DYNAMIC 
OCULAR TESTS 
SHEARD DYNAMIC 
OCULAR TESTS 
Being 
A Compendium Dealing with Certain Phases 
of the Correlation of Accommodation and Conver- 
gence, together with Some Original Objective 
Methods of Investigating the Range and Ampli- 
tude of Accommodation both Monocularly and 
as Associated in Binocular Single Vision. 
BY 
CHARLES SHEARD, Ph. D. 
Director and Professor of Applied Optics, the Ohio State University: 
Collaborator in and Author of the Section on Physiologic 
Optics, The American Encyclopedia of Ophthalmo- 
logy: 'Author of Cylindrical Lenses, Dynamic 
Skiametry and various Physical and 
Physiologic Optical Researches in 
The Ophthalmic Record, The 
Physical Review and 
The Philosphical 
Magazine. 
THE LAWRENCE PRESS CO.. COLUMBUS. OHIO Dedicated to all men 
scientifically interested 
in ocular refraction. 
Copyright 1917 
By Charles Sheard TABLE OF CONTENTS. 
CHAPTER. 
PAGE. 
1. THE OUTLINE OF AN EYE EXAMINATION WITH SPECIAL 
REFERENCE TO CERTAIN DYNAMIC TESTS UPON THE 
EXTRA-OCULAR MUSCLES 7 
II. VARIOUS SUBJECTIVE DYNAMIC METHODS OF INVESTI- 
GATING CONVERGENCE AS ASSOCIATED WITH AC- 
COMMODATION, FUSIONAL CONVERGENCE, AND 
THEIR IMPORTANCE 58 
III. A RESUME OF PRESENT DAY METHODS OF INVESTI- 
GATING THE ACCOMMODATIVE RANGE AND AMPLI- 
TUDE 86 
IV. A RESUME OF METHODS OF DETERMINING THE RELA- 
TIVE RANGE AND AMPLITUDE OF ACCOMMODATION 
AND CONVERGENCE 95 
V. AN OBJECTIVE METHOD OF DETERMINING THE MONOC- 
ULAR AMPLITUDE AND RANGE OF ACCOMMODATION . 104 
VI. AN OBJECTIVE METHOD OF DETERMINING THE BI- 
NOCULAR RANGE AND AMPLITUDE OF ACCOMMODA- 
TION AND THE EFFECTS WHICH LATERAL IM- 
BALANCES HAVE UPON THE SAME 115 
VIL THE PRINCIPLES AND METHODS OF DYNAMIC SKI- 
AMETRY 124 
BOOKS FOR STUDY AND REFERENCE 139 
INDEX BY WAY OF INTRODUCTION. 
When a writer assigns himself the delightful task 
of preparing a brochure upon some central theme he 
is invariably confronted with the problem of what to 
omit. There has been such a development in ophthal- 
mological and optical science within the past twenty 
years, particularly along lines pertaining to investi- 
gations upon the ocular muscles, that one can hope, in 
a compendium of this character, to call attention only 
to some of the most important aspects of the subject. 
We have, up to the present time, insofar as the 
writer knows, been possessed of no objective methods 
of investigating the accommodative resources. One 
of the principal purposes of this rubric is to place be- 
fore practitioners upon the eye some original and very 
simple methods dealing with objective examinations 
upon the accommodation and to point out their im- 
portance. Very naturally monocular tests lead into 
ways and means of making binocular Investigations 
upon such functions; we are, therefore, including a 
brief presentation of some of the valuable subjective 
tests which should be made upon accommodation as 
associated with convergence, and fusion convergence, 
as well as the objective tests peculiar to dynamic ski- 
ametry. 
No single method of examining the ocular resources 
can or should be considered a sine qua non. That 
which one method fails to reveal and disclose may be 
made apparent through another. Hence, it behooves 
all practitioners to engage in dynamic as well as static ocular tests. Data upon ocular functions and 
their correlation should be obtained as a matter of rou- 
tine examination; we cannot hope to scientifically solve 
an intricate ocular problem without the premises from 
which to draw our conclusions. 
The topics which are presented within these pages, 
together with many discussions germane thereto, are 
receiving detailed attention in the author's series of 
articles on ''Dynamic Skiametry and Other Dynamic 
Methods for the Determination of the Proper Coordi- 
nation of Accommodation and Convergence and the 
Conservation of the Visual Functions" now appearing 
in the Keystone Magazine (Philadelphia) of Optics. 
These, when completed, will be published in book 
form by the Keystone Company. 
We are hoping that we shall find the time and have 
the strength to prepare from year to year similar 
brochures to the one now being presented to you. If 
all is well we shall next greet you with a small volume 
on "Prisms-When and When Not t o Prescribe 
Them." 
We hope the reader will pardon any "sins of omis- 
sion or commission." These paragraphs have been 
penned during the leisure moments of a rather busy 
daily life. 
And again, if you disagree with any or all of the 
views herein presented, so much the better, if such dis- 
agreement is not only iconoclastic but constructive. 
Written from my study and office. 
365 W. 10th Ave., 
Columbus, Ohio. 
June, 1917. CHAPTER I. 
The Routine of an Eye Examination With Special Reference 
to Certain Dynamic Tests Upon The Extra- 
Ocular Muscles. 
No two men would, in general, build exactly the 
same kind of a house. Yet, in the last analysis, each 
must have a definite plan of procedure and would 
normally pass from the cellar to the roof, fitting each 
part into symmetry and usefulness to form the whole. 
Fundamentally, there must be order-, it has not been 
granted man to bring order out of chaos at a moment's 
notice or without a study of the problem involved and 
a coordination of the correlated parts. The writer 
hopes, therefore, that the reader of experience will 
pardon these few oncoming paragraphs in which at- 
tention is called to (1) the necessity of orderliness of 
arrangement as well as cleanliness of office and con- 
venience and ease of operation in making ocular tests, 
and (2) the necessity for a complete record of the 
results of the various tests made. 
Nothing disgusts or chagrins me more than to enter 
an office which is untidy, filled with superfluous ma- 
terial or so ordered as to actually if not purposely 
attempt to throw over me some sort of an impression 
as to the eruditeness of the occupant. Simplicity and 
orderliness should be written over everything-includ- 
ing the practitioner. 
Full and accurate data should be preserved in every 
case examined. Paper and cardboard are relatively 
cheap and afford a means of making a permanent 8 
The Routine of an Eye Examination. 
record of one's investigations; man's memory is short 
and his brains are too valuable to be used as an ency- 
clopedia of specific facts in any case. 
The writer uses a plain white card, 5x8 inches in 
size. This is large enough to prevent the very evident 
psychological reaction caused by too small a card and 
yet small enough to be conveniently handled and filed 
away. We have never believed in cards printed in 
various sub-headings for the reason that no two cases 
ever call for the same amount of recorded material 
upon any point. In a word, plenty of space is con- 
ducive to an ample record of data. 
As a general rule we follow the subjoined order of 
procedure, modifying any tests or omitting any which 
we deem best. We believe, however, that it is unwise 
to assume anything in any scientific investigation, least 
of all in ministering to the most precious faculty of 
vision, and that as a general rule all static and dynamic 
tests should be employed. 
1. History. 
2. Ophthalmoscopic and External Eye Examina- 
tion. 
3. Ophthalmometric Examination. 
4. Static Retinoscopic Investigations. 
5. Dynamic Skiametric Tests. 
6. Monocular and Binocular Objective Tests 
Upon the Amplitude and Range of Accommodation. 
7. Subjective Acuity Tests. 
8. Comparison Teets as to Equality of Acuity at 
Distance. 
