a. 
Movement of globe.—The globe is capable of limited movements 
about the center of rotation, these movements being brought about 
by contractions of the extrinsic ocular muscles. The center of rota- 
tion is located about 10 millimeters in front of the posterior pole 
and millimeters behind the anterior pole (Donders). The 
globe may be rotated about three axes, the horizontal axis (as eleva- 
tion and depression), the vertical axis (as abduction and adduction) 
«nd the antero-posterior axis (intorsion and extorsion). 
b. Action of muscles.—Certain of the extrinsic ocular muscles have 
but one action from the position of “eyes front,” these being the 
external rectus (abduction, external rotation) and internal rectus 
(adduction, internal rotation). Each other muscle has a primary 
and subsidiary action. Taking them up in order we find that the 
vertical recti (superior and inferior) in addition to their vertical 
action have an adducting or internal rotating effect because of their 
origins being located more medially than their insertion. In addi- 
tion each has some effect in rotating the globe about its antero- 
posterior axis. Because of the forward and medial origin of the 
obliques and their insertions behind the center of rotation, each is an 
abductor in addition to its elevating and depressing and torsion 
actions. The primary and subsidiary actions of the muscles can best 
be appreciated after a study of diagrams showing their origin and 
insertions. 
116 TM: 8—300 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
93 
Table of primary and subsidiary actions of individual ocular muscles 
(Peter) 
Muscle 
Primary action 
Subsidiary action 
Internal rectus 
External rectus. 
Superior rectus 
Internal rotation 
External rotation 
Elevation 
None. 
None. 
f Internal rotation. 
\lntorsion. 
f Internal rotation. 
\Extorsion. 
j Depression. 
\ External rotation, 
f Elevation. 
1 External rotation. 
Inferior rectus 
Depression 
Superior oblique. 
Intorsion 
Inferior oblique __ _ 
Extorsion 
AB. Orbital axis. 
CF. Optical axis. 
M. Center of rotation. 
Pigdbe 12.—Planes of action of extrinsic ocular muscles. Inferior oblique lies immedi- 
ately beneath superior oblique, and inferior rectus immediately below superior rectus. 
117 TM 8-300 
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MEDICAL DEPARTMENT 
c. Synergists and antagonists.—Xo movement of the globe is ac- 
complished by the action of an individual muscle alone. Those that 
aid one another in a movement are called synergists. For every 
movement made by the globe there is a diametrically opposed move- 
ment. The muscles that oppose one another in contraction may be 
termed antagonists. 
Figure 13.—Diagram showing action of individual muscles in the six cardinal directions 
of gaze from position of “eyes front.” 
118 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
93 
Table of synergists 
(Peter) 
Muscle 
Synergist 
Internal rectus 
1 
\ 
\ 
\ 
\ 
\ 
Superior rectus. 
Inferior rectus. 
Superior oblique. 
Inferior oblique. 
Inferior oblique. 
Internal rectus. 
Superior oblique. 
Internal rectus. 
Inferior rectus. 
External rectus. 
Superior rectus. 
External rectus. 
External rectus. _ _ 
Superior rectus 
Inferior rectus _ _ _ __ __ 
Superior oblique . 
Inferior oblique _ _ 
Figure 14.—Diagram showing conjugate or yoke action of extrinsic ocular muscles ia 
binocular movements. 
119 STM 8-COO 
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MEDICAL DEPARTMENT 
Table of direct antagonists 
(Peter) 
Muscle 
Antagonists 
Internal met,us 
/'External rectus. 
< Superior oblique. 
/Inferior oblique. 
/Internal rectus. 
< Superior rectus. 
/Inferior rectus. 
JInferior rectus. 
\ Superior oblique. 
/Superior rectus. 
/Inferior oblique. 
/Inferior oblique. 
/Superior rectus, 
f Superior oblique. 
/Inferior rectus. 
External rectus 
Superior rectus 
Inferior rectus ' 
Superior oblique __ 
Inferior oblique _ 
94. Binocular movements.—When binocular movements are 
considered it is found that a change of position from “eyes front” to 
a different position within the field of binocular fixation is accom- 
plished by the combined action of muscles of each eye. The muscles 
that by their contraction maintain the two visual lines parallel in 
combined movements of the two eyes are termed conjugate or yoke 
muscles. For example, in looking toward the right from the position 
“eyes front” the right external rectus and left internal rectus contract. 
Below is a table showing the conjugate or yoke muscles brought into 
play in movements in the six cardinal directions from the position of 
“eyes front.” 
Table of conjugate muscles 
Direction 
Muscles 
To right 
Right external rectus and left internal rectus. 
Left external rectus and right internal rectus. 
Right inferior oblique and left superior rectus. 
Right superior oblique and left inferior rectus. 
Left inferior oblique and right superior rectus. 
Left superior oblique and right inferior rectus. 
To left 
Up and to right 
Down and to right. 
Up and to left 
Down and to left 
95. Prisms.—In the recognition of heterophoria and heterotropia 
Idle use of prisms is of great value, particularly in arriving at a quanti- 
120 TM 8-300 
NOTES ON EYE, EAR, ETC., IN AV1IATTON MEDICINE 
95-96 
tative diagnosis. Therefore a consideration of the optical properties 
of prisms is now essential. 
A prism may be defined as a portion of a refracting medium bounded 
by two plane surfaces which are inclined at a finite angle. The two 
plane surfaces are called faces, the line of their intersection the edge, 
the angle between the faces the apical angle, and the side opposite this 
angle the base. If a prism is of a denser medium than that surround- 
ing it (for example, glass in air), a ray of light on entering it will be 
bent toward the base as it enters the prism, upon passing through the 
denser medium and reentering the rarer medium, the emergent ray 
will further be bent toward the base as it leaves the prism. When 
the ray of light, while passing through a prism, is parallel to the base, 
it is said to traverse the prism symmetrically and in this case the 
angles of incidence and emergence are equal. The total amount of 
deviation between the incident ray and the emergent ray is called the 
angle of deviation. A ray of light passing through is deviated toward 
the base, and the image of an object seen through a prism is projected 
or displaced toward its apex (Duke Elder). 
96. Numbering of prisms (Peter).—As to the nomenclature of 
prisms, three methods have been proposed and used: 
a. Numerals indicating angle in degrees formed hy the two refract- 
ing surfaces or faces.—This method is unsatisfactory inasmuch as the 
amount of deviation produced varies with the index of refraction of 
the material as well as the angle of the apex, or in other words depends 
upon the material from which the prism is made in addition to the 
angle of the apex. Therefore, it does not express the amount of 
deviation undergone by a ray of light passing through the prism. 
h. The centrad method of Dennett.—The unit, centrad, is designated 
symbolically by the Greek letter delta inverted (triangle base up). A 
prism of 1 centrad value will deviate a ray of light l/100th part of the 
arc of the radian. The radian of the arc is obtained by measuring 
off on the circumference of a circle a distance equal to the radius of 
the arc. A radian equals 57.295°, therefore one centrad, l/100th part 
of the radian, is 0.57295°. This unit of measure is constant. 
c. Prentice's method of prism diopter.—Designated by the Greek 
letter delta (triangle base downward). A prism of 1 diopter’s strength 
will deviate a ray of light 1 centimeter, at 1 meter’s distance, or 1 inch 
at 100 inches’ distance. It is purely a tangential measurement. One 
prism diopter equals 34.3764B minutes. This unit is not constant, that 
is, a 10-diopter prism does not equal 10 times a 1-diopter prism, but 
equals 5°42.6355'. The two units of measure, centrad and diopter, 
are so nearly equal up to 20 that either system may be used with ap- 
121 TM 8-300 
96-98 
MEDICAL DEPARTMENT 
proximately equal accuracy. But beyond 20, while the centrad con- 
tinues to be uniform the prism diopter loses in value. The prism 
diopter is the method we shall use in the quantitative determination of 
heterophoria. 
97. Rotary prism.—If two prisms of equal value, for example 
10 diopters, are placed together base to apex, one will neutralize the 
other. If one is rotated against the other until the two bases are 
together there will be a prism equal in value to the sum of the two, 
that is, 20 diopters. If the two prisms of equal strength are placed 
together, one (a) base up and the other (h) base down and rotate 
them against one another in opposite directions an equal amount, that 
is, {a) with base up and out at 45°, and (b) base down and out at 
135°, there will be a prism of a certain value base out only, as the 
base up and base down effects are neutralized. This illustrates the 
principle employed in the construction of the Risley rotary prism; 
the two prisms are rotated in opposite directions by a rack and pinion 
arrangement so that when properly calibrated any prismatic effect 
may be obtained from zero to the sum of the two. Further, the base 
may be placed in any position desired, that is, base up or down, in or 
out. A rotary prism amounts to a case of simple prisms and, while 
a great convenience and time saver, is not essential in the determina- 
tion of heterophoria. The prisms from the trial lens case may be used 
quite satisfactorily if a rotary prism is not available. 
98. Maddox rod.—The Maddox rod is used in the determination 
of the existence of heterophoria. In its simplest form it is a section 
of small glass rod, probably 4 or 5 millimeters in diameter, mounted 
in an opaque black disc which is fitted in a trial lens frame. The type 
found on the usual phorometer trial frame is multiple, or compound, 
that is, several rods superimposed with the axes parallel and within 
the same plane. It is believed that the multiple, or compound, Maddox 
rod gives sharper definition. The Maddox rod, either single or com- 
pound, refracts only in one meridian and that at right angles to its 
axis. If a small luminous point is seen through a Maddox rod the 
point appears as a luminous line at right angles to the axis of the rod. 
When the rod is placed in a horizontal position before the eye, and 
a luminous point seen through it, the luminous point appears as a 
vertical line of light. When the Maddox rod is placed before an eye, 
the retinal image of a luminous point is therefore distorted. If a 
Maddox rod is placed before the left eye and the right fixed upon a 
luminous point of light (1-centimeter lamp at distance of 20 feet), 
the left retinal image of the luminous point is so distorted that it is 
not recognized as the same object seen with the right eye, fusion control 
122 TM 8-300 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
98-99 
is greatly weakened or reduced, and the left visual line will follow the 
lines of least resistance. If a muscular imbalance exists, the eye behind 
the rod will deviate inward or outward, etc., as the case may be. We 
may say then that the Maddox rod has the optical effect of converting 
a point of light into a line of light at right angles to its axis, and has 
the psychological effect of weakening or abolishing in part, at least, 
fusion control. 
99. Phorometer trial frame.—a. Description.—The phorometer 
trial frame as used routinely in the examination of Air Corps per- 
sonnel consists of a triple cell trial frame, on© cell capable of being 
rotated, as for cylindrical lenses, a Risley rotary prism, and a com- 
pound Maddox rod for each eye. The rotary prisms and the Maddox 
rods can be swung into place, that is, one each before each triple 
cell, as desired. The rotary prisms may be adjusted to any position, 
A Single Maddox rod. 
B Leveling device. 
C Bubble. 
D Triple cell (one rotary) for trial lenses. 
E Risley rotary prism. 
F Multiple Maddox rod. 
O Adjustment for interpupillary distance. 
Figure 15.—Phorometer trial frame and single Maddox rod. 
123 TM 8-300 
100-101 
MEDICAL DEPARTMENT 
base up or down, in or out, as desired, and with it any prismatic 
effect, from 0 to 30 diopters may be obtained. The Maddox rods may 
be placed with the axes in any meridian, being capable of being rotated 
through 180°. The instrument is equipped with a level bubble and 
leveling device, has an adjustable forehead rest, is adjustable for inter- 
pupillary distance, and mounted on a telescoping floor stand or wall 
bracket. 
b. Use.—It is believed advisable that first the student disregard the 
phorometer trial frame and use only the equipment from the trial lens 
case in arriving at conclusions regarding heterophoria in order to 
realize the optical principles involved. Later the phorometer trial 
frame may be used as a matter of convenience, but as has been stated, 
it is not essential. 
100. Sighting eye.—Before beginning the tests for the detection 
of heterophoria, it is necessary that the sighting or fixing eye be 
determined. When an object is fixed it is habitually done with one 
eye, while the other eye adjusts itself to take up fixation after this act 
has been accomplished by the former. The eye that sights an object 
first is referred to as the sighting, fixing, or directing eye. 
As a rule, a right-handed person will sight with his right eye, and 
a left-handed person with his left. However, this rule is not infalli- 
ble, and too much reliance should not be placed on it. 
Assuming that the eye one employs habitually for sighting is the 
more steady or nondeviating of the two, it is advisable, therefore, 
when measuring deviations to allow the examinee to sight with the 
eye he customarily employs for that purpose. When this is observed 
the tests are carried out with the nonsighting eye, as this is the eye 
that deviates more readily should any deviation occur. Investigations 
show that the findings are considerably more consistent when this 
procedure is followed. 
101. Technique of determining imbalance.—a. Determining 
sighting eye.—For determining the sighting eye, a blank card about 
13 by 20 centimeters, wTith a 1.6-centimeter round hole in the center is 
employed. The examinee is seated facing the spotlight 6 meters 
away; he grasps the card by the short side with both hands. While 
looking intently at the light, he slowly raises the card at arm’s length 
and locates the light through the hole, and the eye selected for this 
purpose is the one used habitually for sighting and fixing. 
b. Adjustment of trial frame.—In using equipment from the trial 
lens case, adjust the spectacle trial frame on the examinee so that it 
is comfortably worn and so that the cells are properly placed as to 
interpupillary distance. 
124 TM 8-300 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
101-102 
c. Imbalance in horizontal meridian.—For determining an imbalance 
in the horizontal meridian, that is, exophoria or esophoria, place the 
Maddox rod in the cell before the nonsighting eye so that the axis of 
the rod is horizontal. Adjust the muscle lamp, or spot of light at 20 
feet distance so that its diameter is about 1 centimeter, and switch off 
all lights in the vicinity of this area. Direct the examinee to fix upon 
the spot of light, and for a few seconds at a time alternately cover 
and uncover the nonfixing eye with an opaque card, allowing the fixing 
eye to maintain fixation constantly. The momentary covering of the 
nonfixing eye aids further in weakening of fusion control. 
d. Orthophoria.—If orthophoria exists the visual line of the non- 
fixing eye will not deviate and the vertical line of light will be seen 
as passing through or bisecting the spotlight. 
e. Heterophoria.—If heterophoria (in this case exophoria or eso- 
phoria) is present, the vertical line of light will be seen to the right or 
left of the spotlight. 
f. Homonymous diplopia.—If the line of light is seen on the same 
side (homonymous diplopia) of the examinee as the Maddox rod is 
placed (for example, the Maddox rod before the left eye and the line 
is seen to the left of the spotlight), the qualitative diagnosis of esopho- 
ria is made, and in order to make a quantitative determination a prism 
must be used base out. Homonymous diplopia indicates esophoria, 
the amount of which is estimated by the use of a prism before the non- 
fixing eye, with base out or toward the temporal side. Place a weak 
prism, that is, of 1 diopter, before the nonfixing eye, and repeat the 
procedure of covering and uncovering the nonfixing eye. It will be 
found that perhaps the line of light has moved nearer the spot of light 
but still does not bisect it. Replace the prism with a stronger one until 
the line of light passes through the spot of light and the strength of 
the prism used indicates the amount of esophoria in prism diopters. 
g. Crossed diplopia.—If the line of light is seen on the opposite side, 
as for example when the Maddox rod is before the left eye and the line 
is seen to the right (crossed diplopia), then a qualitative diagnosis of 
exophoria is made. A crossed diplopia indicates exophoria, the 
amount of which is estimated by the use of a prism before the nonfixing 
eye with base in or toward the nasal side. The procedure is the same 
as with esophoria except that the prism is used base in. The strength 
of the prism used to cause the line of light to bisect or pass through 
the spot of light indicates the amount of exophoria in prism diopters. 
102. Optical principles involved in horizontal deviations.— 
a. Orthophoria.—The sighting eye fixes the spotlight; the nonsighting 
eye, having before it the Maddox rod, sees the spotlight as a vertical 
125 TM 8-300 
102-103 
MEDICAL DEPARTMENT 
line of light. If no deviation is uncovered (orthophoria), the rays of 
light from the spotlight will fall upon the foveae of both eyes and be 
projected into space to the point actually occupied by the light. When 
this occurs, the line of light will be seen passing directly through the 
spotlight. 
h. Deviating eye.—As the Maddox rod possesses the power of weak- 
ening the action of the fusion centers, the eye behind the Maddox rod 
will deviate if it has a tendency to do so, provided the action of the 
fusion centers is reduced below the urge to deviate. 
c. Esophoria.—Assuming the eyes have a tendency to deviate in- 
ward (esophoria), and the right eye is the nonsighting eye, the prin- 
ciples involved remain unchanged insofar as the sighting eye is con- 
cerned, but with the nonsighting (right eye in this case) they are 
different. The rays of light enter the eye as in orthophoria, but in- 
stead of falling upon the fovea they fall upon the retina on its nasal 
side. This occurs because the cornea is rotated inward, and the fovea 
is rotated outward. Therefore, following the law of projection, the 
image of the line of light being formed upon the nasal retina will be 
projected to the temporal field and will be seen as a vertical line upon 
the right side of the spotlight (homonymous diplopia). 
d. Measurement of deviation.—In order to measure the amount of 
deviation that has been uncovered, prisms are utilized to refract the 
rays of light entering the deviating eye, outward or toward the temple 
until they fall upon the fovea. Rays of light passing through a prism 
are bent or refracted toward its base and the object seen through the 
prism is projected toward its apex. Therefore, increasing prisms 
placed base out before the deviating eye will refract the rays toward the 
temporal side, until they eventually reach the fovea, and at the same 
time the line of light will be seen to move over toward the nasal field 
until it passes directly through the spotlight. When this is accom- 
plished the deviation is corrected by the refraction of the rays of light, 
the eye remaining stationary. The strength of prism required to 
accomplish this represents, in prism diopters, the amount of deviation 
uncovered at that time. 
103. Vertical deviations.—a. Hyperphoria.—Ordinarily hyper- 
phoria only is used as a diagnostic term where there exists a deviation 
of the visual lines in the vertical meridian, and the designation is 
made as to right or left, depending upon which of the visual lines is 
the higher, or which tends to deviate upward in comparison with its 
fellow. For the measurement of hyperphoria the Maddox rod is 
adjusted before the nonfixing eye with its axis vertical, hence the line 
of light is seen as horizontal. The nonfixing eye is alternately cov- TM 8-300 
XOTES OX EYE, EAR. ETC., IX AVIATIOX MEDICIXE 
103-104 
ered and uncovered, and if the line of light is seen passing through the 
spot of light there is no hyperphoria. If the line of light is seen below 
the spot of light there is a hyperphoria of the eye behind the Maddox 
rod, and the strength of prism used base down before this eye which 
causes the line to pass through, or bisect, the spot of light represents the 
deviation in prism diopters. If the line of light is seen above the 
spotlight a hyperphoria of the fixing eye is indicated, and the strength 
of prism base up before the eye behind the Maddox rod represents the 
amount of deviation in prism diopters. Suppose the right eye to be 
the fixing eye; the Maddox rod is adjusted with axis vertical in the 
spectacle trial frame. The left eye is covered and momentarily un- 
covered repeatedly. Further, suppose that, in this instance, when 
fusion is weakened the left visual line turns upward (left hyper- 
phoria). Then with the left eye elevated, its fovea would be depressed 
and at a lower level than the fovea of the right eye. In this instance 
the image of the horizontal line of light would be formed above the 
fovea of the right eye, and when an image is formed above the 
fovea it is projected into the visual field below the point of fixation. 
Therefore, the examinee would see the spot of light with the right eye 
and the line of light with the left, and the line would be projected below 
the spot of light, indicating, in this case, a left hyperphoria. By using 
a prism of sufficient strength the position of the image of the line of 
light may be shifted from above the fovea to the level of the fovea, and 
the line of light will be seen as passing through the spot. The strength 
of the prism required indicates the amount of deviation in prism 
diopters. 
b. Heterophoria.—Where the phorometer trial frame with rotary 
prism is used, in testing for heterophoria, the same procedure is used 
except that the examinee, by turning the milled thumbscrew control- 
ling the rotary prism, adjusts the prisms himself so that the line of light 
passes through the spotlight. The nonfixing eye is alternately cov- 
ered and uncovered. In horizontal deviations where the prism is 
adjusted base in (nasally) an exophoria is indicated, where the prism 
is adjusted base out (temporally) an esophoria is indicated. 
c. Amount of deviation.—In vertical deviations the prism adjusted 
base down indicates a hyperphoria of the eye behind the Maddox rod. 
Where it is adjusted base up a hyperphoria of the opposite eye is 
indicated. In all instances the amount of deviation is read in prism 
diopters as the indicator shows on the markings on the rotary prism. 
104. Heterophoria at 33 centimeters.—a. This test is not done 
routinely. The test is carried out in exactly the same manner as 
the test at 6 meters except that a small electric lamp (ophthalmoscope 
127 TM 8-300 
104 
MEDICAL DEPARTMENT 
without head) is held before the examinee at the level of his eyes. This 
is a test for imbalance at the ordinary reading distance, and may give 
the examiner some information as to the existence of refractive error, 
insufficiency of convergence, and may be indicative of a reduction of 
fusion control at usual reading distance. It will be frequently found 
that an examinee who shows a marked exophoria at 33 centimeters will 
also show a low angle of convergence, and under stress of fatigue 
may exhibit a diplopia (crossed) at reading distance. 
Right eye fixing F'—L in left visual axis, F’ the left fovea. Image of A falls on A' to 
nasal side of fovea and is projected at B. Homonymous diplopia. 
Figubb 16.—Esophoria. 
h. Cyclophoria.—The existence of a cyclophoria is not investigated 
as routine, but only when considered as necessary by the examiner. 
In testing for cyclophoria, two Maddox rods with the axes exactly 
vertical, one before each eye, may be used. With the spotlight at 20 
feet a horizontal line of light is seen with each eye, and in order to 
prevent fusion, these may be separated by a strong prism (8 diopters) 
base up or down before one of the eyes. If there is a latent tendency 
128 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
104-105 
toward intorsion or extorsion in either eye, one of the lines will appear 
as at an angle with the other or slanted, and the eye intorted or 
extorted may be determined by the line that does not appear hori- 
zontal. For example, if the prism, base down, is before the left eye 
the upper line is the one seen with the left eye, etc. But with an in- 
torsion the line of light will appear as slanting outward and down- 
ward, and with an extorsion the line will appear as slanting inward 
and downward. 
Right eye fixing L-F’, left visual axis. Image A falls on A', which is on temporal side 
of left fovea and therefore is projected at D. Crossed diplopia. 
Figueh 17.—Exophoria. 
105. Etiology of heterophoria.—a. Deviation.—As previously 
stated the eyes are held in their proper positions in the orbits and in 
the proper relation to one another by the combined action of all of 
the extrinsic ocular muscles. Why one eye will deviate, when the 
action of the fusion centers is partially abolished, is not clear. There 
seems to be, for some reason or other, an urge of one or more of the 
271818°—40 9 
129 TM: 8-300 
105 
MEDICAL DEPARTMENT 
extrinsic muscles to overact or to underact. This action will cause the 
eyes to deviate from the parallel whenever released from control of 
the fusion centers. 
b. Cause.—If the urge for binocular single vision is greater than the 
urge to deviate, the condition of heterophoria will exist; if the urge for 
binocular single vision is less than the urge to deviate, heterotropia 
will exist. If fusion control is habitually weak, or is easily weakened 
by artificial measures, the more significant will be deviation. If fusion 
control is active and not easily weakened, the existing latent devia- 
tion will be unimportant, at least under normal conditions. There 
must be taken into consideration, too, the possibility of anatomical 
defects. It may be that one muscle is actually longer or shorter than 
the normal. 
c. Factors.—Whatever the primary cause of a latent deviation may 
be, certain factors tend to increase its tendency, and produce the con- 
dition of muscular asthenopia. Probably the most common factor 
encountered is an error in refraction, whether it be myopic, hyperopic, 
or astigmatic. This is particularly true when accumulative fatigue 
is superimposed. The fatigue may be induced by the refractive errors 
alone, or it may be secondary to them, originating in nervous or 
physical stress, chronic infection, etc. 
d. Latent deviations.—Latent deviations of low degree, at 6 meters, 
such as 2 prism diopters of esophoria, 1 of exophoria, and y2 of hyper- 
phoria, may be considered ordinarily as orthophoria. Latent devia- 
tions higher than these are in themselves of little significance, and can 
be considered worthy of attention only after all the associated factors 
which apply to the type of deviation have been investigated. 
e. Factors to be considered.—(1) In all forms of latent deviations 
there must be considered: 
(a) Ease with which fusion control is weakened. 
(b) Efficiency with which visual lines are maintained parallel while 
moving in the six cardinal positions. 
(c) Errors in refraction of one-half diopter or higher. 
(2) If esophoria is exhibited there must be considered in addition 
to the above factors: 
(a) Power of abduction (prism divergence;. 
(b) Amount of accommodation that can be exerted. 
(3) If exophoria is exhibited, the power of adduction (angle of 
convergence or meter angle) must be taken into consideration in 
addition. 
/. Increased tendency to deviate.—When the tendency to deviate 
increases, because of errors in refraction and fatigue, this increase 
130 TM 8-300 
105 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
will be accompanied, generally, by defects in one or more of the 
associated factors, which apply to the type of deviation. The asso- 
ciated parallel movements are usually the first to exhibit evidences of 
ocular strain, which is manifested by diplopia in the primary, or 
in one or all of the cardinal positions on the tangential plane. For 
example, an individual exhibiting an exephoria of 2 prism diopters, 
a refractive error of 1 diopter, divergence power of 5 prism 
diopters, and an angle of convergence of 50°, may, after the onset 
of fatigue, exhibit a tendency to deviate 6 or 8 diopters, exhibit 
diplopia in the lateral positions on the tangential plane, and if fatigue 
continues, divergence power may increase to 10 diopters while the 
convergence power drops to 30°, 
g. Return to original level.—After correcting the refractive error, 
thereby inducing ocular rest, all these factors tend to return to their 
original level, the defective parallel movements being the first to 
recover. Horizontal deviations respond much more readily after 
correction of existing refractive errors than do the vertical deviations. 
h. Refractive errors.—It is a generally accepted theory that many 
cases of heterophoria are due entirely to refractive errors. It is 
believed, however, that all cases of heterophoria exist independent 
of refractive errors and that the errors, when fatigue is superimposed, 
only exaggerate the deviation without being the primary cause. 
i. Accommodative theory.—The accommodative theory is as follows: 
Esophoria and exophoria are manifestations of muscular asthenopia 
due to hyperopia and myopia, respectively. This occurs because there 
is believfed to be a definite relation or nervous balance between accom- 
modation and convergence, with accommodation the dominating or 
controlling influence. In emmetropia, when the eyes accommodate 
1 diopter, convergence is sufficient to cross the visual lines at 1 meter 
distance, that is, 1 meter angle of convergence is exerted, at which 
point the obj ect focused upon is located. When this occurs the nervous 
balance between accommodation and convergence is equal. 
j. Hyperopia.—In the hyperope accommodation exceeds conver- 
gence. In order to focus an object at 1 meter distance the eyes may 
have to accommodate sufficiently to focus a normal eye at 50 centi- 
meters. When such accommodation occurs the eyes are still required 
to converge 1 meter angle, that is, the eyes are accommodating 2 
diopters while converging only 1 meter angle. The excessive or unused 
stimulation to converge to 50 centimeters (2 meter angles) is present, 
and this may lead to convergence excess. In order to maintain binoc- 
ular single vision the individual must overcome this convergence excess 
by increased action of his external recti muscles, which is initiated 
131 TM 8-300 
105-106 
MEDICAL DEPARTMENT 
by the fusion centers. When the action of the fusion centers is low- 
ered, one eye will deviate inward as stimulation of the external recti 
is no longer great enough to maintain parallelism of the visual lines. 
Continuing further under accumulative fatigue, the external recti 
can no longer maintain their increased action; therefore, the con- 
vergence excess pulls one eye inward. This deviation will occur, 
in the early stages of fatigue, only when the eyes are turned in one or 
all of the cardinal positions, but in the more advanced stages deviation 
may occur while the eyes are in the primary position and independent 
of the action of the fusion centers. 
k. Myopia.—In myopia the reverse occurs. Accommodation is less 
than convergence. When a myope fixes an object at 50 centimeters 
distance, he may be accommodating only enough to focus an em- 
metropic eye at 1 meter, that is, he is accommodating 1 diopter while 
converging 2 meter angles. When this occurs the urge to converge 
is weak, as accommodation is the dominating impulse. The external 
recti soon take advantage of the weak convergence stimulation and 
divergence excess results. When the action of the fusion centers is 
lowered one eye will deviate outward because of underaction of the 
internal recti, due probably to lowered muscular tonicity. Under 
accumulative fatigue the internal recti cannot overcome the pull of the 
external recti and deviation will occur; first, when the eyes are turned 
in one or all of the cardinal positions, and later, when in the primary 
position, independent of the action of the fusion centers (squint). 
I. A dual findings.—Although the foregoing is the theory generally 
accepted in reference to heterophoria., and squint resulting from errors 
in refraction, in actual practice it does not hold true at all times. 
Twenty-three cases with hyperopic errors exhibited esophoria in six- 
teen instances and exophoria in seven. All of these cases developed 
muscular asthenopic symptoms, under accumulative fatigue, with con- 
siderable increase in deviation. When the errors in refraction were 
corrected, symptoms disappeared and the deviations returned to their 
former levels. It will be noted that in this small series of cases above 
30 percent of hyperopes exhibited exophoria which was influenced by 
the refractive errors. 
106. Incidence of heterophoria.—In a series of 500 unselected 
cases, 244, or 48.8 percent, exhibited a horizontal imbalance above the 
amount considered as orthophoria; 132, or 25.6 percent, of this series 
exhibited a vertical imbalance; 25, or 10.24 percent, of the cases showing 
a horizontal imbalance exhibited, after the onset of fatigue, an increase 
in the deviation (or a greater amount could be uncovered), and devel- 
oped defects in one or all of the associated factors. 
132 TM 8-300 
107 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
107. Other methods of detecting heterophoria.—a. Cover 
test.—The examinee fixes the spotlight at 6 meters’ distance. A card 
is held before one eye for a few seconds, then quickly removed. If 
exophoria exists the eye behind the card will deviate outward, and when 
the card is removed the eye will be seen to swing inward and take up 
fixation with the fixing eye. If esophoria exists the covered eye will 
deviate inward, and will swing outward when card is removed to take 
up fixation as in exophoria. The same applies to hyperphoria. This 
test is repeated by fixing an object or light at 33 centimeters’ distance. 
This test cannot always be depended upon, as considerable heterophoria 
may exist before it can be exhibited by this method. 
l>. Diplopia or displacement tests*.— (1) Horizontal or lateral im- 
balance (esophoria or exophoria).—The trial frame is adjusted to the 
examinee and a strong prism, 8 or 10 diopters, is placed base down 
before the right eye. The spot of light (muscle lamp) is seen at a 
distance of 20 feet and a diplopia is induced, the upper light being the 
image projected by the right eye and the lower light that projected by 
the left. If there is a condition of orthophoria the two images will be 
seen as separated in the vertical meridian only. In heterophoria there 
will be a lateral displacement of the two images as well as vertical. If 
the upper image is displaced to the right (homonymous diplopia), an 
esophoria is indicated, and if to the left, an exophoria. A quantitative 
determination is made with prisms, base in or out, in a manner similar 
to that where the Maddox rod is employed. 
(2) Vertical deviations.—A strong prism is placed, base in, in 
front of the right eye (the prism must be of such strength that 
diplopia is induced, and as the eyes have a stronger converging than 
diverging power, base in is suggested). The image seen by the right 
eye will be displaced to the right (toward the apex of the prism), 
and if no hyperphoria exists the two images will be seen in the same 
horizontal plane. If the right image is higher than the left, a left 
hyperphoria is indicated; if the right image is lower than the left, 
condition is right hyperphoria. Where left hyperphoria is found 
the quantitative estimate may be made by prisms, placed base down 
before the left eye until both images are seen at the same level. In 
right hyperphoria the determination is made by prisms base up 
before the left eye until both images are at the same level (Peter). 
c. Maddox double prism.—The Maddox double prism (two 4- 
diopter prisms, base together, in a trial lens frame) may be used in 
determining heterophoria. The Maddox double prism causes a 
monocular diplopia, an image being displaced toward the apex of 
each prism. When the spot of light is used at 20 feet with the 
Maddox double prism before one eye, three images are seen, the 
133 TM 8-300 
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MEDICAL DEPARTMENT 
upper and lower being images of the eye behind the double prism 
and the middle image that of the fellow eye. In orthophoria the 
three spots of light are seen in line; where heterophoria exists the 
middle image will appear displaced, that is, to right or left, above 
or below (depending upon the position of the double prism). Lat- 
eral and vertical deviations may be determined and prisms used to 
arrive at a quantitative conclusion. 
d. Red lens test.—This test furnishes valuable corroborative evi- 
dence in examining for heterophoria and in some cases of hetero- 
tropia. 
(1) The examinee is seated facing a blackboard, wall, or other flat 
surface at a distance of 75 centimeters. A red glass is placed in 
front of the right eye. Care should be taken to see that the glass is 
large enough and held in such position as to be in front of the pupil 
in all the movements of the eye. 
(2) A small spotlight is now carried over the surface of the 
blackboard from the point of fixation along the eight cardinal merid- 
ians for a distance of 50 centimeters. In the normal individual the 
red and white lights remain fused as a pink light; in cases of 
heterophoria with low fusion; faulty; or in cases of actual hetero- 
tropia which do not suppress, a red and a white light will be seen. 
If the red glass is in front of the right eye and the red light is seen 
on the right side of the white light, then we have homonymous 
diplopia. If the red light appears on the left side, we have crossed 
diplopia. 
(3) The position at which diplopia occurs can be reported in dis- 
tances from the point of fixation or, by referring to the table in the 
chapter on the tangent rule, the distances in centimeters may be 
converted into degrees. Diplopia occurring within 50 centimeters 
of the point of fixation is considered to be disqualifying for flying 
applicants. 
108. Associated factors.—As previously stated, the associated 
factors are vitally important in determining the significance of 
heterophoria. The factors to be considered are— 
a. Power of abduction. 
b. Power of adduction. 
c. Associated parallel movements. 
d. Accommodation. 
e. Errors in refraction. 
/. The power of fusion. 
Only those factors pertaining to the recti muscles will be consid- 
ered here. Accommodation and errors in refraction will be con- 
sidered in their respective sections. 
134 TM 8-300 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
109-111 
109. Power of abduction (prism divergence).—The normal 
power of abduction ranges between 3 and 6 prism diopters with 
an average of 4. When a low prism divergence is exhibited (below 
4 diopters) associated with an esophoria, it indicates an overaction 
of the internal recti muscles, an underaction of the external recti, 
or both. At the same time, the power or urge of the fusion centers 
may be weak. 
The examinee is seated facing a spotlight 6 meters away. The 
rotary prisms of the phorometer trial frame are adjusted before 
the eye so that wdien the milled screw operating the prism is turned 
toward the nose, the prisms will be acting base in, thereby placing 
the apex over the external rectus muscle. With the prism set at 
zero on the scale, the examinee should see but one spotlight. As 
the prisms are slowly rotated, base in, by the examiner, diplopia 
will be produced. The number of prism diopters which cause the 
onset of diplopia is read from the scale and entered on the record 
as abduction or prism divergence. The prisms should be turned 
steadily and at slow speed. 
110. Optical principles involved.—The test is based upon the 
fact that the muscle lying beneath the apex of a prism is stimulated 
to action while the other remains passive, insofar as the action of 
the prism is concerned, and the urge of the fusion centers to main- 
tain binocular single vision. Therefore, in this test care must be 
taken that the fusion sense is not impaired and that the prisms are 
accurately placed. The rays of light enter the eyes, fall upon the 
fovea of each, and the retinal images of the light are projected in 
the point actually occupied by the light, and app°ar as one. The 
prism being operated, base in, before one eye will refract the rays 
of light entering that eye toward the nasal side of the fovea. The 
fusion centers strive to maintain binocular single vision and in order 
to accomplish this the external rectus is stimulated to contract. This 
contraction rotates the cornea outward, and the posterior pole and 
fovea inward. In this way the refracted rays continue to fall upon 
the fovea and binocular vision is maintained. However, a point is 
reached, eventually, when the external rectus can no longer rotate 
the eye outward; the rays continue to be progressively refracted and 
soon travel beyond fovea, thus inducing diplopia. When diplopia 
occurs, the fusion centers instantly lose their urge for binocular 
single vision and the eye rotates back to its normal position. This 
test should not be repeated more than two or three times as the 
strain on the external rectus causes considerable discomfort. 
111. Power of adduction.—There are three principal methods of 
measuring the power of adduction, namely— 
135 TM 8-300 
111-115 
MEDICAL, DEPARTMENT 
a. Prism convergence. 
b. Angle of convergence. 
c. Meter angle. 
The power of convergence should be, normally, three times as great 
as divergence, that is, 1 to 3, or 8 to 24. 
112. Prism convergence.—This test is conducted in the same 
way as that for prism divergence except that the prism is placed base 
out, thereby placing the apex over the internal rectus. The results 
of this test are not as satisfactory as those of divergence, for there 
occurs a marked inconsistency in the findings. It is probable that 
the factor of accommodation plays an important part in convergence. 
The amount of accomodation with the muscle lamp at 20 feet is 
negligible. 
113. Angle of convergence.—This method is much more satis- 
factory than prism convergence. The angle is computed from the 
near point of convergence (PcB) and interpupillary distance {Pd). 
The near point of convergence is represented by the symbol PcB, 
meaning the near point of convergence on the base line. The meas- 
urement is made from an imaginary line connecting the centers of 
rotation of the two eyes, situated 13.5 millimeters behind the anterior 
surface of the cornea. The point to be obtained is to determine the 
greatest amount of convergence that can be exerted and still main- 
tain binocular single vision. 
114. Near point of convergence.—The end of the Prince rule, 
or a modification of the same, is placed edge up at the side of the 
nose ll!/2 millimeters in front of the anterior surface of the cornea. 
A white-headed pin is held 33 centimeters in the median line above 
the edge of the rule, and the examinee is instructed to look at it 
intently. If both eyes are seen to converge upon the pin, it is then 
carried in the median line, along the edge of the rule, towards the 
root of the nose. The examinee’s eyes are carefully watched, and 
the instant one is observed „o swing outward the limit of convergence 
has been reached. The point on the rule opposite the pin is then 
read in millimeters. This test is repeated until a fairly constant 
reading is obtained. To the reading thus obtained 25 millimeters 
are added (the center of rotation is 13.5 mm. behind the cornea, and 
the end of the rule is placed 11.6 mm. in front of cornea, making in 
all 26 mm.), which gives the distance from the near point of con- 
vergence to the base line. The normal eyes should be able to con- 
verge to 80 millimeters or less. A near point more remote than 80 
millimeters indicates an underaction of the internal recti. 
115. Interpupillary distance.—a. The examiner stands with his 
back to the light, face to face with the examinee. The rule is laid 
136 TM 8-300 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
115-116 
across the eisjminee’s nose in line with his pupils, as close to the two 
eyes as possible. The distance is measured from the temporal side of 
one pupil to the nasal side of the other. The examiner closes his 
right eye and instructs the examinee to fix his eyes upon his open 
left. With the eyes in this position a predetermined mark on the 
rule is placed in line with the nasal border of the examinee’s right 
pupil. The rule must be held steadily in this position while the 
examiner opens his right eye and closes his left. The examinee is 
then instructed to look at the open right eye. The point on the rule 
in line with the temporal border of the examinee’s left pupil is read 
in millimeters, and the difference in millimeters between the two 
points on the rule is the interpupillary distance. 
h. Angle of convergence.—The following formula is used to com- 
pute the angle of convergence: Angle of convergence equals one-half 
the interpupillary distance multiplied by 100 divided by the near 
point of convergence plus three, thus: 
y2Pdx 100 10 4 , 
~PcB rd = Angle or convergence 
The above formula for determining the angle of convergence is 
purely empirical, and it is not accurate from a standpoint of pure 
mathematics. It is fairly accurate when PcB and Pd are approxi- 
mately equal. It is suggested that the table showing the angles of 
convergence with different findings as to Pd and PcB be used instead 
(see page 152), as this table is computed accurately from tables of 
tangents. 
116, Meter angle.—a. General.—Another convenient method of 
determining the power of convergence is the employment of the 
meter angle. This method has all the advantages of the angle of 
convergence except that the interpupillary distance is not taken into 
consideration. 
h. Unit of measurement.—The unit of measurement is obtained by 
the eyes fixing an object midway between the two eyes at a distance 
of 1 meter (1,000 mm.). The angle formed by a line joining the 
object with the center of rotation of either eye makes, with the 
median line, 1 meter angle. With an interpupillary distance of 64 
millimeters, the above meter angle equals about 1.5°. 
c. Near 'point of convergence.—The near point of convergence is 
determined as described under angle of convergence. When the 
number of millimeters obtained is divided into 1,000 the result will 
equal the number of meter angles of convergence exerted, thus: if the 
... , inr. 1,000 millimeters 
near point of convergence equals 100 millimeters, millimeters ' 
137 TM 8-300 
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MEDICAL DEPARTMENT 
equals 10 meter angles. Again, if the near point of convergence 
, , 1,000 millimeters , „„ , , 
equals 50 millimeters, then Wf-prs~equals 20 meter anSles- 
d. Convenience.—This method is especially convenient because, in 
the emmetrope, the amount of convergence reckoned in meter angles 
is exactly the same as the amount of accommodation reckoned in 
diopters. 
117. Associated parallel movements.—a. Applicability.—This 
test is applicable almost exclusively to paresis and paralysis of the 
ocular muscles, and offers little information where latent errors are 
concerned. 
b. Test.—The examinee stands near a window where good illumina- 
tion falls on both eyes. The examiner holds a white-headed pin 
about 33 centimeters directly in front of the examinee’s eyes and di- 
rects him to look at it steadily. % Nystagmus in the primary position 
is to be noted at this stage of the test. The examinee is then in- 
structed to hold his head still and watch the pin as it is moved 
slowly in the eight cardinal positions. Care is taken not to carry the 
pin beyond the field of binocular fixation. The eyes are inspected 
to discover any failure in fixing the pin. A lagging or overaction 
of either eye is noted. 
c. Interpretation.—A lagging of either eye in any of the eight 
cardinal positions is due to an underaction of at least one of the 
extrinsic muscles. It may indicate a paresis or complete paralysis. 
d. Recording.—The underaction is recorded by stating which eye 
lags and in which direction the lagging is observed. In the same 
way any overshooting of either eye is recorded by stating which eye 
is involved and in which direction. 
e. Confirmation.—If any underaction or overaction is observed with 
this test the findings are confirmed on the tangent plane. 
118. Squint.—a. Definition.—Squint or strabismus is a term 
which may be applied to those conditions where there is an obvious 
or manifest deviation of the visual axes from the normal. There 
are two general varieties of squint encountered : 
(1) Concomitant.—Concomitant squint, or strabismus (hetero- 
tropia) which is characterized by the two visual axes, although ab- 
normally directed, maintaining their relative position to one another 
with all ocular movements. 
(2) Paralytic.—Paralytic squint or strabismus definitely due to 
a paresis or paralysis of one or more of the extrinsic ocular muscles, 
in which the two visual axes do not maintain their relative positions 
in all positions in the field of binocular fixation. There is another 
138 TM 8-300 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
118 
type of squint due to a defective innervation in which there is an 
unequal stimulation, rather than paralysis, of conjugate muscles. 
This latter type may be encountered where there is an unequal 
stimulation of certain nerve centers as in meningitis, brain tumor, 
cerebral irritation as in epilepsy, etc. 
h. Concomitant squint {lieterotropia').—As stated, in concomitant 
squint the visual axes retain their relation in all positions within the 
binocular field of fixation, differing in that respect from paralytic 
squint. In concomitant squint (this term is being more frequently 
employed clinically than heterotropia) there may be then a con- 
vergent type (esotropia), divergent type (exotropia), and deviation 
of the visual axes in the vertical meridian (hypertropia). 
A Center of rotation, left eye. 
B Center of rotation, right eye. 
D Point of maximum convergence. 
DC Distance from point of convergence to base 
line (PcB). 
Interpupillary distance (Pd) is same as AB. 
Angle of convergence, angle ABB. 
Figure 18.—Angle of convergence. 
U) Convergent squint or esotropia.—Space hardly permits a dis- 
cussion of the etiological factors concerned in esotropia. Associated 
with such a condition are usually refractive errors, and a defective 
or absent fusion faculty. The deviating eye may be constant, that is, 
the deviation is always in the same eye (monocular esotropia), or 
it may be alternating. In either case the angle of deviation remains 
practically the same whatever position the fixing eye assumes. With 
convergent squint there is usually an amblyopia ex anopsia, either 
139 TM 8-300 
118 
MEDICAL. DEPARTMENT 
End of rule is placed 11.5 millimeters In front of cornea, which is 13.5 millimeters in 
front of center of rotation. Therefore 25 millimeters Is added to findings on rule in 
determination of PcB. 
Figobh It).—Point of convergence on base line. 
140 Examinee fixes upon left pupil of examiner, who places end of rule before nasal margin 
of right pupil of examinee. Examinee then fixes upon right pupil of examiner, who 
notes distance to temporal margin of left pupil of examinee. This distance is same as 
distance between centers of rotation of two globes. 
Figure 20.—Measuring interpupillary distance. 
141 TM 8-300 
118 
MEDICAL, DEPARTMENT 
congenital or acquired, of the deviating eye, especially in the monoc- 
ular variety. With any variety of concomitant squint binocular 
single vision is impossible, so there must be either a diplopia or a 
suppression of the image of the deviating eye. The latter almost 
invariably occurs in concomitant squint. Therefore, the absence of 
diplopia is usually characteristic of any type of concomitant squint 
differing from paralytic type. 
Esophoria and esotropia are closely allied, and in conditions of 
extreme stress as fatigue or toxemia, an esophoria may become 
manifest. 
(2) Divergent squint or exotropia.—This is less frequently en- 
countered than convergent. As with esotropia it may be monocular 
or alternating; the fusion faculty is usually weak and the angle of 
squint will be likely to vary at times. Exotropia differs from eso- 
tropia in that the latter more frequently responds to nonoperative 
treatment (correction of refractive errors). Diplopia rarely occurs. 
(3) Hypertropia.—According to Peter, “A vertical deviation which 
exceeds the limits of hyperphoria is comparatively rare. In most 
instances such a deviation is not strictly concomitant, but paralytic 
in character.” Such a deviation is usually due to a muscular anomaly, 
and may frequently be found coexistent with an esophoria or 
exophoria. 
c. Kappa angle.—Even a marked appearance of squint does not 
necessarily indicate that a true squint actually exists, and the squint 
may be apparent only when the visual and optical axes do not coin- 
cide. The existence of a positive angle kappa will give the examinee 
the appearance of a divergent squint and a negative angle kappa will 
simulate a convergent squint. Usually a positive kappa angle is 
found with hyperopia and a negative angle with myopia. By the 
angle kappa is meant the angle formed by the intersection of the 
visual line with the geometric or optic axis, a line connecting the 
anatomical anterior and posterior poles of the eye. The angle kappa 
is of clinical value and has an important bearing on the accurate 
measurement of the angle of squint. The angle kappa can be meas- 
ured on the perimeter; the eye not being examined is occluded; the 
other is carefully centered on the fixation point of the perimeter. 
The examiner rotates the arc of the perimeter until it is in the hori- 
zontal position; a small electric light bulb (ophthalmoscope without 
head) is held at the point of fixation and the examiner determines 
the position of the reflex of the light on the cornea. If the reflex 
is exactly within the center of the pupil (with the examiner sighting 
directly behind the light), the visual and optic axes coincide and 
the kappa angle does not exist. If the reflex is seen on the inner or 
142 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
118 
nasal side of the center of the pupil, kappa angle is positive; the 
light is slowly moved along the arc of the perimeter in the. temporal 
field until its reflex is seen exactly at the center of the pupil, the 
eye continuing to fix on the fixation point of the perimeter; the 
number of degrees read off on the arc of the perimeter indicates the 
value of the positive kappa angle. If the reflex is seen on the tem- 
poral side of the center of the pupil, kappa angle is negative and 
may be measured by moving the light in the nasal field until it 
reaches the center of the pupil. 
F, FOVEA 
M, CENTER OF ROTATION. 
K, NODAL POINT 
A3, OPTIC OR GEOMETRIC AXIS. 
O, POINT OF FIXATION. 
OF VISUAL AXIS, OR LINE. 
ANGLE OCA IS ANGLE KAPPA. 
ANGLE OKA IS ANGLE ALPHA. 
ANGLE OMA IS ANGLE GAMMA. 
Pxgueh 21.—Measuring angle of squint 
In the emmetropic eye angle kappa is usually slightly positive, 
and in hyperopia it may be markedly positive, as much as 5° or 
more, which would cause an appearance of a divergent squint of 
10° or more, as the case may be, when both eyes are casually in- 
spected. Thus an individual may actually have a squint which is 
not apparent. On the other hand, he may present the appearance 
of a marked squint and yet have a condition of orthophoria. 
143 TM 8-300 
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MEDICAL DEPARTMENT 
d. Measuring the angle of squint.— (1) IHrschberg method.— 
There are several methods of determining the deviation of the 
squinting eye, the simplest of which is, perhaps, the Hirschberg 
method. A small lamp is held before the examinee and the posi- 
tion of its reflex on the cornea is noted, if the reflex is noted on the 
pupillary edge (outer edge in convergence, inner in divergence), the 
deviation may be estimated as about 15°. When the reflex is half- 
way between the pupillary border and limbus the deviation is ap- 
proximately 35°, and when the reflex is seen at the limbus the 
deviation may be estimated at 45°. 
(2) Perimeter method.—The perimeter may be used to measure 
the amount of deviation in squint. This method is quite accurate 
but the value of angle kappa must be taken into consideration. The 
chin rest of the perimeter is adjusted so that the squinting eye is 
opposite the point of fixation. The examinee is directed to fix upon 
a point at least 20 feet away, immediately above the point of fixation. 
The small light, as used in measuring angle kappa, is moved along 
the arc of the perimeter until its reflex is exactly in the center of 
the pupil of the squinting eye. The position of the light on the 
arc of the perimeter indicates the number of degrees of deviation. 
e. Paralytic squint.— (1) General.—A paralysis of any one of the 
extrinsic ocular muscles will result in a limitation in the rotation 
of the globe in the direction of the action of that muscle. Instead 
of a complete paralysis there may be a slight paresis and the defect 
of motility may be so slight that it is not recognized upon ordinary 
inspection. 
(2) Detection.—Limitation of movements of the globe may be 
detected in the manner described in paragraph 117, provided they are 
gross enough to be easily noticed. When the limitation is slight 
they may escape detection without the employment of special tests. 
(3) Ghoract eristic symptom.—There is one characteristic symptom, 
or subjective manifestation of paralytic squint, that the patient prac- 
tically invariably complains of—diplopia; it is a valuable point in 
differentiating concomitant and paralytic squint. Unlike concomi- 
tant squint the affected eye does not have its image suppressed, and 
the character of the diplopia in the different parts of the normal 
field of binocular fixation aids the examiner tremendously in arriving 
at a diagnosis as to the muscle, or muscles, involved. 
(4) Differentiation between physiologic and pathologic diplopia.— 
Physiologic diplopia has been referred to repeatedly in connection 
with stereoscopic vision, and is considered as being a regular accom- 
paniment of normal binocular vision. Alexander Duane differen- 
tiated between physiologic and pathologic diplopia, emphasizing the 
144 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
118 
characteristics of each, in a manner that will be found to be extremely 
helpful to the student of ophthalmology. The following table is 
taken from his article “Diplopia and other Disorders of Binocular 
Projection,” appearing in the Archives of Ophthalmology, volume T, 
February 1932. 
Physiologic diplopia 
Pathologic diplopia 
The object of fixation appears single 
The object of fixation appears double, 
and is distinct. 
one image being distinct, the other 
indistinct. 
The only objects seen double are those 
Most of the objects in the field of view 
that are obviously farther or nearer 
appear double, but particularly those 
than the object of fixation. The 
that are close to the object of fixation 
nearer the objects are to the latter, 
and are alongside it. 
the less double they appear, and 
those that are alongside it appear 
single. 
The diplopia is hardly ever recognized 
Diplopia often obtrudes itself on the 
spontaneously and rarely causes 
notice and often causes confusion 
confusion. 
and discomfort. 
If an object is seen double, both images 
When an object is seen double, one 
are indistinct, and are also shadowy 
image has the natural appearance of 
or ghost-like, so that if one is in 
the object itself; the other is more or 
direct line with the object of fixa- 
less indistinct and shadowy. 
tion, the latter can be seen through it. 
The diplopia is not affected by shifting 
The diplopia is often increased or dimin- 
the gaze laterally or vertically, pro- 
ished by shifting the gaze sideways or 
vided the convergence is unaltered. 
up and down. 
The diplopia can be made to disappear 
Frequently the diplopia remains when 
at once by changing the convergence, 
the convergence is altered. 
so as to fix an object nearer or more 
remote, as the case may be. 
/. Symptomatology of paralytic squint.— (1) Deviation.—When 
one of the lateral recti is paralyzed, and its direct antagonist intact, 
the eye will deviate toward the side of the intact antagonist, that is, 
away from the side of the paralyzed muscle. If the degree of in- 
volvement of the affected muscle be slight the deviation may not be 
appreciable upon casual inspection. However, it can usually be de- 
termined by the use of the perimeter and small light, the corneal 
reflex being noted. A paralysis of one of the vertically acting mus- 
cles is even less noticeable upon inspection, due to the compensatory 
action of its synergist. The position of corneal reflex usually will 
show a deviation that is not obvious. The cover test will be found 
271818°—10 10 
145 TM 8-300 
H18 
MEDICAL DEPARTMENT 
to be of value in deviations of paralytic origin, but it does not dif- 
ferentiate heterophoria. 
(2) Primary and secondary deviation.—When directed to fix upon 
an object in the distance, the examinee -with paralytic squint will 
fix with the unaffected eye almost invariably, and the eye having a 
paralyzed muscle will deviate. The deviation in this instance is 
designated as primary. If the unaffected eye is covered, and he is 
directed to fix upon the distant object, the unaffected eye will assume 
the position the affected eye assumed in primary deviation, or 
assume secondary deviation. Secondary deviation is greater, or more 
accentuated, than primary deviation. Quoting Peter directly, 
The reason for the difference in deviation is as follows: The innervation 
required of the non-paralyzed eye to fix when the paretic eye is covered, is a 
normal innervation, the paralytic eye simply failing to follow in this conjugate 
movement because the yoke muscle is paralyzed. In secondary deviation 
when the paralytic eye fixes in primary position or “eyes front,” a greater 
effort is required to hold this eye in position because of the paralytic mus- 
cle, and this same excess of energy goes into the yoke muscle of the non- 
paralytic eye causing it to deviate, excessively. For example, if the right 
internal rectus is paralyzed, in the cover test or without the cover test, the right 
eye will deviate to the right while the left eye fixes. In secondary deviation, if 
the cover is applied to the left or normal eye, and the right eye is forced into fixa- 
tion, it will be noted that the left eye will be turned to the left, and to a greater 
extent than was the primary deviation of the right. 
It is to be remembered that the amount of rotation of the globe 
in one direction is not altogether abolished by the paralysis of a 
muscle, but is lessened only, providing the action of that muscle’s 
synergist is still affected. 
(3) Determination of limitation of globe movement.—In paralytic 
squint there is a limitation in the movement of the globe in the di- 
rection of action of the paralyzed muscle. This limitation may be 
determined objectively by actual perimetric measurements, that is, 
fixation on a small electric light which is moved on the arc of the 
perimeter and the position of the corneal reflex noted; or subjectively, 
by moving a small card with a few test letters along the arc of the 
perimeter, keeping the head fixed and noting the position where 
blurring occurs (beyond the limit of fixation the retinal image will 
not be on the fovea, consequently will not be clearly defined). The 
most peripherally located letter on the card should be used, and 
the amount of rotation in eight positions of the arc of the perimeter 
noted, or more as considered necessary, in the direction of the field of 
action of the paralyzed muscle. The results may be plotted on any 
ordinary perimetric chart, and a comparison made with the normal 
field of fixation or with the field of fixation of the unaffected eye. 
146 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
118 
The limitation in the field of fixation is a valuable point in differen- 
tiating concomitant and paralytic squint. The meridian in which 
the limitation is found indicates the muscle that is paretic. 
g. False 'projection and diplopia.—(1) General.—As has been stated, 
diplopia is a symptom almost invariably complained of by the patient 
with paralytic squint, and is rarely encountered in the concomitant 
type. Frequently, where there exists a diplopia, the patient has con- 
siderable difficulty in determining which is the true and which is the 
false image. The tangent screen, in conjunction with a red glass 
before one eye, greatly facilitates the determination of the muscle 
at fault. By the use of the red glass there may be determined the 
relative position of the two images in position of “eyes front,” the 
direction of movement in which there occurs the greatest separation, 
whether or not the diplopia is in the horizontal or vertical plane (or 
both), and the type of diplopia in the horizontal plane, that is, 
whether crossed or homonymous. The method of use of the red lens 
test has already been described. The red glass before one eye causes 
a red image upon the retina of that eye, and the projection of its 
image upon the screen is noted by the examiner as to the right or 
left, or above or below the image seen by the fellow eye. In the 
diplopia of paralytic squint the false image is always the image more 
distally located, or peripherally projected upon the tangent screen, 
and by the use of the red glass it can be determined to which eye the 
false image belongs. For example, consider a paralysis of the right 
external rectus; the examinee has before his right eye the red glass; 
the small light is moved along the screen horizontally toward the 
examinee’s right. A diplopia is noted, and the separation increases 
as the light moves toward the right side of the screen. The red image 
will be seen to the right of the white image (homonymous diplopia), 
and as the light is moved to the right the two will become 
more widely separated. When the right eye has reached its maxi- 
mum degree of abduction (by action of the synergists of the right 
lateral rectus) the retinal image of the light (red as it is seen through 
the glass) moves away from the right fovea on the nasal side of the 
retina, and is projected falsely in the right temporal field. As the 
light is moved in the cardinal directions of the action of each of the 
six extrinsic muscles, the relative positions of the red and white 
images indicate the muscle at fault. The false image is the image 
more distally located, and it is displaced in the direction of action of 
the affected muscle. 
(2) Red glass equipment.—It is suggested that the frame of an 
ordinary “antiglare” goggle, or automobile goggle, be used with 
147 TM 8-300 
118 
MEDICAL DEPARTMENT 
the tangent screen. The left lens may be removed altogether and 
the right replaced with a red lens. A lens of this size is more satis- 
factory than an ordinary red lens from the trial lens case, 
as it affords a greater field. 
(3) Torsion.—In paralysis of the extrinsic muscles, an oblique 
position of the false image may be noted, which indicates a torsion. 
(4) Disturbances.—Vertigo, dizziness, and even nausea with vom- 
iting, may be complained of by the patient with paralytic squint, 
particularly where there is a vertical diplopia or a torsion. Lateral 
displacement is less likely to give rise to such reflex disturbances. 
(5) Symptom:—A prominent symptom of paralytic squint, and 
one that is easily accounted for, is an abnormal rotation of the head. 
This may be evidenced by face rotation and tilting of the head in 
order to avoid a diplopia and its annoying accompaniments. In 
paralyses of the medial and lateral recti the face is turned toward the 
field of action of the paralyzed muscle. For example, in paralysis 
of the right external rectus the patient in fixing on an object will 
turn his head to the right; by so doing he may adduct his right eye 
and avoid a diplopia which may occur in fixing on an object directly 
ahead, or certainly would occur if looking at an object to the right. 
The medial and lateral recti are mentioned in this instance as each 
of these two muscles has no subsidiary action. In the case of each of 
the other extrinsic ocular muscles, the face turns toward the normal 
maximum vertical pull of the paralyzed muscle. Where there exists 
a torsion of the false image there will likely be an associated tilting 
of the head to the right or left. 
(6) Manifestations.—Below is a summary of the objective and sub- 
jective manifestations of paralyses of the individual ocular muscles: 
(a) Right external rectus. 
Primary deviation.—Bight eye deviates to left. 
Secondary deviation.—Left eye deviates to right. 
Limitation in movement toward right. 
False projections.—Toward right, homonymous diplopia, ac- 
centuated in right temporal field. 
Lace turned to right. 
(b) Right internal rectus. 
Primary deviation.—Bight eye deviates to right. 
Secondary deviation.—Left eye deviates to left. 
Limitation in movement to left, nasalward. 
Crossed diplopia, accentuated toward left. 
Face turned to left. 
148 TjVC 8-300 
118 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
(<?) Right superior rectus. 
Primary deviation.—Right eye displaced down and out with 
some extorsion. 
Secondary deviation.—Left eye up and to left. 
Limitation of movement up and to right. 
Vertical with some crossed diplopia, increasing up and to 
right. 
Face turned up and head tilted to left shoulder. 
(d) Right inferior rectus. 
Primary deviation.—Up and out with some intorsion. 
Secondary deviation.—Left eye down and to left. 
Limitation of movement down and to right. 
Vertical with some crossed diplopia, increasing down and to 
right. 
Face turned down and to right, and head tilted toward right 
shoulder. 
(e) Right superior oblique. 
Primary deviation.—Right eye deviates to left with some 
extorsion. 
Secondary deviation.—Left eye down and to right. 
Limitation of movement down and to left. 
Vertical diplopia accentuated on looking down and to left. 
Face turned down and to left, head tilted toward left 
shoulder. 
(/) Right inferior oblique. 
Primary deviation.—Downward and inward with intorsion. 
Secondary deviation.—Left eye up and to right. 
Limitation of movement up and to left. 
Vertical diplopia accentuated up and to left. 
Face turned up and to left, with head tilted to right shoulder. 
(g) Left external rectus. 
Primary deviation.—Left eye turns to right. 
Secondary deviation.—Right eye turns to left. 
Limitation of movement toward left. 
Homonymous diplopia accentuated in left temporal field. 
Face turned to left, 
(A) Left internal rectus. 
Primary deviation.—Left eye deviates to left. 
Secondary deviation.—Right eye deviates to right. 
Limitation of movement toward right. 
Crossed diplopia accentuated toward right. 
Face turned to right. 
149 TM 8-300 
118-119 
MEDICAL DEPARTMENT 
(«) Left superior rectus. 
Primary deviation.—Down and to left. 
Secondary deviation^—Right eye up and to right. 
Limitation of movement up and to left. 
Vertical diplopia accentuated up and to left. 
Face turned up and to left, and head tilted toward right 
shoulder. 
(j) Left inferior rectus. 
Primary deviation.—Left eye deviates up and to left. 
Secondary deviation.—Right eye down and to right. 
Limitation of movement down and to left. 
Vertical diplopia accentuated down and to left. 
Face turned down and to left, and head tilted toward left 
shoulder. 
[k) Left superior oblique. 
Primary deviation.—Left eye'deviates up and to right with 
some extorsion. 
Secondary deviation.—Right eye deviates down and to left. 
Limitation of movement down and to right. 
Vertical diplopia accentuated down and to right. 
Face down and to right, and head tilted toward right shoulder. 
{I) Left inferior oblique. 
Primary deviation.—Left eye deviates down and to right with 
some intorsion. 
Secondary deviation.—Right eye deviates up and to left. 
Limitation of movement up and to right. 
Vertical diplopia accentuated up and to right. 
Face turned up and to right, with head tilted toward left 
shoulder. 
119. Complete oculomotor paralysis.—The third nerve sup- 
plies all of the extrinsic ocular muscles except the external rectus 
and superior oblique. In addition, it also has branches, by way of 
the ciliary ganglion, to the sphincter fibers of the iris and the ciliary 
muscle. A complete paralysis of the oculomotor nerve would, then, 
be evidenced by— 
a. Internal opthalmoplegia.—Dilated pupil not responding to 
light, convergence, or accommodation, and paralysis of accommoda- 
tion, or cycloplegia. 
b. Ptosis.—Loss of action of the levator which is innervated by 
a branch of the superior division of the third nerve. 
150 TM 8-300 
NOTES ON EYE, EAR, ETC., IN AY3ATI0N MEDICINE 
119 
c. Primary deviation.—Globe rotated downward and outward with 
some intorsion due to the unopposed action of the superior oblique 
and external rectus. 
d. Crossed diplopia which increases on looking toward the normal 
side. 
e. The face will be turned toward the normal side and upward. 
This may not occur, as the ptosis is usually so complete as wholly to 
obscure the vision of the affected eye. 
It is quite obvious that any degree of squint, either concomitant 
or paralytic, should be considered as disqualifying for Hying duty, 
as with such a condition binocular single vision is impossible, cer- 
tainly within the normal field of binocular fixation. The resume of 
the principal features or characteristics of the varieties of squint 
is included in order that the examiner may make an intelligent in- 
terpretation of his findings. The student is cautioned against the 
use of symptomatic terms in the place of actual diagnosis, and again 
he is admonished against jumping at conclusions and too hastily 
arriving at a diagnosis. 
151 !TK S-3C0 
143 
MEDICAL, DEPARTMENT 
Table for computing angle of convergence 
p. Ordinates—PcB 
*a Abscissae—Interpupillary distance 
PcB 
55 
56 
57 
58 
59 
60 
61 
62 
63 
64 
65 
66 
67 
68 
69 
70 
71 
72 
73 
74 
75 
Angle 
40 
69 
69 
71 
72 
73 
74 
75 
76 
76 
77 
78 
79 
80 
81 
82 
82 
83 
84 
85 
86 
86 
41 
68 
69 
70 
71 
71 
72 
73 
74 
75 
76 
77 
78 
78 
79 
80 
81 
82 
83 
83 
84 
85 
42 
66 
67 
68 
69 
70 
71 
72 
73 
74 
75 
75 
76 
77 
78 
79 
80 
80 
81 
82 
83 
84 
43 
65 
66 
67 
68 
69 
70 
71 
72 
72 
73 
74 
75 
76 
77 
78 
78 
79 
80 
81 
81 
82 
44 
64 
65 
66 
67 
68 
69 
69 
70 
71 
72 
73 
74 
75 
75 
76 
77 
78 
79 
79 
80 
81 
45 
63 
64 
65 
66 
66 
67 
68 
69 
70 
71 
72 
72 
73 
74 
75 
76 
76 
77 
78 
79 
80 
46 
62 
63 
64 
64 
65 
66 
67 
68 
69 
70 
70 
71 
72 
73 
74 
74 
75 
76 
77 
78 
78 
47 
61 
62 
62 
63 
64 
65 
66 
67 
68 
68 
69 
70 
71 
72 
73 
73 
74 
75 
76 
78 
77 
48 
60 
60 
61 
62 
63 
64 
65 
66 
67 
67 
68 
69 
70 
71 
71 
72 
73 
74 
74 
75 
76 
49 
69 
59 
60 
61 
62 
63 
64 
65 
65 
66 
67 
68 
69 
70 
70 
71 
72 
73 
73 
74 
75 
60 
58 
58 
59 
60 
61 
62 
63 
64 
64 
65 
66 
67 
68 
68 
69 
70 
71 
72 
72 
73 
74 
61 
57 
58 
58 
59 
60 
61 
62 
63 
63 
64 
65 
66 
67 
67 
68 
69 
70 
70 
71 
72 
73 
52 
66 
56 
57 
58 
59 
60 
61 
62 
62 
63 
64 
65 
66 
66 
67 
68 
69 
69 
70 
71 
72 
63 
55 
56 
56 
57 
68 
59 
60 
61 
61 
62 
63 
64 
65 
65 
66 
67 
68 
68 
69 
70 
71 
54 
64 
55 
66 
66 
57 
68 
59 
60 
60 
61 
62 
63 
64 
64 
65 
66 
67 
67 
68 
69 
70 
65 
53 
54 
55 
56 
56 
57 
58 
59 
60 
60 
61 
62 
63 
63 
64 
65 
66 
66 
67 
68 
69 
66 
62 
S3 
54 
65 
66 
66 
67 
68 
59 
59 
60 
61 
62 
62 
63 
64 
65 
65 
66 
67 
68 
67 
51 
52 
53 
54 
55 
66 
56 
57 
58 
59 
59 
60 
61 
62 
62 
63 
64 
64 
65 
66 
67 
68 
51 
52 
52 
53 
54 
55 
66 
56 
67 
58 
68 
59 
60 
61 
61 
62 
63 
64 
64 
65 
66 
69 
50 
61 
52 
52 
53 
54 
55 
55 
56 
57 
68 
58 
59 
60 
61 
61 
62 
63 
63 
64 
65 
60 
49 
50 
61 
62 
52 
63 
54 
55 
55 
66 
67 
58 
58 
69 
60 
60 
61 
62 
63 
63 
64 
61 
48 
49 
60 
51 
52 
52 
53 
54 
55 
55 
66 
57 
58 
58 
59 
60 
60 
61 
62 
62 
63 
62 
48 
49 
49 
50 
51 
62 
52 
63 
54 
54 
55 
56 
57 
57 
58 
59 
60 
CO 
61 
62 
62 
63 
47 
48 
49 
49 
50 
51 
52 
52 
53 
54 
54 
55 
56 
57 
57 
58 
59 
59 
60 
61 
62 
64 
46 
47 
48 
49 
49 
50 
61 
52 
52 
53 
54 
64 
55 
66 
67 
57 
58 
59 
59 
60 
61 
65 
46 
47 
47 
48 
49 
60 
50 
51 
52 
52 
53 
54 
65 
56 
66 
57 
57 
58 
59 
69 
60 
66 
45 
46 
47 
47 
48 
49 
SO 
60 
51 
52 
62 
53 
54 
55 
55 
66 
56 
57 
58 
59 
59 
67 
45 
45 
46 
47 
47 
48 
49 
50 
50 
51 
52 
52 
53 
54 
54 
55 
56 
57 
57 
58 
58 
68 
44 
45 
45 
46 
47 
48 
48 
49 
50 
50 
51 
52 
52 
53 
54 
54 
55 
56 
66 
67 
58 
69 
43 
44 
45 
46 
46 
47 
48 
48 
49 
50 
50 
51 
52 
62 
53 
54 
.54 
55 
56 
66 
57 
70 
43 
44 
44 
45 
46 
46 
47 
48 
48 
49 
50 
SO 
51 
52 
62 
63 
54 
64 
65 
56 
56 
152 TM 8-300 
119 
:notes on eye, ear, etc., in aviation medicine 
Table for computing angle of convergence—Continued 
p. Ordinates—PeR 
“ Abscissae—Interpupillary distance 
PcB 
55 
56 
57 
58 
59 
60 
61 
62 
63 
64 
65 
66 
67 
68 
69 
70 
71 
72 
73 
74 
75 
Angle 
71 
42 
43 
44 
44 
45 
46 
46 
47 
48 
49 
49 
50 
50 
51 
52 
52 
53 
54 
54 
55 
56 
72 
42 
42 
43 
44 
45 
45 
46 
47 
47 
48 
49 
49 
50 
50 
51 
52 
52 
53 
54 
54 
55 
73 
41 
42 
43 
43 
44 
45 
45 
46 
47 
47 
48 
49 
49 
50 
61 
51 
52 
52 
53 
54 
54 
74 
41 
41 
42 
43 
43 
44 
45 
45 
46 
47 
47 
48 
49 
49 
50 
51 
51 
52 
52 
53 
54 
75 
40 
41 
42 
42 
43 
44 
44 
45 
46 
46 
47 
48 
48 
49 
49 
50 
51 
51 
52 
52 
53 
76 
40 
40 
41 
42 
42 
43 
44 
44 
45 
46 
46 
47 
48 
48 
49 
49 
50 
51 
51 
52 
53 
77 
39 
40 
41 
41 
42 
43 
43 
44 
44 
45 
46 
46 
47 
48 
48 
49 
49 
50 
51 
51 
52 
78 
39 
39 
40 
41 
41 
42 
43 
43 
44 
45 
45 
46 
46 
47 
48 
48 
49 
50 
50 
51 
51 
79 
38 
39 
40 
40 
41 
42 
42 
43 
43 
44 
45 
45 
46 
47 
47 
48 
48 
49 
50 
50 
51 
80 
38 
39 
39 
40 
40 
41 
42 
42 
43 
44 
44 
45 
45 
40 
47 
47 
48 
48 
49 
50 
50 
81 
37 
38 
39 
39 
40 
41 
41 
42 
42 
43 
44 
44 
45 
46 
46 
47 
47 
48 
48 
49 
50 
82 
37 
38 
38 
39 
40 
40 
41 
41 
42 
43 
43 
44 
44 
45 
46 
46 
47 
47 
48 
48 
49 
83 
37 
37 
38 
38 
39 
40 
40 
41 
42 
42 
43 
43 
44 
44 
45 
46 
46 
47 
47 
48 
49 
84 
36 
37 
37 
38 
39 
39 
40 
40 
41 
42 
42 
43 
44 
44 
45 
45 
46 
46 
47 
48 
48 
85 
36 
36 
37 
38 
38 
39 
39 
40 
41 
41 
42 
42 
43 
44 
44 
45 
45 
46 
46 
47 
48 
86 
35 
36 
37 
37 
38 
38 
39 
40 
40 
41 
41 
42 
43 
43 
44 
44 
45 
45 
48 
47 
47 
87 
35 
36 
36 
37 
37 
38 
39 
39 
40 
40 
41 
42 
42 
43 
43 
44 
44 
45 
45 
46 
47 
88 
35 
35 
36 
36 
37 
38 
38 
39 
39 
40 
41 
41 
42 
42 
43 
43 
44 
44 
45 
46 
46 
89 
34 
35 
36 
36 
37 
37 
38 
38 
39 
40 
40 
41 
41 
42 
42 
43 
43 
44 
44 
45 
46 
90 
34 
35 
35 
36 
36 
37 
37 
38 
39 
39 
40 
40 
41 
41 
42 
42 
43 
44 
44 
45 
45 
91 
34 
34 
35 
35 
36 
36 
37 
38 
38 
39 
39 
40 
40 
41 
41 
4P 
43 
48 
44 
44 
45 
92 
33 
34 
34 
35 
36 
36 
37 
37 
38 
38 
39 
39 
40 
40 
41 
42 
42 
43 
43 
44 
44 
93 
33 
33 
34 
35 
35 
36 
36 
37 
37 
38 
38 
39 
40 
40 
41 
41 
42 
42 
43 
43 
44 
94 
33 
33 
34 
34 
35 
35 
36 
36 
37 
38 
38 
39 
39 
40 
40 
41 
41 
42 
42 
43 
43 
95 
32 
33 
33 
34 
34 
35 
36 
36 
37 
37 
38 
38 
39 
39 
40 
40 
41 
41 
42 
42 
43 
96 
32 
32 
33 
34 
34 
35 
35 
36 
36 
37 
37 
38 
38 
39 
40 
40 
41 
41 
42 
42 
43 
97 
31 
32 
33 
33 
34 
34 
35 
35 
36 
36 
37 
38 
38 
39 
39 
40 
40 
41 
41 
42 
42 
98 
31 
32 
32 
33 
33 
34 
34 
35 
36 
36 
37 
37 
38 
38 
39 
39 
40 
40 
41 
41 
42 
99 
31 
32 
32 
33 
33 
34 
34 
35 
35 
36 
36 
37 
37 
38 
38 
39 
39 
40 
40 
41 
41 
100 
31 
31 
32 
32 
33 
33 
34 
34 
35 
35- 
36 
36 
37 
37 
38 
38 
39 
40 
40 
41 
41 
101 
30 
31 
32 
32 
33 
33 
34 
34 
35 
35 
36 
36 
37 
37 
38 
38 
39 
39 
40 
40 
41 
102 
30 
31 
31 
32 
32 
33 
33 
34 
34 
35 
35 
36 
36 
37 
37 
38 
38 
39 
39 
40 
40 
103 
30 
30 
31 
31 
32 
32 
33 
34 
34 
35 
35 
35 
36 
37 
37 
38 
38 
39 
39 
40 
40 
104 
30 
30 
31 
31 
32 
32 
33 
33 
34 
34 
35 
35 
36 
36 
37 
37 
38 
38 
39 
39 
40 
105 
29 
30 
30 
31 
31 
32 
32 
33 
33 
34 
34 
35 
35 
36 
36 
37 
37 
38 
38 
39 
39 
153 TM 8-300 
130 
MEDICAL. DEPARTMENT 
Section XVI 
ACCOMMODATION 
Paragraph 
Changes in dioptric power 120 
Amplitude of accommodation 121 
Far and near points 122 
Influence of age upon amplitude of accommodation 123 
Determining accommodative power 124 
Calculating accommodation in diopters 125 
Near vision 126 
120. Changes in dioptric power.—a. In the normal, or em- 
metropic eye, the dioptric system is so arranged that rays of light 
coming from a point at infinity (or to all intents and purposes beyond 
20 feet) are focused on the retina and a single cone of the fovea may 
be stimulated. For practical purposes it may be considered that 
rays of light from a point 20 feet or farther away are parallel, but 
from a nearer point the rays will be divergent, and in order that 
they be seen clearly some change must take place in the dioptric 
power of the eye, otherwise they will be focused behind the retina, 
resulting in a poorly defined image, due to the stimulation of many 
cones. Obviously, the change that occurs in the dioptric power of 
the eye must be an increase, that is, the lens system becomes stronger 
or more convex. 
1). “Moving the object from infinity to 5 meters moves the position 
of the image only 0,06 millimeters. Since the sensitive layer of the 
retina is just about that thickness the image will still be in focus. 
No perceptible blur occurs until the object moves within 5 meters. 
When this happens the focus falls behind the retina and in place 
of a clear image we now have blurred diffusion circles falling on 
the rods and cones. In order to have a clear focus once more, either 
the dioptric power of the eye must increase, or the eyeball must be- 
come longer.” (Adler, Clinical Physiology of the Eye.) 
c. In the human eye there is an increase in dioptric power caused 
by a change in the contour of the crystalline lens, resulting from 
contraction of the ciliary muscle. The change in contour occurs 
principally on the anterior surface, which becomes more convex. The 
amount of increase depends directly upon the nearness of the point 
of fixation. This phenomenon (the power of increasing the dioptric 
power of the lens) is called accommodation, and it is this factor 
that enables us to see near objects clearly. 
d. It is hardly worth while to discuss at this point the various 
theories as to the method of accommodation. It is apparent that no 
one theory wholly explains the phenomenon in every respect. As 
154 TM 8-300 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
120-123 
lias been stated, accommodation is accomplished by contraction of 
the ciliary muscle which is innervated by the third nerve (oculo- 
motor). It is interesting to note that accomodation is accompanied 
by contraction of the pupil (the sphincter fibers of the iris having 
the same innervation) which further aids in sharper definition of 
the retinal image. 
121. Amplitude of accommodation.—The amplitude of accom- 
modation (A) may be defined as the difference between the dioptric 
power of the eye when accommodation is completely relaxed (static 
refraction) and when it is exerted to its utmost (dynamic refraction). 
In determining the amplitude of accommodation, the far point and 
the near point are taken into consideration. By the far point (punc- 
tum remotum) is meant the farthest distance away in meters an. 
object can be seen distinctly, and as accommodation is measured in 
diopters, it is customary to convert this distance into the dioptric 
equivalent, the refractive power being the reciprocal of the focal 
distance in meters. The dioptric power of the eye with accommo- 
dation relaxed represents the static refraction of the eye and may 
be represented by R. The nearest point seen distinctly with a maxi- 
mum of accommodation exerted is referred to as the near point 
(punctum proximum). The dioptric power with accommodation, 
utilized to its greatest extent (the dynamic refraction of the eye) is 
represented by P. Thus the amplitude of accommodation may be 
represented by the difference between refraction with extreme accom- 
modation and accommodation completely relaxed, thus A = P—R. 
122. Far and near points.—a. Emmetropia.—In emmetropia the 
far point is located at infinity, the dioptric value of which is nil or 
may be considered as zero. A=P—R, or A—P, and the amplitude 
of accommodation is represented by the dioptric value of the near 
point. For example, if the near point is at 10 centimeters (10/100 
meter) the amplitude of accommodation is 10 diopters, the dioptric 
equivalent of this distance. 
h. Myopia.—In myopia R has a positive value; the far point is 
located at some point nearer than infinity; divergent rays of light 
from this point converge upon the retina with accommodation relaxed 
(ref. conjugate foci). For example, let us consider a myope whose 
far point is at 1 meter distance {R in this case is 1 diopter), and 
whose near point is 10 centimeters. 
A—P—R 
= 100-100 
10 100 
= 10-1 = 9 
155 TM 8-300 
122-123 
MEDICAL DEPARTMENT 
There is an amplitude of accommodation in this instance of 9 diop- 
ters, although the near point is at the same distance as that of the 
emmetrope referred to above 
c. Hyperopia.—In hyperopia R is a negative quantity. 
Therefore A=P — (— R) 
=P+R 
If an individual is hyperopic to the extent of two diopters, he must 
exercise two diopters of accommodation at infinity. Further, sup- 
pose that his near point is at 10 centimeters, 
A=P-{-R) 
= 100- (-100) 
10 50 
= 10 + 2=12 
thus it is found that his amplitude of accommodation to be 12 diopters, 
although his near point is identical with the emmetrope and the 
myope considered above. 
d. Therefore consideration must be given to the error of refrac- 
tion an individual may have in conjunction with the dioptric 
equivalent of his near point in determining the amplitude of accom- 
modation. In myopia the refractive error must be subtracted from, 
and in hyperopia it must be added to, the dioptric equivalent of the 
near point in order to make an accurate estimate of the amplitude 
of accommodation. However, in the examination of Air Corps 
personnel this is not done routinely because the standards regarding 
allowable errors of refraction are within 1 diopter. 
123. Influence of age upon amplitude of accommodation.— 
The amplitude of accommodation progressively decreases 'with age. 