9. Binocular and Monocular Tonicity Tests. 
OUTLINE OF THE ROUTINE. The Routine of an Eye Examination. 
9 
10. Monocular Test of the Oblique Muscles. 
11. Duction Tests of the Recti and Oblique Mus- 
cles. 
12. Version Tests. 
13. Accommodative Convergence Tests at the 
Reading Point. 
14. Tests for Cyclophoria and Hyperphoric Con- 
ditions at the Reading Point. 
15. Subjective Monocular and Binocular Near- 
points. 
16. Comparison Tests as to Equality of Accommo- 
dative Amplitude. 
17. Monocular Tests Upon Amplitude of Accom- 
modation (using Concave Lenses, the patient reading 
No. 2 Jaeger type at thirteen inches.) 
18. Fusional Reserve Convergence at the Reading 
Point. 
HISTORY. 
The full data as to name, age, occupation and so 
forth should be initially recorded. The question of 
occupation is most important since many vital points 
of refractive correction are thereby emphasized, par- 
ticularly when the occupation is one demanding chiefly 
distance or near vision as the case may be and in pres- 
byopia. The usual series of questions put to the patient 
should include inquiries upon (a) difficulties in distant 
or near work, (b) headaches and their location, (c) 
ocular fatigue, (d) drowsiness, nausea or dizziness, 
(e) ability to change readily from distant to near see- 
ing and vice versa, (f) diplopia, either at distance or 
near, (g) sensitiveness to light, both natural and arti- 
ficial, (h) diseases, particularly diphtheria, scarlet 10 
The Routine of an Eye Examination. 
fever, recent condition of measles, nervous exhaust- 
ion or anemia, conditions of throat, ears, nose and 
teeth, since these are most important factors in the 
etiology of restricted or weakened accommodation- 
a condition, by the way, very frequently encountered 
-as well as in deficient muscular innervations. 
OPHTHALMOSCOPIC AND BLOOD PRESSURE EXAMIN- 
ATIONS. 
No case should ever fail of an ophthalmoscopic and 
external eye examination. To the refractionist who 
is a non-medical practitioner this is absolutely essen- 
tial as the first step in an examination, since abnormal 
conditions should not in general receive optical treat- 
ment until after the case has been referred back by 
the medical practitioner. All pathologic conditions 
should be immediately referred to the family physician 
or otherwise designated practitioner of medicine. If 
the case is one demanding refractive as well as medi- 
cal treatment the jvriter sees no reason why all the 
ocular comfort possible should not be rendered the 
patient, provided he make the reference referred to 
and provided the results of his investigations will not 
be simply of a temporary nature to be ultimately large- 
ly modified after proper medical treatment. 
Blood pressure tests have been extremely valuable 
in ocular work, especially in cases of very high or low 
pressure. They often serve as corroborative evidence 
of ophthalmoscopic examinations which evidence 
retinal hyperesthesia, constricted papilla, tortuous 
veins, depleted arterial circulation. In fact such blood 
pressure tests may be more prognostic than diagnostic 
and serve as a means, taken with the patient's history, The Routine of an Eye Examination. 
11 
of discovering various impending conditions before 
they are clearly written upon the retina. E. G. Wise- 
man has written a most valuable treatise on "Blood 
Pressure in Ocular Work," which should find a place 
in the study of every refractionist. 
OPHTHALMOMETRIC EXAMINATION. 
While the findings as obtained by the ophthalmo- 
meter upon the amount and axis of the astigmia are 
not in general of sufficient accuracy to enable us to 
prescribe directly therefrom, these findings are, never- 
theless, most valuable. For the cornea is the only por- 
tion of the refractive apparatus which is not subject 
to change during an examination. The location of the 
principal meridians and the refractive differences be- 
tween them serve, when the usual allowance is made 
for the presence of approximately half a diopter of 
physiologic astigmia against the rule, as a valuable 
initial determination of the amount and the axis of 
the probable astigmatism and aid materially in retino- 
scopic determinations. Many reasons can be assigned 
as to why ophthalmometric, retinoscopic and subjective 
findings do not agree in toto in the determination of 
astigmia. Disagreements in such findings in reality 
furnish the examiner with differential tests. The 
normal cornea may be taken as having a radius of 
curvature of about 7.5 mms. or 45 diopters power. If 
both pointers on the instrument or the measurement 
of both meridians indicate radii of curvature greater 
than 7.5 mms. plus cylinders are in general indicated 
with the axis in such a position as to tend to make 
both meridians of equal power, this power being the 
highest obtainable. If both pointers on the instru- 12 
The Routine of an Eye Examination. 
ment indicate radii of curvature less than 7.5 mms. 
minus cylinders may be safely assumed as indicated 
to bring the equality of refractive power as nearly 
a minimum value as possible. A corneal astigmatism 
may be neutralized by a physiologic astigmia of the 
posterior surface of the cornea, by a tilting of the lens 
or lack of alignment of the ocular refractive parts or 
by accommodative astigmia. 
The practitioner must be on his guard that cylinders, 
incorrect in character and axis, are not prescribed. 
We refer to a prescription such as - 0.50 cyl. ax. 180 
whereas + 0-50 ax. 90. should have been prescribed 
and was really demanded. Necessarily, in cases of 
compound corrections, such reversal of character and 
axis of the cylinder may legitimately occur and the 
only question can then be that relative to under-or 
over-correction spherically; the question of the spheri- 
cal element is, after all, one of the most vital points 
in such cases as the following: 
Case i. A young lady, aet. twenty-five years, 
came in complaining of extreme nausea, inability to 
study or concentrate or do anything which in anywise 
demanded the use of her eyes for an hour. She was 
wearing lenses, O. U.-.75 cyl. ax. 180, prescribed 
about a year previously under a cycloplegic. The oph- 
thalmometric determinations showed in each eye the 
following: horizontal meridian (180°) 43.75 D, verti- 
cal meridian 45 D. One would, therefore, presumably 
have looked for a correction involving -|-0.75 cyl. ax. 
90 or its equivalent in transposed form should a spheri- 
cal element enter. Static retinoscopy, after some fifteen 
minutes' inaction of the eyes under fogging lenses, and The Routine of an Eye Examination. 
13 
the subjective determinations disclosed practically the 
same findings as she was then wearing. Dynamic ski- 
ametry at 13 inches indicated O. U. +0-5 D. S. CC 
4- 0.75 cyl. ax. 90 or in transposed form O. U. -J- 1-25 
D. S. 3 --15 cyl. ax. 180. The tests upon convergence 
as associated with the accommodation at the reading 
point, fusion being passive, evidenced some 6° eso- 
phoria. The total amplitude of accommodation was not 
in excess of 6 D, wearing the dynamically determined 
correction. The evidence was clear, therefore, that 
her accommodative needs were not being adequately 
met at the time she consulted us; as a result we 
judged it wise to give her O. U. + 0.75 cyl. ax. 90 
(equivalent, of course, to 4~0.75 D. S. 3-.75 cyl. 
ax. 180) for near work at first, but to be ultimately 
worn, if possible, for all distances. This was done, 
soon affording permanent relief and satisfaction. The 
ophthalmometric findings were to my mind a valuable 
aid in the solution of this ocular problem, demanding 
not only an astigmatic correction but also accommoda- 
tive assistance. Hence the static retinoscopic and sub- 
jective tests must be held in abeyance in view of cer- 
tain ophthalmometric findings and in the face of dyna- 
mic skiametric tests, dynamic tests upon the accommo- 
dation and various dynamic tests upon the correlation 
of accommodation and convergence. 
The ophthalmometric determinations are of consid- 
erable value also in cases of oblique astigmia and in 
cases of cyclophoria when binocular single vision is 
attempted. Cases arise in which static retinoscopic 
and subjective tests conducted at twenty feet disclose 
the axis of astigmatism at 90°, for example, when the 14 
The Routine of an Eye Examination. 
ophthalmometer shows the axis at slightly oblique 
positions, such as 80° or 100°. The writer believes 
that when an eye, not under the influence of a cyclo- 
plegic, looks down the barrel of the ophthalmometer 
it rather definitely fixes monocularly the end of the 
telescopic tube and that, while its mate may be under 
cover, there is a considerable amount of binocular 
activity and convergence under conditions as ordinarily 
found. Hence, it often occurs that ophthalmometric 
axes in cases of oblique astigmia agree better with 
dynamic skiametric or binocular findings than with 
monocular findings obtained by either static retino- 
scopic or subjective methods. This would indicate 
that differences between (a) ophthalmometric and 
(b) retinoscopic or subjective monocular findings as 
to the position of the axis of correcting cylinders may 
be attributed, in part at least, to the fact that in the 
first named set of findings binocular functions are 
more active than in the latter named tests. 
Case 2. We cite at this point the case of a 
woman forty-five years of age who had suffered all 
her life from ocular discomfort and who had not been 
able to do much if any near work. Static retinoscopy 
disclosed O. U. -pO.5 D. S. + +1.25 cyl. ax. 90 and 
subjectively these lenses gave normal visual acuity. 
She was wearing a binocular distance correction of 
+0.62 D. S. + +1-12 cyl. ax. 90, which, in the light 
of all the acuity and muscular poise tests at twenty 
feet, seemed satisfactory. Dynamic skiametry with 
fixation and observation at thirteen inches indicated 
O. D. +2.5 D. S. C +1.25 cyl. ax. 75°-65° and O. 
S.C+2.5D.S.C+1.25 cyl. ax. 105°-115°. The The Routine of an Eye Examination. 
15 
ophthalmometer findings showed the axis at 80 and 
100 degrees respectively; a case, by the way, affording 
evidence of the fact that the ophthalmometric findings, 
in which of course only corneal astigmia is disclosed, 
agreed better with the dynamic than the static findings 
as to the position of the correcting cylinders. Thus, 
in spite of the monocular occlusion, an eye fixing the 
end of the telescope (unless under the influence of a 
complete cycloplegia) will assume a condition of 
muscular poise and balance approximating at least the 
conditions existing under binocular usage. The tests 
at the reading point in the case under discussion were, 
therefore, made by initially inserting the sphere for 
reading as dynamically determined. With such assist- 
ance some of Snellen No. 3 (V=1D. S.) could be 
made out. The insertion of the -f-1.25 cyl. ax. 90 en- 
abled still smaller type to be read, but not with ease 
or clearness; an increase or decrease of spherical ele- 
ment did not benefit conditions. The cylinder was 
turned into the 75° position, when No. 2 Jaeger type 
(V=.5D. S.) was read with ease and comfort and 
evidence afforded of a considerable range of reading 
accommodation. A similar test upon the left eye ex- 
hibited superior acuity results with the cylinder at 
position 105°. The results binocularly with the cyl- 
inders at the oblique axes were infinitely better than 
with the cylinders in the positions statically determined 
and as statically demanded in the distance correction. 
With these corrections before the eyes, a test was 
made for the cyclophoric imbalances by the use of the 
double Maddox prism and a line of test type. (See 
Figures 23 and 25, Chapter II.) A fair degree of 16 
The Routine of an Eye Examination. 
minus cyclophoria was evidenced at the reading point 
and practically none at distance; in the latter tests no 
corrections were inserted before the eyes. Following 
the Steele rules as laid down in Savage's "Ophthalmic 
Neuro-Myology" (see also Savage's "Ophthalmic 
Myology," page 406), this woman was given for read- 
ing O. D. +2.25 D. S. SS- +1.25 cyl. ax. 75 and 
O. S. +2.25 D. S. C +1-25 cyl. ax. 105. 
Such a case as this, to be sure, is not of common 
occurrence. As to the etiology of the rotation of the 
astigmatic planes or torsion of the vertical meridional 
planes nasally we can only conjecture. As Savage 
says: "A too high attachment of the interni or too 
low attachment of the externi would cause a minus 
cyclophoria, while a too low attachment of the interni 
or too high attachment of the externi would cause a 
plus cyclophoria. When there is a normal attachment 
of the interni, there can result from their action no 
cyclophoria." In the case in hand, we may believe 
from the evidence afforded that the interni were 
attached too high (or the externi too low), and that 
in the act of converging there was caused a torsion 
of the eyeballs about their anteroposterior axis turn- 
ing the upper portions of the vertical meridians nasally 
in each case and therefore throwing upon the inferior 
obliques a burden which they could not bear. The 
superior obliques would correspondingly be relieved 
from normal action. 
This account of these interesting ocular conditions 
is inserted at this point to call attention to the possible 
effects which such muscular conditions, because of 
their effects upon the poise of the eyeball and the posi- The Routine of an Eye Examination. 
17 
tions of the vertical and horizontal meridians, may 
have upon the visual tests conducted at the reading 
point and upon the accommodative resources as ap- 
parently or subjectively exhibited. Such a case as this 
as well as many others, exhibiting apparently sub- 
normal or depleted accommodation, as judged by the 
subject's ability to read fine print, emphasizes the 
great need of some satisfactory objective method of 
determining the amount of accommodation possessed 
by a patient. The writer has developed such a method 
and, while it may not be all that might be desired, it 
will be disclosed in later paragraphs and will be found 
most serviceable. 
STATIC RETINOSCOPIC TESTS. 
It is not our purpose to go into the details of the 
methods and practices of static retinoscopy: these 
may be obtained from any of the several standard 
treatises upon this subject. We do desire, however, 
to call attention to some of the factors which may 
cause disagreement between such findings and the 
results of subjective tests. 
(A) Ciliary Relaxation. Fixation Definite but 
Passive. If the patient looks vaguely into space with- 
out the assistance of some definite and partially visible 
fixation point, his gaze is more than likely to be both 
uncertain in direction as well as position. To insure 
this definiteness of fixation the one-hundred-foot let- 
ters may be turned up in the chart and the patient told 
to keep his attention fixed upon them. The great cri- 
terion in static methods is ciliary relaxation. Hence 
monocular fixation must be definite but passive. The 
writer has also found it advantageous in cases of 18 
The Routine of an Eye Examination. 
hyperopia, in suppressing accommodation, to turn up 
in the lens battery of the optometer or insert in the 
trial frame sufficient lens power to considerably over- 
correct and cause opposite retinoscopic motion to that 
initially discovered when only the working lens is 
present. In cases of myopia such a method is not gen- 
erally necessary since the working lenses are sufficient 
for this purpose. The procedure is to then slowly 
reduce lenticular power until the maximum plus and 
minimum minus just before reversal of shadow occurs 
is reached. 
(B) Retinal Sensitiveness. Retinae unduly sensitive 
to light may cause, under the influence of light thrown 
from the observer's mirror into the eye, a temporary 
irritation that will produce a spasm of the ciliary. 
Such reflex actions may be induced to relax by dim- 
ming the source of light used in skiametric work. The 
self-luminous instrument is generally superior to the 
non-luminous mirror in this particular. One may be 
forced to make his findings ad interim by flashing the 
light on and off the eye under examination. 