This phenomenon is ordinarily considered as a physiological rather 
than pathological process. In youth the lens may be considered as 
a capsule filled ■with a gelatinous fluid, and is capable of an extreme 
amount of elasticity. With advancing age there is a steadily pro- 
gressive hardening or sclerosing process until finally the lens contour 
is practically fixed and incapable of any change. When the near 
point of accommodation recedes to 22 centimeters, the individual is 
considered as entering into the presbyopic stage. It is thought that 
in order to accommodate easily and without inducing asthenopia 
there must be about iy2 diopters excess of accommodative power 
that is not called into use. Therefore, a recession of the near point be- 
yond 22 centimeters reduces the accommodation, and reading must be 
carried on at a distance greater than 33 centimeters. Eyentully, the 
loss of accommodative power must be replaced by lenses of the proper 
strength in order that near objects may be seen distinctly. It is 
156 TM 8-300 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
123-124. 
obvious that the hyperope is more hampered by presbyopia than is 
the myope. The following table gives the mean accommodative 
power for ages ranging from 18 to 50 years (Duane) : 
Age 
Diopters 
Age 
Diopters 
18 
11. 9 
31 
8. 6 
19 
11. 7 
32 
8. 3 
20 
11. 5 
33 
8. 0 
21 
11. 2 
34 
7. 7 
22 
10. 9 
35 
7. 3 
23 
10. 6 
36 
7. 1 
24 
10. 4 
37 
6. 8 
25 
10. 2 
38 
6. 5 
26 
9. 9 
39 
6. 2 
27 
9. 6 
40 
5. 9 
28 
9. 4 
45 
3. 7 
29 
9. 2 
50 
2. 0 
30 
8. 9 
Factors other than age may affect the power of accommodation. 
Local affections involving the eye itself, as oculomotor paralysis, 
irido-cyclitis, glaucoma, etc., will interfere with contraction of the 
ciliary muscle. Occasionally, a ciliary spasm may be encountered 
and in such an instance there may be induced an apparent myopia 
which will be misleading. In systemic affections resulting in gen- 
eral debility, particularly diabetes, also influenza and malaria, there 
may be a temporary reduction in accommodative power greater than 
should be expected for the age group of the individual. The action 
of drugs, especially atropine, should be borne constantly in mind, 
as an apparent premature presbyopia, or sudden reduction in visual 
acuity of a young, moderately hyperopic patient may be found to 
be due to the internal use of belladonna for some gastro-intestinal 
ailment or even due to the continued use of an ointment containing 
belladonna in the treatment of hemorrhoids. Drugs having a cyclo- 
plegic action are in particular atropine, homatropine, cocain, and 
scopolamine. Occasionally an examiner may determine that an ap- 
plicant for enlistment has attempted to conceal his real age, by 
comparing his amplitude of accommodation with the mean for his 
age group, after taking into consideration errors of refraction and 
other conditions. 
124. Determining accommodative power.—This test is per- 
formed with a card bearing letters subtending angles of 5 minutes 
157 TM 8-300 
124-125 
MEDICAL DEPARTMENT 
at approximately 620 millimeters and requiring 1.6 diopters of 
accommodation to focus them correctly. This test differs from the 
Jaeger test in that the card is read at varying distances while the 
Jaeger is read at a given distance and the size of the letters employed 
is varied when necessary. 
The accommodation card is mounted upon a slide which can be 
moved along a rule; the Prince rule, or a modification of the same, 
is generally employed. The rule is calibrated in diopters and in 
millimeters. 
Accommodation is measured from the anterior focus of the eye, 
which is, roughly, 11.5 millimeters in front of the cornea. Using 
a millimeter rule, a pencil mark is made in each side of the ex- 
aminee’s nose 11.5 millimeters in front of the right and left cornea, 
respectively. In measuring the accommodation of the right eye, 
the flat side of the Prince rule is laid against the right side of the 
examinee’s nose, with the end of the rule at the pencil mark. The 
rule is held horizontally and extends directly to the front, edge up. 
The card of test letters is held not more than 5 centimeters in front 
of the examinee’s right eye. His left is screened from sight of the 
letters by the fiat side of the rule. The card of test letters is now 
Carried slowly away from the eye and the examinee instructed to 
begin reading the letters aloud as soon as they become legible. The 
card is halted the instant he begins to read the letters correctly, and 
the point on the rule opposite the card is read off in diopters. This 
is the measurement of the greatest amount of accommodation that 
can be called into service with his right eye. To test the left eye 
the rule is changed to the left side of the nose and the above pro- 
cedure is repeated. 
125. Calculating accommodation in diopters.—The Prince 
and Thorne accommodation rules are calibrated in diopters and the 
amount of accommodation exerted at any given distance my be read 
off the scale. However, any centimeter or inch rule may be employed 
and the accommodative power calculated. 
As previously stated, an emmetropic eye fixing an object at 6 meters 
does not accommodate, but accommodation is resorted to for all objects 
nearer than 6 meters. To fix an object located at 1 meter (40 inches), 
1 diopter of accommodative power must be exerted as it requires 1 
diopter of refraction to focus parallel rays of light this distance. 
Rays of light from an object at 1 meter are divergent and the emer- 
gent rays from an emmetropic eye are parallel, and the addition of 
1 diopter of refraction will render the divergent rays parallel when 
they enter the eye and will focus the emergent parallel rays at 1 meter 
where the object is located. An object located at 50 centimeters (20 
158 TIVE 8-300 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
125-126 
inches), 2 diopters of refraction are required, as it requires 2 diopters 
to render divergent rays of light from 50 centimeters parallel when 
they enter the eye and to focus the emergent parallel rays at the same 
distance. If an object is located at 33 centimeters, 3 diopters of re- 
fraction are required to focus it. Assuming an individual reads 
clearly at 12 centimenters, then to determine the number of diopters 
of accommodative power he is exerting, 100 centimeters is divided by 
12 centimeters, which gives— 
= 8.33 diopters 
Again, letters are read clearly at 8 centimeters. Therefore— 
diopters of accommodation 
O 
If desired, inches may be employed, in which case 40 inches is used 
as the basis of calculation. Thus, letters are read clearly at 4 inches, 
then— 
40 
— = 10 diopters of accommodation 
The amplitude of accommodation may be estimated by using spheri- 
cal concave lenses before the eye, beginning with weaker lenses and 
replacing each with the next stronger until the examinee’s visual 
acuity has dropped below his normal. For example, one who has an 
acuity of 20/20 and can still read 20/20 with a minus 6 sphere but 
cannot with a minus 6.50 sphere, has an amplitude of accommodation 
of 6 diopters provided he is emmetropic. If he is hyperopic his cor- 
rection must be added to the strongest lens with which he has normal 
vision. If he is myopic his correction must be subtracted. 
126. Near vision.—The object of the test for near vision is to 
determine whether or not the individual can call into use 3 diopters 
of accommodation, and the Jaeger test card is commonly employed 
for this purpose. The Jaeger card is prepared with six series of 
words. The first series should be read by the normal eye at a distance 
not greater than 37 centimeters; the second at 50 centimeters; the 
third at 62 centimeters, etc. The card is held before the examinee at 
a distance of 33 centimeters and he is directed to read the first series. 
If he does so, his near vision is recorded as J-l-13", indicating that 
he reads Jaeger No. 1 at 13 inches or 33 centimeters. If number two 
is the smallest that he can read easily, his near vision is recorded as 
J-2-13", indicating that he reads Jaeger No. 2 at 33 centimeters, or 
or 13 inches. The smallest type that he can read at 33 centimeters 
is the basis of his near vision. The normal eye should read J-l-13". 
If this cannot be done it indicates that his near vision is defective, 
and if distant vision is normal, he is presbyopic. 
159 TM 8-300 
126 
MEDICAL DEPARTMENT 
J. 1 (Sn. O.C). 60 cm. 
A* alif i|'ok«. Moim c»me*lo*lf on xnJ sweating under tlie r!«al box nliltb he ktd atr.pt round Ma ahouldrn like » 
pe.llar ** Welcome, walcoma. Moaea* well, my boy, «hat have you brought ua from the fair* *-*'| lute brought you 
myieir ' cried Moaoa, with % aly look, nod reatmg the box on tbe dresser "Ay. Moaea," cried my *ife, "that «e 
J. 2 (Sn. 0.6). 60 era. 
five skillings and twopence is no bad day s work Come, let us have it then."—"I have brought 
tack no money," cried Moses again. " I have laid it all out in a bargain and here it is," pulling 
out a bundle from bis breast ' here they are, a gross of gieen spectacles, with siher rims and 
J. 4 (Sn. 0.8). 80 cm. 
mother,” cried the boy, " why won’t you listen to reason ’ I had them a dead 
bargain. or I should not have brought them. The silver lims alone will sell for 
double the money “ A tig for the silver rims,” cried my wife, in a passion " I dare 
J. 0 (Sn. 1). 1 m. 
tho rims, for they are not worth sixpence ; for 1 perceive they are 
only copper varnished over.”—“What!” cried my wife, “not 
silver! the rims not silver? No,” cried I, “no more silver 
J. 8 (Sn. 1.25). 1.25 ra 
with copper rims and shagreen cases ? A murrain take 
such trumpery! The blockhead has been imposed upon, 
and should have known his company better.”—“ There, 
J. 10 (Sn. 1.5). 1.6 m, 
tho idiot! ” returned she, “ to bring me such stuff: 
if I had them I would throw them in the fire.”— 
“There again you are wrong, my dear,1’ cried I, 
J. 12 (Sn. 1.75). 1,75 m. 
By this time the unfortunate Moses was 
undeceived He now saw that he had 
J. 14 (Sn. 2.25). 2.25 m 
asked the circumstances of his 
deception. He sold the horse, it 
Jaeger test types, with approximate Snellen equivalents and the most remote dis- 
tances at which each should be read with average normal vision. 
Figuee 22.—Test types for near vision. 
160 TM 8-300 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
127-128 
Section XVII 
INSPECTION OF THE EYE 
Paragraph 
Genera! 127 
Focal or oblique illumination 128 
Binocular loupe 129 
Hand slit-lamp 130 
Examination of eyelids 131 
Lacrimal apparatus 132 
Inspection of sclera 133 
Anterior chamber and iris 134 
Examination of pupils 135 
Lens 1 136 
Opacities of vitreous 137 
Nystagmus 138 
127. General.—a. Equipment.—The inspection of the eye, or the 
external examination, is altogether objective. In this part of the 
examination a great deal can be observed with the unaided eye, but 
for detailed examination some artificial assistance will be required. 
b. Structures.—The examiner should adopt a definite routine in the 
inspection of the eye, which he may work out to his best advantage 
considering the equipment he has available. It is suggested that the 
following structures be inspected in turn, although the steps or phases 
of the examination may be varied as a matter of convenience. 
(1) Eyelids. 
(2) Lacrimal apparatus. 
(3) Conjunctiva. 
(4) Globe as a whole. 
(5) Cornea. 
(6) Sclera. 
(7) Iris and anterior chamber. 
(8) Lens and vitreous. 
c. History.—While proceeding with the inspection of the eye the 
examiner should obtain a history of any ocular defect, affection, or 
injury. 
128. Focal or oblique illumination.—Focal or oblique illumi- 
nation affords the opportunity of a detailed examination with mag- 
nification of the structures examined, and yet requires only the 
simplest of equipment. It-can be carried out best in a darkened 
room with the examinee seated near a lamp located about 2 feet 
above and to one side of his head. A strong convex spherical lens 
is held between the examinee and the source of illumination in such 
a position that the divergent rays are brought to a focus or con- 
centrated on the structure being examined. This causes an intense 
271818°—40 11 
161 TM 8-300 
128-131 
MEDICAL DEPARTMENT 
illumination of the cornea, iris, etc., and may enable the examiner 
to uncover some abnormality with his unaided eye. However, a 
greatly enlarged image of the structure under observation may be 
obtained by the use of a second strong convex lens being held by 
the other hand between the eye of the examiner and the eye being 
examined, and through which an enlarged image may be seen. It 
is advisable that the eye of the observer be near the second lens, which 
may be moved back and forth until a sharply defined image of the 
part under examination is obtained. To be adept in the handling 
of the two lenses requires some practice, and it is advisable that the 
student repeatedly attempt the procedure with a normal eye until it 
is mastered. In addition, such practice will enable him to be familiar 
with the appearance of normal structures, which is essential before 
attempting to recognize abnormalities. 
129. Binocular loupe.—The binocular loupe, such as the Beebe 
in particular, has a distinct advantage over the use of a single mag- 
nifying lens, in that a true stereoscopic effect is obtained in addition 
to magnification. This aids materially in appreciating depth. Fur- 
thermore, the binocular loupe is worn as spectacles and leaves the 
hands free to manipulate the lids, etc., during the examination. 
130. Hand slit-lamp.—a. Method.—The hand slit-lamp affords 
an opportunity every examiner should take advantage of, if he has 
one available, for the examination of the cornea, anterior chamber, 
iris, and lens. It is a simple, compact little instrument that is an 
improvement over oblique illumination. From its aperture there is 
projected a beam of light, the dimensions of which may be varied as 
desired, which “cuts” sections through the transparent structures. 
These sections are examined through a system of magnifying lenses 
attached at an angle to the head of the instrument, or through the 
binocular loupe. As with oblique illumination, the hand slit-lamp 
gives better results when used in a dark room. 
h. Microscopy.—Actual microscopy of the living eye has been made 
possible by the use of the -slit-lamp of Gullstrand in conjunction 
with the binocular corneal microscope. In addition to the fact that 
such an instrument is rarely available, the technique of its method 
of use is so complicated that a description of the instrument is hardly 
justifiable. 
131. Examination of eyelids.—Even a casual inspection will 
reveal a malposition, distortion, enlargement, or contracture involv- 
ing the lids, and in making such an inspection the examiner should 
be particularly observant as to their motility, which may be altered, 
as in ptosis and facial paralysis. The lid margins should be noted 
as to the existence of entropion, ectropion, trichiasis, blepharitis, cica- 
162 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
131-132 
trices, chalazia, and sties; the history or presence of sties may be 
symptomatic of errors of refraction. Deformities of the lids that 
appear at a glance to be insignificant may be actually of a serious 
Figure 23.—Bauscb and Bomb band slit-lamp (above) and Beebe binocular loupe (below) 
nature and the danger of corneal irritation and interference with 
proper function of the lacrimal apparatus should be borne in mind. 
132. Lacrimal apparatus.—a. The lacrimal apparatus may be TM 8-300 
132 
MEDICAL DEPARTMENT 
inspected along with the examination of the lids and of the conjunc- 
tiva. Affections involving the secretory portion are unusual but when 
enlargements are present, if not seen readily, they may be palpated. 
These enlargements may account for a defect in the movements of the 
globe. The excretory portion may show many defects, either con- 
genital or resulting from disease or trauma. The puncta may be so 
displaced that normal drainage from the conjunctival sac is impos- 
sible, and such a condition may cause an epiphora with a chain of 
comnlications, interference with normal visual acuity, blepharitis, or 
eczema of the lower lid. Where there exists a doubt as to the patency 
Figukb 24.—Use of Beebe binocular loupe in conjunction with hand slit-lamp. 
of the canaliculi, the lacrimal sac or the naso-lacrimal duct, a lacrimal 
syringe may be used (argyrol should not be used due to possibility 
of argyrosis). Acute and chronic dacryocystitis are conditions that, 
as a rule, are recognized without difficulty, but any enlargement in 
the location of the sac, or pain on pressure in this locality, should 
arouse some suspicion on the examiner’s part. Pressure over the sac 
causes a back flow through the canaliculi, and where the secretion is 
of a mucoid or purulent nature it is significant of dacryocystitis. 
1). Other abnormalities may be noted at this point before pro- 
ceeding with a detailed examination of the globe itself, particularly TM 8-300 
132 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
the position of the globe within the orbit, enophthalmus, exophthal- 
mos, and also abnormal position of the visual axes, although in 
this connection the angle kappa must be borne in mind. When 
positive, the examinee will have the appearance of divergent squint, 
and when negative a convergent squint will be simulated. Positive 
kappa angle is more frequently found associated with hyperopia 
and a negative kappa angle with myopia. 
c. Next the examiner’s attention should be directed to an investiga- 
tion of the palpebral portions of the conjunctiva and the fomices. 
The lower palpebral conjunctiva and the lower fornix are exposed 
easily by exerting slight pressure with downward traction on the 
skin of the lower lid and at the same time directing the examinee 
to look upward. The upper palpebral portion and fornix are exposed 
by everting the upper lid. Without some practice this may occasion 
the examiner difficulty. Probably the easiest as well as the simplest 
method is as follows: The examiner faces the examinee and the 
latter looks downward. With the right hand the left lid is everted. 
The right index finger is placed horizontally over the closed left lid 
and the cilia gently grasped between the index finger and thumb. 
Slight traction is made toward the temporal side at the same time 
the tip of the index finger is a point around which the lid can be 
vertically rotated. The tarsus is everted, exposing the palpebral con- 
junctiva. The left hand of the examiner is used to evert the ex- 
aminee’s right upper lid. This enables the examiner to use only one 
hand but does not expose the superior fornix thoroughly, and is a 
difficult procedure where the eyes are not prominent. Another 
method, which may be found to be more satisfactory, is to place 
a blunt probe (or eustachian catheter) at the upper edge of the su- 
perior tarsus with the lid closed and the examinee looking downward. 
The lashes are grasped between the thumb and index finger and the 
lid pulled away from the globe. The end of the probe is depressed 
as the lid is everted. By moving the probe laterally back and forth 
while the examinee looks downward the whole of the superior fornix 
may be exposed. 
d. In examining the tarsal conjunctiva attention must be paid to 
scarring, as from trachoma, evidence of inflammatory conditions, 
follicles, etc. Especially any alteration should be noted in the 
character of the secretion in the conjunctival sac. 
e. The bulbar conjunctiva may be examined in its entirety without 
eversion of the lids by widely separating them and at the same time 
directing the examinee to look up and then down. Any abnormality 
should be noted, particularly hyperemia. In this connection, the 
165 TM 8-300 
132-133 
MEDICAL DEPARTMENT 
differential points of conjunctival and ciliary injection may be 
mentioned. 
Conjunctival injection 
Ciliary injection 
(1) Derived from posterior conjunc- 
tival vessels. 
(2) Accompanies diseases of the con- 
junctiva. 
(3) More or less muco-purulent or pu- 
rulent discharge. 
(4) Most marked in fornix conjunc- 
tivae. 
(5) Fades as it approaches the cornea. . 
(6) Bright, brick-red color 
(1) Derived from anterior ciliary vessels. 
(2) Accompanies diseases of the cornea, 
iris, and ciliary body. 
(3) Often lacrymation, but no con- 
junctival discharge. 
(4) Most marked immediately around 
the cornea; hence called “cir- 
cumcorneal.” 
(5) Fades toward fornix. 
(6) Pink or lilac color. 
(7) Composed of small, straight vessels, 
placed deeply, so that individual 
vessels cannot be recognized eas- 
ily, but are seen indistinctly as 
fine, straight lines radiating from 
the cornea. 
(7) Composed of a network of coarse 
tortuous vessels, anastomosing 
freely, and placed superficially, 
so that the meshes are easily 
recognized. 
f. The presence of a pterygium should be noted and, if present, 
a conclusion reached as to whether it is progressive or nonprogressive, 
the former being more vascular with the head distinctly elevated 
above the level of the cornea. True and false pterygia should be 
differentiated, and where a pterygium exists the encroachment, in 
millimeters, on the cornea should be noted. Pinguecula must be 
differentiated from pterygia, the former being a triangular patch of 
yellowish, thickened conjunctiva, base toward the limbus, more fre- 
quently located on the nasal side, but not encroaching on the cornea, 
as does the pterygium, nor is it so vascular. 
g. Other abnormal conditions of the conjunctiva to be looked for 
are concretions, ecchymosis, chemosis, xerosis, argyrosis, cysts, and 
tumors. 
133. Inspection of sclera.—a. Inspection of the sclera may re- 
veal evidences of episcleritis or scleritis (eleyated and discolored 
nodules) or protrusions (staphylomata) resulting from a localized 
thinning of scleral tissue from inflammatory changes. 
b. The normal cornea is quite transparent, avascular, and shows 
bright, sharply defined reflexes on its convex surface. Wherever there 
is an abrasion, or facet, or depression, the reflex of an object a few 
feet away, as, for example, a window, will appear somewhat dis- 
166 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
133 
torted. Opacities of the cornea may be so slight that some magnifi- 
cation will be required for their detection. A dense and entirely 
opaque area is ordinarily designated as a leucoma; one having a 
more translucent appearance, as of ground glass, a macula; and one 
that amounts to a faint clouding only, a nebula. The position of an 
opacity is of significance. A large, centrally located nebula actually 
interferes with vision more than a smaller, although quite dense 
Figure 25.—Section made by slit-lamp through cornea and lens as seen through the loupe. 
leucoma located near the periphery. Where a cicatrix of the cornea 
exists the normal curvature of the cornea may be interfered with over 
an area larger than that of the opacity itself, causing an irregular 
astigmatism. 
c. In the examination of the cornea, focal illumination is essential, 
and the value of the hand slit-lamp, either with the monocular or 
binocular loupe, cannot be overemphasized. The student is encour- 
167 TM 8-300 
133-134 
MEDICAL DEPARTMENT 
aged to practice at every opportunity, in order to familiarize himself 
with the use of this instrument. In particular he should learn to 
focus the beam of light so that a sharply defined corneal parallele- 
piped is obtained; then he should learn by experience how to avoid 
annoying corneal reflexes. 
d. The student should first devote considerable time to the examina- 
tion of the normal cornea before attempting to diagnose pathological 
conditions. By the slit-lamp many abnormalities may be determined 
much more readily than otherwise; for example, thickening or thin- 
ning, opacities, superficial or deep, vascularity (superficial in pannus, 
deep in interstitial keratitis), degenerative changes, deposits on the 
posterior surface of the cornea (keratic precipitates), and anterior 
synechiae. 
e. The electric ophthalmoscope, with a strong convex lens rotated 
in the aperture, is of value in the examination of the cornea. 
Opacities observed in this manner appear much darker than they 
actually are due to the fact that they are in part illuminated from 
behind, and hence in a manner cast shadows of themselves. 
134. Anterior chamber and iris.—a. Anterior chamber.—The 
anterior chamber may be observed in conjunction with the examina- 
tion of the cornea and the iris. Normally, it is approximately 2.5 
millimeters deep. Its depth is estimated by the position of the iris 
which, when viewed through the strongly convex cornea, appears 
enlarged and further forward than it actually is. Binocular vision, 
as with the Beebe loupe, is a valuable aid in estimating the depth 
of the anterior chamber. Again, the value of the hand slit-lamp may 
be emphasized. The normal aqueous of the anterior chamber is a 
colorless and perfectly transparent fluid, and where a beam of light 
can be seen in the anterior chamber, when the slit-lamp is used, it is 
definitely indicative of an alteration in the character of the aqueous, 
as may result from an irido-cyclitis. A comparison may be made 
to a narrow beam of light entering a darkened smoke-filled room. 
The anterior chamber may contain blood (hyphaema) or pus 
(hypopyon). 
b. Iris.—In examining the iris attention is paid to the color and 
definition of the lace-like pattern. A comparison should be made 
with the fellow eye. Normally, the crypts are clearly defined and 
the surface of the iris appears rather brilliant, regardless of dis- 
position of pigment. At the pupillary margin there is a definite 
continuous ring of somewhat nodular dark brown pigmented 
epithelium, the anterior termination of the pars iridica retinae. Im- 
mediately around the pupillary margin and concentric with it, are 
circular ridges indicating the location of sphincter fibers of the iris. 
168 TM 8-300 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
134-135 
A “muddy-colored” iris with an apparent diminution in size of the 
crypts associated with an irregularly contracted pupil, sluggish in 
reaction, is suggestive of iritis. Further, a break in the continuity 
of the epithelial ring of the pupillary margin should arouse one’s 
suspicion as to the history of iritis—occasionally the detached por- 
tion of epithelium may be found adherent to the anterior capsule of 
the lens, indicating the site of a previous posterior synechiae. Par- 
ticular attention should be paid to the presence of synechiae. 
Posterior synechiae are definitely indicative of a past or present iritis, 
the etiology of which is of importance (possibility of rheumatc or 
luetic history). Congenital anomalies of the iris are not infrequently 
encountered, especially persistent pupillary membrane. This may 
vary from a single delicate thread-like structure hanging across the 
pupil, or below it, to a fairly heavy band. The latter, however, is 
uncommon. This abnormality can be differentiated from post- 
inflammatory lesions by the fact that the strand of tissue in persistent 
pupillary membrane is attached to the iris definitely outside the 
margin of the pupil. Furthermore, persistent pupillary membrane 
does not, as a rule, interfere with dilatation when a mydriatic is 
used. 
135. Examination of pupils.—a. In the examination of the 
pupils the examinee should be seated facing the light and each of the 
two pupils should receive an equal amount of illumination. Both eyes 
should be shaded from the light by the examiner’s hands; one hand is 
removed, exposing the eye to the light and the contraction of the pupil 
noted (direct reaction). The same is done with the fellow eye. Next 
observe the pupil of the eye shaded from the light when the other eye 
is exposed (consensual reaction), the procedure being repeated with 
the opposite eye. The reaction to accommodation is noted by first 
directing the examinee to fix upon an object in the distance, then sud- 
denly to fix upon a point about 10 centimeters away. A.s accommoda- 
tion occurs the normal pupil will contract. 
h. In the condition commonly referred to as the Argyll Robertson 
pupil the pupils usually are contracted appreciably; they do not react 
to light but do react to accommodation. This is a symptom commonly 
found in luetic diseases of the central nervous system. 
g. There is assumed to be located in the floor of the aqueduct of 
Sylvius near the nuclei of the third cranial nerves two nuclei or centers, 
one on each side, known as the photomotor nuclei. These nuclei are 
the cerebral centers which govern contraction of the pupil when the 
retina is stimulated by light. 
d. The theory is that there are two reflex arcs which control pupillary 
contraction and are independent of each other. One of these arcs 
169 TM 8-300 
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MEDICAL DEPARTMENT 
causes contraction of the pupil when accommodation occurs, while 
the other causes it to contract when the retina is stimulated by light. 
(1) The reflex arc governing pupillary contraction during accom- 
modation is formed by nerve fibers passing from the retina to the circu- 
lar muscle fibers of the iris by way of the optic nerve and tract, the 
ganglion of the third cranial nerve, and the ciliary ganglion. 
(2) The reflex arc governing contraction of the pupil following 
stimulation of the retina by light is found by nerve fibers passing from 
the retina to the circular muscle fibers of the iris by way of the optic 
nerve and tract, the photomotor nucleus, and the ciliary ganglion. 
This system of two independent reflex arcs explains the Argyll Rob- 
ertson phenomenon, that is, the pupil that reacts to accommodation 
but not to light. A lesion involving the photomotor nucleus breaks the 
reflex arc governing light stimulation and the pupil fails to react. The 
nucleus of the third cranial nerve not being involved, the reflex arc 
remains intact and consequently the pupil will react to accommodation. 
Association fibers are supplied from the primary optic ganglia to the 
ganglia of the fourth and sixth cranial nerves to control the superior 
oblique and the external rectus mucles. 
e. Unusually large pupils may be indicative that a mydriatic has 
been used, either locally or possibly as an internal medication. In 
this instance there will be an associated diminution of accommoda- 
tion power. Dilated pupils are also found in complete optic atrophy, 
in glaucoma (immobile and oval with axis vertical), cervical sympa- 
thetic irritation, and from trauma (iridoplegia). 
/. Small pupils are frequently found with central nervous disease 
associated with the use of drugs, either locally as eserine or internally 
as morphine, or may be indicative of an old iritis. 
g. The degree of contraction when the pupil is exposed to light 
is to be observed, as well as whether or not the contraction is well 
maintained. In retrobulbar neuritis, while the pupil reacts readily 
upon exposure to light, it may slowly dilate upon continued exposure 
to brilliant illumination. 
136. Lens.—a. Examination.—In the examination of the lens 
some artificial aid is necessary. Again the hand slit-lamp will be 
found to be of great value. Furthermore, the lens in its entirety 
cannot be inspected thoroughly through a contracted pupil. Conse- 
quently, the use of a mydriatic will be found to be of considerable 
benefit. Where a transient dilatation of the pupil is desired without 
a pronounced cycloplegia, euphthalmine in a 4-percent aqueous solu- 
tion will ordinarily be effective, although the examiner will find as 
a rule that euphthalmine is much more effective upon blondes than 
upon brunettes. The same is true as regards homatropine. In many 
170 TM 8-300 
136-137 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
instances even the repeated instillation of euphthalmine in the eye 
of the Negro will have only a barely appreciably effect in dilating the 
pupil. In the examination of applicants for flying training, a cyclo- 
plegic is used (prior to retinoscopy), and the examination of the lens 
may be postponed until the ophthalmoscopic examination is made. 
b. Opacities.—Opacities in the lens substance or upon either capsule 
appear both with oblique examination and with the slit-lamp as grayish 
or yellowish areas. With the ophthalmoscope they will appear very 
much darker, and for this reason may be detected more readily. In 
inspecting the crystalline lens a strong convex lens is rotated before 
the aperture of the ophthalmoscope. This affords considerable mag- 
nification. The pupillary margin is then brought into sharp focus 
and, as the pupillary margin is in direct contact with the anterior 
capsule of the lens, this focus must be that for the anterior surface 
of the lens. The hand slit-lamp with the binocular loupe is especially 
useful in locating the position of opacities of the lens, that is, whether 
on the anterior capsule within the lens substance or on the posterior 
capsule, as the case may be. The hand slit-lamp does not replace 
the ophthalmoscope in the examination of the lens, but it is a very 
desirable adjunct to it. In the inspection of the lens, using the hand 
slit-lamp or the ophthalmoscope, particular attention should be paid 
to the periphery of the lens. Iritis often leaves its indelible mark 
on the anterior capsule as detached portions of the pars iridica retinae, 
dark brown pigmented patches firmly adherent to the capsule. 
Rarely there may be seen remnants of persistent pupillary membrane 
occurring as minute, usually stallate, pigmented patches on the anterior 
capsule. The latter, of no significance, must be differentiated from 
evidences of an old iritis. 
Since the lens is an isolated portion of epithelial structure it is sub- 
ject to degenerative rather than inflammatory changes. Such changes 
result eventually in opacities (cataract). The student is advised to 
review, in any text, the objective findings with the varieties of cataract. 
137. Opacities of vitreous.—a. Means of observation.—Opacities 
of the vitreous may be observed by means of the ophthalmoscope, and 
with the slit-lamp when they are located anterior to the equator. 
With the ophthalmoscope they appear as shadows; with the slit-lamp 
they show in their natural appearance. 
b. Method.—The examinee may be directed to look from the right 
to the left suddenly, or his temporal region may be jarred by a gentle 
blow, which may bring into view floating opacities in the vitreous. 
When opacities in the vitreous are found, and they are quite motile, 
the conclusion may be reached that the vitreous is abnormally fluid in 
character. In using the ophthalmoscope, after inspecting the lens sub- 
171 TM 8-300 
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MEDICAL DEPARTMENT 
stance, the convex spherical strength of the lenses should be gradually 
reduced, thus bringing into focus any structure that may exist between 
the posterior lens capsule and the retina. 
c. Palpation of globe.—Finally, the globe should be palpated and an 
estimate of intra-ocular tension made. The examiner stands facing the 
9Ni 
"8th 
6th 
rods_an_d_con_es 
Mh_CELLS 0 FT H E_FI R_ST0 RDE R_ _ 
F_3rd_ 
4th 
CELLS OF THE_SECO_ND_0_RDE_R_ 
TO_CILIARY BODY 
TO IRIS 
IjOiNTERNAL RECTUS 
PUPIJLLAJRY UGHT_RE_FLEX A_RC 
CaiARY_G_ANGL10N_ 
OPTIC NERVE 
PUP 1LL A RY_ R_E F_LEX_AJC 
"A^fOMMO'DATlON- 
OPTIC TRACT 
EXT. GENICULATE 
PULV1NAR 
PRIMARY OPTIC GANGLIA 
CELLS OF THE 3rd ORDER 
C.QUADJRIGF_MJNUM j 
photomotor’nucleus 
3rd NUCLEUS 
OPTIC RADIATIONS 
VISUAL CENTER 
Figure 26.—Visual pathways (diagrammatic). 
examinee who is directed to look downward. The examiner 
index finger of each hand upon the skin of the upper lid immediately 
beneath the aperture of the orbit and above the superior tarsal plate. 
One finger is held still, maintaining a steady pressure upon the globe 
through the lid, and with the other gentle indentations are made upon 
the globe pressing downward. In the meantime the examiner 
172 NOTES ON EYE, EAR, ETC,, IN AVIATION MEDICINE 
TM 8-300 
137 
concentrates his attention upon the impression which is conveyed to 
the finger which remains stationary. The student must practice this 
maneuver on many normal eyes, and thus obtain a mental estimate of 
what may be considered as normal tension, recorded as Tn. In cases 
of extreme increase in intra-ocular tension, as in absolute glaucoma, 
where the globe is palpated as having a strong or boardlike hardness, 
the tension may be recorded as T plus 3. Various estimates may be 
made, in comparison with palpation of the normal globe and findings, 
as T plus 1, or T plus 2, recorded. In a similar manner diminished 
tension may be recorded as T-\, 71-2, T-3, etc. Accurate estimations 
Figure 27.—Slit-lamp study of anterior segment of eye. 
require considerable experience and the student is encouraged to prac- 
tice making an estimate of intra-ocular tension at every opportunity. 
He always has his own eyes to palpate. 
d. Tonometer.—The intra-ocular tension may be estimated more 
accurately by the use of a tonometer, which records the approximate 
intra-ocular tension in millimeters of mercury. The use of such an 
instrument, which presses against the corneal curvature, must be pre- 
ceded by a local anaesthetic, as a depth of indentation of the cornea is 
used as an indication of the intra-ocular tension. There are several 
tonometers made, and each has its own characteristic as to interpreta- 
173 TM 8-300 
137-138 
MEDICAL DEPARTMENT 
tion of findings, and each has its own so-called range of normalcy. It 
is advisable that, except in cases of quite obvious marked increase in 
intra-ocular tension, repeated readings be taken before arriving at a 
conclusion. 
e. Normal tension.—The normal intra-ocular tension is about 25 
millimeters of mercury above atmospheric pressure, and this pressure 
is probably higher than that developed inside any other organ in the 
human body. It must be remembered that the tonometer, as used 
clinically, really measures the tension of the ocular coats, rather than 
the actual intra-ocular tension. 
138. Nystagmus.—a. Description.—In the inspection of the eye 
nystagmus should be noted when present. By nystagmus is meant 
rapid oscillatory involuntary movements of the globe independent of 
the normal ocular movements, which are not affected. These move- 
ments are more frequently lateral but may be vertical or rotary, or even 
mixed. The condition is usually bilateral, but one eye may be more 
markedly affected than the other. 
h. Source.—Nystagmus may be congenital or acquired. When con- 
genital it is associated frequently with other stigmata, as albinism and 
total color-blindness. The acquired form in adults may occur with 
disease of the cerebellum and vestibular tracts, Friedreich’s ataxia, dis- 
seminated sclerosis, and affections involving the semicircular canals. 
It may also occur as an “occupation neurosis,” the commonest type 
being coal miner’s nystagmus. 
c. Nystagmoid movements.—Nystagmoid movements, jerky and 
somewhat irregular in character, which are noted only at extreme 
limits of the normal ocular movements, are of no significance and must 
be differentiated from a true nystagmus. Such movements may be 
found in normal individuals and may be more accentuated with 
fatigue. 
Section XVIII 
COLOR VISION 
Paragraph 
General 139 
Physical basis of color vision 140 
Trichromic color perception 141 
Dichromic color vision 142 
Effect of a shortened red 143 
Military significance of color-blindness 144 
Tests of color vision 145 
Examination of color perception 146 
First examination 147 
Second examination 148 
Ishihara test 149 
174 TM 8-300 
139 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINI 
Paragraph 
Stillings test 150 
Jennings test 151 
Holmgren test 152 
Proposed method of examination 153 
Directions for use of Ishihara test plates 154 
Directions for Holmgren (yarn) test 155 
139. General.—a. Detection.—Considerable embarrassment has 
been caused by the failure to detect and properly report color-blind- 
ness on the examination of applicants for commission, and for en- 
trance to West Point. Examples of the difficulty that has been ex- 
perienced may be cited. Two officers who were commissioned in the 
Medical Corps of the Regular Army with color vision reported as 
normal were found to be color-blind on their first annual physical ex- 
amination. A number of flying cadets have been relieved from the 
Air Corps Training Center because of color-blindness, though in each 
single instance the color perception had been reported as normal on 
one or more previous examinations. Aside from the embarrassment 
which such an oversight causes the Medical Department, it is ob- 
vious that considerable unnecessary expense is incurred in ordering 
these officers to the school only to find that they are physically dis- 
qualified for flying. It is equally obvious that if this gross disqualify- 
ing defect can be so easily detected by one group of examiners, it could 
have been detected in the first instance with material advantage to 
the Government. During the years 1934 and 1935, 2,355 candidates 
have been examined for admission to West Point. Of this number 
20, or 0.84 percent, were reported as color-blind. It is known that ap- 
proximately 3y2 percent of the male population are dangerously color- 
blind; hence there is every reason to believe that in this group some 
62 cases of color-blindness are not accounted for. A few were de- 
tected on the preliminary examination and did not come up for final 
examination. It is known that the number thus eliminated is small, 
however, and the not infrequent discovery of color-blindness on casual 
examination after appointment leads to the disturbing conclusion that 
the great majority of the 62 cases were accepted as normal because of 
faulty methods of examination, or failure to evaluate correctly such 
defects as were detected. Moreover, in the reports of examination re- 
ceived in The Surgeon General’s Office it is quite apparent from the 
entries in cases of defective color perception that many medical officers 
have a very vague or a completely erroneous conception of what color- 
blindness is and of the proper procedure for its detection. When one 
considers that the detection of this rather common defect is not more 
difficult than the ordinary refraction, there seems to be little excuse 
for the very poor showing made. It is obvious that more careful at- 
175 TM 8-300 
139 
MEDICAL DEPARTMENT 
tention to the details of the examination of the color perception will 
remove a cause of embarrassment to the Medical Department and will 
be to the material advantage of the Government. 
b. Treatment of subject.—The subject is here treated from the prac- 
tical standpoint, with a desire to limit the discussion to those features 
that may be usefully applied in the routine physical examination for 
the detection of this defect and to leave the more theoretical aspects 
to others who are better qualified to discuss them. It is proposed to 
discuss the nature of color-blindness, to classify the various types that 
may be found, to show why color-blindness disqualifies for commission 
in the Regular Army, to indicate the best procedures foy the detection 
of the defect, and finally to supply a list of references for the conven- 
ience of those who wish to pursue this very interesting subject further. 
c. Definition.—It is common knowledge that the color vision of cer- 
tain persons differs from that of the normal. Such persons are called 
“color-blind,” a very unfortunate term, for it implies that they are 
blind to all color, and that all such persons have the same color per- 
ception. Neither of these implications has any basis in fact. The 
color-blind may be understood to include all of those persons whose 
color vision is different from that of the normal, and whose perception 
of color is, in general, more limited. They may be divided at once 
into two classes—the congenital and the acquired. We will not con- 
sider acquired color-blindness, for this type is uncommon in the age 
groups with which we are concerned; moreover, in these cases the de- 
fective color vision results from a grave intoxication or is but a part— 
usually a minor part—of a serious ocular or neurological disorder. 
d. Congenital color-blindness.—Congenital color-blindness is a de- 
velopmental defect. It almost always affects both eyes. The other 
ocular functions are not affected. It is hereditary, and tends to be 
transmitted through the females, and to be manifest in the males. 
The condition cannot be corrected, or even improved, though the color- 
blind do learn to conceal the defect. They are frequently ignorant of 
the defect themselves, but even when they realize that their color vision 
is not as good as normal they tend to minimize it as color ignorance, 
poor shade discrimination, etc. 
e. Occurrence.—It is estimated that about 80 percent of the popula- 
tion have normal color vision. Of the remaining 20 percent, a con- 
siderable proportion are the acquired color-blind. Congenital color- 
blindness of some degree occurs in from 8.5 percent to 10 percent of 
men and about 2 percent of women. Color-blindness of such degree 
as to be disqualifying in occupations requiring color discrimination 
occurs in approximately 3.5 percent of men and 0.7 percent of women. 
It is this 3.5 percent of the candidates for commission with whom we 
176 TM 8-300 
139-140 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
are concerned. In examining applicants for flying training, effort 
must also be made to detect the milder grades of defect and to eliminate 
the entire group (8.5 percent to 10 percent) with subnormal color 
perception. 
140. Physical basis of color vision.—a. Retina.—In addition 
to the inability to discriminate between light waves of varying 
lengths by the fovea or central portion of the retina, there are other 
factors which render color-blindness still more complicated. 
(1) Zones.—If all the area of the retina were sensitive to color 
stimulation to an equal degree, the problem of color-blindness would 
be somewhat simplified. The retina, however, is divided into three 
zones, each having varying boundaries in different individuals and 
possessing varying degrees of color sensitivity and discrimination. 
These three zones are: 
{a) Central zone (normal color vision). 