(C) Irregular and Peripheral Refraction. The 
cornea and other refractive media may not be prop- 
erly centered or regularly curved. Hence exact neu- 
tralization of the skiascopic shadow may be imposs- 
ible or difficult, (see the section on "Scissor Move- 
ments.") The "visual zone" or the portion of the 
pupil surrounding the visual axis should be regarded 
in retinoscopic testing. Very frequently hyperopic 
cases will arise in which, due to large pupils with the 
existence of positive aberration, a shadow will be 
apparently neutralized or even reversed when the The Routine of an Eye Examination. 
19 
motion at the center of the pupil will still be "with", 
or hyperopic. 
(D) Macular vs. Non-Macular Refraction. In 
static retinoscopic tests as usually conducted, the 
patient's gaze as to his right eye is directed over the 
operator's right shoulder and over his left for the left 
eye. The portion of the retina thus made conjugate 
to the point passively fixed, due allowance being made 
for the working lens, is not the same as is made con- 
jugate to the observer at this working distance. In 
other words, the refraction is not determined along 
the visual axis. We cannot assume a uniformly curved 
or spherical retinal surface; the fovea is known to be 
a slight depression in the macular area; hence objective 
findings may differ considerably when the light spot 
upon the retina falls at or remote from the fovea. 
The vital point is, therefore, that the skiascopic find- 
ings are not ordinarily made along the visual axis and 
hence many irregularities, due to obliquity of lenses, 
non-macular conjugate point and so forth may arise 
and disagreements between objective and subjective 
methods result because of lack of proper precaution 
in knowing the conditions under which each is carried 
out. 
Eberhardt's macular reflectoscope. 
John C. Eberhardt has devised a simple and ingen- 
ious method of testing very close to the fovea centralis 
and the writer is pleased to say from experience that 
he has found it most serviceable. The "macular re- 
flectoscope" as constructed by the inventor consists 
of a stand placed, say, forty inches from the patient 20 
The Routine of an Eye Examination. 
and carries two mirrors. The device is diagram- 
matically shown as a horizontal cross-sectional cut in 
Figure 2. 
The macular reflectoscope is represented at D and 
consists of two parallel, plain mirrors, L and N, so 
placed before the eye of the person being examined 
as to enable an illuminated eighty or one hundred foot 
letter (B in the figure) to be seen or at least fixed 
upon by the eye, A, in its primary position by virtue 
of the double reflection of light by the mirrors L and 
N placed at an angle of about forty-five degrees with 
the line of sight. The double mirror device causes a 
lateral shifting of the letter or letters viewed; a single 
ray of light from the illuminated letter (B) to the 
macula (M) or fovea centralis is shown as B-L- 
N-M. The operator, O, with retinoscope at R, may 
then proceed to the skiametric refraction of the eye 
in a direction approximating the direct line of sight. 
By this device the possibility of incorrect findings will 
be reduced to a minimum if, by the use of mirrors as 
described, we can test close to the visual axis. 
The writer uses the macular reflectoscope attached 
to the rod of his phoro-optometer by means of a spe- 
cial sleeve sliding along the rod ordinarily attached to 
the instrument and employed for carrying the reading 
and near muscle-test cards. This sleeve carries a 
screw permitting of its rigid clamping; through a 
socket at the side of this movable sleeve runs the rod 
carrying the mirrors. This gives practically every 
motion as to angle and height of mirrors desired and 
allows of its ready attachment to or removal from the 
optometer or can be swung by means of the rod out The Routine of an Eye Examination. 
21 
\F13l 
Pig Z. 
Figure 1. Illustrative of the Mechanism of Scissor Move- 
ment. 
Figure 2. Diagrammatic Scheme Showing the Use of the 
Eberhardt Macular Reflectoscope. 
of the way when not in use. It can likewise be placed 
as near or as far from the patient as desired (up to 
twenty-six inches approximately), so that when -J-1.5 
D. S. is used as a working distance lens the observer's 22 
The Routine of an Eye Examination. 
retinoscope is stationed just back of one of the mirrors. 
This or any other scheme similar to the macular re- 
flectoscope can also be used without trouble when a 
chart over the patient's head and a mirror at ten or 
so feet away are used in the testing room. 
In his published writings, Eberhardt has called at- 
tention to some of the differences between ophthal- 
mometric, subjective and retinoscopic findings upon 
the axis of cylinders correcting astigmia and has 
pointed out the diagnostic value of retinoscopic find- 
ings made with the use of the macular reflectoscope 
in cyclophoric imbalance. Quite recently the writer 
has been the recipient of some very interesting letters 
from Mr. Eberhardt containing his expressions of 
opinion upon this topic and takes the liberty to quote 
from these communications the following sentences: 
"This procedure, being monocular, the binocular 
functions become passive, the eye under observation 
assuming the position of greatest comfort. This has 
been found to be an important factor in oblique astig- 
mia, particularly where the obliquity of the axis is 
greater in one eye than in the other, thus imposing an 
abnormal demand upon the oblique muscles. Cyclo- 
phoric imbalances are often due to this condition. 
This enforced malfunctioning, if extended over a 
number of years, frequently manifests itself by ap- 
parently contradictory results obtained by subjective 
and objective procedures, a discrepancy being found 
in the position of the axis in subjective acuity tests, 
skiascopic refraction and corneal readings by the aid 
of the opthalmometer." 
And, again in another connection he writes: "In The Routine of an Eye Examination. 
23 
the study of oblique astigmia coupled with cyclophoria, 
I have found the macular skiascopic procedure most 
interesting; the very discrepancies between results ob- 
tained subjectively, by the skiascope and by the oph- 
thalmometer furnished that differential data which 
enables an operator to make logical deductions by 
reasoning from cause to effect, always having in mind 
that the law of self-preservation dominates the human 
functions. This can be particularly appreciated in the 
case of irregular oblique astigmia when, for example, 
the obliques have been forced over an extended period 
of years to rotate the two eyeballs so as to make fusion 
of the two retinal images possible, force of habit is 
such that, under the binocular acuity tests, the prime 
desire of vision will naturally bring with it, at least 
in part, the former torsional excursion. Under the 
condition of fog existing in skiascopy this is partially 
made passive, although the involuntary activity of the 
binocular functions still will dominate this acquired 
faulty functioning, whereas when corneal conditions 
are studied through the telescope of the ophthal- 
mometer but little visual stimulus is present, as one 
eye simply looks into the tube and, one eye being 
occluded, binocular activity becomes passive. This is 
a fertile field for thought. I have hundreds of interest- 
ing cases on record where the solution was found 
* * * * to indicate a discrepancy between axes of 
cylinders accepted at infinity and those shown at the 
reading distance." 
THE SCISSOR MOVEMENT IN RETINOSCOPY. 
"Scissor movement" is a form of irregular astigma- 
tism and is of sufficiently frequent occurrence in 24 
The Routine of an Eye Examination. 
retinoscopy to warrant further description and meth- 
ods of handling such cases refractively than are given 
in our textbooks. In general terms, the shadow is 
split into two portions which, as the mirror is rotated, 
advance from opposite sides of the pupil and merge 
into one band giving the effect of closing a pair of 
scissors. On rotation of the mirror in the direction 
the reverse of that first employed the two oppositely 
moving reflexes again appear distinct and separate 
with a dark space intervening. Some uncertainty 
exists as to the cause of this phenomenon but it has 
probably been properly attributed, in general, to ectasia 
corneae and slight tilting of the lens. In this latter con- 
dition the antero-posterior axis of the lens is not at 
right angles to the plane of the cornea. This tilted 
lens would cause one portion of the skiametric reflex to 
act myopically (light area moving against motion of 
plane mirror) and the other portion hyperopically. 