(&) Medial zone, surrounding the central zone, in which only two 
colors, yellow and blue, are discernible. In the medial zone, reds 
appear as dark yellow or browns and long wave greens appear pale 
yellow, while bluish-greens are pale blue, and violet appears dark 
blue. Some greens intermediate between those that appear yellow 
and those that appear blue are practically colorless. 
(c) Marginal zone, in which all color stimuli appear colorless and 
only form and shade are discernible. 
(2) Factors influencing zone.—These three zones are not sharply 
separated, but grade into each other and the character of vision in 
any case is dependent not alone on exact position, wave length, sat- 
uration, and intensity of stimulus, but also upon its duration and 
motion and upon the amount of practice of the individual in dis- 
crimination and the degree of attention which is given the particular 
observation. External conditions of smoke, fog, dust, and contrast 
of light with other colors are also influential when the sources of 
light are at some distance from the observer. 
(3) Varying degree of color perception.—Accurate and rapid dis- 
cernment of color is limited to central vision (that is the condition 
in which the eye is directed immediately upon the light). In peri- 
pheral vision (when the medial and outer zones of the eye are used), 
while discrimination may under test conditions be more or less possi- 
ble, colors are susceptible to confusion under many conditions. In 
the color-blind, the defect may occur in a restricted portion of tho 
central area or it may cover the whole central area, so that there is 
no distinction between the central and medial portions of the retina 
in color perception, aside from the factor of greater practice in tho 
use of one portion. The varying degree of color perception in tho 
271818°—40 12 
177 TM 8-300 
140 
MEDICAL DEPARTMENT 
various areas of the retina makes the division between the normal 
and the color-blind somewhat arbitrary. Added to this is the fact 
that brightness, saturation, and other conditions influencing color 
discrimination cause the degree of apparent color weakness to vary 
according to the conditions of the test 
(4) Secondary criteria.—The presence of secondary criteria of 
brightness and saturation make it possible for many color-blind 
people to pass tests of varying types. This is especially true of indi- 
viduals who have had considerable practice in handling colored 
materials. The opposite is likewise true; the lack of practice of 
individuals in the discrimination of colors of low saturation confuses 
them on many of the tests. 
b. Spectrum.—(1) Description.—A beam of sunlight passed 
through a prism is broken up and appears as the six colors of the 
solar spectrum. Light is due to the undulations of the luminiferous 
ether, the motion of the wave being perpendicular to the path of 
the ray. The longest rays perceived as color are at the extreme left 
end of the spectrum, the red end, and are estimated to have a vibra- 
tion rate of 395 billions per second. At the extreme right end of 
the spectrum, that is, in the violet, the waves have a vibration rate 
of 763 billions per second. Between these two extremes, from left 
to right, the rays are arranged in a series with regularly increasing 
vibration rate and regularly decreasing wave length. Beyond the 
left or red end of the spectrum the rays (infra-red or heat rays) are 
not perceived by the light sense at all; likewise beyond the violet the 
ultraviolet or actinic rays give rise to no sensation of light or color. 
Hence, when one looks at the spectrum both of these regions are 
black. 
(2) Psychophysical series.—This arrangement of the light waves 
constitutes a physical series. The sensations resulting from the ac- 
tion of this physical series on the sensory apparatus may be termed 
a psychophysical series. Given a sensory apparatus sufficiently sensi- 
tive, it is conceivable that each single ray would give rise to its corre- 
sponding sensation or color. The human visual apparatus, however, 
is not so sensitive. When the spectrum is viewed by the normal eye 
six bands of color are perceived. The spectrum may be represented 
as shown in figure 28. 
(3) Psychophysical units.—The numerals represent the wave 
lengths that are commonly accepted as the dividing lines between the 
several colors. It will be noted from the distribution of these wave 
lengths that the bands of color are not of equal width. It is to be 
remembered also that the division between the colors is not a sharp 
and well defined one, as the lines in the figure indicate, but that each 
178 TM 8-300 
140 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
color merges by fine gradations into the next one. Pure yellow and 
pure green, for example, are found at Y and G, respectively, and 
somewhere to the right of Y, say from a to h, the varying shades are 
properly described as shades of greenish yellow, while those occurring 
from b to c are yellowish green, and so on through the spectrum. 
Such areas are termed modified psychophysical units. There is a 
space extending on either side of F, however, represented in our dia- 
gram by the space a to a?, in which, although the waves differ slightly 
in length, no difference in color is perceived and the color from one 
part of this area is to the eye exactly the same as that from all other 
parts of the area. Such an area in the psychophysical series is termed 
an absolute psychophysical unit. By an approximate psychophysical 
unit is meant one that contains physical units which give sensations 
that are only nearly and not exactly alike; for example, the varying 
shades of yellow that make up the yellow band. An approximate 
Bed 
Or 
Yellow 
Green 
Blue 
Violet 
Figure 28.—Spectrum. 
psychophysical unit, therefore, may contain a number of absolute 
psychophysical units which greatly resemble one another. When we 
keep in mind the fact that the total physical series with which we 
are dealing, namely, the solar spectrum, is incapable of being extended, 
it follows that if the size of some of the absolute units be increased 
the size of the approximate units must also be increased and that this 
increase must be at the expense of other units and may result in the 
complete obliteration of certain units. If in our diagram the blue and 
yellow bands are progressively expanded the green band between 
them will be correspondingly decreased and will finally be obliterated 
by the meeting of the blue and yellow. In an individual in whom 
such a change has occurred, light rays from the green band will give 
rise not to the sensation of green but to the sensation of blue or yellow, 
depending on which of these units has encroached on the part of the 
green band from which the rays come. Such an increase in one or 
more of the units of the psychophysical series, then, may result in any 
degree of encroachment on the remaining units. Instead of six colors, 
only five or four or three, or even less, are to be seen. Finally, there 
179 TM 8-300 
140 
MEDICAL DEPARTMENT 
is one other factor to be considered. If for any reason the sensory 
apparatus is not sensitive to the rays from any portion of the physical 
series, no color at all will be perceived in that area, that is, it will 
appear black. If this condition obtains at either end of the spectrum 
the spectrum is said to be shortened. If it is shortened at the red end, 
the red wdll appear black. If the shortening merely encroaches on 
the red band, only the corresponding shades of red will appear black, 
and the other shades will still be perceived as red. If, however, the 
shortening obliterates the red area, the ability to perceive red will be 
lost and all shades of red will appear as black. When this defect in 
the spectrum occurs, not as a shortening at the end but as a hiatus 
somewhere along its length, it is spoken of as a neutral band, and the 
color that should be seen in this area is replaced by black or gray, ac- 
cording to the intensity of the illumination. This then may be ac- 
cepted for practical purposes as the mechanism by which the various 
types and degrees of “color-blindness” are produced, and all individuals 
may be classified as to color perception according to the number of 
psychophysical units that they perceive in the solar spectrum. 
(4) Maximum luminosity.—Another factor that is operative in the 
production of the difference in sensation in the color-blind as compared 
to the normal is the shift in the point of maximum brightness. In 
the normal, with a brilliant spectrum the maximum brightness is in 
the yellow but with a feeble illumination it shifts to the green. As the 
light is diminished the red end becomes darker, while the green, blue, 
and violet appear relatively bright. In one type of color-blindness 
the maximum luminosity occurs in the rreen, as it tends to do in the 
normal with feeble illumination. We si: oil see later that relative 
luminosity is of great importance to the color-blind, since it is on this 
basis that they distinguish colors rather than by an actual difference 
in hue, as do the normal-sighted. 
(5) Units of perception.—The normal-sighted individual distin- 
guishes six distinct bands of color in the spectrum. If the intensity 
of the illumination is progressively diminished, however, the tendency 
is to a reduction of color perception so that the normal six unit or 
hexachromic is reduced to five units—pentachromic; then to four 
units—tetrachromic, etc. Finally, with further reduction of the light, 
all colors are lost and a condition of achromatism is reached in which 
the sensation is limited to the black, gray, and white series. This is the 
condition that obtains in many of the lower animals. Indeed, it is 
not improbable that the color vision of man was evolved by the reverse 
of this process. The animal that can perceive only light and shade 
can discriminate only in a rough way between varying intensities of 
the stimulus. It is apparent that the sense of sight must have de- 
180 TM 8-300 
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NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
veloped first and then the sense of color. In the physical stimulus 
producing the sense of light there are two factors to l)e considered, 
the length of the wave and its amplitude; the greater the amplitude, 
the greater the stimulus. Therefore, the wave length of the physical 
stimulus is the physical basis of the sensation of color. When evolu- 
tion has proceeded to the point where the organism is sensitive to rays, 
considerably above and below those which first caused a sensation of 
light, we have an eye that is sensitive to the greater part of the rays 
that form the visible spectrum; devoid, however, of any sense of color. 
No matter from what part of the spectrum the rays are taken, the only 
difference appreciated will be one of intensity. There now appears 
a fresh power of discrimination—the ability to discriminate between 
different wave lengths. Probably the wave lengths of greatest dif- 
ference would be the first discriminated because of their very dif- 
ference. It is presumed, then, that the first colors discerned were at 
opposite ends of the spectrum, namely, red and violet, provided the 
eye had become sensitive to this range. The individual would now 
see the spectrum a uniform gray of different degrees of luminosity, 
with a touch of red at one end and a tinge of violet at the other. 
(6) Trichromic spectrum.—In the degree of color-blindness, just 
preceding total, the spectrum is seen in this way. The next stage in 
the evolution of the color sense was when the color receiving center 
had developed sufficiently to discriminate a third color, namely, green, 
which is in the center of the spectrum, the third point of greatest 
physiological difference. About 1.5 percent of men see the color spec- 
trum in this way, namely, red, green, and violet. These are the so- 
called trichromic types. They describe the spectrum as consisting of 
red, red-green, green, green-violet, and violet. They do not see yellow 
and blue as distinct colors. They will declare that patches of green- 
ish-yellow and orange-yellow are absolutely monochromatic. These 
cases often pass matching tests with ease. 
(7) Tetrachromic spectrum.—In the next stage of evolution, four 
colors are seen in the spectrum, the fourth appearing at the fourth 
point of greatest physiological difference, namely, at the orange- 
yellow of the hexachromic, or six color people. These cases see red, 
yellow, green, and violet, but do not see blue as a definite color, classing 
this color with green. 
(8) Pentachromic spectrum.—In the next stage of evolution, there 
appear those who see five colors in the spectrum; namely, red, yellow, 
green, blue, and violet. These are the pentachromic groups and these 
cases pass the tests in general use with ease. They cannot, however, 
see orange as a definite color. 
181 TJVE 8-300 
140 
MEDICAL DEPARTMENT 
(9) Hexachromic spectrum.—In the next stage of evolution, orange 
is recognized and we have the normal or hexachromic group; the 
yellow now being separated into two colors, namely, yellow and orange. 
In the last stage of evolution that we have reached are those who 
see seven colors in the spectrum, the additional one being indigo, 
which appears between the blue and the violet as a distinct color. 
(10) Classification of types of color vision.—This concept of the 
evolutionary development of the color sense in a man very naturally 
lends itself to a classification of the various types of color vision. 
The normal-sighted may be termed as hexachromic; those with five 
colors, pentachromic: those who see four, tetrachromic; those who see 
three, trichromic; those who see two, dichromic; those who see one, 
monochromic; and those who see none, achromic, or totally color-blind. 
(11) Causes of congenital color-blindness.—From what has been 
said, it is evident that the congenital type of color-blindness may be 
due to two causes: a reduction in the number of psychophysical units, 
or inability of the sensory apparatus to react to rays from certain 
portions of the spectrum. Further modification may be produced 
by displacement of the point of maximum luminosity. 
(12) Description of units.—On the basis of the “unit” conception 
as outlined in the preceding pages a simple and workable classification 
of the types of color vision is easily made. It should be stated, paren- 
thetically, that there are other classifications, some of which have 
features of value and which seem to be sound from the scientific stand- 
point. FTo attempt is made to pass on the relative validity of these 
conceptions. The unit classification is employed because of its sim- 
plicity, the ease of its application, and because it does seem to fill 
all requirements for the solution of the problem. 
(a) Seven unit; heptachromic.—There are a few fortunate indi- 
viduals (1 in several thousand) especially favored by nature, who 
have a seven-unit spectrum. The additional unit is described as an 
indigo and is distinct from the blue on the one hand and the violet 
on the other. The orange is also increased and there is a heightened 
perception throughput the whole spectrum. Hence they perceive 
differences of color that are not apparent to others and make facile 
discriminations that are accomplished with uncertainty and hesita- 
tion, or not at all, by their less fortunate brothers. 
Six unit; hexachromic. 
1. Normal.—The normal six-unit spectrum, as described. This 
group comprises about 80 percent of the total population. 
2. Shortened spectrum.—The shortening may occur at either 
the red or the violet end. If at the violet end of the spec- 
trum, the defect is of little or no practical importance ; 
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if at the red end, however, the individual may be in the 
dangerous color-blind group. If a red signal light or 
rocket is viewed at a distance or through the obscurity 
of a thick fog or smoke it may appear green to the six 
unit with shortened red. This is due to the fact that the 
red lights in common use contain not only red rays but 
green rays as well. Under conditions of obscurity the 
fog may blot out the few red rays that are capable of 
causing a sensation, while the green rays are perceived 
and give rise to the sensation green. 
(c) Five unit; pentachromic.—The spectrum contains red, yellow, 
green, blue, and violet. The five unit is unable to see the orange 
band and the distinction between modified units is less sharp than 
in the normal person. The estimated incidence of this type of color 
perception is 7 to 10 percent. 
(d) Four unit; tetrachromic.—Here the orange and the blue are 
not seen. The spectrum contains the red, yellow, green, and violet. 
Blue and green cannot be distinguished without direct comparison, 
and then only as slightly different shades of the same color. Since the 
green has encroached on the blue, blue is called green, but green is 
not called blue because the tetrachromic has no adequate conception of 
blue. About 3 percent of all persons are in this group. They are 
detected infrequently in the ordinary examination, any confusion that 
may be evident being ascribed to “color ignorance.” The defect, how- 
ever, is of little practical importance except in the Air Corps and the 
Veterinary Corps. 
(e) Three unit; trichromic.—The spectrum is limited to the red, 
the green, and the violet. This type of defect is of a gross nature 
and gives rise to characteristic confusions in colors. Green is confused 
with brown (a dark shade of yellow or orange) because the green 
has encroached on the yellow area of the spectrum. He does not mis- 
take red for green, however, unless the red end of the spectrum is 
shortened for him. About iy2 percent of the population are in this 
group. They are detected somewhat more frequently than the tetra- 
chromic but when detected are often reported as “impaired color 
sense for green; not a true color-blindness” or some similar phrase. 
(/) Two unit; dichromic.—This is the ordinary red-green type 
of color-blindness and is present in approximately 2 percent of per- 
sons examined. The dichromic spectrum is made up of two colors, 
dark yellow and blue, gradually shading into one another. Red, 
orange, yellow, and green, then, are seen as slightly different shades 
of the same color (yellow) while blue and violet are seen merely as 
shades of blue. Recent investigations indicate that the spectrum in 
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MEDICAL DEPARTMENT 
one type of dichromatism consists of green and blue; in these cases, 
therefore, red, orange, yellow, and green are perceived in terms of 
green; violet and blue in terms of blue. In addition to the reduction 
in the number of the approximate psychophysical units in dichro- 
matism, there is also often found a displacement of the point of maxi- 
mum luminosity from the yellow to the green, a shortening of the 
spectrum at either end, more commonly in the red, and the appearance 
of a neutral band in the middle of the green. This neutral band 
may widen until it occupies the entire spectrum and produces com- 
plete color-blindness. These variables give rise to certain main types 
of dichromatism, which embrace cases of all degrees of severity. 
These will be discussed more in detail a little later. 
iff) One unit; monochromic.—The one unit or true monochromic 
with a spectrum that contains but a single color from end to end 
propably does not exist, since if any color at all is left in the spectrum 
there will be a short band in the extreme red and another in the 
ultimate violet. An individual with such a spectrum belongs for 
all practical purposes in the following class. 
(h) Golor-blind; achromic.—The total color-blind or achromic, 
happily, is very rare. A few cases are on record and have been care- 
fully studied. The entire spectrum is devoid of any vestige of color. 
The more luminous portions appear gray, the less luminous dark gray 
or black. The external world is perceived in black and white and the 
intermediate grays. The fact that the totally color-blind have great 
aptitudes as engravers is but a sorry compensation for the tremen- 
dous esthetic deprivation. 
This classification (adapted from Eldridge Green) is adequate for 
our purpose, since it embraces all of the main types of color vision 
that may be encountered and it indicates the great variation in 
degree that may be found within the several classes. Other writers 
divide the dichromats, or red-green blind, into two classes: those 
who have the yellow-blue spectrum with a neutral band of variable 
width centering in the green are called “deuteranopes” or green blind; 
those, some of whom are now believed to have a green-blue spectrum 
with a shortening at the red end, are termed “protanopes” or red 
blind. The tetrachromic, pentachromic, and the hexachromic with 
shortened spectrum are termed anomalous trichromates. The tri- 
chromics are sometimes included in this group, and sometimes are 
termed “tritanopes.” 
(13) Dangerous color-blindness.—It has been indicated that cer- 
tain types of impaired color vision, that is, the pentachromic, are of 
little or no practical importance and are not readily detected by the 
ordinary methods of examination. Certain others, however, are of 
184 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
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serious consequence in any individual whose occupation requires 
accurate and rapid discrimination between colors under varying 
conditions. Individuals with these types of defective color percep- 
tion are properly described as “the dangerous color-blind” and are 
disqualified for commission in all arms and services except the Corps 
of Chaplains. They are those with a color perception containing but 
three units or less, or those with a color perception containing more 
than three units who have the red end of the spectrum so shortened 
that the shortened red can be detected by the ordinary tests. Before 
we go on to a more detailed consideration of these dangerous types, 
there are certain features that are common to all types that should 
be mentioned. 
(14) Elementary facts.—On investigating the subject of color per- 
ception one is impressed by the extraordinary degree of confusion 
that is found. This confusion seems to arise from two causes. First, 
the theories of color vision. The tendency has been to start with 
some special theory and so far as possible to make all observed facts 
fit the particular theory. The second cause of the confusion is due 
to the nature of the subject itself. In investigating color-blindness 
we are dealing not with ponderable realities of the external world 
but with sensations, that is, the effect produced in the consciousness 
of the individual by certain stimuli. The stimulus, the series of 
light waves that make up the solar spectrum, is constant and immuta- 
ble; the sensation, the color excited by the action of these rays on the 
sensory apparatus, has no reality save in the consciousness of the 
observer and may vary greatly in different individuals. If two 
individuals look at a colored object and both call it green it is 
assumed that both have the same sensation. It is not known, and 
cannot be known, whether both have exactly the same sensation, 
or even that the sensations of the two remotely resemble one another. 
On the other hand, if one observer says that an object is red and 
another calls it orange, it cannot be assumed that their sensations are 
necessarily different. It may be a mere difference in nomenclature. 
The term “orange” denoting a color is not included in the vocabu- 
laries of many persons. They are content to refer to the shades 
of orange as red or yellow, yellowish-red, etc. Now consider the 
possibilities when an examinee selects a bright green and a bright 
red as perfect matches. It is known.at once that the two look the 
same to him. The question arises as to whether he sees the green 
as red or the red as green, or whether he sees both red and green as 
some other color, yellow for example, or as devoid of color—gray. 
In examining for color-blindness it must be remembered that naming 
a color correctly does not necessarily mean that the examinee sees 
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MEDICAL DEPARTMENT 
the color correctly. Red to him may be merely a matter of luminosity 
and, although he uses the term glibly and in the main appropriately, 
he has never experienced red as a sensation and it is as impossible for 
us to tell him what we mean by red as it is for us to describe light 
to a person who has been blind from birth and has never experienced 
light. If these elementary facts are not borne in mind, confusion is 
the result and erroneous conclusions are almost inevitable. Thus a 
simple dichromat may be called “color-blind to brown, weak for 
green” on one occasion and “color-blind for red and blue” on another 
and on reexamination be reported “color-ignorant, not a true color- 
blindness.” 
(15) Color-blind individual.—The color-blind individual is actually 
blind to color only in those portions of the spectrum, usually limited in 
extent, where a neutral band occurs. These neutral colorless areas 
occur at either end or centered in the green. The remainder of the 
spectrum contains color, though the number of distinct units is reduced. 
At least two units are preserved. If the spectrum is shortened, the 
point of maximum luminosity is shifted away from the shortened end. 
With such an equipment he is able to see two of the six primary colors 
almost as well as the normal. Under ordinary conditions he is able to 
compensate for his defect so that it is not apparent to his associates. 
From childhood he has become familiar with color names as applied to 
common objects and uses these correctly. In other words, although 
he sees but a limited number of colors, he has adopted the nomenclature 
of the normal. He soon learns that other people use a color classifica- 
tion that is unnecessarily complex and full of hair-splitting distinctions 
and that his own ideas of color are apt to excite amused comment. 
Color to him is not a conspicuous quality of objects and he is not 
interested in it. He avoids using color names for unfamiliar objects 
until he has first heard them named by others and then employs them 
as a matter of memory. His memory for color itself is very poor. He 
looks at a red brick house surrounded by a green lawn adorned with 
red and yellow flowers. He sees all of these as varying shades of yellow 
but names the color of each correctly because he has learned by ex- 
perience that bricks are called red and grass is called green and that 
this particular shade of yellow is usually called red and that one green. 
He will avoid referring to the color of the scarlet sweater lying on the 
lawn, however, because of uncertainty as to whether that shade of dark 
yellow should be called red, or brown, or green. He easily distinguishes 
traffic lights by a similar difference in shade because traffic lights are 
standard in color and intensity. If the intensity of the light were 
varied, he would be forced to rely on the relative positions of the red 
and green or to govern his own movements by those of the traffic. 
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Color to th© normal-sighted is a conspicuous quality of objects; to the 
color-blind it is much less so. To the normal, colors differ from one 
another as to hue, luminosity, and saturation, that is, degree of ad- 
mixture with white. Color differences are heightened by contrast. If 
a red is compared with a blue-green, the red becomes brighter and the 
blue-green becomes more blue. In the dichromat true perception is 
reduced from six units to two, but the contrast effect seems to be 
heightened and colors other than the two visible primaries are judged 
almost entirely by shade. Finally, the rays from the shortened end of 
the spectrum or the neutral band of the color-blind are not perceived 
at all; for him they are practically nonexistent. He can form no opinion 
in regard to their qualities, and in any mixture in which these physical 
units form a part of the exciting stimuli they will have to be subtracted 
before the result can be obtained. For this deficiency he is unable to 
compensate. 
141. Trichromic color perception.—The spectrum consists of 
three colors: red, green, and violet (the latter often called blue). 
There may or may not be shortening at either or at both ends. The 
three primaries are distinct colors and are never mistaken for each 
other. They are in strong contrast as between their central points. 
The region of transition from one unit to the adjoining unit, how- 
ever, partakes of the qualities of both and becomes a modified unit. 
The red-green junction appears as a mixture of red and green just 
as the yellow-green junction appears as a modified yellow-green 
unit in the normal spectrum. Trichromics frequently employ the 
term “reddish-green” or “greenish-red” in referring to this area. 
Such terms can have no meaning for the normal. Since the red- 
green junction of the trichromic lies in the yellow of the normal, 
he confuses shades of yellow with green and with red. Orange, 
yellow, and red-brown are put with red. Some yellow-browns are 
matched with red, others with green. Blue will be matched with 
violet or green. Red-violet causes much confusion; it is matched 
with red if the red element predominates in the mixture, with violet 
if either violet or blue is in excess, and with green when the red 
and the violet elements are approximately equal, that is, a mixture 
of the two end units of the three unit spectrum gives the middle unit. 
Certain grays may be confused with green, but green is never 
called gray. The latter fact eliminates the possibility of a neutral 
band in the green. If red and blue are combined to form rose and 
the rose is then mixed with green, neutralization results and gray is 
produced for the normal. To the trichromic, however, blue lies in 
the violet and a mixture of red and blue is equivalent to mixing the 
two ends of the spectrum and, according to the laws of color, pro- 
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MEDICAL DEPART ME 1NT 
duces the intermediate unit—green. If now green be added the 
result is not gray as in the normal but merely more green. 
Normal: Red plus blue=rose. Rose plus green=gray. 
Trichromic: Red plus blue=green. Green plus green= 
green. , 
In figure 29 the spectrum in an actual case of trichromatism re- 
ported by Edridge Green is compared with the normal. 
The yellow and orange region was not a distinct color to him 
but a transition from red to green which he thought should be called 
“reddish-green.” The color was exactly the same to him as that of 
a field of red clover in full bloom. His matches were as follows: 
Yellow.—All light colors. Red, orange, greenish-yellow, and 
brown. 
RED 
GREEN 
VIOLET 
RED 
OR 
YELLOW 
GREEN 
BLUE 
VIOLET 
Figure 29.—Trichromic spectrum compared with normal. 
Lavender.—Violet, purple, and gray. 
Red.—Red, crimson, and orange. 
Green.—Green and blue. 
When told he had matched a gray with a lavender he showed 
the heightened simultaneous contrast phenomenon as follows: He 
compared the gray directly with the lavender and found that ths 
gray now looked green. He then compared it with an olive-green 
and said that it now appeared purple. The lavender and the purple 
were placed side by side a few inches apart and the gray laid across 
them. The end resting on the lavender was green, the end resting 
on the green was purple, and the middle portion neutral in shade. 
When tested with lanterns, red and green were named correctly 
under all circumstances, but yellow lights were confused with both 
red and green. 
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142. Dichromic color vision.—The various types of this, the 
most dangerous and the most common form of color-blindness, will 
now be considered; first, one of its rarer forms—simple dichroma- 
tism. Edridge Green states that he had examined 101 cases of 
color-blindness before he found an example of simple dichromatism 
(see fig. 27). The spectrum was of normal length; there was no 
neutral band. Only two colors were seen, yellow and blue, fading 
into one another; the neutral point was at the blue-green junction 
of the hexachromic; the center of the yellow, its most character- 
istic point and the most luminous point of the spectrum at the 
orange-yellow junction; most typical blue in the violet, just beyond 
the blue. Ho did not know that he was color-blind but said that he 
was not interested in color and knew little of it. Questioned as 
to the color of well-known objects, he answered correctly almost 
invariably, but called yellow bricks red; the orange glow of a coal 
fire, yellow in its brightest, and red in its darker part, and green 
where the coals were obscured by white ash; a man’s complexion was 
white shaded with blue or purple, etc. Some of his matches were 
as follows: 
Yellow, yellow-green, and orange. 
Blue-green, gray, and crimson. 
Red, orange, and yellow-brown. 
Rose red, crimson, and purple. 
Deep red, green, and brown. 
Olive green, pure green, brown, and gray. 
Blue-green, blue, purple, pink, and gray. 
Blue, violet, and purple. 
White, with very light shades of pink, green, brown and gray. 
Tested with lights he called a yellow light, red; green obscured by 
a ground glass, yellow; a plain ground glass bulb was white over 
the filament and red elsewhere; on another occasion the same bulb 
was white and green; red obscured by a ground glass was green, etc. 
It is scarcely necessary to state that this individual would be seri- 
ously handicapped in any occupation that required recognition of 
color or that his judgments based on color discrimination would be 
utterly unreliable. In fact, at first glance, it seems that there is no 
order or system in these diverse errors and we would be apt to assume 
that he is totally color-blind and that his matches are mere guesses. 
Such is not the case, however, and we will attempt to show by figure 
30 that he has a color system ,of his own and to discover its rationale. 
In this connection two facts should be borne in mind. First, since 
there are only two colors in this spectrum, a mixture made up of 
color from one of its ends with the proper shade from the other end 
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MEDICAL DEPARTMENT 
will give white or a gray; that is, the two colors are complementary. 
Second, mixtures of spectral colors and mixtures of pigment colors 
are not exactly comparable. Spectral colors are pure colors. A 
quantity of spectral yellow can be represented by the formula 3F2; 
the same quantity of a spectral blue by 3B2. On mixing these light 
rays, ST2+SB2, the result is neutralization of both colors, white or 
gray. Pigment colors are not pure, but reflect waves of different 
lengths. The pigment owes its color to the fact that most of 
the rays of the other colors are absorbed whilst most of the rays of 
the typical color are reflected. A common pigment yellow then would 
have the formula ?>Y2+1G2+1GZ and a pigment blue the formula 
3i?2+26?3+lF1. Now if these two are mixed the yellow absorbs 
the blue rays and the blue absorbs the yellow rays and only the 'ireen 
rays are reflected. (3Y2 +1#2 +1£3) + (3£2+2£3 + IF1) = 1G2+3G3 + 
IF1. In other words, when the spectral colors are mixed the result 
is obtained by addition; when pigment colors are mixed the result 
is obtained by subtraction. 
DARK 
LIGHT 
DARK 
YELLOW 
BLUE 
RED 
OR 
YELLOW 
GREEN 
BLUE 
VIOLET 
Figure 30.—Simple dichromatic spectrum. 
The point of maximum luminosity of the spectrum and the most 
typical yellow are represented by X\ the most characteristic blue 
by Z; the shades of the several colors by the appropriate initial fol- 
lowed by a numeral. The dichromic equivalent of any color in the 
normal spectrum can be approximated by direct comparison of the 
two spectra. Likewise, if the exact composition of a mixed color is 
known the dichromic equivalents can be substituted in the formula 
and the dichromic result can be calculated, for example, R2+B2=rose. 
Dichromic equivalent : F2+.Z?2=gray, or more commonly (due to the 
fact that the blue is less luminous than the red) a shade of blue or 
bluish gray. 
Consider the match, blue-green, gray, and crimson, made by this 
examinee; 
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Hexachromic perception 
Dichromic equivalent 
Blue-green=-B2 + G2 _ _ 
B2+ F8=a shade of gray. 
Gray. 
3 yi + .B®=dark brownish gray. 
Gray 
Crimson=3/2' + V2 
Brown is a shade of dark yellow or orange. In this case a part 
of the yellow is neutralized by the blue and makes gray, so the 
end result is a blend of gray and brown with the brown predominat- 
ing. If the proportions of red and violet in the crimson be varied 
the result for the dichromat may be dark bluish gray or a blue. 
In the match yellow, yellow-green, and orange, the three shades are 
on the same side of the spectrum and would be perceived as three 
values of yellow, Y5, Y7, and Y8. 
This case of simple dichromatism is not an extreme example of 
color-blindness; on the contrary, his color perception is much better 
than that of any of the common types of dichromatism. These types 
arise when the dichromic spectrum is still further impaired by the 
presence of a neutral zone in which no color is perceived. The 
neutral area may occur as a shortening at the red end, as a shortening 
at the violet end, as a band of variable width centering in the green, 
or as combinations of these three. 
In figure 31 types B and C are ordinarily referred to as deuter- 
anopes or green blind, the most common form of dichromatism. 
Types E and F are called protanopes or red blind. This classifi- 
cation is based on the location of the neutral band. It is apparent 
that if the neutral band is located in the green, the defect in per- 
ception of green will be more obvious than the defect in red percep- 
tion, since there is no sensory basis for a judgment respecting green, 
whereas an opinion as to red can be reached on the basis of the 
shades of yellow that are perceived in the red area. In this classifi- 
cation a spectrum shortened at the violet end would be called violet 
blind, but since inability to distinguish between dark violet and black 
is of little practical importance, there are relatively few references 
to this type. This nomenclature, therefore, is based on the location 
of the neutral band and takes no account of the reduction in the 
number of psychophysical units. 
All types of dichromatism will make mistakes similar to those 
made by the simple dichromic case that we have considered. In 
addition to these the dichromat with a shortened spectrum or a 
neutral band will match colors corresponding to the neutral area 
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MEDICAL DEPARTMENT 
with black if the color be dark, with gray if it be more luminous. 
In mixed colors the color from the neutral area does not enter into 
the mixture except as a black or gray. The only effect of its pres- 
ence, therefore, is to produce a darkening of the mixture. Since 
the green is a very luminous area of the spectrum, the neutral band 
in the green appears gray, and these individuals frequently match 
RED 
OR 
YELLOW 
GREEN 
BLUE 
VIOLET 
YELLOW 
BLUE 
YELLOW 
BLUE 
GREEN 
BLU E 
YELLOW 
BLUE 
A Normal hexachromic spectrum. 
B Spectrum of normal length. Neutral band in green. 
C Spectrum shortened at violet end. Neutral band in green. 
D Very wide neutral band. Practically totally color-blind. 
E Spectrum shortened at red end. 
F Spectrum shortened at both ends. Neutral band in green. 
X Indicates point of maximum luminosity. 
Figure 31.—Various types of dichromatic spectra. 
dirty white or white shaded with some color with the green. The 
ends of the spectrum being darker appear black if there is a terminal 
shortening; hence deep, pure reds or violets are matched with black; 
pale shades of pink (red and wdiite) may be put with light grays, 
etc. 
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143. Effect of a shortened red.—A shortening of the red end of 
the spectrum produces defects that are of considerable practical 
importance. The red rays from the extreme left of the spectrum 
are the most penetrating and visible under conditions of obscurity. 
This explains the red appearance of the sun through a smoked glass. 
The other rays are cut off, but the extreme red penetrates the smoked 
glass. We have seen that signal lights, rockets, flares, etc., are com- 
posed of a mixture of rays; hence, if the observer is unable to per- 
ceive the red rays because of a shortened spectrum, the red signal 
light will be invisible at a distance o: under conditions of obscurity; 
on approaching closer to the liglu the perception of green and blue 
rays will cause the light to appear green. 
All colors reflecting rays from the shortened portion appear darker 
than they do to the normal-sighted and are matched with darker colors 
that reflect rays from a point more internal. Hence a dichromat with 
a shortened red will match a red with a darker green. Another com- 
mon mistake is the confusion of pink and blue. If the pink is com- 
posed of red and violet and the red rays come from the shortened por- 
tion of the spectrum, only the violet is perceived and it is seen as a 
blue. The effect, then, is blue mixed with black; that is, a dark blue. 
Hence the common confusion of pink with a darker blue or violet. 
For convenience in reference two tables are now given. The first 
shows the common color confusions of the color blind and indicates 
the diagnostic significance of each. In the second table the result of a 
mixture of spectral colors is found at the intersection of the horizontal 
and vertical columns. It should be remembered that these results do 
not apply in mixtures of pigment colors, since these are compound 
colors and the result is obtained by subtraction. 
Table I.—Diagnostic import of common color confusions 
Table I.—. 
Confusion of 
Significance 
Red and black 
Shortening of red end of spectrum. 
Shortening of violet end of spectrum. 
Neutral band extending into violet. 
A dichromat with neutral band in blue-green. 
A dichromat for whom two colors are comple- 
mentary; that is, when mixed, they form gray. 
Practically diagnostic of dichromatism (2 unit). 
Practically diagnostic of trichromatism (3 unit). 
Practically diagnostic of tetrachromatism (4 unit). 
Violet and black 
Blue and black 
Green and black 
Any mixed color with black 
or gray. 
Red and green 
Green and brown 
Blue and green 
271818°—40 13 
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MEDICAL DEPARTMENT 
Table II.—Results of mixture of primary (spectral) colors 
Violet 
Blue 
Green 
Yellow 
Red 
Red 
Purple 
Rose 
Dull yellow 
Orange 
Red. 
Yellow 
Rose 
White 
Yellow-green 
Yellow. 
Green 
Pale blue 
Blue-green 
Green. 
Blue_ 
Indigo 
Blue. 
Violet 
Violet. 
144. Military significance of color-blindness.—a. General.— 
The various types and degrees of defective color perception give rise 
to a great diversity of color confusion, many of which are of a bizarre 
nature and are apparently inexplicable on superficial examination. 
The color-blind learn to adjust to the defective color perception and 
some cases compensate so well that the defect is not only not apparent 
to their associates but may not even be known to themselves. The dark 
yellow, the bright yellow, and the pale yellow traffic lights of the 
dichromat are, for all practical purposes, as effective as the red, orange, 
and green lights of the normal-sighted. In fact, it seems probable 
that a totally color-blind individual would be able to distinguish the 
traffic lights by the difference in luminosity; if not, a satisfactory ad- 
justment could easily be made on the basis of the relative position of 
the lights; as a last resort he could always follow the traffic. The 
military significance of color-blindness is discussed below. First it 
is considered in relation to the arm that has a very high standard, the 
Air Corps. 
5. Air Corps.—In the physical examination of applicants for flying 
training considerable importance is attached to the detection of color- 
blindness. The reason for the stress placed on the detection of this 
condition in prospective military aviators may be briefly outlined as 
follows: 
(1) Requirements.— (a) Recognition of various luminous signals 
such as field boundary lights, obstruction lights, navigating lights, 
and rocket signals. Distinctive colors are employed to signify various 
vital conditions and prompt comprehension of their portent is 
essential for efficient military flying. 
(h) Recognition of colored flags and other daytime signaling 
devices. 
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(<?) Ability to discriminate between varying conditions of terrain 
by the colors thereof. For example, a field of a certain shade of green 
may indicate a pasture or similar area or short grass whereon a safe 
landing can probably be made. An adjacent flat area of different 
slide of green may indicate a soft boggy marsh where a dangerous 
nose-over or even a bad crash may be anticipated. Again, a brown 
area indicates a plowed field with soft and dangerous surface, and in 
some eases its condition as to saturation with water may even be 
detected by variations in shade. Nearby may be an area of yellowish- 
brown differing very little from the plowed field in color, but with 
sufficient difference to indicate that this is a field of dried grass or 
short dry weeds, which may prove a safe place to put the wheels 
down. In a forced landing on difficult or dangerous terrain, when 
the pilot has but a few seconds to locate the most desirable spot to 
effect a landing, the accuracy of color discrimination is of vital im- 
portance, because once he has chosen a field and has lost altitude in 
reaching it, there is no opportunity to make a second choice. Rain, 
light fog, and cloudy conditions, especially in the early morning or 
toward evening, render color discrimination from an altitude very 
difficult, even for the normal eye; for the individual with inadequate 
color discrimination, such conditions will prove supremely hazardous 
and may easily end in disaster. 
(2) Elimination.—It is believed that the elimination from flying 
training of individuals with moderate degrees of color-blindness 
should be accomplished. The following classes, therefore, should be 
excluded: 
(a) Those who see three or less colors in the spectrum. 
(h) Those who, while being able to perceive four or five colors, 
have the red end of the spectrum shortened to a degree incompati- 
ble with their recognition of a red light at a distance of 2 miles. 
(c) Those who are unable to distinguish between red, green, and 
white lights at the normal distance, through insensitiveness or defect 
of the cerebral retinal apparatus, when the image on the retina is 
diminished in size. 
(d) Those who have difficulty in distinguishing varying shades 
of yellow, orange, and brown. This would include the four-color 
individuals, tetrachromics, and the five-color individuals, the pen- 
trachromics. 
(3) Acceptance.—This leaves only the six-color or hexachromic 
individuals, the so-called normal, who should be accepted for train- 
ing in military aviation. 
(4) Effect of excitement.—It has been found that individuals with 
defective color vision, even almost approaching the normal, when 
195 TM 8-300 
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MEDICAL DEPARTMENT 
subjected to excitement or nervousness, frequently suffer a reduction 
in their color discrimination, reducing them to a lower grade. Thus, 
while the trichromics do not mistake red for green ordinarily, but 
confuse yellow with red and green, they may, when subjected to 
excitement, find their color discrimination reduced to the dichromic 
state and are apt to mistake a red light for a green one or vice versa. 
Persons eliminated in the second class, namely, those with shortening 
of the red end of the spectrum, should be excluded because, while 
they may be able to distinguish red lights of certain shades and of 
sufficient intensity, which they are very close to, may fail to dis- 
tinguish them at a distance or when dim, or if that particular shade 
of red is outside their range. Unfortunately, many signal lights 
are of a shade of red near the end of the spectrum. 
c. Arms.—For the majority of line officers, color-blindness probably 
interferes chiefly in the ability to recognize signal lights, especially at 
a distance or through fog or smoke. The use of maps printed in sev- 
eral colors would be difficult until the defective color perception could 
be compensated for by practice. In various kinds of observation work, 
inability to distinguish tints and shades in the landscape would be a 
serious drawback. Satisfactory artillery observation would probably 
be impossible. The colored markings of the various types of shell, 
grenades, gas shell, etc., would present great difficulties. The officer 
of the Signal Corps would have great difficulty with the colored stripes 
woven into the insulation of wires and cables. 
d. Veterinary Corps.—In order to grade hay, the officer of the Vet- 
erinary Corps must have hexachromic color perception, with good 
shade discrimination. The color shades of hay are just the shades 
that a color-blind individual has trouble with and he would be un- 
able to compensate for the defect. His ability to inspect meat would 
be impaired to some extent, but the possibility of compensatory ad- 
justment would be greater-. 
e. Medical Corps.—Perhaps the most obvious handicap is in the 
chemical laboratory; so many tests depend on color reactions. It 
would be difficult to imagine an individual more seriously handicapped 
for colorimetric work than a dichromat with extensive neutral areas in 
the spectrum. In microscopy, also, with its dependence on differential 
staining, the color-blind find it extremely difficult or impossible to com- 
pensate for the defect. Take the case of a dichromat who describes a 
man’s complexion as “white shaded with purple or blue,” and a child’s 
red lips as a “sort of blue.” One can only speculate on his sensations 
when viewing the rash of scarlatina or measles, the retina through the 
ophthalmoscope, icteric skin, and sclerae. What would he make of 
Koplick’s spots, of a strangulated loop of gut, of the streptococcus 
196 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
144—145 
throat, of the cyanosis of decompensated heart disease, of a furuncle, 
of lupus erythematosus? How accurate would he be in Fehling’s or 
Benedict’s test; in testing for occult blood, for biliuria; in hemoglobin 
estimation; in differential blood counts, or in examining stained slides 
for malarial parasites or Gram negative organisms ? It is undeniable 
that the color-blind compensate surprisingly well in many such situa- 
tions ; nevertheless, they are at a distinct disadvantage as compared to 
individuals with normal color perception. The color-blind medical 
officer can conduct the examination for color-blindness in a mechanical 
way and if he knows the exact nature of his own defect may be able to 
use the wools satisfactorily. The handicap is obvious, however. 
145. Tests of color vision.—a. General.—Of the great number 
of tests that have been devised for the detection of defective color per- 
ception, only three types will be mentioned. Representatives of these 
three types are in common use and it is on these that we rely in our 
examinations. The advantages and limitations of each and the rela- 
tive value of the three are of practical importance. These tests are: 
(1) Self-recording type—exemplified by the Jennings. 
(2) Pseudo-isochromatic plates—exemplified by the Stillings and 
the Ishihara. 
(3) The wool yarn tests—usually the Holmgren or one of its 
numerous variants. 
h. Jennings self-recording test.—The advantages of this test as 
usually recited are: it is compact; the skeins are not exposed to 
fading or soiling; the examinee makes a permanent record of his 
own color perception; it can be given rapidly and is well adapted 
for the processing of large numbers of examinees. The objections 
are that the results are not uniform; the examiner is often in doubt 
as to whether the candidate should be accepted or rejected; normals 
not infrequently make mistakes with the test and many of the color- 
blind pass it without difficulty. As a result of this, some examiners 
adopt a working rule to accept the candidates who do not make more 
than a given number of errors and reject those who do. Such 
practice merely multiplies the imperfections of the test, and if the 
number of allowed errors is considerable, render it practically value- 
less, for it is the kind of mistake and not the number of mistakes 
that is significant. It is obvious that to punch a lavender as a 
shade of the rose test skein might have no significance, whereas if blue 
is punched in rose test or red in the green test we would be correct 
in concluding that the individual is markedly color-blind. To 
consider a lavender a pale shade of rose is a mistake that is made 
by normal hexachromics. To match a pure blue with rose or red 
197 TM 8-300 
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MEDICAL DEPARTMENT 
with green is comparable to mistaking a 5-ton truck for a baby’s 
perambulator, and is conclusive evidence that the individual is color- 
blind. 
The Jennings test, like the Holmgren, uses the shade of green that 
corresponds to the usual location of the neutral band in dichroma- 
tism. The punching of grays, therefore, or the omission of some 
of the greens is highly significant. The rose skein is composed of 
equal values of red and blue. A match with a darker blue would 
indicate a shortened red, etc. 
In the opinion of the writer this test is of limited value. It is 
not so flexible as the Holmgren test and the suitability of some of 
the yarns seems open to question. Some dichromats pass the test 
even under the best conditions. If the test is not carefully given 
and interpreted a considerable proportion will pass it. The test is of 
value when a large number of candidates are to be examined in a 
limited time. The entire group can take the Jennings test in a short 
time, those making a perfect score can be passed without more ado, 
and all of those who make any mistakes can be reexamined by more 
accurate methods. 
c. Pseudo-isochromatic 'plate tests.—These tests, familiar as the 
Ishihara and the Stillings, are by all odds the best tests to use in 
routine examinations. The test can be given quite rapidly and a 
permanent record of the result can easily be made on a typed or 
mimeographed sheet by filling in the numbers as called by the 
examinee, opposite the proper plate designation. The plates should 
be exhibited in irregular order and the plate designation should 
always be concealed from the examinee. These tests are now quite 
well known and the possibility that a poor color sense may be forti- 
fied by an excellent memory should be kept in mind. This is espe- 
cially true in the Ishihara test with its less numerous plates. The 
Stillings test is facilitated if one of the obvious plates (XIII 1 or 
XIII 2) is shown first. Much time is often saved if the examinee 
is told at the beginning of the test that he will be shown a series 
of colored plates, some of which bear numerals, others do not, and 
that he is not to wraste time in looking for numerals that he does 
not see. Plates XIII 1, XII, and XIII 2 are then exhibited in the 
order named, the responses are recorded, and the remaining plates 
are shown in irregular order. 
d. Wool yam test.—This familiar test employs the green and the 
rose test yarns as does the Jennings test. In fact the Jennings is but a 
modification of the Holmgren. In addition a bright red skein is used. 
This gives but little additional information as a rule, unless there is 
considerable shortening of the red. If the wools are used carefully 
198 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
145 
according to directions, most of the dichromats and some of the short- 
ened red cases will be detected. If the examiner is content when the 
examinee puts up one or two skeins for each of the test skeins, the 
test may be almost valueless. Hesitancy, selecting a skein as a match 
and then withdrawing it after direct comparison with the test skein, 
and failure to put up all skeins are all as significant as actual errors 
in matching. An individual with normal color perception does not 
examine a skein of a color different from the test skein carefully and 
critically, turning it over in his hands the while; nor is it necessary 
for him to make a direct comparison to determine that a gray skein is 
not green or that a blue skein is not pink. In such cases the existence 
of defect in color perception is evident; it is only necessary to con- 
tinue the test in order to determine its type and degree. When skeins 
that are of the proper color are not put up with the test skein the 
examiner should at once ask himself why these skeins were omitted. 
The omitted skeins should be noted, all skeins should be mixed to- 
gether, and then one or more of the omitted skeins should be used 
as test skeins. 
The wool test should be regarded not as a set test to be carried out 
according to certain printed instructions but should be considered 
rather as a convenient source of colored materials for the detailed 
investigation of the color perception. If the set contains a large 
number of skeins, a rough though adequate representation of the 
hexachromic spectrum can be outlined and the examinee can be asked 
to make matches from one end to the other; or he can be tested for 
shortened red by laying out a red series for matching, likewise for 
the violet and the green. The problem can then be approached by 
laying out several series of confusion colors for matching, black to 
gray, brown to tan, purples, olive greens, etc. The examinee should 
always be afforded opportunity to make the characteristic confusions. 
Used in this way the wool skeins are of great value and given a fairly 
accurate picture of the state of the color perception. 
e. Conclusion.—It is believed that the Jennings test should be re- 
served for the preliminary survey of large groups; that the pseudo- 
isochromatic plates should be used whenever it is practicable to do so; 
that final decision in doubtful cases or in cases in which there is some 
indication of abnormality should be made on the result obtained with 
the plates; and finally that a set containing a large number of wool 
skeins should be available for the further investigation of some special 
defect or to confirm the results obtained with the plates. With this 
procedure very few cases of defective color perception will escape 
detection. 
199 TM 8-300 
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MEDICAL DEPARTMENT 
146. Examination of color perception.—In an article in Army 
Medical Bulletin No. 34 (January 1936) attention was called to the 
unsatisfactory results that were being obtained in the examination of 
the color perception of candidates for West Point, candidates for com- 
mission, and applicants for appointment as flying cadets. Since that 
time progress has been made in the detection of this defect and a 
study of this subject has been carried out. An effort has been made 
to determine the relative value of the various tests that are in common 
use and it is believed that a method of examination can now be out- 
lined that will meet the requirements of the Medical Department as 
to simplicity, speed of examination, and a reasonable degree of 
reliability. 
During the years 1934 and 1935, 2,355 candidates were examined for 
admission to West Point, Of this number 20 or 0.84 percent were found 
to be defective in color perception. During the year 1936, 1,751 
candidates were examined; of this number 47 or 2.68 percent were dis- 
qualified because of this defect. This indicates that there has been 
considerable improvement in the conduct of this examination and that 
we now accept fewer candidates than formerly who are actually dis- 
qualified because of defective color perception. It is noted, however, 
that this improvement was by no means universal and that there was 
great discrepancy in the findings of the various examining boards and 
that some of these boards still fail to detect this very common and 
obvious defect. This is best illustrated by comparing the findings of 
some of the boards that conducted the examination in March 1936. 
Board number 
Total exam- 
inees 
Cases of de- 
fective color 
perception 
Percentage 
1 — 
7 
2 
28. 56 
2 ... 
16 
0 
3 
22 
0 
4 
23 
2 
8. 19 
5 
25 
0 
6 
26 
3 
11. 43 
7 
28 
2 
7. 14 
8 
32 
0 
9 
51 
3 
5. 88 
10 
' 98 
7 
7. 14 
11 
102 
4 
3. 92 
12 
154 
10 
6. 49 
13 
100 + 
0 
200 NOTES ON EYE, EAR, ETC,, IN AVIATION MEDICINE 
TM 8-300 
146 
Where small numbers are involved, discrepancies are naturally to 
be expected. It may be said that Boards 1, 4, 6, 7, 9, 10, 11, and 12 
probably detected every case of significant impairment of the color 
perception among the candidates examined. It is quite likely, but by 
no means certain, that Boards 2, 3, 5, and 8 did also. As for Board 
13, which examined more than 100 candidates and found them all 
normal as to color perception, the chances are somewhat more than 200 
to 1 that a group of this size selected at random would contain at least 
one individual with defective color perception. Results of this kind 
are usually obtained when the examination of the color perception 
consists of a perfunctory test with the yarns. 
One board that examined a large number of candidates found the 
normal number of cases of color-blindness by use of the pseudo- 
isochromatic plates. These candidates were then put through the yarn 
test and all of them were reported as normal to the yarn test. Such 
results are reminiscent of certain recent nation-wide polls and like 
them justify the assertion that “somebody was wrong.” If a candidate 
reads plate 3 of the Ishihara test as “5” or is unable to read the numbers 
of plate I 2 of the Stillings (17th edition), it can mean only one thing; 
namely, that the shades of red and green in these plates are to him so 
nearly alike that the red numeral does not contrast with the green 
background sufficiently for him to see it. Likewise, obvious difficulty 
in reading these plates—tracing out the numeral with the finger, 
changing the angle of illumination, etc.—are certain indications that 
although the two colors (red and green) are not quite the same the 
contrast between them is much less than to the individual with normal 
color perception. 
Now, if the examinee is unable to distinguish between the shades of 
red and green in these plates he will have the same difficulty in dif- 
ferentiating the same shades of red and green yarns. The woolen 
skeins possess no superior chromatic quality; there is no magic that 
will enable him to distinguish between these shades in the one situation 
when he is unable to do so in the other. In using the yarn test, two 
things are necessary: first, the set must contain a sufficient number of 
skeins of unsaturated reds and greens, the same, or similar shades, as 
those used in the plates, and a large number of confusion skeins; 
second, the examinee must be required to distinguish between them. 
If the test is conducted so as to give him an opportunity to make the 
characteristic mistakes, he will make them. 
Such discrepancy in the results of the examination with the plates 
and with the yarns is apparently due to two causes: first, improper 
conduct of the examination; second, a set of yarns that is inadequate 
for the purpose. Some sets of yarns are so abbreviated that only the 
201 TM 8-300 
146 
MEDICAL DEPARTMENT 
well marked cases of dicliromatism can be demonstrated with them. 
This phase of the problem will be discussed in more detail when we 
consider the tests themselves. 
The Surgeon General’s Office frequently receives reports of physi- 
cal examination in which it is set forth that the examinee fails to 
pass the Stillings or the Ishihara test, but makes no errors when 
tested with the Holmgren (yarn) test. Often this supposed ability 
to pass the yarn test is made the basis for a recommendation for 
waiver. Inquiries have been received as to the “official test” of the 
color perception and whether an examinee can be considered normal 
when he passes the yarn test but fails to read the plates correctly. 
When this proposition is stated in clear terms the answer is at 
once evident. The question of color-blindness, like other disqualify- 
ing defects, is a question of fact and not a matter of being able, under 
certain abnormal conditions, to get through a particular test. Any 
material impairment of the ability to perceive red or green or violet 
disqualifies under the regulations. The particular method employed 
for the detection of the defect is of no special importance. It is 
important that the defect be detected. In the examination of the 
color perception, as in all other examinations, the method of choice 
is the one that gives the most accurate results—that reveals the de- 
fect in the greatest number of cases and fails to reveal it in the 
smallest number of cases. 
Consider the case of the examinee who fails when examined by 
the Ishihara test, but is said to make no errors with the yarns. This 
anomalous finding, as well as some of the other problems that arise 
in the examination of the color perception, is best illustrated bv 
reporting an actual case in which the Holmgren yarn test was first 
used incorrectly, with the usual result that the chromatic defect was 
not demonstrated. On reexamination some weeks later with the 
Holmgren test, employing the proper technique, the impairment of 
the color perception was at once evident. In the period intervening 
between the two examinations, however, the examinee had familiar- 
ized himself with the Ishihara and the Stillings plates, with results 
which he considered highly satisfactory, but which to the experienced 
examiner merely served to confirm the known fact that there was a 
red-green deficiency and revealed the lengths to which the candidate 
would go in order to conceal it. 
202 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
147 
147. First examinnation.—a. Ishihara plates 
Plate number 
Reading 
1. .. . ___ ... 
12. 
3. 
5. 
2. 
21. 
No numeral. 
No numeral. 
No numeral. 
No numeral. 
5. 
2. 
26 (hesitant on the 6). 
42 (hesitant on the 2). 
Traces blue lines—hesitant. 
Cannot trace. 
Traces blue line easily. 
2. - -- - - 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 --- - 
13 . -- 
14 
15 - ... 
16 
b. Holmgren test (improperly given). 
Examiner: [Spreads yam on table; holds up green test skein.] What 
color is that? 
Candidate: Green. 
Examiner: All right, pick out some greens. 
[Candidate rapidly selects six well-saturated green skeins and 
puts them with test skein.] 
Examiner: [Picks up red test skein.] What color is that? 
Candidate: Red. 
Examiner: All right, pick out some reds. 
[Candidate rapidly selects four typical reds.] 
Examiner: [Exhibiting rose skein.] What color is that? 
Candidate: [Handling skein.] I don’t know much about the names 
of colors. It is a reddish purple or lavender. It has 
blue in it and some pink. I guess I am color ignorant, 
but I am not color-blind. I can see them all right, even 
if I don’t know all of the names. 
Examiner: All right, pick out some skeins that are the same color. 
[Candidate somewhat hesitatingly selects one dark red and 
two rose skeins.] 
Examiner: [Exhibits several blues and yellows, which are correctly 
named.] Have you ever had any trouble in distinguish- 
ing colors? 
203 TK 8-300 
147-148 
MEDICAL DEPARTMENT 
Candidate: No, never, I don’t know the names of a lot of different 
shades, but I can see them all right. I drive a car and 
I never have any trouble with the traffic lights. 
The examiner reports as follows: “Fails to read the Ishihara plates 
correctly, but is normal to the yarn test. Not a case of true color- 
blindness, but is color ignorant. No clinical significance.” “Does he 
meet physical requirements?” “Yes.” 
Note.—The set of yarns used was an adequate one and would have revealed 
the defects under proper conditions. 
When a candidate is examined in this manner, it is to be expected 
that he will select those skeins that seem to him to have a definite 
color and that he will avoid all doubtful skeins. There are very few 
dichromats who cannot identify some reds and greens. They per- 
ceive both red and green as shades of yellow, but have little difficulty 
in distinguishing well-saturated reds and greens by the difference in 
brightness. As a matter of fact, such methods of examination have 
resulted in the detection of only about one-sixth of the candidates 
who have significant abnormality of color perception. 
148. Second examination (three weeks later).—a. Ishihara 
plates.— (1) Test.—Plates 1, 2, 3, 4, and 5 were read correctly, with 
slight hesitation in the case of plate 5. Plates 6, T, 8, and 9 were shown 
in irregular order. All were read correctly, but with obvious difficulty; 
the book was held at varying distances from the eyes and the angle 
at which it was held was changed. It was plain that the numerals on 
these plates afforded no effective contrast with the background. 
With plates 10 and 11 there was a rather elaborate show of close 
scrutiny, but after an interval the candidate stated that he could see 
nothing in the plates. Inability to read these plates is not compatible 
with difficulty in reading plates 6, 7, 8, and 9. In addition, it was 
known that when first examined the candidate had read plates 10 
and 11 without difficulty. Plates 12 and 13 were read correctly 
without hesitation. He was then asked which of the two numerals 
in each of these plates stood out more clearly. This was apparently 
a difficult question, for he had difficulty in understanding it. He 
then made a show of scrutinizing the plates while he thought the 
matter over. He finally stated that the first digit (2) in plate 12 
and the second digit (also a 2) in plate 13 were more distinct than 
the others. Plates 14 and 15 could not be traced satisfactorily, 
though by close application he was able to follow the line slowly for 
short distances. In plate 15 he tended to jump across the inter- 
vening spaces where the loops came close together. In plate 16 he 
made a show of attempting to follow the irregular reddish lines. 
204 TM 8-300 
148 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
(He had traced the pale blue line with ease and confidence at the 
first examination.) 
(2) Comment.—Reading of the first five plates correctly seems to 
indicate normal color perception, but the difficulty in reading plates 
6, 7, 8, and 9 shows that the ability to distinguish between red and 
green is much impaired. This is confirmed by the inability to trace 
the line in plates 14 and 15 easily and rapidly. The alleged inability 
to read plates 10 and 11 and to trace plate 16 is incompatible with 
the difficulty manifested in reading plates 6, 7, 8, and 9 and in tracing 
plates 14 and 15. Finally, there is the discrepancy in his statement 
about the relative distinctness of the digits in plates 12 and 13. 
If the candidate reads plates 12 and 13 correctly he should always 
be questioned as to the relative distinctness of the two numerals on 
each of these plates. Often the manner of reading will give a clue. 
The protanope sees the first digit as a shade of black; that is, gray. 
It may match the background so perfectly that it is invisible; there 
may be enough difference so that he can make it out. He sees the 
second digit as a darker blue or purple, but it affords an effective 
contrast; hence is read without difficulty. The deuteranope sees 
the first digit as a shade of yellowish brown, a fairly strong con- 
trast to the background. The second digit is made up of equal 
values of red and blue, rose to the normal. These shades come from 
opposite sides of the dichromic spectrum, they are to him comple- 
mentary colors and when combined produce not rose but neutrality or 
gray. Hence there is little or no contrast to the background; hence 
the deuteranope sees the second digit with difficulty, if at all. 
(3) Conclusion.—Candidate is an individual with defective color 
perception who has studied the plates and who, in attempting to 
conceal his defect, does not hesitate to make untruthful statements 
about what he actually §ees. 
b. /Stillings 'plates.—(1) Test.—Most of the plates were read cor- 
rectly, though there were errors as between 3 and 8, 3 and 5,7 and 9, etc. 
A few major errors were made, and two and one-half plates could not 
be made out at all. All of the plates were read with great difficulty 
after the manner of one who is trying to solve a difficult puzzle. 
No plate involving a discrimination between red and green was read 
with ease and certainty. In some of these the reading was made 
only after the numerals had been laboriously traced out with the 
finger. The plates that require a discrimination between blue and 
green were read with greater facility than the red-green, the red- 
brown, and the green-brown ones. The ability to read these blue- 
green plates seems to equal that of many normals. 
205 TM 8-300 
148 
MEDICAL DEPARTMENT 
(2) Comment.—It is evident that the shades of red and of green 
used in these plates are so nearly alike to the examinee that there is 
no effective contrast and that he probably could not read these plates 
at all if he had not previously studied them. It is as though a 
normal individual attempted to visualize a numeral delineated in 
light gray against a gray background that is only slightly darker. 
c. Holmgren yarn test (properly conducted).—(1) Test.—The 
yarns are spread on a table that is covered with a sheet. The examinee 
is seated at the table. The yarns are illuminated by diffused daylight 
(not sunlight) that comes from the windows behind and to the left of 
the examinee. The yarn box is placed at the right and the top of the 
box at the left of the yarns. The red test skein is placed against a piece 
of cardboard at the other side of the table, directly opposite the 
examinee. The distance from the examinee is 3y2 feet. The test skein 
is so placed that both it and the small skeins are not in the examinee’s 
visual field at the same time. He must raise his head slightly to see 
the test skein and must look down to see the heap of small skeins. To 
bring them both into his visual field he must take up a small skein and 
extend his arm slightly. Only by doing this can he make matches by 
direct comparison, and it is important for the examiner to know if it is 
necessary for him to resort to direct comparison in order to make a 
decision. The normal individual does not need to bring a gray skein 
or a brown skein into the same visual field with the test skein in order 
to decide that it is not red. The color-blind often find this necessary. 
If it is done it is positive evidence of defective color perception, 
whether the skein is properly classified in the end or not. 
Examiner: \Takes up a skein from the tabled] I want you to take 
up these skeins one by one and look at them. All skeins 
that are a shade of that color [points to test skein] put in 
this box on your right. All skeins that are not a shade 
of that color put in this box on your left. 
Candidate: Do you want me to put everything that has red in it in this 
box ? I am not sure that I know what you mean by shades 
of colors. 
Examiner: Name some colors for me. 
Candidate: Yellow, blue, red. 
Examiner: Now, what do you mean by a shade or tint of yellow or 
blue? How do you refer to shades of a color? Do you 
refer to them as rough or smooth, as sweet or bitter, as 
large or small? 
Candidate: Dark or light. 
Examiner: Then you would refer to shades of blue as dark blue, 
medium blue, light blue, and so forth ? 
206 TM 8-300 
148 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
Candidate: Yes. 
Examiner: But they are all blue ? 
Candidate: Yes. 
Examiner: All right. Put in this box all shades of that color. Put all 
shades of all other colors in that box. 
Candidate: But suppose that a skein has both blue and green in it, 
how will I know whether to call it blue or green? 
Examiner: Look at it and make up your mind whether it should be 
called a blue or a green and place it accordingly. After 
all, fine distinctions of shade are matters of opinion and 
there is no reason to think that your opinion is not as 
good as anybody’s. This test is not designed to trick you, 
but merely to find out whether you have the normal ability 
to perceive colors. We are not interested in your ability to 
name or to classify shades and tints, but in your ability to 
perceive colors. So, put all shades of that color (point- 
ing to red test skein) in this box and all shades of all other 
colors in that box. Now, let’s get started. 
(2) Comment.—This rather tedious colloquy is fairly characteristic 
of the questions that some candidates ask. All of them do not ask so 
many, some ask more. Numerous questions and objections are raised 
by two classes of examinees. First, those who are defective in color 
perception. They ask questions in an attempt to establish some crite- 
rion other than their own sensations by which a decision can be made. 
Second, the overconscientious introvert type. Their sense of color 
may be above the average, but in this as in other matters they want 
specific directions, which they will then follow with exactitude down 
to the most minute detail. It is believed that the examiner’s part in 
this discussion is of some importance. For example, if the examiner 
gives an affirmative answer to the question, “Do you want me to put 
everything that has red in it in this box?” the protanope will have 
an alibi when he selects dark purples as matches for the rose or the 
red test skein. Such instructions will sometimes lead the intellectual 
and overconscientious examinee into the same error, not because of 
defective color perception, but because of his judgment as to the com- 
position of the color in question. The examiner should avoid, so far 
as possible, the mention of color names or reference to their composi- 
tion, and should limit himself to directions to, “Put all shades of that 
color in this box and all shades of all other colors in that box.” The 
meaning of the terms “shade” or “tint” should, of course, be made clear 
if they are not understood. 
207 TM 8-300 
148 
MEDICAL DEPARTMENT 
(3) The candidate proceeds with the sorting. Results as follows: 
Red test skein; 
Number of red skeins selected—21. 
Number of red skeins omitted—none. 
Number of other colors selected—1 bluish gray. 
Manner of performance—confident and fairly rapid. 
Matches by direct comparison—none. 
(4) The examiner checks and records the results. He notes the 
gray skein selected as a red, but gives no indication of his opinion of 
any selection. The skeins are mixed and spread on the table; the 
examiner replaces the red test skein with the green test skein and says, 
"Put all shades of that color in this box and put all shades of all other 
colors in that box.” 
Green test skein: 
Number of green skeins selected—26. 
Number of green skeins omitted—none. 
Number of other colors selected—1 light brown. 
Manner of performance—confident and fairly rapid. 
Matches by direct comparison—none. 
(5) The examiner records the results, makes a mental note of the 
erroneously selected brown skein, but gives no indication of his im- 
pression. The skeins are again mixed and spread on the table, the 
green test skein is replaced with the rose and the directions are re- 
peated. The candidate leans forward and looks at the test skein in- 
tently for a moment and then proceeds with the sorting. He works 
rapidly, but shows a tendency first to pick out yellows, well saturated 
greens, and bright blues and put them into the box on his left. He 
picks up a gray skein that has no vestige of color; he turns it in his 
hand; he raises the hand, extends the arm, and looks over the gray 
skein at the test skein. He decides that it is not rose and tosses it 
into the box on his left. He takes up a light gray and tosses this into 
the right hand box as a shade of rose without direct comparison. Final 
sorting as follows: 
Number of rose skeins selected—24. 
Number of rose skeins omitted—none. 
Other skeins selected—4 (1 pale lavender, 1 light gray, 2 steel 
gray). 
Manner of performance—fairly confident. 
Matches by direct comparison—3 (2 gray, 1 lavender). 
(6) The procedure is repeated, the light brown skein that was se- 
lected as a green is used as a test skein and the candidate is again in- 
structed to sort the skeins. 
Number of brown skeins selected—34. 
208 TM 8-300 
148 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
Number of brown skeins omitted—3. 
Number of other colors selected—none. 
Manner of performance—confident. 
This result was rather surprising, as it had been expected that he would 
select some pale greens as matches for the tan. 
Note.—The more usual result is that obtained in the recent examination of a 
deuteranope who selected a gray skein a: a match for the green test skein. This 
gray was noted and after the sorting had been completed and the skeins mixed 
this gray was put up as the test jkein. The examinee studied it for a moment 
and then remarked, “Anothe; greei eh!” He then proceeded to select most of 
the greens and all of the grays that were about the same shade. No more con- 
clusive evidence of the defe t in jolor perception could have been given. 
(7) The skeins are mixed, one >f the gray skeins that was selected 
as a rose is put up as a test skein, and the instructions are repeated. 
Number of gray skeins selected—1. 
Number of gray skeins omitted—I. 
Other colors selected—i (1 light blue, 1 bluish white, 1 light 
pink, 1 pale lavender). 
Manner of performance—confident. 
Selections by direct comparison—none. 
Examiner: [Spreads yams on table.'] I want you to cast your eyes 
over these yarns and pick out for me the three skeins 
that are the most brightly colored. It makes no differ- 
ence what the color is or whether they are all the same 
color or not. Just get the three that seem to stand out 
most distinctly. 
Candidate: Selects (1) bright yellow; (2) bright orange; (3) dark 
red. 
(8) Comment.—(1) and (2) can fairly be considered as among the 
brightest colored skeins on the table, but there are at least 12 skeins 
that are more conspicuous than (3), the well saturated red. It has 
been observed that in this simple test the color-blind tend to select 
yellows and blues rather than reds or greens, and that when reds 
or greens are selected they are the darker, well-saturated shades; 
for example, this candidate passed over four vivid reds that were 
conspicuously placed to select a dark, inconspicuous shade. 
(9) Impression.—A very mild degree of deuteranopia or red-green 
color-blindness of the green type. This is based on the following 
consideration: 
(a) Difficulty in reading and in tracing plates involving red-green 
discrimination shows that to him there is but little difference in the 
shades of red and green used in the plates. He probably sees them 
271818°—40 14 
209 TM 8-300 
148 
MEDICAL DEPARTMENT 
as two shades of brownish yellow. This is confirmed by the match- 
ing of a brown skein with the green. 
(&) A mixture of red and blue that makes rose for the normal 
individual is gray to him or nearly so. In other words, red and blue 
are complementary colors for him. This is evidenced by the indis- 
tinctness of the rose-colored numerals against a gray background 
in Ishihara plates 12 and 13 and by matching gray skeins with rose 
in the Holmgren test. 
(10) In view of the fact that color blindness disqualifies under the 
regulations and the disqualification includes the mild as well as the 
pronounced cases, the examiner properly reported that he did not 
meet the prescribed standards. It was thought, however, that the 
defect in this candidate was of such mild degree that it was devoid 
of any practical significance and could not possibly interfere with 
the performance of any military duty. It became necessary to revise 
this appraisal after further investigation. 
(11) An opportunity was found to give this candidate a practical 
test; that is, to test his ability to distinguish standard signals under 
service conditions. The test was carried out as follows: A night 
was selected when the conditions for visibility were good. The can- 
didate was posted at a suitable point with three individuals of 
normal color perception as controls. Nine shots of various colors 
were fired from a Very pistol from a point y2 mile distant. The 
candidate and each of the controls made a record of the color of the 
shots. The distance was then increased to 1 mile and the procedure 
was repeated. 
Distance % mile 
Shots fired 
Candidate’s 
reading 
Shots fired 
Candidate’s 
reading 
Red. 
Red 
Red. 
White. 
White 
White. 
White. 
White. _ 
White. 
Green. 
Green 
Green. 
Red 
Red. 
Distance 1 mile 
Shots fired 
Candidate’s 
reading 
Shots fired 
Candidate’s 
reading 
Green 
Green, 
Red 
Red. 
Red 
Red. 
Red 
Red. 
Green 
Green. 
Green 
Green. 
White 
White. 
White. 
White. 
White 
Green. 
210 TM 8-300 
148 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
(12) This candidate had been passed as having normal color per- 
ception by more than one examiner. Even after the defect was de- 
tected by the use of the plates, another examiner who had been 
informed of the nature and the degree of the defect failed to demon- 
strate it with the Ishihara and the Holmgren tests, certified him as 
normal with respect to color perception, and stated that he met the 
physical requirements. When the Holmgren test was properly con- 
ducted, however, the defect was at once evident and subsequent test- 
ing under service conditions showed that this individual cannot al- 
ways distinguish a green light from a white light or a white light 
from a green one when he is deprived of all secondary criteria for 
a judgment and is forced to make his decision solely on the basis 
of the chromatic quality of the lights in question. One is forced 
to conclude that he is incompetent to make any decision of conse- 
quence that depends on a recognition of white or green Very flares. 
The three controls recorded the shots correctly in each instance. 
(13) A second case of deuteranopia in which the gross discrepancy 
of findings on successive examinations was the cause of some em- 
barrassment is quoted in order to illustrate another error of tech- 
nique in the conduct of the Holmgren test that may vitiate the 
results. This candidate on preliminary examination read the Ishi- 
hara plates in the manner characteristic of the green blind. He was 
informed that he was disqualified because of color-blindness. Sev- 
eral months later he asked for another preliminary examination and 
then read the Ishihara and the Stillings plates fairly well. His per- 
formance was quite similar to that of the first case referred to. The 
hesitancy in reading plates 6, 7, 8, and 9- and the difficulty expe- 
rienced in tracing plates 14 and 15 led to careful checking with the 
yarns, with the following results: 
Red test skein. 
Selected—18. 
Omitted—2. 
Included—1 bright orange yellow and 1 paler orange yellow. 
Performance—confident. 
Direct comparisons—none. 
Rose test skein. 
Selected—23. 
Omitted—2, 
Included—3 grays, 2 reds, 2 dark blues, 1 dark purple. 
Performance—hesitant. 
Direct comparisons—with gray and with dark blue and 
purple. 
211 TM 8-300 
119 
MEDICAL, DEPARTMENT 
Green test skein. 
Selected—5. 
Omitted—21. 
Included—none. 
Performance—hesitant. 
Direct comparisons—none. 
Gray test skein. 
Selected—7. 
Omitted—3. 
Included—5 rose. 
Performance—very hesitant. 
Direct comparisons—many with gray and rose. 
(14) The candidate then secured a third examination elsewhere. 
He read the plates in a manner that was apparently satisfactory to 
the examiner, but since he had been warned that the candidate was 
definitely color-blind he put him through the Holmgren test as well. 
This was conducted in the following manner: The yarns were spread 
on a small table in bright light; direct sunlight fell on the corner of 
the table, but not on the yarns. The three test skeins—red, rose, and 
green—were laid side by side at the edge of the heap of yarns and 
instructions were given to sort the yarns, one by one, into four piles, 
one for each test skein and one for the remaining yarns. The candi- 
date stood beside the table. When he picked up a skein and held it 
in his hand, it and the three test skeins were in the central visual 
field in very strong light. He then had to decide by direct com- 
parison whether a given skein looked more like the red, the green, 
or the rose test skein, or whether it was some other color (yellow or 
blue) or whether it had no color at all. Since his ability to see 
yellow and blue is not impaired, it is not surprising that he made 
but few errors and that they were minor ones. The examiner was 
unable to concur in the diagnosis of deuteranopia and expressed the 
opinion that at most there was only a slight weakness of green 
perception that was of no practical importance. 
(15) Other cases could be cited to show that there are many possi- 
bilities for error in the conduct of the examination of the color 
perception. Unfortunately, an error in technique that may seem to 
be of no consequence may render the examination completely value- 
less. The surest way to avoid such errors is to acquire at least an 
elementary knowledge of the two main types of defective color per- 
ception which concern the military service. These are dichromic 
color perception or red-green color-blindness, subdivided into prota- 
nopia or red-blindness and deuteranopia or green-blindness; and 
trichromic color perception, also called tritanopia and anomalous 
212 NOTES OX EYE, EAR, ETC., IX AVIATION MEDICINE 
TM 8-300 
148-150 
trichromatism. Both of these disqualify for the military service. 
The latter is much more difficult to detect than the former, especially 
when the examinee has familiarized himself with the test plates. It 
is believed, however, that the vast majority of both types can be 
detected by the use of the common tests, if they are carefully con- 
ducted by an observant examiner who has given some thought to the 
matter. 
149. Ishihara test.—a. This test is very effective, provided the 
examinee has not had an opportunity to study the plates. Unfortu- 
nately, many of them have done so; hence it is necessary for the 
examiner to have a very low threshold of suspicion, especially in 
“reexamination” cases, when using this test. Familiarity with the 
test is to be suspected when: 
(1) The plates with alternative readings (plates 2, 3, 4, 5) are 
read with greater facility than are the plates that have only one 
reading (plates 6, 7, 8, 9). 
(2) Greater difficulty is experienced in tracing the line in plates 
14 and 15 than in reading any of the plates. 
(3) There is any indication that the numerals do not stand out in 
bold relief as they do to the normal. 
b. The Ishihara test can be conducted quite rapidly, IV2 to 2 minutes 
for an alert, intelligent normal, and for this reason is very useful 
when a large number of candidates are to be examined. It is be- 
lieved that this test will disclose practically all cases of significant 
abnormality of the color perception and that it will never lead to a 
diagnosis of color-blindness in a normal individual or in one who is 
not disqualified by regulations. A new seventh edition of this test 
is now available in two forms, the reduced and the complete edition. 
No new principle is involved. The plates are similar to those of the 
sixth edition. One, the abbreviated edition, contains 11 plates and 
is not as good as the sixth edition; the other contains 32 plates and 
has the advantage that it has more plates to be traced end that the 
lines are more tortuous—a very difficult problem for tne examinee 
who can see but little difference between the colors employed. 
150. Stillings test.—Several editions of this test are in use. 
When detailed report is made of the results of this test the edition 
used should be stated. The seventeenth edition contains 32 plates, 
most of them double ones. The plates are arranged in groups that 
are designed to demonstrate the various types of defective color per- 
ception. Hence, if the examinee’s readings are recorded, it is possible 
to analyze the results and make a reasonably accurate differential 
diagnosis. Due to the number of the plates and the fact that there 
213 TM 8-300 
150—153 
MEDICAL DEPARTMENT 
are no alternative readings for the color-blind, this test cannot be 
given as quickly as the Ishihara test. On the other hand, the indi- 
vidual with defective color perception has much more difficulty in 
familiarizing himself with these plates, and even if he has done so, 
the results of his study of them can be largely nullified by the simple 
expedient of turning the book upside down. Many normals have 
some difficulty in reading the plates that involve discrimination be- 
tween red and brown, red and orange, and green and blue, (Groups 
VI, VII, IX, XI of seventeenth edition). The test is considered 
highly effective in determining the true state of color perception, 
but there seems to be no doubt that the milder types of dichromatism 
and the anomalous trichromats can improve their reading materially 
by familiarizing themselves with the test before they come up for 
the final examination. 
151. Jennings test.—Some normals make errors in this test and 
many of the color-blind go through it without making a mistake. For 
this reason, the results are not considered conclusive unless confirmed 
by some other test, except in those cases where the examinee makes 
errors that are characteristic of the color-blind, such as punching red, 
brown, or gray for green; green, gray, blue, or purple for rose; or 
failure to punch green and rose. Any of these errors are conclusive 
evidence of a disqualifying defect of the color perception. It is 
necessary to reverse the opinion expressed in Army Medical Bulletin 
Xo. 34 that the Jennings test is suitable for the processing of large 
numbers of candidates. Further experience shows that it is not 
reliable enough for this purpose and that it is more time-consuming 
than either the Ishihara or the Stillings. It is believed, however, 
that the test has a certain field of usefulness in that it can be conducted 
in a mechanical manner, and in some apparently borderline cases it 
may afford confirmatory evidence of color-blindness that is surpris- 
ing in its completeness and its finality. It should be reiterated that 
a negative Jennings test is of little value in determining the quali- 
fications of a candidate and that significance can be attached to the 
results only when it is positive; that is, when errors characteristic of 
the color-blind are made. 
152. Holmgren test.—a. This is regarded as the basic simple 
test, for it is possible to obtain more accurate information about the 
state of the color perception with the yarns than by any other simple 
method. It is believed that this test if conducted carefully and under- 
standingly will reveal all defects of the color perception that are dis- 
qualifying for the military service, and that no individual who is 
214 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-3UU 
152 
not actually disqualified will fail to pass the test with ease. From 
a practical point of view, however, the test has certain limitations 
that largely destroy its usefulness. 
(1) It is tedious and time-consuming. An adequate examination 
of an alert individual of normal color perception can be done in about 
10 minutes. The color-blind case, especially if mild in degree, may 
require one-half hour or even more. This fact alone makes the test 
unsuitable for use in the examination of a considerable number of can- 
didates. 
(2) In addition to the matter of time, the test does not lend itself 
to a routine technique of administration as do the plates, and minor 
variations in technique often produce great discrepancy in the results. 
Such errors, apparently inconsequential, but actually decisive in their 
effects, are quite apt to be made unless the examiner has some special 
knowledge of the common types of defective color perception. 
(3) Many of the sets of yarns supplied contain so few skeins and 
so few of the paler shades apt to be confused by the color-blind that 
they are practically worthless in the detection of the trichromats and 
the milder cases of dichromatism. Even a careful examination with 
one of these abbreviated sets may reveal only the well marked dichro- 
mats (red-green blind). The haphazard use of these inadequate sets 
of yarns is sufficient to account for the fact that in the past we have 
detected only one in each six color-blind individuals examined. 
h. One of these inadequate sets of skeins was recently examined. 
There are no directions with it. It is made up of 51 skeins, distrib- 
uted as follows; 
Green 13 
Red- 4 
Rose 6 
Blue 5 
Orange and yellow 11 
Lavender 2 
Confusion skeins (gray, brown, etc.) 10 
Total 51 
This set is not only faulty because of the small number of skeins, but 
also because most of the skeins are the well saturated shades with 
which the color-blind have the least difficulty. In contrast to this 
set is a set of 125 skeins that has been used at every opportunity 
during the past year to examine individuals who have failed to pass 
the Ishihara or the Stillings test. In every case the results of the 
plate tests have been confirmed. Some of them made few errors, but 
215 TM 8-!i00 
15&-153 
MEDICAL DEPARTMENT 
all of them made some errors that were characteristic of defective 
color perception. This set is composed of the following skeins: 
Red 15 
Green 27 
Rose _ 10 
Blue-purple 13 
Orange-yellow 13 
Gray 10 
Brown, tan, etc 37 
Total 125 
This set contains too few gray skeins and a disproportionate number 
of the brown confusion skeins, but even with this obvious defect it has 
proved to be reliable enough for all ordinary purposes. 
c. It is believed advisable before using a set of skeins to examine 
it critically to determine whether it is suitable for the purpose, for 
there is little use in using a set that in all probability will not give 
accurate results. It appears that a good set should contain about 
100 skeins. There should be a good assortment of green, of rose, and 
of red, which must include the lighter shades. The gray skeins should 
range from very pale gray to very dark gray. It is much better if 
the gray skeins are not tinted with color; that is, they should be pure 
neutrals. It is essential that there be such a variety of shades of the 
different colors that the color-blind individual will find at least some 
skeins that he is unable to classify. If the set fulfills this require- 
ment, it is necessary only to require the examinee to examine the 
skeins one at a time and reach a conclusion as to its chromatic quality 
purely on the basis of his own sensations and without the aid of any 
secondary criteria. 