Scissor movement may therefore be due to coma on 
account of the obliquity of one or more surfaces of 
the dioptric media to the path of the incident light. 
This hypothesis is in part substantiated by the follow- 
ing facts:- (1) in an eye having a normal reflex by 
direct illumination, the scissor movement may be ob- 
tained by directing the beam of light obliquely, (2) a 
tilted spherical lens, especially if of fairly high power, 
in front of an eye may produce such an effect, (3) 
the effect can be artificially produced with schematic 
eyes by the use of obliquely directed light and (4) by 
a combination of lenses, in bifocal form or character, 
giving for example an effect of -3.00 D. in upper 
portion and ff-3.00 D. in lower portion placed before a The Routine of an Eye Examination. 
25 
schematic eye set in emmetropic condition as described 
by James Thorington, M. D., in the Journal American 
Medical Association, Dec., 1897. 
Coma is aberration produced by the unequal refract- 
ing effects of different parts of the various meridians 
of the eye, or lens, on oblique pencils of light. It is, 
in brief, spherical aberration for oblique light; if this 
condition is produced optically we do not get a point 
image of a point object but rather a confusion disc 
which is non-symmetrical. In Figure 1 let L represent 
the crystalline lens in an oblique position. Assume 
that light has been thrown from the retinoscopic mir- 
ror into the eye; let A B represent the retinal area of 
illumination. The working distance lens is represented 
by W; for example, 1 D, for 1 meter. We are inter- 
ested solely in the retinal reflexes or illumination re- 
turning to the observer assumed stationed at O. Let 
rays A N and B K be parallel rays of light emanating 
from the retinal area; the ray C M D E is the oblique 
principal axis. The ray B K reaches the surface of 
the lens sooner than the ray A N, and since B K de- 
parts more from minimum deviation than does A N 
(since the lens L may be considered as consisting of 
an infinite number of prisms) the emergent ray K D 
cuts the axial ray C E at D sooner or ahead of the 
emergent ray N E which cuts the axial ray at E. 
With the observer's eye at O we see from the diagram 
that it is possible (1) for the two reflexes, one myopic 
and one hyperopic, to be made to occupy one and the 
same position and (2) on motion of the mirror, since 
D is in front of the observer's nodal point and E is 
behind it, there will arise with and against mover 
ments or shadows. 
♦For Figure 1, see page 21. 26 
The Routine of an Eye Examination. 
Without doubt scissor motion may arise due to 
the obliquity of the light incident upon the eye under 
test. In the ordinary methods of procedure the patient 
is directed to look past the operator's ear and vaguely 
into space or at an illuminated test-type. A much 
better procedure and one which eliminates quite fre- 
quently these scissor movements, which are in these 
cases false in the sense that they are due to physical 
rather than anatomical reasons, has been devised by 
John C. Eberhardt, of Dayton, Ohio. Not only does 
this device do away with the liability to the above men- 
tioned effects but it also insures the operator that the 
refraction at or near the macular area is being made 
retinoscopically which is a most important considera- 
tion. The device is diagrammatically shown in Figure 
2 and has been described in some detail under the 
previous caption. 
Laurance, in his Visual Optics, says: "In an eye 
suffering from a considerable degree of irregularity 
or aberration, the application of retinoscopy with suc- 
cess is difficult if not impossible. In many cases, how- 
ever, a considerable improvement in the action of the 
shadow may be obtained by the observer shifting his 
position from one side to the other in order to utilize 
the areas of least error." Thorington, in his brochure 
on Retinoscopy, says: "These cases are more or less 
difficult to refract, but the presence of the two areas 
of light with the dark interspace will often assist in a 
correct selection of glasses, for while they are gen- 
erally of the compound hyperopic types, calling for a 
plus sphere and plus cylinder, yet practice and the 
patient's statement often call for a plus sphere and The Routine of an Eye Examination. 
27 
minus cylinder* * * * The writer's method of 
procedure when he recognizes the scissor movement 
is to tilt the mirror until the two areas are brought 
into one band of light and then to reflect the light 
through the meridian of this band. Having obtained 
the lens which neutralizes the movement in this meri- 
dian, the writer does not attempt to find the neutraliz- 
ing lens for the opposite meridian but goes from the 
dark room to the trial case and places before the 
patient's eye that sphere which corrects the refraction 
in the one meridian." 
These statements are quoted at some length from 
these treatises because they contain about the only in- 
formation available. For my own part, I have made 
a study of some fifty cases of scissor movement and 
shall present some few here, with diagrams, to illus- 
trate the general methods of procedure and the de- 
termination of the proper cylinders to be prescribed. 
Above all it is important and essential that the retino- 
scopic refraction of such cases be made as nearly as 
possible in the direct line of sight; this is possible by 
the use of a device such as the so-called macular re- 
flectoscope previously referred to or by dynamic ski- 
ametry. In this latter method fixation is elicited for a 
letter or set of letters or points on a card attached 
close to the mirror of the retinoscope; a neutraliza- 
tion skiascopically of one meridian by a sphere then 
leaves the opposite meridian to be corrected with cyl- 
inders, hence making it possible to determine the 
cylindrical element correctly irrespective of the oper- 
ator's opinion as to the refractive accuracy of the 
spherical element found. When an eye is under com- 28 
The Routine of an Eye Examination. 
plete cycloplegia these methods are still applicable al- 
though, of course, the dynamic method is not dynamic 
but simply serves as a method of directing the patient's 
gaze; under cycloplegics the refraction in the line of 
sight can be accomplished very readily except for the 
disadvantage of peripheral rays which add to the al- 
ready complicated problem. The general mode of 
procedure is, then, to neutralize the motion in the 
meridian opposite to that in which the scissor move- 
ment arises, keeping the two bands together as is ad- 
vocated by Thorington. Having neutralized this 
meridian with spheres the writer then proceeds to the 
correction of the meridian in which the scissor move- 
ment has evidenced itself in the following manner; 
the two bands are brought together and the position 
of the line of union into a single band in the pupil is 
noted, i. e. whether, as it forms, it is the nasal, tem- 
poral, supra or infra side. The mirror is then rotated 
in the opposite direction slowly and the positions of 
the two bands just at their line of separation are noted 
and that portion of the double reflex which contains 
within itself the center of the pupil, or which in any 
way gives evidence that it discloses the chiefly usable 
portion of the eye, is corrected with cylinders. In case 
of doubt as to which shadow to heed, since the line of 
demarcation may arise near the pupillary center, I 
have found it in general proper procedure to neutralize 
the nasal or the infra portions respectively. The 
greater percentage of cases show the scissor bands 
lying at or near the 180° line of the trial frame, but 
some few cases, particularly those giving a history of 
traumatism in the temporal region, exhibit these bands 
at or near the 90° point. The Routine of an Eye Examination. 
29 
Case 3. (See Figure 3 A.) O. D.-0.62 D. S. 
-0.50 cyl. ax. 90 ; V=20/20 O. S. -0.62 D. S, O 
+0.37 cyl. ax. 90; V-20/20. Left eye exhibited scis- 
sor motion after the addition of -0.50 D. S. (+1 D. 
Ftg3 
Figure 3. Illustrative of the Position of the Bands in 
Scissor Movement. 30 
The Routine of an Eye Examination. 