153. Proposed method of examination.—Put the candidates 
through either the Ishihara or the Stillings test. Display plates 6, 
7, 8, and 9 of the Ishihara in irregular order, and note particularly 
any difference in the facility with which the two types of plates are 
read and any discrepancy between the reading of the numeral plates 
and the tracing of the line plates. Display the Stillings plates in 
irregular order and show some of them upside down. If the read- 
ings in either of these tests are characteristic of the color-blind, a 
diagnosis of color-blindness is warranted without further examina- 
tion and the candidate should be disqualified. If the plates are 
read in the same way with the same facility that the normal read 
them, appropriate entry (“Normal Ishihara; Normal Stillings”) 
is made on the form and the candidate is reported as physically 
qualified. If there is any evidence that the plates do not afford 
216 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
153-154 
the normal contrast to the candidate, or if because of the discrepan- 
cies previously referred to it seems probable that the candidate has 
studied the plates, a detailed record is made of the readings and the 
examination is continued with the Holmgren test; a detailed record 
of the results is made and the report is forwarded, with appropri- 
ate recommendations, for the action of the War Department. 
An attempt has been made to draw up detailed instructions for 
the conduct of the Ishihara and the Holmgren tests and to devise 
forms for the reporting of the results. The ideas expressed have 
been derived from a number of sources and revisions have been 
made in the light of knowledge gained from further experience. 
No claim of finality is made for these instructions; on the contrary, 
it is anticipated that further revisions will be necessary. They are 
reproduced here in the hope that they may prove helpful to some 
examiners and that they may serve as a basis for criticism and for 
suggestions for improvement. It would seem highly desirable to 
devise an effective and uniform system for the examination of the 
color perception and for the reporting of the results, and thereby 
bring some order and clarity into a situation that at present is con- 
fused and obscure. 
154. Directions for use of Ishihara test plates.—a. The book 
of colored plates consists of a series of 16 plates (32 in last edition), 
most of which contain numbers of uniform size and shading, placed 
in the center or to one side of the center of the circles. Plate 1, 
containing the figure 12, which is visible to the color-blind as well 
as to those of normal color sense, shows the size and shading of the 
other numbers. 
h. The candidate is considered to have failed on this test if he 
does not read the plates in approximately the same way as a person 
of normal color sense. The examination for color sense is to be 
conducted only by medical officers found to have normal color sense. 
c. To a person of defective color sense, some of the plates seem 
to show numbers different from those seen by a person of normal 
color sense, or to show no number at all. Others of the plates 
appear to contain no number to a person with normal color sense, 
while the color-blind will read numbers in these plates. 
d. The test is made by the examiner holding the book on a table, 
or in his hands, in good, diffused daylight, between 20 and 30 inches 
from the eyes of the candidate being tested. The test is made on 
both eyes together, since for practical purposes defective color sense 
may be considered as always binocular. The candidate is first asked 
217 TM 8-300 
154 
MEDICAL DEPARTMENT 
to read the figure on plate 1 and is told that the other figures which 
he is expected to read (plates 2 to 13) are of the same size and type 
of shading. The other plates, 2 to 13, are then shown to him in turn, 
allowing him from 2 to 5 seconds to read aloud the figure on each 
plate—2 seconds for the more alert and intelligent and for those 
who may have familiarized themselves with the plates previously, 
and 5 seconds for those who are slower to comprehend. The same 
time is allowed for plates on which the normal eye can see no fig- 
ures as for the others, and the examiner is not to signify by tone 
or motion whether the candidate has read a plate correctly or not. 
Plates 14, 15, and 16 (see e below) may take longer than 5 seconds 
apiece to explain and trace, but for all the plates the ease with 
which the plates are read is to be taken into consideration as well 
as the final answer; thus, some individuals of normal color sense 
may make out a well shaped 5 and a similar 2 on plates 10 and 11, 
respectively, but less easily than the figures on the other plates. 
e. No numbers are to be read on the three plates, 14, 15, and 16, 
but they are to be used by having the candidates try to trace a curv- 
ing line across each plate from the X at the left-hand margin to 
the X at the right-hand margin, each line being more or less of the 
same color. These lines should be traced without pressing on the 
plate, with the rounded wooden end of a penholder, a rounded glass 
rod, a fine dry camel’s hair brush, or other instrument which will 
not mark the plate. The color-blind may trace a line different from 
the line traced by the normal, trace no line at all where a line is 
visible to the normal eye, or trace a line where no continuous line 
from one X to the other X is seen at all by the normal eye. The 
examiner is not to name the color of the line to the candidate, but 
may ask the candidate the color of the line. Before each test care 
should be taken to see that no telltale line has been left on any of 
these three plates from previous use. 
/. In every case where color perception is found deficient, the 
results of the test will be recorded on the attached or a similar form, 
the figures as read by the candidate being placed after the number 
of each plate, a dash indicating that no figure was read. In the 
case of plates 14, 15, and 16, the word “red” indicates that a reddish 
or pinkish line was traced by the candidate, while “blue” indicates 
that a blue line was traced, and a dash indicates that no line was 
traced. If the applicant reads both numerals on plates 12 and 13, 
he will be asked which numeral stands out more distinctly and his 
answer recorded in the space provided on the blank. 
218 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
154 
Result in typical case 
Plate 
Reads 
Plate 
Reads 
Plate 
Reads 
1 
12 
7 
12 
2 
2 
3 
8 
13 
4 
3 
5 
9 
14 
Blue 
4 
2 
10 
5 
16- 
5 
21 
11 
2 
16 
Blue 
6 
— 
Tho person whose record is given above is called typically “green- 
blind” and exhibits the commonest form of color-blindness. If the 
figures 6 and 2 had been read on plates 12 and 13 respectively, the 
person would have been called “red blind.” All of these responses, 
except that for plate 1, are different from those given by a person 
of normal color sense, and yet such a “green-blind” or “red-blind” 
person can distinguish some red and some green at ordinary distances 
and in ordinary weather conditions. 
g. If there is a possibility of the candidate’s having memorized the 
correct answers, the order of the plates may be changed by slipping 
them out of the slots at the four corners and reinserting them at dif- 
ferent places. The original order may be determined by reading the 
small numbers in the margins of the plates with a magnifying glass. 
h. The plates must be kept out of direct sunlight and the book 
should be closed except when actually being read. The book and all 
directions accompanying it are to be safeguarded from scrutiny by 
persons not officially responsible for conducting the test. Provided 
the applicant is found to have normal color vision on this test, no 
further tests need be used. If color perception is found to be deficient 
by this test, then the Holmgren yarn test will be given as outlined in 
the instruction sheet and chart. 
219 TM 8-300 
154-155 
MEDICAL DEPARTMENT 
Plate 
Examinee 
Report of Ishihara test of tbe color perception of 
number 
reads 
Applicant for 
1 
Plate No. 12, number . 
is more distinct. 
2 
Plate No. 13, number . 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
Place._ 
/ 
Date.. 
Examiner _ 
Medical Corps. 
155. Directions for Holmgren (yarn) test.—The test is to be 
conducted by a medical officer who has normal color perception. 
Seat the examinee at a table with his back to the window. Place 
skeins on the table in good diffused daylight—not in direct sunlight. 
Place the test skein 3 or 4 feet away, so that matches will not be made 
by direct comparison unless the examinee makes a special effort to do 
so. Instruct the examinee to take the skeins from the heap one by 
one and sort them into two piles, the first pile to contain all shades 
of the color of the test skein, the second pile to contain all other skeins. 
Go through this procedure separately with the green, the rose, and the 
red test skeins, mixing the skeins after each sorting. Make no com- 
ment on the examinee’s selections, but note carefully any erroneous 
selections, any skeins of the test color that are overlooked, and any 
skeins that seem to be difficult to classify. (See 2, 3, 46, 4c of report, 
sheet.) Then use these skeins as test skeins and go through the pro- 
cedure as before, entering the color of such additional test skein in one 
of the blank columns of the report sheet. Spread the skeins out on 
220 TM 8-300 
155-156 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
the table and instruct the examinee to select the three most brightly 
colored skeins in the lot. 
Report of yarn test of the color perception of 
Applicant for _ 
Test skein used 
Green 
Rose 
Red 
1. Number of skeins of test color selected. 
2. Number of skeins of test color omitted. 
* 
3. Were any skeins other than test color selected? 
If so, report color and shade of each. 
4. Manner of performance: 
а. Hesitant or confident? 
б. Were any selections made only by 
direct comparison with test skein? If 
so, report color and shade of each. 
c. Was classification of any skein changed 
after direct comparison? Report color 
and shade of each. 
Selected as brighest colors: (1) (2) (3) 
Does the examiner agree with this selection? (1)_ _ (2) _ (3) 
Medical Corps. 
Section XIX 
FIELD OF VISION FOE FOEM AND COLOES 
Peripheral vision 15$ 
Confrontation test 157 
Perimeter 158 
Form and color fields 159 
Tangent screen and rule 169 
Classification of defects in visual fields 161 
Physiologic blindspot 162 
Paragraph 
156. Peripheral vision.—a. In the testing of visual acuity the 
ability to perceive form is determined in only the foveal region of 
the retina. This portion of the retina represents a very minute frac- 
tion of the entire percipient retina which extends as far forward as 
the choroid, that is, to the ora serrata, which is about 6 millimeters 
221 T3Vt 8-300 
156 
MEDICAL DEPARTMENT:1 
from the limbus. Normally, this entire surface of the retina, with 
the exception of that portion occupied by the structures of the optic 
nerve, functions, but in a somewhat different manner than at the fovea. 
h. Structurally and functionally the fovea and peripheral portions 
of the retina differ. At the fovea only cones are found, but at a 
distance of only 3,4 millimeter from center or 1° away from the fovea 
the rods are more numerous than the cones; 4° away the rods are ten 
times as numerous and at 10° there are about twenty rods to one cone. 
Visual acuity, as such, diminishes rapidly away from the fovea. 
According1 to Burckardt's formula, the acuity of a point of the 
retina may be estimated as y3 n. n oeing the number of degrees away 
from the center of the fovea. Other estimates of peripheral acuity 
have oeen made wbicb may be at fault, as it is practically impossible 
to compare by the same test two portions of the retina that are so 
little alike. “As soon as any test object approaches the proximity 
(5°-10°) of the fixing area, it exerts so powerful an attraction upon 
the attention and powers of the central few degrees, that it is almost 
impossible to resist the impulse to use direct vision55 (Lloyd). Binoc- 
ular fixation, as is obtained with the Stereo-Campimeter, permits more 
accuracy in determining acuity away from the fovea, fairly accurate 
findings within the central 20° being obtained. It is evident that we 
use a surprisingly small portion of the macula for ordinary reading. 
c. In the periphery of the retina detection of moving objects is 
remarkably keen, although fixed objects are not seen with a sharp 
definition of detail. This function of the retina is one that we do 
not consider ordinarily, but it is by this function that we are able 
to orient ourselves in relation to objects within the field of vision. 
We constantly use the periphery of our retinae in any form of loco- 
motion. walking, driving an automobile, and flying. Further, such 
function may be considered as a very valuable protective device or 
warning mechanism. 
d. The macula area, where central vision is concerned, is less sen- 
sitive to low degrees of illumination, or, in comparison with peripheral 
points of the retina, is “night blind51 normally. One authority has 
found the most sensitive portion of the retina in recognizing barely 
luminous points to be between 11° and 18° away from the fovea. This 
can be determined by observing a barely perceptible star at night; 
it will disappear on direct fixation, but reappears when the point of 
fixation is 10° to 15° away from it. 
e. We may appreciate the value of peripheral vision by occluding 
all but the central portion, as looking through a tube of small diameter 
and attempting to walk across the room. Thus, in a way, the function 
222 TM 8-300 
156-157 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
of the peripheral portion of the retina is as important as that of the 
highly developed fovea. 
157. Confrontation test.—In determining the extent of the field 
of vision there are two methods that may be used, but at the same time 
there are several factors that must be taken into consideration. First, 
a “rough and ready” method is the confrontation test, or fixation and 
finger test which, while appearing to be very crude and inaccurate, 
is very useful when it is done carefully. The examiner stands about 
2 feet in front of the examinee, facing him, with a window at one side. 
The examiner covers his left eye with his left hand and directs the 
examinee to cover his right eye in a similar manner. Next the ex- 
aminee is told to fix upon the exposed pupil of the examiner, who in 
turn fixes upon the examinee’s left pupil. The examiner moves his 
right hand in from the periphery toward the line of fixation, with 
one or more fingers exposed, keeping his hand at all times as nearly 
as possible in a vertical plane halfway between him and the examinee. 
The hand movement is carried out in the vertical, horizontal, and 
two oblique meridians, and the examiner makes a comparison of the 
left visual field of the examinee with his own right visual field. The 
examinee, if his visual field is normal, will identify fingers and finger 
movements at the same instant as does the examiner, provided the 
field of vision of the latter is normal. In this manner, an estimate 
is made of the examinee’s left visual field. The examiner and ex- 
aminee may then change places, and in a like manner the latter’s right 
field of vision may be approximated. This method, quite simple and 
rapid in its application, will detect any gross defect in the extent 
of field for form. It has the following advantages: it is quick, re- 
quires no special equipment, and enables the examiner to be assured 
that throughout the test the examinee is maintaining fixation con- 
stantly. Its disadvantages are the inability to make accurate quan- 
titative determinations, the impossibility of carrying the test objects 
(fingers in this case) to the full extent of the normal temporal field 
(90° or more), and the possibility of overlooking such defects as 
homonymous and bitemporal hemianopsia, “They may be roughly 
tested for by telling the patient to look straight at the surgeon, sit- 
uated as before, both eyes being open. The surgeon holds up both 
hands, one in each temporal field, and the patient is told to touch 
the surgeon’s hand. If he asks, ‘Which one?’ he has not bitemporal 
hemianopsia, since he sees both hands. If he promptly points to one, 
he should be asked if he sees the other; if he does not, he probably 
has homonymous hemianopsia” (Parsons). 
223 TM 8-300 
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MEDICAL DEPARTMENT 
Where a defect in the visual field is found, or suspected by the 
fixation test, a more accurate examination using the perimeter should 
be made. 
Figure 32.—Perimetric field studies. 
158. Perimeter.—The perimeter consists essentially of an arc of 
90° or more (more frequently of 180° or more) which may be ro- 
tated about a pivot upon which the examinee fixes with the eye 
being examined. The eye being examined must be situated exactly 
224 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
158-159 
before the point of fixation and at a distance equal to the radius of 
the arc of the perimeter. The examinee must be seated with his 
back to the light, which should be uniform on the arc of the per- 
imeter regardless of its position. The eye not being examined must 
be completely screened, as with an eye patch, or the lids may be 
closed with a strip of adhesive. 
With the arc of the perimeter adjusted horizontally the extent of 
the temporal field for form should be determined by bringing the 
test object (white in this instance) inward along the arc toward the 
point of fixation, noting where it is first observed (not where thei 
color is identified) by the examinee (the back of the perimeter are 
is marked in degrees away from the point of fixation). At least 
eight meridians should be investigated, that is, temporal, upward and 
temporal, directly upward, upward and nasalward, nasalward, down- 
ward and nasalward, directly downward, and downward and out- 
ward; or, in other words, at intervals of 45°. In each of these 
meridians the test object should be carried to the fixation point in 
order to determine the presence of scotomata. The examinee should 
be cautioned repeatedly to maintain fixation, which is quit© difficult, 
particularly as the test object approaches the point of fixation. Fur- 
ther, the examiner should observe the eye under examination to be 
sure that fixation is maintained. In outlining the form field, the 
test object should be gently agitated as the normal limit for each 
meridian is approached, as the function of the peripheral portion of 
the retina is primarily to detect moving objects. 
159. Form and color fields.—a. Plotting field.—The form field 
is plotted upon the perimetric chart which has concentric circles 
corresponding with degrees on the arc of the perimeter. Where a 
defect is noted, as many additional meridians as may be necessary 
must be investigated. 
b. Determination of blue, red, and green fields.—After mapping the 
field for form using the white test object, the extent of the fields 
for blue, red, and green should be determined, using appropriately 
colored test objects. “The limit of a field for a color is the point at 
which, passing from the periphery to the center, the color first 
becomes evident” (Parsons). This is a point that is difficult to 
determine even with the help of a very cooperative examinee. 
c. Color perception at extreme periphery.—It has been thought, and 
taught, that the extreme periphery of the retina is color-blind, but 
by many authorities today this is not considered as being strictly 
true. “Although it is relatively color-blind, compared to the acuity 
of the color sense at the fovea, all the colors can be perceived in the 
periphery in a normal individual if the test object is large enough” 
271818°—40——15 
225 TM 8-300 
159 
MEDICAL DEPARTMENT 
(Adler). “There is overwhelming proof—that the peripheral vision 
behaves in exactly the same manner as central vision but with 
diminished sensitivity. Greater stimuli are required to produce simi- 
lar responses, but if the stimuli are sufficiently great, the differences 
disappear, including even qualitative differences so that the fields of 
vision for colors extend to the extreme periphery” (Parsons). 
Apparently the size of the test object used for outlining color fields 
is of the greatest importance, in addition to the intensity of the 
colors used in test objects. Otherwise, the determination of the so- 
Figueh 33.—Hand perimeter with spherical test objects. 
called color fields, as so frequently conducted, may be of little if 
any value. 
d. Conditions to he observed in color tests and apparatus.—The fol- 
lowing is quoted from Visual Field Studies y by Ralph I. Lloyd: 
Conditions to t>e observed in Color Tests and Apparatus.—If color tests are 
to be used, it is absolutely essential that certain conditions be complied with. 
The background must be colorless grey which is of the same brightness as the 
colors used. The tests must be conducted in full “daylight” or the equivalent, 
which means “standard daylight” obtained by filtering electric light through 
blue grass to remove the yellow. The test must be done in full illumination 
and a dark room or low illumination is not permissible because this introduces 
226 TM 8-300 
159 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
the question of dark adaptation whereby “twilight worth” is substituted for 
“periphery worth.” A red and a blue which are of the same brightness by 
“twilight vision,” when observed by the light adapted eye, are peripherally 
colorless and not of equal brightness. In one case, the dark adapted rods are 
tested and in full light the peripheral cones. The size of the test discs will 
be decidedly larger than those we have been accustomed to use, because to obtain 
peripherally similar colors, the saturation must be lowered. The colors should 
be invariable, that is, they must pass from the peripheral colorless zone wherein 
they appear without color, into the zone where they are recognized as true 
colors, without passing through intermediate phases. They should also be 
of the same brightness as the background against which they must appear, 
when observed by the peripheral retina. The test object must be protected 
from the light and should be replaced at regular intervals. 
The use of colored test objects will be referred to again in this 
section in connection with certain abnormal conditions. The tests 
of the fields of color are not made in the regular examination of appli- 
cants and flyers. 
e. Test object.—Going back to the use of the white test object in 
delineating the field of form; in using the white object, two pre- 
cautions should be observed; the examinee must be told to indicate 
when the object is first seen, not to identify it as white; and the test 
object should be moved back and forth as it is brought in from the 
periphery. Further, the white test object should be of a certain 
size. The size of the test object should be noted in degrees rather 
than its diameter in millimeters. The size of a test object, either 
spherical or of disc shape, may be estimated fairly accurately by 
first determining the radius of the perimeter used: 
2 X 3.1416 X radius . „ 0 
— ggQ = diameter or a 1 test object. 
2 X 3.1416 X radius . . 
= diameter ot a 2° test object. 
2X3.1416Xradius = diameter of a go tes( ob]-ect- 
= d;am(ster rf & 1QO object_ 
Or, in other words, the circumference of the circle (of which the 
perimeter is an arc) divided by 360, the number of degrees in a circle, 
will be the approximate diameter of a 1° test object. The word ap- 
proximate is used as in this instance the arc is being used rather than 
chord to determine the diameter. In outlining the field for form a 1° 
white test object is ordinarily employed. In plotting the outlines of a 
scotoma, particularly if it is near the point of fixation, smaller test 
objects may be used for greater accuracy. The test objects should be 
illuminated by not less than T-foot candles. 
227 TM 8-300 
159-160 
MEDICAL DEPARTMENT 
/. Field for form.—The average normal field for form is approxi- 
mately as follows: 
Out, 90°. 
Out and up (45° from horizontal), 62°. 
Vertically, 52°. 
Vertically and inward (45° from horizontal), 55°. 
Inward, 60°. 
Inward and downward (45° from horizontal), 55°. 
Downward, 70°. 
Downward and out (45° from horizontal) ,85°. 
As a rule, emmetropes and hyperopes have wider fields than myopes. 
Any contraction of the form field of 15° or more in any meridian dis- 
qualifies for flying. 
g. Field for color.—The field for blue should be about 10° to 15° 
smaller than the field for form, and roughly concentric with it; the 
field for red about 15° less than that for blue; and the green field is 
usually the smallest, being 10° to 20° smaller than that of the red. 
As has been shown, the value of color fields as commonly determined 
is at best questionable. It is not the intention of the writer to advocate 
abolishing the use of colored test objects altogether, but the student 
should bear in mind the criticisms of certain authorities before making 
a definite interpretation of the extent of the various fields for color. 
Particular attention should be paid to the investigation of the central 
portion of the field with colored test objects, as central relative scoto- 
mata, an acquired color-blindness, may be indicative of toxic amblyopia 
or retrobulbar neuritis. In such conditions there may be a red-green 
blindness. In optic atrophy there may be found early a marked con- 
traction of the color fields altogether out of proportion with the con- 
traction of the form field, which shows some degree of contraction. 
h. Divisions of visual field.—The visual field, as a whole, may be 
divided for descriptive purposes as follows (Fuchs) : 
(1) The central area, from the point of fixation to about 2° around it. 
(2) The paracentral zone, from the peripheral limits of the central 
zone to about 8° on the nasal side and 12° on the temporal side. 
(3) The coecal zone, from the limits of the paracentral zone to 
approximately 25°. 
(4) Intermediate zone, from 25° to 60°. 
(5) The peripheral zone, beyond 60° in all meridians. 
160. Tangent screen and rule.—a. Use.—The use of a tangent 
plane is a recognized and established procedure in the determination 
of the central, paracentral, and coecal zones of the visual field, for 
both form and color. For this purpose various campimeters are 
employed, and in particular the Bjerrum tangent screen or curtain. 
228 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
160 
Such a device has its limitations in visual field studies, for an attempt 
to project the entire visual field of a normal eye upon a plane surface 
is quite impossible. The difficulty lies in the fact that toward the 
periphery of the field the tangent increases enormously, the limiting 
value of the tangent of a 90° angle being infinity. For this reason 
the use of a plane surface in delineating visual fields is limited to 
the vicinity of approximately 45° which includes the central, para- 
central, coecal, and a good portion of the intermediate zones. 
h. Advantages.—The method of employing the tangent screen as 
an adjunct to perimetry is simple and need not be discussed at length. 
The disadvantages are, as already stated, the limitations of its appli- 
cation to certain zones, and the difficulty experienced with the vary- 
Figurb 34.-—Projection of visual field upon plane surface. 
ing size of the retinal image produced by a given test object at 
different distances from the point of fixation. The advantage of a 
plane surface is the magnification or enlargement of a scotoma in its 
projection which assures greater accuracy. Furthermore, the exam- 
iner obtains a true and realistic projection of that portion of the 
visual field which is covered by the screen or plane surface. The 
ordinary perimetric record does not quite accomplish this result. To 
interpret the flat perimetric record properly the perimetrist must 
imagine that he is examining the interior of a hemisphere rather than 
a plane surface. 
c. Equipment.—(1) Screen.—A blackboard about 6 feet square, or 
even smaller, will answer the purpose admirably. Blackboard cloth 
on an ordinary window shade will serve the purpose if wall space 
229 TJVt 8-300 
160 
MEDICAL DEPARTMENT 
is not available. For “rough and ready” use the blackboard is not 
necessary, for a blank portion of wall space may be utilized. The 
blackboard or wall space may be used at the convenient working 
distance of 75 centimeters, or at any distance; the value of the tan- 
gents, of course, varying with different distances. Any given dis- 
tance may be halved, quartered, or doubled whiie using one rule. 
(2) Buie.—The tangent rule may be made from a yardstick, or a 
light strip of lath such as is used as a stiffener for the common roller 
■window shade. A more elaborate one may be made from one-eighth 
inch celluloid, such as is used in making the triangles, protractors, 
and irregular curves employed by draftsmen. A protractor at one end 
may be included, which will be found to be very helpful. The values 
of the tangents should be etched or scratched upon one edge of the 
rule. 
d. Values of tangents.—The exact distance, or values of the various 
tangents, may be easily computed; but for convenience they are tabu- 
lated as follows (for a working distance of 75 cm.) : 
Degrees 
Distance from 
end of rule (in 
centimeters) 
Degrees 
Distance from 
end of rule (in 
centimeters) 
1 
1. 31 
26 
36. 58 
2 
2. 62 
27 
38. 21 
3 
3. 93 
28 
39. 88 
4 
5. 24 
29 
41. 57 
5 
6. 56 
30 
43. 30 
6 
7. 88 
31 
45. 07 
7 
9. 21 
32 
46. 87 
8 
10. 64 
33 
48. 71 
9 
11. 88 
34 
50. 69 
10 
13. 22 
35 
52. 52 
11 
14. 58 
36 
54. 49 
12 
15. 95 
37 
56. 52 
13 
17. 32 
38 
58. 60 
14 
18. 70 
39 
60. 74 
15 
20. 09 
40 
62. 93 
16 
21. 50 
41 
65. 20 
17 
22. 93 
42 
67. 53 
18 
24. 37 
43 
69. 94 
19 
25. 82 
44 
72. 43 
20 
27. 30 
45 
75. 00 
21 
28. 79 
46 
77. 60 
22 
30. 30 
47 
80. 43 
23 
31. 84 
48 
83. 296 
24 
33. 39 
49 
86. 28 
25 
34. 97 
50 
89. 385 TM 8-300 
160 
Centimeters 
Centimeters 
75 Centimeters 
TANGENT RULE 
beveled Edge Length Of Rule 
. Beveled Edge Stops Here 
Beveled Edge 
TANGENT RULE. 
Material % Inch Clear Celluloid. 
Scale Equals 1 Centimeter 
All Dimensions Expressed In Centimeters 
Note: AH Lines And Letters Cut And 
Black Filled On Back Side Of Rule. Front 
Face Shown On Drawing. 
Figure 35.—Tangent rule. 
271818°—40 (Face page. 230) NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TIVi 
160 
It must be borne in mind that these figures are computed for a work- 
ing distance of 75 centimeters, and to obtain accurate findings the 
scale and blackboard are to be used with the examinee’s eye at exactly 
this distance from the fixation point on the blackboard. 
e. Procedure.—The examinee should be seated comfortably in front 
of the blackboard at the proper distance, which may be maintained 
with a fair degree of accuracy by using the back of a chair as a chin 
rest. The blackboard should have daylight illumination, that is, 
should be located before a window in such position that a uniform 
illumination is assured. The eye not being examined is screened. 
The tangent rule may be placed against the blackboard as a T-square 
and adjusted until a point is found directly before the eye being 
examined, and at this point a dot is made with crayon. This dot is 
used as a fixation point during the examination. 
The test objects are brought in from the periphery of the black- 
board toward the fixation point in as many meridians as desired, and 
where any point of significance is noted, as for example the border 
of a scotoma, or the limitation of the field for form, a minute crayon 
mark is made upon the board. The significant points, or marks, in 
the various meridians may later be connected by lines, and these 
points and lines measured in degrees from the fixation point by the 
tangent rule. If a protractor is included with the tangent rule, the 
exact meridians may be drawn on the board after the examination 
is completed. Thus we have a fairly accurate outline of the field of 
v,v' n within 50° of the fixation point, and from it we may arrive at 
conclusions or make a definite diagnosis just as readily as by study- 
ing a record obtained by a perimeter. 
/. Record of findings.—When a permanent record of the findings 
is desired, the tracings on the blackboard may be transferred to an 
ordinary perimeter form by using the tangent scale, locating points 
of significance in degrees away from the point of fixation and the 
exact meridians in which these points are found. If the tangent rule 
is not provided with a protractor at one end, the various meridians 
may be determined accurately by again using the measurements on 
the rule for the tangential values of angles. The horizontal meridian 
may be determined by measuring the distance from the point of fix- 
ation to the floor, and locating a point on the margin of the black- 
board at exactly this distance from the floor. A line joining these 
two points indicates the horizontal meridian. At a point 75 centi- 
meters from the point of fixation on the horizontal meridian, the 
tangent rule may be placed at right angles to the horizontal meri- 
dian; then lines joining the point of fixation and the various points 
231 TM 8-300 
160 
MEDICAL DEPARTMENT 
on the tangent rule indicate the meridians of corresponding degrees 
(see fig. 33). The same procedure may be adopted for locating the 
meridians beyond 45° by using the tangent rule at right angles to the 
vertical meridian, at a point 75 centimeters from the point of fixa- 
tion. The tangent rule combined with a protractor at one end 
greatly facilitates this procedure. 
g. Test objects.—As to test objects, the following suggestion is 
offered. Again referring to the tangent rule, we find that the diameter 
of a 1° test object at 75 centimeters is 1.31 centimeters (approxi- 
mately, as we are dealing with an arc rather than a chord), and that 
a 10° test object would be 13.22 centimeters in diameter. But this 
holds true only when the test object is at the point of fixation on the 
blackboard. The retinal image of it decreases in size as it is moved 
Horizontal M eri-dian 
Fixoti'on Poinf 
Figure 36.—Use of tangent rule to determine meridians. 
toward the periphery, and at 45° away from the point of fixation the 
size of its retinal image has decreased about 33ys percent. This fact 
should be borne in mind and appropriate allowances made. Test 
objects for form only may be procured in the form of white beads 
of spherical shape in any required diameter, which may be mounted 
upon piano wire. Colored beads are available, but here a difficulty 
presents itself that is hard to overcome, that is, the standardization of 
the colors. For accurate results in color fields, it is advisable to obtain 
the discs made of Heidelberg paper. 
h. Supplemental use.—Another valuable use of the tangent rule in 
connection with the blackboard is the determination of the kind and 
amount of diplopia. For this purpose the blackboard is employed 
exactly as is the Bjerrum curtain, the red glass before the right eye 
and the point of illumination being carried outward from the central 
232 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
160-161 
point in the six cardinal directions. The point where diplopia occurs 
is noted by making a small crayon mark upon the board, red crayon 
being used to indicate the location of the red image, and white crayon 
for that of the white image. By using the tangent rule, the locations 
of these positions can be determined in degrees, and the amount of 
separation noted. The plot formed by the location of the crayon marks 
may be transferred to a blank form for this purpose, or any perimetric 
form, with appropriate notations as to whether the diplopia is crossed, 
vertical, and so on. 
161. Classification of defects in visual fields.—a. General.— 
In addition to a constriction of the visual field, visual field defects 
may be classified as follows (Lloyd) : 
(1) Scotomata, which may be— 
(a) Negative. 
(&) Positive. 
(c) Relative. 
(d) Absolute. 
(e) Coeco-central. 
(/) R^g. 
(2) Hemianopsia, which may be— 
(a) Homonymous. 
(h) Heteronymous. 
(3) Sectorial defects. 
(a) Quadranopsia. 
(5) Hemichromatopsia. 
(4) Blindspot scotomata. 
(a) Seidel’s sign. 
(6) Bjerrum’s sign. 
(c) Roenne’s nasal step. 
h. Scotomata.—“Scotoma is usually defined as an insular defect in 
the visual field” (Lloyd). A positive scotoma is one that the patient 
is aware of, that he sees as a shadow, as may be caused by an opacity 
in the vitreous near the retina. A negative scotoma is one that the 
patient is not conscious of, such as that that occurs where there has 
been degenerative changes in recipient layer of the retina (choroido- 
retinitis, etc.). Where a positive scotoma is found it is assumed that 
the perceptive portion of the retina is functioning in part at least. 
A negative scotoma indicates that a certain area of the retina has lost 
its funtion. 
A relative scotoma is one within which an object is seen as being 
distorted, or in which the color is not recognized. In an obsolute sco- 
toma the patient does not recognize the object either by form or color. 
233 TIYL 8-3UU 
161 
MEDICAL DEPARTMENT 
Coeco-central scotomata, as the name implies, interferes with central 
vision; the ring types are more peripherally located, the latter are 
often roughly concentric in outline. 
c. Hemianopsia.—By hemianopsia, or hemianopia, is meant a loss 
of half of the visual field. It may be homonymous, that is, corre- 
sponding halves affected, both right halves for example. Or it may 
Figure 37.—Tangent screen record for findings •within 35° of point of fixation. 
be heteronymous, which would include the binasal and bitemporal 
types; “the former points to a lesion crippling both uncrossed bundles 
which supply the temporal halves of each retina which, in turn, means 
a loss of each nasal field. To do this the lesion must affect the lateral 
angle of the chiasm. Bitemporal hemianopsia is the classic sign of 
pituitary pressure upon the crossed bundles of the chiasm which sup- 
ply each nasal retinal half which, in turn, implies a loss of each tern- 
234 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
161 
poral field” (Lloyd). There is a type of hemianopsia classified as 
altitudinal which is characterized by a loss of function of the upper or 
lower halves of the retina. Bilateral altitudinal hemianopsia is very 
rare, but the monocular type is not infrequently encountered (detached 
retina, optic nerve lesions, etc.). 
d. Sectorial defects.—Sectorial defects include losses which are less 
than quadrants of the visual field, and may be indicative of lesions of 
Figure 38.—Tangent screen record for findings within 50° of point of fixation. This 
form may be used for recording diplopia with red glass and tangent screen. 
the cortex. By hemichromatopsia is meant a loss of half the field for 
color only. 
e. Blindspot scotomata.— (1) Seidel's sign.—“Seidel’s sign” is a 
slender, finger-like scotoma extending from the physiologic blindspot 
upward or downward and is found in early glaucoma. It usually 
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MEDICAL DEPARTMENT 
requires the employment of quite small test objects with the tangent 
screen for its detection. 
(2) Bjernvm's sign.—The Bjerrum sign is a finger-like scotoma 
extending from the physiologic blindspot above or below, or both, 
assuming the form of an arc and possibly involving the fixing area. 
Early it is a relative (color) scotoma, but later it is absolute in glau- 
coma. The tangent screen, or campimeter, with small test objects, is 
required for its detection. In addition, it may be found in the senile. 
(3) Roenne’s nasal step.\—Eoenne’s nasal step is a scotoma involving 
the nasal quadrant, more frequently the inferior nasal quadrant. 
Figure 39.—Outlining physiologic blindspot, right eye, on blackboard. 
The scotoma is usually roughly right-angular in outline, and its apex 
advances toward the physiologic blindspot. Such a finding is indica- 
tive of glaucoma. 
162. Physiologic blindspot.—The physiologic blindspot repre- 
sents the entrance of the optic nerve into the globe, and therefore cor- 
responds with the anatomical location of the disc in the fundus. 
Obviously it is within the temporal field of vision of each eye, and is 
located about 15° away from the macula. Usually it is approximately 
a little less than 5° in diameter, and its center is situated a little below 
236 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-30Q 
162 
the horizontal meridian. As a rule, its vertical diameter is somewhat 
longer than the horizontal. Clinically its size is important; an en- 
largement may be indicative of glaucoma, optic atrophy, toxic ambly- 
opia, posterior ethmoidal or sphenoidal sinus disease, arterio-sclerosis, 
and opaque nerve fibers. An enlargement of the physiologic blindspot 
is usually found in high degree of progressive myopia. 
Figukd 40.—Using tangent rule in locating position and size of physiologic blindspot. 
The tangent screen, with small test objects, is more valuable in out- 
lining the physiologic blindspot than is the perimeter. With the latter 
its location only can be determined. It is suggested that the student 
outline his own blindspots upon the tangent screen at a distance of 75 
centimeters. 
The position of the physiologic blindspot may be useful in determin- 
ing the angle of squint. 
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Section XX 
Paragraph 
Classification of lenses 163 
Principal focus—focal length 164 
Combination of lenses 165 
Analysis of lenses 166 
Classification of errors of refraction 167 
Determination of errors of refraction 168 
Correction of presbyopia 169 
Transposition of formula 170 
Decentering of lenses 171 
REFRACTION 
163. Classification of lenses.—a. Before considering methods of 
quantitatively determining refractive errors, it is advisable that some 
points in elementary optics be reviewed. 
The action of a prism has already been considered, but it must be 
remembered that a prism will form no image and it has no focus. If 
two prisms are placed together base to base and viewed from the side, 
their faces appear somewhat similar to the cross section of a convex 
spheric lens; the similarity becomes more marked when a comparison 
is made with a series of truncated prisms placed one above the other, the 
larger two being base to base. (See fig. 41.) It is easily seen that a 
lens toward its periphery has the effect of a prism. 
b. Lenses may be classified as follows: 
(1) Spherical (abbreviated as S, or sph).—In such lenses the curved 
surfaces represent sections of spheres, and a spherical lens refracts 
rays of light equally in all meridians. Spherical lenses may be— 
(a) Convex (synonyms plus, positive, collective, magnifying),—Of 
the convex variety there may be plano-convex, bi-convex, and concavo- 
convex types. All convex lenses are thickest at the optical center. 
{b) Concave (synonyms minus, negative, dispersive, minifying).—• 
Such a lens may be plano-concave, bi-concave, or convexo-concave. All 
concave lenses are thinnest at the optical center. 
Any spherical lens, on section, may be compared to a series of truncated 
prisms gradually increasing in strength from the center toward the 
periphery. In a convex lens the bases of the prisms are toward the 
center; in a concave lens they, are toward the periphery. This com- 
parison enables us to realize the effect a lens has upon parallel rays 
of light. 
(2) Cylindrical lenses (abbreviated as C or cyl).—A cylindrical 
lens is so termed because it is a segment from a cylinder. There is one 
meridian of a cylindrical lens in which the lens is of uniform thickness, 
and this meridian is parallel to the axis of the original cylinder of 
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which the lens is a segment. This meridian is designated as the axis 
of a cylindrical lens. A cylindrical lens has no focal point, but has 
a line of foci, and this line is parallel to the axis. Cylindrical lenses 
may be concave or convex and may be made with both surfaces curved 
(bi-convex, bi-concave, etc.). In addition to the designation of the 
strength of a cylindrical lens, the position of its axis must be noted, 
when it is prescribed. The commonly accepted designation of axes 
positions on the spectacle trial frame is 0° to 180° (both these extremes 
being the same, axis horizontal), increasing in an anticlockwise man- 
ner, for each eye, when facing the spectacle trial frame. Consequently, 
axis 90° is vertical for each eye, but axis 45° is up and out for the left 
eye, and up and in for the right. 
Figure 41.—Aggregation of prisms forming bi-convex lens. F, real focus. 
164. Principal focus—focal length.—a. Principal focus.—The 
principal focus of a lens is the point where parallel rays of light, 
after refraction by the lens, intersect the axial ray; it is the point, as 
a matter of fact, where all parallel rays are brought to a focus after 
being refracted by the lens. In a spherical lens this is a point, in 
cylindrical lenses the principal focus is a line. In concave lenses, the 
principal focus is located at the intersection of a backward prolonga- 
tion of the emerging divergent rays (see fig. 42). The optical center 
(nodal point) of a simple spherical lens with equal curvature on both 
sides may be described as a point within the lens equidistant from its 
two surfaces in the thickest part of a plus lens, and in the thinnest 
part of a minus lens. It is through this point the axial ray passes. 
239 TM 8-300 
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MEDICAL DEPARTMENT 
Figure 42.—Aggregation of prisms forming bi-concave lens. F, virtual focus. 
A Plano-convex. 
li Plano-concave. 
C Meniscus. 
D Convexo-concave. 
E Convex cylindricaL 
F Concave cylindrical (concavo-convex) 
Figure 43.—Lenses. 
FIGURE 44.—Convex cylindrical lens considered as segment of cylinder. 
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The optical center and the geometrical center of a lens do not neces- 
sarily coincide. The optical center of a cylindrical lens lies within 
the plane of the axis of the cylinder and is not a point but a line. 
J>. Focal length.—The focal length of a lens is the distance from the 
optical center to the principal focus, and this distance determines the 
strength of the lens. The focal length is measured in the metric system 
almost universally, and from it the dioptric value of a lens is easily 
determined. A lens of 1 diopter strength has a focal length of 1 
meter, one of 2 diopters has a focal length of 50 centimeters, one of 10 
diopters has a focal length of 10 centimeters. Lenses used in the cor- 
rection of errors of refraction are graduated in one-eighth diopter, 
expressed decimally; for example, plus 0.12 JS, plus 1.75 JS, plus 0.50 O, 
minus 0.87 JS, minus 2.25 G, etc. The focal length of a lens is easily 
computed, as the dioptric power of a lens is the reciprocal of the focal 
distance in meters; for example— 
Focal length of 1 diopter lens=j meter. 
Focal length of 2 diopter lens=i meter. 
Jj 
Focal length of y2 (0.50) diopter lens=—_— meter. 
0.50 
c. Conjugate points.—A lens has two principal foci, depending upon 
the direction from which the parallel rays of light striking a surface 
come. These are, of course, the same distance from its optical center. 
So far the effect of a lens on parallel rays of light has been considered. 
We may now consider rays of light emanating from a point exactly the 
focal length away from the optical center of a convex lens; such 
divergent rays, after passing through the lens would emerge parallel 
to one another and would never intersect. Rays of light from a point 
at a distance from the optical center of a greater distance than its 
focal length would eventually converge at a point after passing 
through the lens. The point from which rays of light diverge and the 
point at which they converge after passing through such a lens are 
the conjugate points or'foci. 
165. Combination of lenses.—a. Rules.—Lenses may be com- 
bined, as a bi-convex spherical lens is actually in effect two spherical 
lenses together. There are seven rules regarding the combination of 
lenses that will enable the student to understand more thoroughly 
problems in the quantitative estimation of errors of refraction, as well 
as their correction. 
(1) Two spheres of the same sign are equal to a sphere having the 
strength of the sum of the two; for example, plus 2.00 JS combined with 
plus 3.00 /S'=plus 5.00 iS. 
271818°—40—16 
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MEDICAL DEPARTMENT 
(2) Two spheres of opposite sign are equal to a sphere having the 
strength of the difference of the two; for example, plus 4.00 S com- 
bined with minus 3.00 1.00 S. 
(3) These above rules apply to two cylindrical lenses when both 
have the same axis; for example, plus 2.00 Cx 90° combined with minus 
1.00 Cx 90° = plus 1.00 Cx 90°; and minus 4.00 Gx 180° combined 
with plus 3.00 Cx 180° = 1.00 Cx 180°. 
(4) Two cylinders having the same sign and strength when placed 
with their axes exactly at right angles make a sphere of the same sign 
and strength as one of the cylinders; for example, plus 3.00 Cx 90° 
combined with plus 3.00 Cx 180° = plus 3.00 S. 
(5) Two cylinders having same sign but different strengths wdien 
placed with their axes crossed at right angles form a sphere of a 
strength of the weaker cylinder combined with a cylinder equal in 
strength to the difference between the two and having the axis of the 
stronger cylinder; for example, plus 3.00 Cx 90° combined with plus 
4.00 Gx 180°=plus 3.00 JS combined with plus 1.00 Cx 180°. 
(6) A cylinder combined with a sphere of equal strength but op- 
posite sign is converted into a cylinder of the same strength and sign 
«s the sphere but with an axis at right angles; for example, plus 2.00 
Cx 90° combined with minus 2.00 JS=minus 2.00 Cx 180°; and minus 
1.00 Gx 45° combined with plus 1.00 >S'=minus 1.00 Cx 135°. 
(7) This concerns the result of a combination of two cylinders of 
opposite sign when crossed with their axes at right angles. Two 
cylinders, one being plus (a) and the other minus (&), when crossed 
with their axes forming a right angle, form a plus sphere of the same 
strength as (a) combined with a minus cylinder of a strength of (a) 
and (b) with the axis of (&); or they form a minus sphere having 
the strength of (b) combined with a plus cylinder of a strength of 
(a) and (5) and having the axis of (a). For example, -we may con- 
sider a plus 2.00 Cx 90° combined with a minus 2.00,Cx 180°. This 
would result in a plus 2.0Q S, combined with a minus 4.00 Cx 180°, or 
a minus 2.00 jS combined with plus 4.00 Cx 90°. The two are optically 
the same. 
b. Application.—As will be seen later these rules are particularly 
applicable in arriving at a conclusion regarding what lenses to place 
in the trial frame for subjective check on the objective findings of re- 
tinoscopy. 
c. Validity.—The above rules do not hold strictly true except when 
the lenses are in absolute contact and when ground into a single lens, 
the two surfaces of which are very close together; that is, a very thin 
lens. A lens with a plus 10 curve on one surface and a minus 10 on 
242 TM 8-300 
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NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
the opposite will not make a piano lens in effect unless the lens is very 
thin. 
d. Combination of sphere and cylinder.—A sphere and cylinder can 
be combined on one surface of a lens. Such a combination can be 
visualized by considering a section taken from an automobile tire or 
a doughnut. In such an instance, there will be a curvature of a cer- 
tain radius in one meridian, and in the meridian at a right angle a 
curvature of a much shorter radius. A section from a rather wide pul- 
ley with a shallow groove would be an example of a lens that is minus 
in one meridian but plus in the meridian at the right angle. 
166. Analysis of lenses.—It is important to be able to analyze 
a lens in order that its optical value can be known. This can be done 
in a number of ways but the simplest is by “neutralization.” First, 
we may consider a simple spherical lens: If we look at an object in 
the distance through the lens and move the lens we note the direction 
®f the apparent movement of the object; if it moves in a direction op- 
posite to the movement of the lens it is a plus lens; if the object moves 
in the same direction it is a minus lens. This is easily accounted for 
when we remember that a spherical lens on section appears as an ag- 
gregate of prisms gradually increasing in strength as the periphery is 
approached. For example, if we view a point in the distance through 
a plus lens and the visual axis passes through the lens near the peri- 
phery the object will be displaced toward the periphery as we are get- 
ing a marked prismatic effect; apex toward the periphery; we then 
move the lens so that the visual axis passes through a point nearer the 
optical center, here the prismatic effect is not so great, so the object 
appears less displaced toward the periphery than before. Then the 
lens is moved so that the visual axis passes through the optical center 
of the lens and here there is no displacement of the object. Next the 
lens is moved laterally in the same direction as before and as the pris- 
matic effect increases toward the periphery the movement of the ob- 
ject toward the periphery becomes accentuated. Consequently, as a 
plus lens is moved back and forth before the eye, objects seen through 
the lens appear to move in the opposite direction or “against” the 
movement of the lens. The reverse is true regarding a minus lens 
which is made up of an aggregate of prisms apex toward the optical 
center and base toward the periphery. Therefore when a minus lens 
is moved back and forth before the eye objects appear to move in the 
same direction as the movement of the lens, or, as it is usually ex- 
pressed, “with” the movement of the lens. A lens in this manner may 
be easily identified as being plus or minus. A quantitative determina- 
tion may be made by “neutralizing” the lens, by using lenses of opposite 
sign from the trial lens case. The strength of an unknown lens is 
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MEDICAL DEPARTMENT 
determined by the strength of the lens of opposite sign that, combined 
with the lens of undetermined strength, causes no movement of an ob- 
ject seen through the two combined. For example, a plus 2.00 JS is neu- 
tralized by a minus 2.00 S. 
“A cylinder when moved in a direction at right angles to its axis 
causes a parallactic movement like a convex or concave spherical 
glass. When moved in the direction of its axis it acts like a piano 
glass” (Fuchs). In addition, a cylinder causes a certain amount 
of distortion of objects seen through it. To test for the presence 
of a cylinder in a lens, two lines crossed at right angles are viewed 
through it and the lens slowly rotated. In certain positions the 
lines will appear as being at right angles, but whenever either arm 
of the cross coincides with the axis of the cylinder the lines will 
appear at right angles. For example, take a strong plus cylinder 
(plus 3 or 5) and with its axis vertical (90°) observe a vertical 
line through it; the vertical line will appear continuous above and 
through the lens when the line is seen through the optical center 
of the lens; it will appear displaced toward the periphery if seen 
through a portion of the cylinder lateral to the optical center, but 
the displaced line through the lens will be parallel to the line seen 
above and below the lens. Now rotate the cylinder so that the 
axis is about 45°, that is, clockwise; now the line, as seen through 
the cylinder, will appear as leaning in the opposite direction or 
toward axis 135°. The portion of the line nearest the periphery 
is farthest displaced. Therefore the line appears to rotate in a 
direction opposite to the rotation of the cylinder. The reverse is 
true with a minus cylinder. 
To analyze a lens two lines crossing at right angles are observed 
through it and the lens is moved and rotated until they appear as 
being continuous with the lines seen beyond the periphery of the 
lens. Spheres of opposite sign are added until there is no movement 
of the vertical line; thus the strength of this meridian is obtained. 
Then the meridian at right angles is neutralized and from the com- 
bination of the two the value of the lens is obtained. 
First determine the presence of a cylinder, and if such exists, its 
axis; then neutralize the meridian of the axis, and then the meridian 
at right angles to its axis; the spherical value and the cylindrical 
strength with its axis may thus be obtained. 
167. Classification of errors of refraction.—a. (1) Emme- 
tropia.—The normal eye is emmetropic. Quoting Thorington, the 
following definitions of the emmetropic eye as listed: 
An emmetropic, eye is one which, in a state of rest (without any effort 
of accommodation "whatever), receives parallel rays of light exactly at a focus 
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upon its fovea. An emmetropic eye, therefore, is one which, in a state of rest, 
emits parallel rays of light. 
An emmetropic eye is one whose fovea is situated exactly at the principal 
focus of its refractive system. 
An emmetropic eye is one the vision of which, in a state of rest, is adapted 
for infinity. 
An emmetropic eye is one which has its near point consistent with its age. 
An emmetropic eye is one which does not develop presbyopic symptoms 
until 45 or 50 years of age. 
(2) Ametropia,.—An ametropic eye is one which in a state of com- 
plete rest does not focus parallel rays of light on the retina. This 
condition may result from the retina’s being too near or too far 
away from the nodal point (axial ametropia), or due to a defect 
in the curvature of one or more of the refracting surfaces (curva- 
ture ametropia). 
(a) Hyperopia (hypermetropia, H, farsightedness).—In such a 
condition parallel rays of light are not brought to a focus on the 
retina, with accommodation relaxed, and the focal point is behind 
the retina; therefore a plus lens is required for its correction. The 
hyperopic eye must accommodate for infinity, consequently must 
accommodate more than the emmetropic eye for distances nearer 
than 6 meters. Hyperopia may be subdivided into the following 
varieties: 
1. Facultative hyperopia {Hf).—Can be overcome by using 
the power of accommodation. 
2. Absolute hyperopia {Ha).—Cannot be overcome by accom- 
modative effort. 
3. Manifest hyperopia {Em).—Is represented by the strong- 
est plus lens the patient will accept, 
4. Latent hyperopia {HI).—Is the additional amount revealed 
mnder a cyclopleglic. 
5. Total hyperopia {Ht).—Is the manifest plus the latent 
hyperopia, and is represented by strongest plus lens 
required for distinct vision with accommodation com- 
pletely paralyzed. 
Facultative hyperopia becomes absolute after middle life; manifest 
hyperopia increases with age, while latent hyperopia decreases. 
With accommodation completely gone Hm=Ht. 
(b) Myopia {M. nearsightedness).—In such a condition parallel 
rays of light are brought to a focus before they reach the retina. 
This may be due to an antero-posterior axis too long for the dioptric 
system, or to an excess in power of the dioptric system. Accommo- 
dative power cannot in any manner come to the aid of the myope; 
245 TM 8-300 
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MEDICAL, DEPARTMENT 
therefore at distances farther away than his far point all objects 
are seen indistinctly. 
(c) Astigmatism (As).—In such a condition the dioptric power 
of the eye is not the same in all meridians. It frequently is the 
result of a difference in the corneal curvature in different meridians. 
The anterior surface of the cornea, in such instances, may be com- 
pared to a combination of plus sphere with plus cylinder. It is 
almost invariably a curvature ametropia. Cylindrical lenses are used 
for the correction of astigmatism. Astigmatism may be— 
1. Irregular.—As •when the cornea is irregularly distorted, 
that is, the curvature may not be uniform in a single 
meridian. The irregular type of astigmatism may be 
impossible to correct by ordinary lenses. 
2. Regular. 
(a) Simple hyperopic (as corrected by plus Gx 90°). 
(b) Simple myopic (as corrected by minus 1.00 Gx 
180°). 
(c) Compound hyperopic (as corrected by plus 2 S plus 
1.00 Gx 90°) . 
(d) Compound myopic (as corrected by minus 2 S 
minus 1.00 Gx 180°). 
(e) Mixed astigmatism.—Hyperopic in one meridian and 
myopic in another (as corrected by plus 2 S minus 
3.00 Gx 180°). 
h. Regular astigmatism may be further classified as to the strength 
and position of the axis, as— 
(1) “With the rule”—As plus cylinder axis 90° or within 45° 
either side of 90°, or minus cylinder axis 180° or within 45° either 
side. 
(2) “Against the rule.”—As plus cylinder axis 180° or within 
45° either side of 180°, or a minus cylinder axis 90° or within 45° 
either side. (These descriptive terms are based on statistical tables 
on astigmatism. As a rule plus cylinders are required axis vertical 
or nearly so, and minus cylinders at about axis 180°.) 
(3) Symmetric astigmatism.—“When the combined value, in degrees, 
of the meridians of shortest or longest radii of curvature in both eyes 
equal 180° (no more and no less), then the astigmatism in the two 
eyes is spoken of as symmetric” (Thorington). For example, OD 
plus 1.00 Cx 45°, OS plus 1.00 Gx 135°; or OD plus 0.50 Gx 75°, OS 
plus 0.50 Gx 105°, etc. 
(4) Asymmetric astigmatism.—When the combined values, in de- 
grees, of the two axes are not 180°. For example, OD plus 0.75 Gx 
246 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
1IT1 O—OW 
167—168 
35°, OS plus 0.75 Cx 90°. Asymmetric astigmatism frequently accom- 
panies facial asymmetry. 
(5) Homonymous astigmatism.—When the axis of the cylinder is 
the same in each eye. 
(6) Heteronymous astigmatism.—One eye with astigmatism “with 
the rule” and the fellow eye “against the rule.” 
(7) Homologous astigmatism.—Symmetric astigmatism “with tho 
rule.” 
(8) Heterologous astigmatism.—Symmetric astigmatism “against 
the rule.” 
(9) Oblique astigmatism.—When the axis is neither vertical nor 
horizontal. 
168. Determination of errors of refraction.—a. Methods.— 
There are a number of methods employed to determine quantitatively 
the existence of ametropia, and these may be divided into two gen- 
eral methods, that is, objective and subjective. Whenever possible, 
both methods should be employed, one being used as a check on the 
other. 
b. Scheiner method.—One method, more interesting than practical 
however, is that of Scheiner. It is very rarely used but may be of 
value to emphasize to the student optical principles involved. Two 
minute openings are made, a few millimeters apart, through an opaque 
disc, which is placed in the trial frame before the eye being examined. 
Accommodation is paralyzed and the pupil dilated to the extent that 
its diameter is greater than the distance between the two pinholes. 
Over one of the holes is pasted a bit of red translucent paper. The 
patient is directed to observe, through these pinholes, a point of light 
6 meters away. If the eye is emmetropic there will be but one image 
of the point of light seen. If ametropia exists there will be two images 
of the point of light seen (a monocular diplopia), one of which will 
be red and the other white. Let us suppose the disc is placed before the 
eye with one pinhole directly above the other, and the upper pinhole 
is covered with the red paper (or red glass); if the eye is hyperopic, 
two images will be seen and the red image will be seen below the white 
(crossed diplopia). The strength of the plus lens required to bring 
the two images together represents the amount of hyperopia in the 
vertical meridian. Next the disc may be rotated so that the two pin- 
holes are in the horizontal plane and the amount of hyperopia in this 
meridian determined. The correction required would be the value of 
the two cylinders crossed at right angles. In myopia the red image 
will be seen above the white and the strength of a minus lens required 
to bring the two images together indicates the amount of myopia, etc. 
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MEDICAL, DEPARTMENT 
c. Cycloplegics.—The use of a cycloplegic in estimating errors of 
refraction enables the examiner to arrive at a definite conclusion, and 
further, the dilatation of the pupil renders the objective method of 
refraction much easier. Cycloplegics commonly used in refraction 
are atropine, in 1 percent solution (in children) and homatropine, 
2 percent solution. Cycloplegia may be induced more quickly by 
scopolamine hydrobromide, 0.2 percent solution, but the possibility 
of the drug’s toxicity must be remembered. The use of paredrine 
with atropine or homatropine is now widely advocated. Atropine 
2 percent, 1 drop, followed in 5 minutes by paredrine 1 percent, and 
1 more drop of atropin after 15 minutes will produce satisfactory 
cycloplegia in 45 minutes for the examination of children. For adults 
we use 1 drop of 5 percent homatropin followed in 5 minutes by 1 
drop 1 percent paredrine; then in 5 more minutes 1 drop 5 percent 
homatropine and refracting 35 minutes later. It is seldom neces- 
sary to use a cycloplegic after the age of 45 or 50 years. Where it 
is necessary to employ a cycloplegic in patients who are older, one of 
the weaker drugs, as homatropine, should be used, as the effect may 
be counteracted by the use of a miotic (eserin, y2 percent solution). 
Cycloplegics should never be used when glaucoma is suspected. 
Homatropine is used more universally for young adults, as its 
effect is transient, and complete recovery of power of accommodation 
occurs within 2 days. 
d. Retinoscopy.—(1) General.—Retinoscopy is the most popular 
objective method employed in estimation of errors of refraction. It 
has many advantages; it is quickly learned, is altogether objective, 
requires little time and only inexpensive apparatus, and is remark- 
ably accurate. The procedure of retinoscopy is simple. Rays of 
light from a mirror are reflected into the eye being examined, and 
as the mirror is tilted back and forth the direction of movement of 
the light as seen in the pupillary area is noted. For practical pur- 
poses it is not considered necessary to go into detail regarding the 
optical principles involved. Either a plane or concave mirror may 
be used, but with a concave mirror all movements of the spot of light 
will be in a direction opposite to those when the plane mirror is used. 
The plane mirror is more commonly used and henceforth any refer- 
ence to the retinoscope will be to the retinoscope with the plane mirror. 
(2) Simple retinoscope.—The simple retinoscope is a small cir- 
cular mirror with a hole through the center, or instead of a hole a 
minute portion of the “quicksilver” may be removed at the center, 
through which the examiner observes the reflex in the eye of the pa- 
tient. A handle is attached to one margin of the mirror. This 
retinoscope is used in conjunction with a source of light placed 
248 NOTES ON EYE, EAR, ETC., IN AVIATION MEM CINE 
tm 
168 
alongside the examinee. The light should be screened, asi with 
an opaque chimney, which has an opening approximately 1 centi- 
meter in diameter on the side facing the examiner. 
(3) Electric retinoscope.—The electric retinoscope has its own 
source of illumination placed below the mirror which is set at an 
angle'that reflects the rays of light at a right angle, that is, when 
the retinoscope is held vertically the rays of light pass forward from 
the mirror in a horizontal plane. 
(4) Purpose.—The purpose of retinoscopy is to neutralize as 
nearly as possible the movement of the illuminated area within the 
examinee’s pupil by the interposition of suitable lenses. The illumi- 
nated area is called the “shadow,” and when it has no movement 
with movements of the retinoscope, that is, neither “with” nor 
“against,” it is an indication that the emergent rays of light from 
the eye of the examinee are brought to a focus at the eye of the 
Figure 45.—Electric retinoscope, simple retinoscope, and electric ophthalmoscope (May 
model). 
examiner. The lens which accomplishes this neutralization of move- 
ment is the lens which will correct the examinee’s vision for the 
distance at which the retinoscope is used. 
(5) Distance.—It is impractical to attempt retinoscopy at a dis- 
tance of 6 meters. One meter is a convenient working distance, and 
is the distance at which the retinoscope is used ordinarily. In addi- 
tion it is simpler, particularly for the beginner, to make the deduction 
249 xm u-juu 
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MEDICAL, DEPARTMENT 
for a working distance of 1 meter, which is the focal distance of a 
lens of 1 diopter. The student must remember that with the retino- 
scope he is obtaining the correction required by the patient at 1 
meter’s distance; this correction is 1 diopter more than that required 
for infinity. Therefore, a correction of 1 diopter deduction must be 
made for the correction for infinity. 
(6) Method.—The examinee is seated at a meter’s distance in front 
of the examiner in a darkened room, and the examinee is directed 
to look fixedly at the forehead of the examiner but not directly at 
the mirror. A soft, clear light, not too brilliant, is reflected into 
the eye of the examinee by the retinoscope held firmly before the 
examiner’s right eye with the sighthole immediately before the 
pupil. The beginner probably will have some difficulty at first in 
finding the examinee’s eye with the beam of light; it is suggested that 
first it be directed toward the examinee’s chest, where it is easily 
located, and then the spot of illumination slowly raised by tilting 
the retinoscope until it reaches the eye being examined. 
With the retinoscope held in this manner the examiner will obtain 
a reflection from the pupillary area of the examinee’s eye, which will 
vary in its appearance depending on the amount of illumination used 
and the refractive error. The periphery of the so-called “shadow” 
is to be ignored and only the central point noted. If it is circular 
it is an indication that there is no great difference in the two princi- 
pal meridians, and very little, if any, cylinder will be required in 
the correction. A band-shaped reflex or “shadow” is indicative of 
cylinder being required, and the position of the band indicates the 
axis. Next the retinoscope is gently tilted back and forth not more 
than 2 or 3 millimeters or the reflex will be lost. The most common 
two principal meridians are at 90° and 180°, but they may be at 
any axis; they are always at right angles to one another. “The 
axes are indicated by the direction in which the shadow moves when 
the mirror is tilted. If the mirror is tilted in the vertical meridian 
and the shadow slides off toward 45°, we know that the two principal 
meridians are at 45° and 135°. We must shadow these two meridians” 
(Knighton). The examiner notes the form of illuminated area, its 
direction of movement in the different meridians, and the rate of 
movement. 
(?) Axis of cylinder required.—If the mirror is tilted vertically 
it is rotated about its horizontal axis, and if it is tilted laterally it is 
rotated about its vertical axis. The axis about which the mirror is 
tilted indicates the axis of the cylinder required. 
250 NOTES ON EYE. EAR, ETC., IN AVIATION MEDICINE 
168 
Figure 46.—Spectacle trial frame and diagram showing positions of axes of cylindrical 
lenses. 
251 TM 8-300 
168 
MEDICAL DEPARTMENT 
(8) Type of lens.—A movement of the illuminated area with the 
movement of the retinoscope indicates hyperopia, emmetropia, or 
myopia of less than 1 diopter, and a “with” movement is neutralized 
by a plus lens. A movement “against” the movement of the retino- 
scope indicates a myopia greater than 1 diopter. An “against” 
movement is neutralized by a minus lens. Spheres are used to 
neutralize the movement in the two principal meridians. 
.(9) Point of neutralization.—The exact point of neutralization is 
difficult to obtain, consequently the point of reversal is recorded. The 
weaker sphere that causes a reversal of the movement is recorded 
as the end point. Where a movement “against” is found, it may be 
overcorrected by a minus lens that is obviously too high, thus giving 
a movement “with,” and then plus lenses added until the first move- 
ment against is noted. The value of the combination of the two 
lenses is noted and recorded. 
(10) Recording findings.— (a) Method.—It is suggested that the 
beginner use an inverted letter T in recording his findings. He may 
imagine that the cross bar indicates the horizontal meridian and the 
upward stroke the vertical meridian. If the inverted T is considered 
as being placed before the examinee’s face, the right angle to the left 
side of the examiner will indicate the findings of the right eye and the 
right angle on the right will indicate the findings of the left eye. 
(&) Examples. 
1. First consider one eye alone. With the retinoscope at 1 
meter there is a “with” movement in all meridians. Place 
a plus 1.00 S, in the trial frame, before the eye and 
movement is still “with”. Replace the plus 1.00 S with 
a plus 1.25 /S; the movement is still “with,” Gradually 
increase the strength of the sphere until a reversal is 
obtained. Suppose in this case a reversal in all me- 
ridians is obtained first with a plus 2.00 S. The findings 
are then recorded thus: 
+2.00 
+ 2.00 
and, since 1 diopter must be deducted for correction for 
infinity— 
+ 2.00 .. +1.00 o -e • n •, 
+2 00 ~-‘-==+100 = +1.00 JS for infinity 
In this instance two cylinders of the same sign and 
strength crossed at right angles are dealt with (rule (4) 
in combination of lenses). 
252 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8—300 
168 
2. Next consider several other types of cases, as for example— 
a. 
+ 3.00 + 4.00 _ .+2.00 I +3.00 OD +2.00 £ 
+3.00 + 4.00 1~+2.00 | +3.00 ~OS +3.00£ 
b. 
OD+2.00 £ 
+ 3.00 +2.00 .+2.00 1+1.00 +1.00 Ox 90° 
+4.00 + 2.50 “1~+3.00 | +1.50 =(9£+1.00 £ 
~~ “ — - +0.50 Ox 90° 
Here is an application of rule (5) in combination of 
lenses. For the right eye there is a reversal with vertical 
tilting of the retinoscope (axis 180°) with a +3.00 £, 
and a reversal with horizontal tilting (axis 90°) with a 
+ 4.00 £. In this case, a +3.00 Ox 180° combined with 
+ 4.00 Ox 90° is actually dealt with. This is equivalent 
to +3.00 £ (which is +3.00 in all meridians) combined 
with a +1.00 Ox 90° (the meridian that requires a total 
of +4.00 £). 
c. 
—1.00 —1.25 ._-2.00-2.25 OD-1.00£-1.00Ox 180° 
0 -0.25"1 ~-1.00-1.25=OS -1.25 S-1.00 Ox 180° 
a. 
+0.50+0.75 . _—0.50 —0.25 6>Z>-0.25 £-0.25 (7a? 180° 
+ 0.75 + 0.75~1 ~- 0.25 - 0.25~OS- 0.25 S 
e. 
+ 1.75 +2.00 ,_+0.75 +1.00 _ 
+ 0.25 -0.25 1~-0.75 -1.25 ~ 
OD + 0.75 £-1.50 Ox 90°, or -0.75 £+1.50 Ox 180° 
OS+1.00 £-2.25 Ox 90°, or -1.25 £+2.25 Ox 180° 
In this instance there is a mixed astigmatism; rule (7) in 
combination of lenses applies in this case, as in the 
retinoscopic findings a plus cylinder in one meridian and 
a minus cylinder in the other are dealt with. 
f. In oblique astigmatism the inverted T has to be modi- 
fied ; it is suggested that in such instances a right angle 
for each eye be used, the arms of which indicate the 
principal meridians, as— 
+2d)050 . +F00'\^'+T50 
4-3^00/^^,+ 3.25 ~"1— +2^00^^\+2^25 
_ OD+1.00 £+1.00 Ox 135° 
~ OS +1.50 £+0.75 Ox 75° 
253 TM 8-300 
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MEDICAL DEPARTMENT 
(11) Subjective check.—From the findings that have been de- 
termined by retinoscopy, the examiner has the data necessary for the 
subjective check. If the cycloplegic is complete and the retinoscopy 
done carefully the correction for infinity as found by retinoscopy 
should obtain an acuity of 20/20 or better, that is, with accommoda- 
tion paralyzed. There are several factors that necessitate a subjective 
test immediately after retinoscopy, particularly the exact determina- 
tion of axis of a cylinder as well as strengths of both sphere and 
cylinder. In the subjective examination the formula will be found to 
be somewhat less, as to spherical value (less plus or more minus). 
The addition of a minus 1.00 S to the findings at 1 meter corrects for 
infinity; with the Snellen test types at 6 meters there must be brought 
into play either one-sixth diopter of accommodation, or one-sixth 
diopter added to the formula. Consequently, when the patient is fully 
corrected for a distance of 6 meters he may be slightly overcorrected 
for infinity. One quarter diopter sphere is usually subtracted from 
the trial lens for 6 meters distance for actual correction for infinity. 
(12) Subjective examination.—A subjective examination should 
follow retinoscopy immediately. This is of particular value where 
there is a cylindrical correction, and both the strength and axis of the 
cylinder should be checked carefully. Each eye should be checked 
separately. 
(13) Checking axis of cylinder.—In checking the axis of the 
cylinder, it is shifted quickly from one side to the other (about 15° to 
20°) from that found by retinoscopy, and the degree of rotation 
gradually decreased until maximum vision is obtained. The position 
of the axis of a cylinder may be confirmed by employing a stronger 
cylinder than that found by retinoscopy. This naturally will result 
in some blurring of vision, but is of value as the axis may be shifted 
back and forth until all vertical lines appear as vertical to the patient, 
then the stronger cylinder may be replaced by one of the strength as 
found by retinoscopy. 
(14) Astigmatic died.—The “clock face” or “sunburst” (astigmatic 
dial), consisting of radiating lines is of value in determining both 
the axis and the strength of a cylinder. This is based on the fact that 
in astigmatism lines in different meridians are not seen with equal dis- 
tinctness. The meridian of the eye which corresponds to the most 
sharply defined lines, or the blacker, is the meridian of the greatest 
ametropia, and the median at right angles to this is the most nearly 
emmetropic. The axis of the cylinder required will be at right angles 
to the meridian of the darkest lines. The greater number of test 
cabinets and charts for visual acuity have an included astigmatic dial 
or chart. 
254 NOTES ON EYE, EAR, ETC., IN AYIATTON MEDICINE 
TM 8-300 
168 
e. Stenopaeic slit.—The stenopaeic slit may be used for the subjective 
determination of astigmatic errors of refraction, with test types at 
6 meters, or in connection with the astigmatic dial. The stenopaeic 
slit consists of an opaque disc with a very narrow {y2 to 1 mm.) slit in 
one diameter. The slit is of the same size as the trial lens and may 
be placed in the rotating cell of the trial frame; the slit, before the eye 
being tested, is rotated until it reaches the meridian where clearest 
vision is obtained; the sphere is then changed until 20/20 is seen, 
and a notation is made of the strength required for this meridian. Next 
the disc is rotated exactly through 90°, and spheres added until 20/20 
Figure 47.—Retinoscopic findings. 
vision is secured. The total correction may be estimated fairly ac- 
curately by these two findings. For example, with slit placed ver- 
tically the patient reads 20/20, and with- the slit horizontal he only 
reads 20/40. But with a plus 1.25 S before the slit (placed hori- 
zontally) he reads 20/20. We may conclude that his correction is 
plus 1.00 Ox 90°. The slit is used at right angles to the axis of the 
cylinder required. The slit may be of value in determining ac- 
curately the position of the principal meridians. 
/. Cross cylinder.—The, cross cylinder is used to a distinct advantage 
in finding the strength and axis of a cylinder where such is indicated. 
255 TM 8-300 
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MEDICAL DEPARTMENT 
The method of its use is altogether subjective. The cross cylinder, 
as its name implies, is a compound lens made up of two cylinders of 
opposite sign with axes crossed at right angles; these two cylinders 
are of the same strength and, of course, are equivalent to sphero- 
cylinder combination. For example, a minus 0.12 Cx 90° combined 
with a plus 0.12 Cx 180° would be equivalent to a minus 0.12 S com- 
bined with a plus 0.25 Cx 180°. Cross cylinders are used in strengths 
of 0.12 to 1.00 diopters; more frequently the middle strengths are used. 
The lens is mounted in a circular frame to which a handle is at- 
tached radially at a midpoint between the tw© principal axes, and is 
not placed in a cell of the trial frame but held by the handle before it. 
By rotating the handle 180° about its own axis, the examinee can make 
a decision as to> the better of the combination. For example, the 
handle may be held obliquely up and out so that the cross cylinder 
amounts to a plus Cx 90° and minus Cx 180°. By flipping it over 
(rotating the handle), it becomes minus Cx 90° and plus Cx 180°. 
In using the cross cylinder for a determination nf cylindrical 
strength the lens is held with first one and then the other of its 
principal axes coinciding with the axis of the cylinder already placed 
in the trial frame, or coinciding with any axis in regard to which the 
presence or absence of astigmatism is to be determined. A notation 
is made as to which position gives the best acuity, although either 
of the two may blur the test types to some extent. The position of 
the cross cylinder selected by the examinee is an indication of the 
change to be made in the cylinder in the trial frame, that is, an in- 
crease or decrease in strength. “Thus if the trial frame contains a 
minus cylinder with its axis at 60°, and the preferred position of the 
cross cylinder is that in which its minus axis is at 60°, the strength 
of the cylinder in the trial frame should be increased. The reverse 
would be true if the preferred position of the cross cylinder were that 
in which its plus axis was held to correspond with the axis of the minus 
cylinder in the trial frame. And vice versa, if the cylinder in the 
trail frame is a plus cylinder” (Crisp). In instances where the 
astigmatism is practically vertical or horizontal this determination 
may be somewhat at fault, as regards an exact determination, as the 
examinee may select the position of the cylinder which causes a ver- 
tical rather than horizontal distortion of the test letters. 
In the description of the use of the cross cylinder for the location 
of the exact axis required, the following is quoted directly from Dr. 
Crisp: 
The cross cylinder test for axis is at first sight rather more complicated. It 
Is based on the principle that two cylinders of like denomination, superimposed 
with their axes at an acute angle with one another, form a new cylinder of 
256 TM 8-300 
168 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
different strength, whose axis is somewhere intermediate between the two axes 
of the separate lenses. 
If we lay a plus 1.00 D. cylinder upon another plus 1.00 D. cylinder, so that 
the two plus axes are 45° apart, the combination will be equivalent to a plus 
0.25 D. sphere combined with a plus 1.50 cylinder, whose axis is exactly half 
way between the two separate axes. If the two cylinders are of unequal 
strength, the new axis will be nearer the axis of the stronger individual cylinder. 
Suppose now that we have in the trial frame a minus 1.00 D. cylinder with 
its axis at 90°, and we wish to determine whether the axis should be changed 
in either direction from the exactly vertical position. A cross cylinder—say 
minus 0.50 sphere combined with plus 1.00 cylinder—is held with its two axes 
at 45° with the axis of the cylinder in the trial frame. If the minus axis of 
the cross cylinder is at 45° there is produced before the patient’s eye a new 
cylindric effect at an axis midway between 90° and 45°, that is at If, 
on the other hand, the minus axis of the cross cylinder is at 135°, the resulting 
minus cylinder has its axis midway between 90° and 135°, or at 112 If 
the axis of the patient’s astigmatic error lies nearer 45° than 135°, he may find 
the test type blurred by either position of the cross cylinder, but the blur will 
be less pronounced when the cross cylinder is held with its minus axis at 45° 
than when it is held with its minus axis at 135°. The change in position of 
the cross cylinder is again made by a simple rotation of the handle between 
the examiner’s thumb and index finger. 
The patient having expressed a preference as between the two positions of 
the cross cylinder, we must move the minus axis of the lens in the trial frame 
toward the preferred position of the minus axis of the cross cylinder. We have 
no exact indication as to how far this change of axis should be carried. But 
the cylinder in the trial frame is moved arbitrarily any distance in the indicated 
direction, and the test with two positions of the cross cylinder is again made, 
only this time the axis of the cross cylinder must be at 45° with the new 
position and not with the original position of 90°. 
At every new test, it is important that the cross cylinder shall follow the changed 
position of the cylinder which is in the trial frame. We may have shifted the 
position of the cylinder in the trial frame either too far or not far enough. In 
either, case the next test with the cross cylinder will tell us whether to go 
farther or to come part way back. But as we gradually diminish the range 
of alteration in the position of the cylinder in the trial frame, we shall at last 
reach a position in which the patient is unable to read any more or fewer of 
the letters with one position of the cross cylinder than with the other. We 
have then reached the desired point and have determined the correct axis 
required by the patient, subject to any change which may be obtained in check- 
ing up the strength of sphere and cylinder. 
Like all other astigmatic tests, this one is more likely to he successful if 
the accommodation is relaxed and, therefore, if whatever spherical lens is in 
the trial frame is so strong a plus or so weak a minus as barely to allow the 
patient to obtain his full visual acuity. Further, the patient must base his 
comparison of the two positions of the cross cylinder upon a study of the lowest 
line of letters which he can even partially or imperfectly read. It must also 
be remembered that the vision with the cross cylinder before the eye is very 
commonly less distinct than without it, and especially that at the final axis 
obtained the cross cylinder blurs the vision equally in both positions of the 
test. 
271818°—40 17 
257 TM 8-300 
168 
MEDICAL DEPARTMENT 
For eyes with good visual acuity the test for axis may usually be mad© 
satisfactorily by means of the cross cylinder of minus 0.25 sphere and plus 
0.50 cylinder. For the earlier stages of testing a high error, or sometimes as 
a check in unusually variable cases, the minus 0.50 sphere combined with plus 
1.00 cylinder is useful. The minus 1.00 sphere combined with plus 2.00 cylinder 
is of value in relatively amblyopic cases. 
In making the cross cylinder tests, the patient should usually not be asked 
whether he sees better with the cross cylinder or without it. What is needed 
is the choice between its two positions. Furthermore, there is almost never 
any advantage in checking the cross cylinder test for axis by means of the old- 
fashioned method of turning the cylinder in the trial frame in either direction 
until the patient decides that the vision is blurred. 
g. Fogging method of refraction.—In instances where the ampli- 
tude of accommodation is obviously within a narrow range, as with 
presbyopes, the “fogging” method of refraction may be resorted to. 
This is purely subjective and does not require the use of a cycloplegic, 
therefore is particularly adaptable to those who are past midlife, or 
those patients in whom the use of a cycloplegic is contraindicated. 
It is not so satisfactory in young adults, and its use is usually limited 
to patients who are over 45 years of age. This method simulates a 
cycloplegia by the induction of ciliary relaxation by the interposition 
of a plus sphere which is obviously of sufficient strength to over- 
come any ciliary muscle power the eye might otherwise use when 
looking at a distance of 6 meters. The eye being examined is rend- 
ered artificially myopic temporarily by the strong plus sphere causing 
the ciliary muscle to relax. This method is especially applicable in 
cases of hyperopia, hyperopic astigmatism, and mixed astigmatism. 
As an example, the patient is 47 years of age and-has a visual acuity 
of barely 20/20, obviously with effort. A plus 4.00 sphere is placed 
before the eye examined and the test types at 6 meters are illumi- 
nated. His vision is blurred or fogged, and in an effort to see more 
clearly his accommodation will relax. Minus spheres, gradually in- 
creasing in strength, are placed before the plus 4.00 S, until he can 
read 20/20. Suppose in this instance the strength of minus sphere 
required is 2.50. He is hyperopic to the extent of 1.50 diopters (plus 
4.00 S combined with minus 2.50 >S'=plus 1.50 S). 
h. Strength and axis of cylinder.—Where there exists an astigma- 
tism, the astigmatic dial, the stenopaeic slit, and the cross cylinder 
may be used in testing strength and axis of cylinder required, after 
maximum acuity has been obtained by spherical correction alone. 
The stenopaeic slit may be utilized, as the two principal meridians 
may be located and each fogged separately. 
i. Manifest method.—In the manifest method, lenses are added un- 
til normal vision is obtained without the induction of ciliary relaxa- 
258 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
168 
tion. Therefore, it is not applicable to hyperopes under 45 years of 
age. Where myopia is suspected in markedly defective visual acuity, 
the use of the pinhole disc is of value, as with it vision will be greatly 
improved, if the visual defect is due to the myopia alone. The man- 
ifest method should be restricted to patients who are over 45 years 
of age, and in some instances, cases of compound myopia in young 
adults where a cycloplegic is contraindicated. “The rule is to employ 
the strongest plus lenses or the weakest minus lenses which will give 
normal vision” (Thorington). 
Figueb 48.—Trial lens case. 
j. Post-cycloplegic test.—The post-cycloplegic test (indicated 
where glasses are to be prescribed) should be done after complete 
recovery of the power of accommodation. This will be 3 to 4 days 
after retinoscopy where homatropine has been used, and by the find- 
ings at this time we are guided as to the tolerance of the patient for 
his full correction. It will be found as a rule young adult hyperopes 
will not accept the full spherical correction as determined by retin- 
oscopy and confirmed subjectively with cycloplegia. In the young 
hyperope there has been a habit acquired of correcting, either wholly 
259 TM 8-300 
168-169 
MEDICAL DEPARTMENT 
or in part, his refractive error, and this habit will not be broken 
easily. 
(1) Hyperopes.—In hyperopes it is suggested that the full correc- 
tion (as determined previously) be placed on each eye and the two 
eyes checked together. If this results in blurring, add weak minus 
spheres (minus .12) to each eye until normal vision is obtained 
(20/20), and the strongest sphere giving 20/20 is that indicated to 
be worn. However, never add minus sphere until the total sphere 
becomes minus. The same strength of minus sphere must be added 
to each eye (otherwise an anisometropia will be induced) provided 
the retinoscopy and previous subjective findings have been accurate. 
For example, from tlie examination under cycloplegia tlie follow- 
ing is found: 
OD + 2.75o . 
05+2.25/5 
Four days later, after restoration of the power of accommodation, it 
is found that the above formula causes a marked blurring and an 
acuity of only 20/40, binocularly. Add a minus 0.12/5, then minus 
0.25S, and eventually a minus 0.505, until 20/20 is obtained. The 
following acceptable formula is derived: 
OD + 2.75£ combined with — 0.505= +2.25$ 
05+2.255 combined with — 0.50/5= + 1.755 
The hyperope should wear as much plus sphere as he will accept. 
(2) Myopes.—The myope, at the post-cycloplegic test, will usually 
accept his full correction. In no instance should he be given more 
minus than required to give his normal vision, consequently weak 
minus spheres are not to be added to the full minus correction at the 
post-cycloplegic test, although he will probably accept more minus 
readily. 
The strength and axis of the cylinder should be checked on each eye 
separately. As a rule the full cylindrical correction will be accepted, 
even in hyperopes, and will require no reduction in strength although 
the sphere is reduced. However, it may be found that cylinders of 
high strength may not be accepted or tolerated unless the patient has 
worn such a correction previously. A very strong cylinder may have 
to be reduced in strength before being worn comfortably. 