S. used throughout these cases as the working distance 
lens.) It was found that -0.62 D. S. neutralized all 
motion in the vertical direction ; in the horizontal direc- 
tion the two bands united into one in the temporal 
quadrant; upon separation the hyperopic (with) reflex 
occupied three-fourths of the pupil; +0.37 cyl. ax. 90, 
in addition to the lenses used previously to neutralize 
the first meridian, corrected the with motion and -0.25 
cyl. ax. 90 corrected the against movement occupying 
the temporal quadrant. With -0.62 D. S. 3 +0.37 
cyl. ax. 90 V=10/10 readily; with -0.62 D. S. O - 
0.25 cyl. ax. 90 V=7/10 to 8/10 with two errors; had 
been wearing for some years -0.50 D. S. -0-37 
cyl. ax. 90 and told the writer that the vision in this 
eye was not very good and never had been. Under 
oblique illumination, by the way, an operator would 
have been justified in concluding that the minus cyl- 
inder was demanded. The ophthalmometer showed no 
corneal irregularity; the clock-dial test elicited some- 
what uncertain and changeable answers. 
Case 4. (See Figure 3B.) Right eye; division line 
above the center of the pupil; attention given to the 
lower portion only. A +1.50 D. S., working at one 
meter, gave neutral shadow in the horizontal meridian; 
in addition thereto -1.50 cyl. ax. 180 neutralized 
motion in lower portion of pupil. With +0.50 D. S. 
C-1.50 cyl. ax. 180, V=20/20 to 20/16. A+1.00 
cyl. ax. 180 apparently neutralized the upper and hy- 
peropic portion, but subjectively +0.50 D. S. +1-00 
cyl. ax. 180 gave V=10/20 to 12/20 with two errors. 
Case 5. (See Figure 3C.) Right eye; band forms 
and division occurs along the 30° line; the hyperopic The Routine of an Eye Examination. 
31 
or with portion constituted about three-fourths of the 
total reflex. A-1.50D. S. neutralized motion along 
the 30° line or the line of the single band when the 
two were brought together. The upper, temporal por- 
tion of the scissors movement was neutralized with 
-f-2.00 cyl. ax. 30, the lower or against movement with 
a-1.50 cyl. ax. 30. The subjective tests showed 
that with-1.50 D. S. + +2.00 cyl. ax. 30, V=9/10, 
while the minus-minus combination was absolutely 
impossible. The ophthalmometer showed a slightly 
irregular cornea; the amount of corneal astigmatic 
error did not exceed 0.75 D. as nearly as could be 
determined. As a further test this case was clini- 
cally checked by use of a narrow stenopaic slit; the 
best vision slit position was at 120°, the poorest 
vision slit position was at 30°. With the slit in the 
120° position +0.50 sphere gave V=10/10 and with 
the slit at the 30° position-1.50 sphere gave V=9/10. 
This gives as the cylindrical corrections +0.50 cyl. ax. 
30 3 -1-50 cyl. ax. 120 and as a sphero-cylinder 
-1.50 D. S. C +2.00 cyl. ax. 30 or +0.50 D. S. C 
-2.00 cyl. ax. 120°. In this instance, as in many others, 
it was discovered that one equivalent form was much 
more satisfactory to the patient than the other; why. 
the writer is unable to state except that the irregular 
astigmatic condition apparently demands that it be cor- 
rected per se; it is also to be noted that, in nearly all 
cases, the lens values needed to correct the two por- 
tions of the scissor motion are not equal. The satis- 
factory results to be obtained by the use of a narrow 
stenopaic slit in such cases, either in the initial or 
corroborative testings, is worthy of comment.  The Routine of an Eye Examination. 
32 
The chief points to which attention has been 
called are briefly as follows: (1) The desirability 
of and necessity for obtaining the retinoscopic findings 
as nearly as possible in the direct line of sight. Many 
scissor movements will not then evidence themselves 
although present under oblique examination (2) When 
a scissor movement arises, determine position of the 
single band just as the two bands close together and 
again the position of the division line just as the two 
bands re-appear; correct retinoscopically by the addi- 
tion of cylinders to the lens quantity already present 
the astigmatic band which contains within itself the 
center of the pupil or which gives evidence that it dis- 
closes the chiefly usable portion of the eye. (3) In 
case of doubt correct retinoscopically the nasal or the 
lower (infra) portion of the double reflex respectively 
and subject to rigid subjective testings. (4) A slight 
overcorrection of the meridian first corrected may 
either do away with the scissor movement or aid in 
the determination of which portion thereof is to be 
corrected. (5) The use of a narrow stenopaic slit in 
such cases is a valuable corroborative test. 
We shall pass over and deal in subsequent chapters 
with the topics of Dynamic Skiametric Tests, Mono- 
cular and Binocular Objective Tests upon the Ampli- 
tude of Accommodation, Accommodation Associated 
with Convergence as Tested at the Reading Point, 
Tests upon Cyclophoria and Hyperphoric Conditions 
at the Reading Point, Fusional Reserve Convergence 
and Monocular Tests upon the Amplitude of Accom- 
modation using Concave Lenses at the Thirteen Inch 
Point. We shall omit all discussion upon Subjective The Routine of an Eye Examination. 
33 
Acuity Tests and allied topics, except to point out some 
of the niceties of subjective testing as made possible 
by Comparison Tests as to the Equality of Visual Acu- 
ity and the Range and Amplitude of Accommodation. 
COMPARISON TESTS AT DISTANCE USING SMALL, EQUAL 
PRISMS BASE UP AND DOWN BEFORE EACH 
EYE RESPECTIVELY. 
Immediate contrast is the keynote of success in the 
equalizing of visual acuity-whether the tests be con- 
ducted at distance or reading points. The alternate 
and rapid occlusion of first one eye and then the 
other is a simple means of obtaining this contrast, but 
it can be improved upon greatly both as to ease of 
comparison and lack of annoyance to the patient, who 
generally makes the request, under the card occlusion 
test, to "please repeat the test" just described. The 
writer generally makes this alternate occlusion com- 
parison test before trying out for muscular imbalances 
at distance. Immediately after, or sometimes between 
the tests for lateral and vertical equipoise, the writer 
turns back from the "muscle light" to the 20 or 24-foot 
line on the Twentieth Century Test Cabinet-thus far 
this is probably the best test chart of its kind on the 
market-and places a 1° to 2° prism base down before 
the right eye and a corresponding prism base up before 
the left eye. The purpose of the division of the prism 
between the eyes is to insure equality of optical condi- 
tions in so far as the testing appurtenances are con- 
cerned. By this statement we do not refer to distor- 
tion or similar effects, because these are small and 
negligible when such low prism diopters are used, and 
if any such effects should occur they would not be 34 
The Routine of an Eye Examination. 
alike in both eyes, since one of the prisms is base up 
and the other is base down. We have reference to the 
fact that a total of 2° to 4° is generally insuperable to 
the vertically acting recti and hence insuperable di- 
plopia will result; if the prism were wholly before one 
eye the "un-prismed" eye would be fixing macularly, 
while if the prism is divided between the two eyes the 
retinal images are received at an equal angular dis- 
tance from the fovea centralis in each eye and are 
therefore received upon normally equally form-sensi- 
tive portions of the retinas. Hence, with these low 
powered prisms, base up and base down respectively 
before each eye, the patient sees simultaneously two 
lines of test type and can rapidly and with ease direct 
his or her attention to first one space-image or line of 
type seen and then to the other and intelligently re- 
port upon their equality. A point, which is psycholog- 
ical in nature, which adds to the value of this test, is 
that the subject's interest is aroused in the actual cre- 
ation of the diplopia and his co-operation is engen- 
dered. Such changes are then made as ensure equal 
acuity; these findings may be subsequently binocularly 
increased or decreased in spherical values in the light 
of various dynamic tests upon the accommodation and 
convergence. 
The practitioner should never be at a loss as to which 
image corresponds to or belongs to which eye; if the 
prisms are O. D. base down, and O. S. base up, the 
upper image or line of type will be seen in space by 
the right eye and the lower by the left eye. The prisms 
placed before the eyes cause deviations of rays of light 
toward their bases; the retinal images are projected The Routine of an Eye Examination. 
35 
back into space through the ocular nodal points of 
each eye according to the fundamental law of projec- 
tions. The images in space, i. e., the objects seen, will 
therefore be seen displaced in all cases such as this 
toward the apex of the prism or away from its base. 
In passing let it be stated that the cover test, in- 
volving an alternate, rapid occlusion of each eye in 
turn, furnishes a delicate test for small amounts of 
vertical imbalance, i. e., hyperphoria or hypophoria. 
The patient is requested to note whether, as the card is 
shifted quickly from one eye to the other, the line of 
type appears to remain fixed or constant in a horizon- 
tal direction or whether there is a slight alternate up- 
ward and downward motion of the images as seen by 
the eyes in turn. To illustrate: Assume that under this 
test the image as seen by the right eye appears higher 
than that seen by the left, such that on rapid oscilla- 
tion of the card the image of the right eye seems to 
ascend and that of the left eye to descend. Or assume, 
for purposes of further illustration, that the two lines 
of type shown in Figure 5 (supposedly representing 
a line of type on the distance chart) diagram the rela- 
tive positions of the images as seen by the two eyes. 
Let the upper be seen by the right eye and the lower 
by the left so that under rapid alternate occlusion 
there is what may be designated as a "step-up, step- 
down" performance. We should conclude from this 
evidence that the right eye turns downward, relatively 
speaking, or the left eye relatively upward, requiring 
a prism base up O. D. or prism base down O. S. to 
produce equality of level of these images and hence 
correct the vertical imbalance. 36 
The Routine of an Eye Examination. 
THE COMPARISON TEST AT THE READING POINT AND 
SOME IMPORTANT CONSIDERATIONS IN 
CONNECTION THEREWITH. 
Comparison tests at the reading point may be made 
by either of the two methods described above; in fact, 
both of them should be used in the course of an exam- 
ination. The ordinary near-test card is handed the 
patient and reading is engaged in while the cover is 
fairly rapidly passed from one eye to the other. Dif- 
ferences in apparent size and color are often notice- 
able; this test should be safeguarded against false 
color impressions, such as the appearance of a reddish 
or bluish background upon which the printed words 
occur, by the exclusion of auxiliary sidelights; that is, 
the illumination should be uniform and by the indirect 
lighting system where possible or subdued in character 
and the card so held as to prevent direct reflection of 
light from the surface of the reading card into the sub- 
ject's eyes. The test type, usually No. 2 Jaeger 
(Snellen V=.5 D.), should be then approached toward 
the eye and the monocular near point determined for 
each eye and their equality or inequality determined 
upon. This affords a test upon the range and the ampli- 
tude of accommodation as subjectively determined 
from near point investigations. Many cases will arise 
in which the addition of a small sphere to one or the 
other eye will establish conditions of equality and 
which, upon subsequent test at distance, will prove as 
satisfactory from that standpoint also. 
The writer is, however, rather partial to and prone 
to depend upon a comparison test at the reading point 
by the method of prisms. The procedure is practically The Routine of an Eye Examination. 
37 
the same as outlined in connection with the use of this 
method as employed by the author in distance observa- 
tions. Quite commonly a 4° base down before the 
Applied Optic#-Ohio State University 
Fc^- 4> 
Figure 4. Test Line Used in The Comparison of Acuity and 
Equality of Range and Amplitude of Accommodation. 
right eye and a 4° base up before the left eye are used 
and a test card carrying a single dot with a line of 
type, such as shown in Figure 4, has been used by the 
writer. This card is held at about thirteen inches for 38 
The Routine of an Eye Examination. 
the initial comparison test. The card is then slowly 
approached by the patient toward his eyes and the 
equality or inequality of range and amplitude of ac- 
commodation established. The positions of the images 
as seen by each of the eyes thus fusionally dissociated 
-i. e., in which binocular vision is not in vogue but in 
which monocular accommodation can be brought into 
play-follow the rule that the space-image appears in 
each case displaced toward the apex of the prism or 
away from its base. 
Under what we believe to be normal conditions of 
convergence as associated with accommodation at the 
thirteen inch reading point, with fusional convergence 
passive, there will be found a physiologic exophoria 
of 5° to 6° (vide, the writings of Maddox, Stevens, 
Howe and Worth'). Bearing in mind the law of pro- 
jection and the physiology of exophoria-in which, for 
example, if the eyes are relatively exophoric, the 
retinal image in the right eye will be received on the 
temporal side of the macula and hence be projected 
through the nodal point into space and produce the 
spatial image to the nasal side, and so forth-there 
will be a condition of crossed (heteronymous) images. 
If, therefore, normal relations between accommoda- 
tion and the associated convergence exist, some 5° to 
6° of prism, base in, will be needed to bring the two 
dots into a vertical line or row. These innervational 
conditions, as well as those pertaining to equality of 
visual acuity and which are here assumed to be a true 
test for equality of accommodative action when equal- 
ity of acuity exists at twenty feet, may be simultane- 
ously investigated. These optical effects under fu- The Routine of an Eye Examination. 
39 
sional dissociation by means of equal prisms base up 
and base down before each eye respectively are dia- 
grammed in Figure 5. 
Applied Optics-Ohio State University 
£ Applied Optics-Ohio State University 
Fl^.5 
Figure 5. Images as Seen Under Fusional Dissociation by 
Means of Vertically Placed Prisms. 
To revert to the question of equality of accommo- 
dative amplitude and range, the writer has found that 
the use of a 4° prism respectively before each eye pro- 
duces at thirteen inches a separation of the two spatial 
images of such large extent as to make easy compari- 
son somewhat difficult and less certain than is desir- 
able. The procedure in this test has, therefore, been 
modified somewhat as follows. The card, Figure 4, 
of extra quality as to weight and whiteness of sur- 
face, about 4 by 5 inches in size and printed in No. 2 
or No. 3 Jaeger type, is inserted in the carrier attached 
to the rod of the phorometer and the two rotary prisms 
are then thrown into position and each rotated equally 
but in opposite directions until two lines of type, situ- 
ated about one-half inch apart, are seen. Equality of 40 
The Routine of an Eye Examination. 
acuity, if not present, is next established and the 
card is then approached to the approximate punctum 
proximum and the prism powers increased (since the 
two images, for obvious optical reasons, approach each 
other and may merge into one another as the card is 
moved nearer the eyes) until they are about a half 
inch apart vertically. Should the image as seen by 
the right eye, for instance, be readable at a closer point 
than that seen by its mate, the operator knows that 
the range and equality of accommodative action are 
unequal and proceeds to establish such equalization 
when possible. 
If an additional quarter or half diopter is needed 
before an eye to re-establish visual equality, this fact 
is noted in the record of the case and subsequent tests 
are made at distance to determine whether or not full 
accommodative relaxation has previously been ob- 
tained in the distance tests, or whether or not this 
additional correction is not practically as acceptable 
for distant vision as the finding initially determined 
upon. The writer has come to look upon such inequali- 
ties under such conditions as portrayed at the reading 
point or at the punctum proximum as in general indi- 
cative of failure to obtain as complete an accommoda- 
tive relaxation at distance as possible. When this is 
not the case, and when inequalities of accommodation 
do present themselves, we have present those extreme- 
ly interesting ocular conditions which demand skill in 
their handling and which often demand separate dis- 
tance and near corrections. 