169. Correction of presbyopia.—In cases of presbyopes the cor- 
rection for near vision must be obtained, either for reading glasses 
260 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
169-170 
or for bifocals. The usual distance considered for a reading correc- 
tion is 33 centimeters. However, the patient’s vocation and habits 
must be taken into consideration. If he has formed a habit, as work- 
ing at a desk, his near correction will be for about 50 centimeters. 
The amount of plus sphere addition required will vary with several 
factors, principally age. The Jaeger, or some similar near vision 
card should be used at the distance the patient is accustomed to read, 
and plus spheres added to the distance correction in gradually in- 
creasing strengths, until Jaeger No. 1 can be read in comfort. It is 
better to add too little plus sphere for reading than too much. The 
total addition should never exceed plus 3.00N; if the patient is cor- 
rected for distance, he is, to all intents and purposes, emmetropic, 
and only 3 diopters of accommodation are required by the emmetrope 
for reading at 33 centimeters. Consequently, no more than 3 diopters 
are required even if the patient has no accommodative power as an 
addition for reading. 
As a general rule in regard to the addition required for near vision 
the following plus spherical lenses will be required for reading in 
addition to the distance correction: 
Age 
Plus sphere addition 
+ 0.50 S to +1.00 S. 
+ 1.00 S to +1.50 S. 
+ 2.00 S to +2.50 S. 
+ 2.50 S to +3.00 S. 
Practically invariably the same addition in plus sphere will be 
required for each eye. Care should be taken in prescribing a different 
“add” for reading for each eye, such may indicate an error in the 
correction for distance, or in some instances, rarely encountered, may 
mean a difference in accommodative power of the two eyes due to 
disease or injury. 
170. Transposition of formula.—Transposition of a formula 
may be useful in order to utilize a thinner lens, to compare two for- 
mulae, and to make similar prescriptions in the two eyes. In the trans- 
position of any formula the sign of the cylinder is changed, and 90° 
261 TM 8-300 
170-171 
MEDICAL DEPARTMENT 
added to the axis to obtain the new cylinder. The new sphere is the 
algebraical sum of the sphere and cylinder. For example— 
+ 3.00 £ with -4.00 Gx 90°= -1 £+4.00 Gx 180° 
and 
-2.00 £-1.00 Cx 90° = - 3.00 £+1.00 Cx 180° 
and 
+ 1.00 £+0.50 Gx 180° =+1.50 £-0.50 Gx 90° 
and 
+ 1.00 £-1.00 Gx 90° = O £+1.00 Gx 180° 
The transposition of a sphere does not change its optical value. The 
optical principles involved are those of rule (7) in the combination 
of lenses. For example— 
' +2.75 Cx 45°-3.25 Gx 135°= +2.75 £-6.00 Cx 135° 
or (transposing) 
-3.25 £+6.00 Cx 45° 
As an example, in the comparison of prescriptions we may deter- 
mine by retinoscopy that a patient, in our opinion, should wear a 
minus 0.75 £ plus 1.00 Cx 90°. He has been wearing habitually minus 
1.00 Cx 180°. These two formulae appear at a glance to be quite dis- 
similar. Nevertheless, they are almost the same; transposing our find- 
ings we have plus 0.25 £ minus 1.00 Cx 180°, and the difference between 
the two is only minus 0.25 £. Minus 0.25 Cx 45° and plus 0.25 Cx 135° 
appear at first to be two entirely different formulae, but actually there 
is a difference of 0.25 £ between the two. 
The optician who grinds the lenses may transpose a formula to 
obtain a lens that is thinner or thicker, as the case may be. 
A formula may be transposed for the purpose of making prescrip- 
tions for the two eyes similar, that is, plus or minus cylinder for each 
eye, instead of a plus cylinder for one and a minus cylinder for the 
other. 
171, Decentering of lenses.—Occasionally a spectacle lens may 
be decentered to obtain a prismatic effect. Decentering a plus sphere 
gives the effect of a prism base toward the direction of decentering 
(base will be toward the optical center). A decentered minus sphere 
gives the effect of base away from the optical center. The same is true 
of a cylinder decentered at right angles to the axis. 
The prismatic effect of a decentered lens will vary with the refractive 
index of the glass, but as a rule, for every centimeter of decentering 
there will be produced as many prism diopters as there are diopters 
in the meridian which is decentered. For example, consider a plus 
4.00 £; if the lens is decentered out (the optical center 1 cm. lateral 
262 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
171-173 
to the geometric center) the effect is a 4 diopter prism base out. Or 
another method— 
number of millimeters decentering 
where n equals prism diopters required and d equals dioptric strength 
of the lens. For example, 2 prism diopters are required in a plus 
10 X 2 
4.00 S\—-—=10 millimeters. The optical center would have to be 
placed 10 millimeters to the nasal side of the geometric center in this 
instance. 
Section XXI 
OPHTHALMOSCOPIC EXAMINATION 
Paragraph 
Ophthalmoscope 172 
Examination of media 173 
Indirect method 174 
Direct method 175 
Color of normal fundus 176 
Optic disc 177 
Retinal blood vessels 178 
Central area of retina 179 
Periphery of retina 180 
172. Ophthalmoscope.—a. Use.—The invention of the ophthal- 
moscope by Helmholtz in 1851 opened a new field of possibility in the 
diagnosis of systemic disease as well as affections involving the eye 
alone. By the use of this instrument the interior of the living eye may 
be examined, that is, those structures behind the lens, the vitreous, 
retina, choroid, intraocular nortion of the optic nerve, and the retinal 
blood vessels. 
b. Description.—Essentially the simple ophthalmoscope consists of 
a mirror, plane or concave, with a perforation or “peephole” at the 
center. Kays of light are reflected by the mirror through the pupil 
illuminating the interior of the eye and the details of the fundus. The 
dioptric system of the eye itself is utilized in obtaining an image of the 
structures under observation through the aperture or perforation in 
the mirror. The instrument is augmented by the use of lenses, plus 
and minus spheres, so placed in a disc that any one desired may be 
rotated before the opening in the mirror. 
c. Modifications.—There are many designs and modifications of the 
ophthalmoscope, of which the electric, which has its own source of 
illumination, is particularly useful, especially in the examination of 
patients who are bedridden, although the older type, as the Loring, 
263 TM 8-300 
172 
MEDICAL DEPARTMENT 
still has some distinct advantages which are not replaced entirely by 
the more modern electric types. The more popular models employed 
are those designed by May, Morton, Jackson, and Marple. Some of 
the electric ophthalmoscopes use prisms to deflect the emergent rays of 
light rather than mirrors. Further, some are designed to use ordinary 
110-volt current through a transformer or from dry cells carried in the 
handle of the instrument. Regardless of the type or model, all ophthal- 
moscopes are designed for the purpose of inspecting the media and 
fundus of the eye. 
d. Pupil in examination.—The ophthalmoscopic examination is ac- 
complished more thoroughly through a widely dilated pupil and with 
the accommodation of the examinee relaxed. The reasons are quite 
obvious. In the examination of applicants for Air Corps training the 
ophthalmoscopic examination should follow refraction routinely, while 
the pupil is still widely dilated and accommodation paralyzed. The 
examiner should wear his own correction for error of refraction when 
using the ophthalmoscope. 
e. Practice.—The student is advised that upon every opportunity 
he take advantage of the occasion to use the ophthalmoscope in a 
routine manner and that he adopt a definitely outlined procedure in 
order that no detail be overlooked, even where no pathology of the 
media or fundus may be suspected. Every fundus, normal or other- 
wise, is within itself a most interesting and instructive study, and 
every fundus is a new story, as no two are alike. The use of the 
ophthalmoscope is not limited to the ophthalmologist but is a diag- 
nostic instrument that is utilized to an advantage by the internist, 
the surgeon, the pathologist, obstetrician, and the general practi- 
tioner. The latter should familiarize himself with its use as he 
does his stethoscope. But to be adept in the use of the ophthalmo- 
scope, and particularly in the interpretation of ophthalmoscopic 
findings, will require an infinite amount of practice, perseverence, 
patience, and study; otherwise, the fundus of the eye may be a 
meaningless, although interesting and beautiful picture. 
/. Abnormal conditions of fundus.—It is not possible nor practi- 
cable in this section to describe the various appearances of abnormal 
conditions of the fundus; the student is encouraged to avail him- 
self of the opportunity to study the colored plates of Wilmer, Adam, 
and Clarke, and the stereoscopic plates of Oatman when possible, 
as so much more may be expressed by a picture, in colors, than by 
pages of description. 
g. Light.—The ophthalmoscope should be used in a darkened 
room, or at least the amount of light falling upon the eye being 
264 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
172-174 
examined should be reduced to a minimum, that is, light from 
sources other than the ophthalmoscope. 
173. Examination of media.—In the examination of the media 
the examiner, standing or sitting on the right side of the examinee 
when examining the right eye, holding the ophthalmoscope in his 
right hand before his right eye (in a manner similar to the retino- 
scope) approaches the examinee until the details of the iris pattern 
are seen through the aperture. The pupillary area will appear as a 
dull red reflex. Where there exists an opacity (in cornea, anterior 
chamber, lens, or vitreous) it will appear dark against the red back- 
ground—a bit darker than it actually is, as it is seen partially by 
reflected light. The approximate location of the opacity may be 
determined by having the examinee shift his visual axis slightly 
from the right to the left, or up and down; if the opacity is anterior 
to the pupillary plane it will move “with” the eye movement, if it 
is posterior to the pupillary plane it will move “against” the move- 
ment of the eye. The strength of the lens before the aperture may 
be increased or decreased as desired, but with any change in the 
lens strength the position of the ophthalmoscope before the eye must 
be altered, that is, brought closer to the eye with a stronger and 
farther away with a weaker lens. The self-illuminating types of 
ophthalmoscopes are equipped usually with a rheostat which controls 
the amount of illumination, and faint and diffuse opacities may be 
seen more easily with illumination reduced (Wilmer). The exam- 
iner should always use his right eye in examining the right eye, and 
left when examining the left eye of the examinee. 
174. Indirect method.—After the media has been inspected the 
fundus may be examined by the indirect method. And for this pur- 
pose the older type of reflecting ophthalmoscope, as the Loring, may 
be used to an advantage. The indirect method of ophthalmoscopy 
is not employed as frequently as it should be in many instances. It 
should be remembered that it has several distinct advantages; a 
greater portion of the fundus is seen at one time than by the direct 
method, and it is particularly applicable in high degrees of ame- 
tropia and where there exist slight opacities in the media. A plus 
4 to 8 diopter lens is rotated before the aperture of the ophthalmo- 
scope, and a plus 18. diopter lens (from the trial lens case) is held 
before the examinee’s eye with the other hand. The examinee is 
directed to look directly forward. The plus 18. lens, held between 
the thumb and forefinger of the examiner, is held before the eye 
being observed and steadied by the other fingers resting against the 
forehead. The examiner then approaches the examinee until a view 
of the fundus is obtained. By shifting the position of the plus 18. 
265 TM 8-300 
174-176 
MEDICAL DEPARTMENT 
lens the details may be brought more clearly into focus. Various 
portions of the fundus may be brought into view by having the 
examinee shift his visual axis. The indirect method gives a magni- 
fication of 3 to 5 diameters and the image of the fundus seen is 
always inverted. It is to be remembered that the room must be 
darkened, and after the student has once seen the fundus clearly he 
may change the lens from the trial lens case, increasing or decreas- 
ing its strength, and change the strength of the lens in the aperture 
of the ophthalmoscope until he finds the combination best adapted 
for his purpose. 
175. Direct method.—In the direct method of using the ophthal- 
moscope the examiner holds the instrument as near the examinee’s 
eye as possible, using “right eye for right eye and left for left.” 
The strength of the lens to be used in the aperture will depend upon 
the dioptric power of the eye being examined and the ability of the 
examiner to relax his own accommodation (taking for granted he is 
wearing his correction for ametropia). If the examinee is em- 
metropic and the examiner can voluntarily relax his accommodation 
no lens will be required in the aperture. As a rule the beginner will 
have some difficulty in learning to relax Ms accommodation and at 
first will prefer to use a weak concave lens in the aperture. He 
should learn to use the ophthalmoscope with both eyes open and in 
examining the fundus should imagine that he is looking at a picture 
some distance away in order to relax his accommodation. In ex- 
ploring the fundus the position of the ophthalmoscope may be shifted 
and the position of the examinee’s visual axis changed to bring into 
view different portions. By the direct method of ophthalmoscopy 
a magnification of about 14 diameters is obtained and the image is 
upright. 
In the examination of the fundus by the direct method a change 
in the dioptric strength of the lens in the aperture of the ophthal- 
moscope of 3 diopters represents an approximate difference in depth 
of 1 millimeter. For example, with no lens in the aperture the level 
of the outer portion of the disc is clearly seen but the bottom of 
the physiologic cup is blurred; if a minus 3 diopter sphere in the 
aperture gives a sharp definition of the bottom of the cup we may 
conclude that it is 1 millimeter below the level of the disc itself. 
176. Color of normal fundus.—The color of the normal fundus 
varies with individuals and in general is in keeping with the amount 
of pigment of the skin and hair, and depends upon the amount of 
pigment in the epithelial layer of the retina and in the choroid. 
Consequently the fungus of the pure-blooded negro is chocolate 
colored due to the fact that the amount of pigment in the epithelical 
266 NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
TM 8-300 
176-177 
layer of the retina is so dense that very little of the underlying 
choroid may be seen through it. In the brown mulatto it may be 
described as being of a chocolate red color. In the Indian and 
Chinese it begins to assume a more stippled appearance, and in the 
latter has a distinct yellowish tinge. With the Caucasians it varies 
from an orange red in the Mediterranean types to a light orange red 
in the pronounced blondes. With the latter the retinal pigment is 
so scanty that the underlying choroidal vessels are seen distinctly 
and even certain portions of the sclera may show either faintly or 
distinctly, due to scantiness of pigment of the choroid. In the albino 
pigment is lacking altogether in the retina and choroid, so portions 
of the sclera that are not obscured by retinal and choroidal vessels 
are seen distinctly, especially toward the periphery. 
177. Optic disc.—The optic disc (papilla) or the intraocular por- 
tion of the optic nerve is perhaps the most noticeable feature of 
the fundus and by its diameter as a standard of comparison the lo- 
cation of other points of interest are noted. The disc is located 
somewhat to the nasal side of the posterior pole of the eye (about 
15°). It is roughly circular in form and from it the retinal blood 
vessels radiate. The disc is made up of innumerable nerve fibers 
of the optic nerve spreading out from the main trunk over the entire 
surface of the retina, in a manner somewhat similar to a strand of 
rope being frayed at one end and evenly distributed over a concave 
surface after passing through a perforation in the surface. How- 
ever, these fibers are transparent. Consequently, the disc presents 
normally a depression or physiologic cup more or less centrally 
located. At the bottom of this depression there may be found the 
reticular or mesh-like strands of the lamina cribosa, the net-like 
fibers of the inner third of the sclera bridging across the opening. 
At the lamina cribosa the nerve fibers normally lose their medullary 
sheaths for the sake of transparency. The depth and diameter of 
the physiologic cup vary a great deal in normal eyes, and it may 
be so noticeable that it resembles a glaucomatous excavation. This 
portion of the disc is the paler in color, that is, whiter than the 
peripheral portion which may be described as being a pearl pink, 
which is derived from the capillaries invading its substance. The 
disc is usually paler on its temporal side, inasmuch as there are 
fewer nerve fibers emerging from this side. Immediately surround- 
ing the disc and more noticeable on the temporal side there may be 
seen a white ring concentric with the disc, which represents, where 
it does exist, a portion of the surrounding sclera which is visible 
because the retina and choroid do not quite meet the disc margin. 
267 TM 8-300 
177-179 
MEDICAL DEPARTMENT 
Frequently there may be found an accumulation of granules of pig- 
ment from the choroid, usually on the temporal side of the disc 
which may fill in partially the scleral ring. In myopia the scleral 
ring may be so marked that it assumes a crescentic form. 
178. Retinal blood vessels.—The retinal blood vessels emerge 
from the disc for their distribution over the retinal surface. The 
retinal circulation is terminal and normally does not anastomose 
within itself nor does it anastomose with the choroidal circulation. 
It can best be visualized after a review of its ontogenetic develop- 
ment. Occasionally there may be found an anastomosis (cilio- 
retinal) with a branch from one of the short posterior ciliary 
vessels, which enter the globe immediately around the optic nerve. 
Such an anastomosis is the exception rather than the rule. 
179. Central area of retina.—a. Blood supply.—The central 
artery of the retina is the first branch of the ophthalmic (a branch 
of the internal carotid) after it enters the orbit. It enters into the 
substance of the optic nerve 7 millimeters to 12 millimeters back 
of the lamina cribrosa and passes forward to emerge on the optic 
disc where it divides into a superior and inferior branch, each of 
which subdivides into temporal and nasal branches. The bifurcation 
of the central artery may occur behind the lamina cribrosa, or on 
the other hand some distance after it has passed beyond the margin 
of the disc on the retinal surface. The two temporal branches (su- 
perior and inferior) appear to encircle almost completely the macular 
region and send numerous branches toward it. Veins accompany the 
arteries in their distribution and are distinguished from them by the 
fact that the arteries are of a brighter red appearance, are narrower, 
and in their course are more direct or less tortuous than the veins. 
The central vein emerges from the globe by way of the optic disc 
and optic nerve. “The vein has a longer course in the subarachnoid 
space of the optic nerve than the artery. Therefore, in cases of in- 
creased intracranial pressure, it is more subject to engorgement from 
compression” (Wilmer). The vein usually empties directly into the 
cavernous sinus, ©r it may join the superior ophthalmic vein. 
The walls of the blood vessels or of the retina are transparent nor- 
mally, and what is seen as a vessel is the column of blood within its 
lumen. The vessels, both arteries and veins, show a definite light 
streak along their axes. This is more pronounced, that is, wider and 
brighter, on the arteries. This difference is probably due to the 
reflex from the thicker media of the arterial walls, while the reflex 
on veins is due to the reflection from the anterior surface of the 
column of blood alone (Wilmer). 
268 TM 8-300 
179-180 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
Where choroidal vessels are seen, as in the fundus of a blonde in- 
dividual, they may be distinguished easily from the retinal vessels, 
as they appear flat, show no light streaks, anastomose freely, and 
appear deeply embedded. 
h. Nutrition.—The retina as a whole is dependent upon two sources 
for its nutrition. The central artery of the retina with its branches 
takes care of the inner layers to the depth of the outer nuclear layer. 
The epithelial layer of the retina is dependent upon the capillary 
bed of the choroid underneath. Consequently it is readily under- 
stood that retinal degeneration will follow invariably degenerative 
or atrophic changes in the choroid. 
c. Crossing vessels.—Veins and arteries frequently cross one an- 
other in the retina but never does a vein cross a vein nor an artery 
cross an artery. 
d. Pulsation.—Venous pulsation in the retina is frequently en- 
countered and usually is of no significance. It is diastolic and is more 
noticeable at the disk where the vessel bends abruptly. During the 
acme of systole the intraocular tension presumably rises to the ex- 
tent that the walls of the veins collapse. Arterial pulsation, as seen 
with the ordinary ophthalmoscope, is considered as definitely patho- 
logic and may be indicative of increased intraocular tension, orbital 
tumors, hyperthyroidism, and aortic insufficiency. Under good illumi- 
nation and magnification arterial pulsation may frequently be seen 
in normal eyes. 
e. Central area.—After locating the disc, if the area temporal to it 
is explored, the central area of the retina will be found. This region 
will be noted in contrast with other portions of the fundus, as it 
appears to be shunned or avoided by the larger blood vessels. It is 
an area about 7 millimeters in diameter and contains the macula lutea, 
the fovea centralis, the fundus foveae and the foveola. The macula 
lutea is an area centrally located in the central area of the retina about 
1.5 millimeters to 2 millimeters in diameter, generally circular in out- 
line. It is noticeably darker in color than other portions of the retina 
and frequently will be found to be somewhat granular in appearance. 
The fovea centralis occupies the central portion of the macula lutea 
and represents approximately the posterior pole of the eye, being about 
3.6 millimeters to the temporal side of the disc. It is actually a funnel- 
shaped depression at the bottom of which is the fundus foveae, which 
is the thinnest portion of the retina. The minute foveola is at the 
center of the fundus foveae. 
180. Periphery of retina.—a. The extreme periphery of the 
retina is quite difficult to bring into view. However, with a widely 
269 TM 8-300 
180 
MEDICAL. DEPARTMENT 
GLASS' I 2 3 
VISION 20/20 20/40 20/100 
D.R 50 55 
USO. MX 10 M.T.IO . MX 12 
MX4 WITH I5.13 LX 4 _ 
L/ 0 ■ mx 5 m.t.5 mx t 
HYPER mtI MX I mt2 
p.l) . M.T. 15 C) R L.T, 5 - P. IX MUST HQU A L 
OR EXCEED ANY ESC), 
RJ.ENS DIPLOPIA V/ITH IN 50 CM. 
ANGLE 40° 40° 
IUJ R. M.T. 1.5 TOTAL OR M.T. 50 CYL. 
AfM'M thread 
A U w ll. A G E DIOPTERs 
IB B.B APEX IN ESC). 
IB 0.7 
20 0.5 APEX OUT EXO. 
21 0.2 
22 7 9 APEX UP HYPER 
'j'i /.(> THAT EYE 
24 7.4 
25 7- 2 
20 0 • 9 
27 0 • 0 
Figure 49.—Summary of minimal visual requirements for flying. 
270 TM 8-300 
180 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
dilated pupil and cooperative patient a view may be obtained slightly 
anterior to the equator. Each quadrant should be explored carefully. 
h. Upon the completion of the ophthalmoscopic examination it is 
suggested that a miotic (eserine salicylate % percent solution) be 
instilled. 
g. For a very complete review of pathological conditions of the 
fundus the student is advised to study carefully the colored plates 
from Atlas Fundus Oouli, by Dr. William H. Wilmer. 
271 TM 8-300 
180 
MEDICAL DEPARTMENT 
Appendix 
ABBREVIATIONS AND REFERENCES 
1. Abbreviations and signs used in ophthalmology. 
A or Acc Accommodation. 
Am Ametropia. 
As Astigmatism, astigmatic. 
As. H Hyperopic astigmatism. 
As. M Myopic astigmatism. 
Ax : Axis (of cylindrical lens). 
B Base (of prism). 
C or cyl - Cylindrical lens or cylinder. 
cm Centimeter. 
D Diopter. 
E Emmetropia, or emmetropic. 
F Field of vision. 
H Hyperopia, hyperopic, horizontal. 
HI -i Hyperopia latent. 
Hm Hyperopia manifest. 
Ht Hyperopia total. 
L or L. E Left eye. 
M Myopia or myopic. 
m Meter. 
M. A Meter angle. 
mm Millimeter. 
n Nasal. 
O. D. (R. or R. E.) Genius dexter (right eye). 
O. S. (L, or L. E.) Genius sinister (left eye). 
O. U Genius uterque (both eyes). 
Gph Opthalmoscope or opthalmoscopic. 
P. D Prism diopter. 
P. L Perception of light. 
P, p Punctum proximum (near point). 
P, r Punctum remotum (far point). 
Pr Presbyopia. 
R. or R. E Right eye. 
S or Sph Spherical lens. 
t Temporal. 
272 TM 8-300 
180 
NOTES ON EYE, EAR, ETC., IN AVIATION MEDICINE 
T Tension. 
Y Vision, visual acuteness, vertical, 
w With. 
+ Plus or convex. 
— Minus or concave. 
Equal to. 
Combined with. 
Infinity (20 feet or more distance). 
Foot, minute. 
Inch, second. 
Line. 
Degree (prism). 
Centrad (prism). 
Prism diopter. 
271818°—40 18 
273 TM 8-300 
180 
MEDICAL. DEPARTMENT 
2. References.—The part of this manual devoted to otolaryn- 
gology is not intended to be a textbook on otolaryngology, nor is it 
written for the purpose of supplanting existing textbooks on the sub- 
ject. The purpose of the outline is to stress important points in the 
examination of the eye, ear, nose, throat, and adjacent structures, to 
enumerate and explain the disqualifying findings prescribed in regu- 
lations, to review certain conditions affecting these parts of particular 
importance to the flyer, and to bring out certain practical points in 
the treatment of these conditions. 
No attempt has been made to give a detailed description of the 
anatomy or the physiology of the parts under discussion, except the 
labyrinth, as these are fully described in the standard anatomies and 
textbooks of otolaryngology. 
The material presented in this manual was derived from lectures 
on the examination of the eye, ear, nose, and throat given at the School 
of Aviation Medicine during the past several years. It is obvious 
that such a manual must be, of necessity, a compilation from various 
texts and authors. Further, the student should have reviewed clinical 
ophthalmology or should study some standard text in conjunction with 
this manual. 
The following smaller texts are recommended: 
Diseases of the Eye, by Sir John Herbert Parsons. 
Diseases of the Eye, by Charles H. May. 
The Eye, by C. W. Rutherford. 
For reference reading the following are recommended: 
Textbook of Ophthalmology, volumes I and II, by Duke Elder. 
Fuchs'1 Textbook of Ophthalmology. 
Diseases of the Eye, by De Schweinitz. 
Anatomy of the Human Orbit, by Whitnall. 
Clinical Physiology of the Eye, by Adler. 
Anatomy of the Eye and Orbit, by Wolff. 
Anatomy and Histology of the Human Eyeball, by Salzmann. 
Clinical Ophthalmology for the General Practitioner, by 
Ramsay. 
The Pathology of the Eye, by Friedenwald. 
Squint, by Claude Worth. 
Atlas of External Diseases of the Eye, by Neame. 
Medical Ophthalmology, by Moore. 
Visual Field Studies, by Lloyd. 
Methods of Refraction, by Thorington. 
Practice of Refraction, by Duke Elder. 
274 TM 8-300 
.180 
NOTES ON EYE, EAR, ETC., IN’ AVIATION MEDICINE 
Outline of Ocular Refraction, by Maxwell. 
Ophthalmic Optics, by Cowan. 
Errors of Accommodation and Refraction, by Clarke. 
Outline of Refraction, by Knighton. 
An Illustrated Guide to the Slit Lamp, by Butler. 
Slit Lamp Microscopy of the Living Eye, by Koby. 
Diagnostics of the Fundus Oculi, by Oatman. 
Atlas Fundus Oculi, by Wilmer. 
Interned Disease of Eye and Atlas of Ophthalmoscopy, by 
Troncosos. 
The Eye and Its Diseases, by Berens. 
It is suggested that where some point is not made clear in the 
manual the student should avail himself of the opportunity of a better 
and more detailed explanation in the above texts. 
AR 40-110 (Standards of Physical Examination for Flying) is not 
included in this manual for two reasons. Primarily, it would be a 
needless duplication as these regulations are available to the student 
in a bound volume, and secondarily the regulations themselves are 
subject to change from time to time. Upon the completion of each 
section of the manual the student should study carefully the para- 
graph of AR 40-110 pertaining to that particular phase of the examina- 
tion, paying special attention to the procedure, precautions, and 
interpretation of findings. 
275 TM 8-300 
INDEX 
Paragraphs Pages 
Abbreviations App. 271 
Abduction, power of 109 135 
Optical principles involved 11Q 135 
Accessory sinuses 15 11 
Accommodation of eye 120-126 154 
Amplitude 121 155 
Influence of age 123 156 
Calculating in diopters 125 158 
Changes in dioptive power 120 154 
Determining power of 124 157 
Far and near points 122 155 
Near vision 126 159 
Acuity, visual 71-79 91 
Alining power of eye 75 93 
Conditions that interfere with 76 93 
Factors— 
Physiological 71 91 
Psychological 71 91 
Formation of retinal image 72 91 
Of retina 74 92 
Resolving power of the eye 73 92 
Adduction, power of HI 135 
Adjunctive group of factors, depth perception 86 101 
Aero-otitis media 30-36 22 
Complications 34 26 
Definition 30 22 
Diagnosis! 33 26 
Etiology 31 22 
Pathology 36 28 
Symptomatology 32 23 
Treatment 35 26 
Analysis of lenses 166 243 
Anatomy of— 
Middle ear 27 18 
Inner ear 38-43 29 
Angle of convergence H3 136 
Meter H6 137 
Anterior chamber, inspection 134 168 
Apparatus, lachrimal 132 163 
Associated factors, heterophoria 108 134 
Auditory nerve, branches 40 35 
Binocular— 
Factors, depth perception 82 98 
Loupe 126 162 
Movements 64 120 
Parallax 35 101 
Projections 60 111 
277 TM 8-300 
INDEX 
Paragraphs Pages 
Blind flying 61, 62 54, 66 
Essentials 61 54 
Medical contribution 62 66 
Blind spot, physiologic 162 236 
Blood vessels, retinal 178 268 
Bones, facial, fracture of 19 13 
Branches of auditory nerve: 
Cochlear 40 35 
Vestibular 40 35 
Calculating accommodation in diopters 125 158 
Caloric douche test 60 54 
Cavity of nose 11 9 
Central area of retina 179 268 
Classification of defects in visual fields 161 233 
Cochlea 43 40 
Cochlear branch, auditory nerve 40 35 
Color blindness, military significance 144 194 
Color— 
Field of vision 159 225 
Confrontation test 157 223 
Perception: 
Examinations 146-148 200 
Methods 153 216 
Tests 149-152 213 
Directions for use 154,155 217,220 
Trichromic 141 187 
Vision 139-155 175 
Definitions 139 175 
Dichromic 142 189 
Effect of shortened red 143 193 
Physical basis 140 177 
Tests of 145 197 
Holmgren 152 214 
Ishihara.. 149 213 
Jennings 151 214 
Stillings 150 213 
Complete oculomotor paralysis 119 150 
Complications of aero-otitis media 34 26 
Conditions interfering with normal usual acuity 76 93 
Confrontation test, field of vision 157 223 
Convergence, vision 112-114 136 
Angle of 113 136 
Near point 114 136 
Prism 112 136 
Correction of presbyopia 169 260 
Coston’s syndrome 63 81 
Deafness in aviation 67 86 
Decentering of lenses 171 262 
Defects in visual field, classification 161 233 
278 INDEX 
TJVl 8-300 
Paragraphs Pages 
Depth perception 80-89 98 
Defective, etiology 88 105 
Definition 80 98 
* Factors: 
Adjunctive group 81, 86 98, 101 
Basic 81 98 
Binocular 82 98 
Diplopia, physiological 84 100 
Monocular 82 98 
Parallactic angle, measuring 87 104 
Retinal image, size of 83 99 
Determining accommodative power 124 157 
Deviations, optical: 
Horizontal, principles involved 102 125 
Vertical 103 126 
Diagnosis of aero-otitis media 33 26 
Dichromic color vision 142 189 
Diopters, calculating accommodation 125 158 
Dioptric power, changes in 120 154 
Directions for use of tests 154-155 217 
Holmgren (yarn) 155 220 
Ishihara plates 154 217 
Distance, interpupillary 115 136 
Ear: 
Anatomy • 27 18 
Conditions 63-68 81 
Coston’s syndrome 63 81 
Deafness in aviators 67 86 
Labyrinthitis 66 84 
“Leans” 68 87 
Meniere’s symptom complex 65 83 
Tinnitus aurium 64 83 
External 21-25 14 
Inner, anatomy and physiology 38-43 29 
Middle, effects of flight on 26-37 18 
Errors of refraction, classification 167 244 
Essentials of blind flying 61 54 
Etiology of— 
Defective depth perception 88 105 
Heterophoria 105 129 
Middle ear 31 22 
Examinations; 
Color perception 146-MS 200 
Eye 69, 70 88, 90 
Equipment 69 88 
Lens... 136 170 
Pupils 135 169 
Purpose 70 90 
Sighting 100 123 
279 TM 8-300 
INDEX 
Examinations—Continued Paragraphs Pages 
Eyelids 131 162 
Media 173 265 
Methods: 
Direct 175 266 
Indirect V. 174 265 
Ophthalmoscopic 172-180 263 
Vitreous, opacities of 137 171 
External— 
Ear 21-25 14 
Nose 10 8 
Extrinsic ocular muscles, physiology 93 116 
Eye: 
Alining power 75 93 
Equipment 129-131 162 
Examination 69, 70 88, 90 
Illumination, focal or oblique 128 161 
Inspection 127-138 161 
Structure *._■ 127 161 
Face 2 3 
Facial— 
Bones, fracture 19 13 
Injuries, maxillo 16-20 12 
Lacerations 17 12 
Field of— 
Fixation 91 113 
Vision 156-162 221 
Color 159 225 
Confrontation test 157 223 
Defects in, classification 161 233 
Form 159 225 
Perimeter 158 224 
Peripheral 156 221 
Tangent screen 160 228 
Flight effects on middle ear 26-37 18 
Focal illumination 128 161 
Formation of retinal image 72 91 
Fractures, facial bone 19 13 
Hand slit-lamp 130 162 
Hearing tests 23 15 
Heterophoria 92 115 
Associated factors 108 134 
At 33 centimeters 104 127 
Etiology.: 105 129 
Incidence 106 132 
Methods of detecting 107 133 
Holmgren test 152 214 
Horizontal deviations, optical principles involved 102 125 
Illumination, focal or oblique 128 161 
Influence of age upon amplitude of accommodation 123 156 
280 INDEX 
TM 8-300 
Paragraphs Pages 
Imbalance, technique of determining 101 124 
Injuries: 
Maxillofacial ; 16-20 12 
Nose 18 13 
Orbit 20 14 
Inner ear: 
Anatomy and physiology 38-43 29 
Cochlea 43 40 
Labyrinth: 
Membranous 39 32 
Osseous 38 29 
Semicircular canal f 42 37 
Sense organs, special 41 36 
Vestibule, physiology 42 37 
Inspection of eye 127-138 161 
Anterior chamber 134 168 
127 161 
Binocular loupe 129 162 
Hand slit-lamp 130 162 
Examination of eyelids 131 162 
Iris 134 168 
Lacrimal apparatus 132 163 
Lens 136 170 
Nystagmus 138 174 
Opacities 137 171 
Pupils 135 169 
Sclera 133 166 
Vitreous 137 171 
Intensity of sound 25 16 
Interpupillary distance 115 136 
Ishihara test 149 213 
Plates, use, in 154 217 
Jennings test 151 214 
Labyrinth: 
Membranous 39 32 
Osseous 38 29 
Labyrinthitis 66 84 
Lacerations, facial 17 12 
Lacrimal apparatus 132 163 
Larynx 8 7 
“Leans” - 68 87 
Lens examination 136 170 
Lenses 163-171 238 
Analysis 166 243 
Classification 163 238 
Combination 165 241 
Decentering 171 262 
Focal length 164 239 
Principal focus 164 239 
Transposition of formula 170 261 
281 TM 8-300 
INDEX 
Paragraphs Pages 
Maddox rod 98 122 
Maxillo facial injuries 16-20 12 
Bones, fracture 19 13 
Lacerations 17 12 
Nose 18 13 
Orbit 20 14 
Media, examination of 173 265 
Medical contributions, blind flying 62 66 
Membrane, tympanic 22 14 
Membranous labyrinth 39 32 
Meniere's symptom complex 65 83 
Meter angle, convergence 116 137 
Metric system in visual acuity 78 95 
Methods of detecting heterophoria 107 133 
Middle ear 21-25 14 
Aero-otitis media 30-37 22 
Anatomy 27 18 
Definitions 1 30 22 
Effect of flight on 26-37 18 
Etiology 31 22 
Pathology 36 28 
Physiology 28 20 
Symptomatology 32 23 
Terminology , 29 22 
Military significance of color blindness 144 194 
Monocular— 
Factor of depth perception 82 98 
Projections 90 111 
Mouth 1 2 
Movements: 
Ocular 90-119 111 
Binocular 94 120 
Near point, convergence 114 136 
Near vision 126 159 
Nose r 9-15, 18 8, 13 
Cavity 11 9 
External 10 8 
Injuries 18 13 
Obstruction 12 9 
Polyps 14 11 
Septum 13 10 
Sinuses 15 11 
Numbering of prisms 96 121 
Nystagmus: 
Ocular, physiological, and vestibular, differentiation 
between 45 43 
Inspection for 138 174 
Test 57 53 
Oblique illumination 128 161 
Obstruction of nose 12 9 
282 INDEX 
TM 8-300 
Ocular— 
Movements 90-119 111 
Nystagmus 45 43 
Oculomotor paralysis 119 150 
Opacities of vitreous 137 171 
Ophthalmoscope 172 263 
Optic disc 177 267 
Optical principles: 
Abduction 110 135 
Adduction 111 135 
Horizontal deviations 102 125 
Orbit, injuries to 20 14 
Organs, special sense, inner ear 41 36 
Orthophoria 92 115 
Osseous labyrinth 38 29 
Parallactic angle 87 104 
Parallax, binocular 85 101 
Past-pointing 49 47 
After douching 50 49 
Pathology of aero-otitis media 36 28 
Perception: 
Color, trichromic 141 187 
Depth 80-89 98 
Perimeter, field of vision 158 224 
Peripheral vision 156 221 
Periphery of retina 180 269 
Phorometer trial frame 99 123 
Physical basis of color vision 140 177 
Physiologic blind spot 162 236 
Physiological— 
Diplopia 84 100 
Nystagmus 45 43 
Physiology of— 
Inner ear 38-43 29 
Middle ear 28 20 
Extrinsic ocular muscles 93 116 
Pitch -v 24 16 
Point of convergence 114 136 
Meter angle 116 137 
Pointing test 58 53 
Polyps 14 11 
Power, eye: 
Abduction 109 135 
Optical principle involved 110 135 
Accommodative, determining 124 157 
Adduction 111 135 
Determining accommodative 124 157 
Dioptric, changes in 120 154 
Presbyopia, correction of 169 260 
Paragraphs Pages 
283 TM 8-300 
INDEX 
Paragraphs Pages 
Prisms 95 120 
Convergence 112 136 
Numbering 96 121 
Rotary 97 122 
Projection; 
Monocular 90 111 
Binocular 90 111 
Pupils, examination 135 169 
Ranula 5 6 
Readablity of various letters 79 96 
Red spectrum end. shortened, effect of 143 193 
References App. 271 
Refraction 163-171 238 
Errors— 
Classification 167 244 
Determination 168 247 
Formula transposition of 170 261 
Resolving power of eye 73 92 
Retina: 
Acuity of 74 92 
Central area 179 268 
Periphery of 180 269 
Retinal—■ 
Blood vessels 178 268 
Image; 
Formation 72 91 
Size 83 99 
Rotary prism 97 122 
Sclera- inspection of 133 166 
Seasickness 48 47 
Semicircular canals, physiology — 42 37 
Septum 13 10 
Sighting eye 100 124 
Sinuses 15 11 
Snellen test letters 77 94 
Squint 118 138 
Stillings test 150 213 
Symptomatology of aero-otitis media 32 23 
Syndrome Costen’s 63 81 
Tangent- 
Rule - — 160 228 
Screen 160 228 
Technique of determining imbalance 101 124 
Teeth - 3 4 
Terminology middle ear 29 22 
Tests: 
Color vision 145 197 
Hearing 23 15 
Heterophoria, at 33 centimeters 104 127 
284 TM 8-300 
INDEX 
Tests—Continued 
Holmgren 152 214 
Ishihara 149 213 
Jennings 151 214 
Stillings 150 213 
Vestibular 56-60 52 
Tinnitus aurium 64 83 
Tongue 4 5 
Tonsils 6 6 
Transposition of refraction formula 170 261 
Treatment ot aero-otitis media 35 26 
Trichromic color perception 141 187 
Tympanic membrane 22 14 
Vertical deviations 103 126 
Vertigo, vestibular 46-55 45 
After douching 47 47 
Definitions 46 45 
Falling 52 51 
After douching 54 52 
After turning 53 51 
Past-pointing 49 47 
After douching 50 49 
Cerebral function 51 50 
Vestibular- 
Branch, auditory nerve 40 35 
Nystagmus 44, 45 41, 43 
Definition 44 41 
Tests 56—60 52 
Caloric douche 60 54 
Falling 59 54 
Nystagmus 57 53 
Pointing 58 53 
Vertigo 46—55 45 
Vestibule, physiology 42 37 
Vision: 
Color 130-155 175 
Dichromic 142 189 
Near 126 159 
Peripheral 156 221 
Visual acuity 71-79 91 
Alining power of eye 75 93 
Factors concerned : 71 91 
Metric system in 78 95 
Normal, conditions interfering with 76 93 
Retina ■ 74 92 
Retinal image, formation of 72 91 
Snellen test letters 77 94 
Readability of various letters 79 96 
Visual fields- classification of defects in 161 233 
Vitreous, opacities of 137 171 
[A. G. 062.11 (8-24-40).] 
Paragraphs Pages 
285 TM 8-300 
INDEX 
By order op the Secretary of War; 
G. C. MARSHALL, 
Chief of Staff. 
Official : 
E. S. ADAMS, 
Major General, 
The Adjutant General, 
286 
B. S. GOVERNMENT PRINTING OFFICE: 1940 
For sale by the Superintendent of Documents, Washington, D. C. Price 35 cents