The value of this method in presbyopia must like- 
wise be apparent to the reader. There is no more The Routine of an Eye Examination. 
41 
reason for believing and assuming, as is generally 
done, that the accommodative reserve and the accom- 
modative assistance demanded in presbyopia should be 
the same in both eyes than there is in pre-presbyopic 
conditions. Equality of range and amplitude of ac- 
commodation in presbyopic cases and the near and 
far reading points can be determined upon with rapid- 
ity, ease and accuracy by means of this comparison 
test involving fusional dissociation while accommoda- 
tion and its associated convergence are left active. 
THREE ESSENTIAL DYNAMIC TESTS FOR THE EXTRINSIC 
EYE MUSCLES. 
We have quoted almost verbatim the title of one 
of the sections in Dr. G. C. Savage's essay on ''Ocular 
Muscles" appearing in the tenth volume of The Amer- 
ican Encyclopedia of Ophthalmology. We quote lit- 
eratim from his statements upon this topic. "There are 
three tests which should be made of every pair of eyes 
as part of the work of refraction. To neglect the mak- 
ing of these tests will mark many failures against the 
oculist. Tonicity, duction and version are the names 
of these tests. The two first mentioned are indispens- 
able; the last one named is of so much value as to 
command attention. In a very crude way the tonicity 
and fusion tests may be made with the loose prisms 
in the refraction case, but better far is the monocular 
phorometer. The binocular phorometer should not be 
used for either of these tests, for the fundamental rea- 
son that the image of the test object in one eye should 
be undisturbed. The principle on which all the tests 
possible to a phorometer rest, is that the image in one 
eye, throughout every test, shall be undisturbed; that 42 
The Routine of an Eye Examination. 
the head shall be erect; and that both eyes and the ob- 
ject-better a white dot on a black background-shall 
be on the extended horizontal plane of the head. The 
false object must have its image thrown outside the 
area of binocular fusion in the eye under test * * 
In our opinion, however, many of these tests are not 
as valuable to the refractionist as are the tonicity tests 
conducted at twenty feet when taken in conjunction 
with the findings upon the accommodative amplitude, 
the accommodation as associated with the convergence 
and the fusional convergence at the reading point or 
thirteen inches. These distance tonicity, duction and 
version tests do, however, form a valid basis for the 
determination of whether or not innervations or 
strengths or attachments of muscles are at fault since, 
in general, practically normal duction and verting 
powers indicate-in cases of tonicity excesses or lack 
of proper coordination between accommodation and 
convergence-innervational excesses or deficiencies 
and not inherent muscle abnormalities. For instance, 
if tonicity tests indicate several degrees of exophoria, 
adduction powers considerably below the normally ac- 
cepted three to one ratio as compared with abduction, 
and adversion low or abversion excessively high we 
may with reason conclude that there is a muscular 
rather than innervational deficiency of the interni. It 
is, however, to be remarked that duction tests at 20 
feet, with the patient wearing his full distance correc- 
tion, presume that positive or negative convergence 
and so forth are exercised with the function of accom- 
modation passive. Such duction tests conducted at 
distance must, therefore, be a measure of the ability The Routine of an Eye Examination. 
43 
of the fusional centers, wholly independently of ac- 
commodation, to overcome the tonicity defect (or be 
aided by it, dependent upon whether this equilibrium 
condition is one of exophoria or esophoria) and to 
maintain binocular single vision. In the customary cir- 
cumstances under which convergence is called into play 
accommodation is also demanded and, as we hope to 
show later on, there is normally associated with the 
accommodation about two-thirds of the full positive 
convergence needed for binocular single vision at any 
given point, the remaining demand being met by the 
fusional or reserve convergence. If, again, it is 
assumed, as so many writers do, that convergence and 
accommodation are so closely related that the accom- 
modation and accommodative-convergence points are 
one and the same, then the duction tests at infinity are 
presumed, it seems to the writer, to measure simply the 
power to overcome tonicity deficiencies and to supply 
any needed positive or negative convergence, if such 
is needed, at near points. We do not, therefore, as a 
general rule, take the duction and version tests unless 
the tonicity tests show large errors, but are prone to 
depend in general upon the disclosures at the reading 
point. And again, one of the inflexible rules which 
must underlie the investigation of any given ocular 
function is "that such investigations must be conducted 
under conditions of activity and quiescence which con- 
form to the philosophy of the particular phase of its 
activity under consideration." Convergence demands 
are normally made and met at points inside of infinity 
(practically, 20 feet). Maddox, to my mind, comes 
nearer the true method when he writes :-"To measure 44 
The Routine of an Eye Examination. 
more accurately, we should first discover the near 
point of accommodation, and while looking at an ob- 
ject at that distance from the double rotating prism 
frame, rotate the edges of the prism inwards until 
diplopia commences. By adding the maximum con- 
vergence thus found to the already ascertained prism- 
divergence for distance, we get the 'absolute range 
(amplitude) of convergence', of which according to 
Dr. Landolt, not more than one-third, or one-fourth 
can be continuously in exercise for comfortable vis- 
ion." 
The monocular tonicity and duction tests are most 
valuable, however, in locating the single weak muscle 
of a pair of muscles and often show that the ductions 
of the extrinsic muscles of one eye are normal while 
the abduction, adduction, superduction or subduction 
of its mate is faulty. Hyperphoria and hypophoria 
are relative conditions corrigible by prisms base up 
before one eye or base down before the other or 
vice versa, or the prismatic assistance may be divided 
between the eyes. Vertical imbalances are generally 
of much greater importance than are the lateral imbal- 
ances and greater care and skill are demanded in their 
optical treatment than in low degrees of exophoria or 
esophoria; it is, therefore, very essential that the weak 
ductioned muscle or muscles be determined in order 
to logically proceed to its alleviation or optical assist- 
ance in a manner such as will tend to restore its normal 
functions where possible. Since the duction powers 
of the vertical muscles are low, great care needs to be 
exercised in their treatment; if such is true, the writer 
believes that some auxiliary device should be provided The Routine of an Eye Examination. 
45 
in our modern phorometers in order that our vertical 
ductions may be determined with more certainty than 
is possible with our present rotary prisms in which 
the prismatic power changes are too rapid for the 
small amount of mechanical motion involved. 
Duction is fusional and not volitional and is under 
the control of the fusion centers operating in the in- 
terests of binocular single vision. If, in an eye, the 
image is displaced into any part of its fusional domain, 
the fusional faculty will move the macula to it when 
possible. As Savage says:-"When an image is dis- 
placed by a prism to any point within the field of 
fusion of an eye, while the image in the other eye 
remains upon the macula, an effort at fusion will be 
made, and if the muscle that must respond is suffi- 
ciently strong, fusion will at once take place, caused 
by such a rotation as will bring the macula under the 
displaced image. When the image is thrown, by a 
stronger prism, entirely outside of the field of fusion, 
the guiding sensation, which seems to reside in this 
area only, will not call on any muscle to move the eye 
for the purpose of fusion. The nasal limit of this 
retinal area, as measured by a prism in front of the 
eye, is 8° ; the temporal limit, 25° ; the upper limit, 
3°, and the lower limit, 3°. The line drawn through 
these four points marks the entire boundary of the 
field. These may be considered as the normal size of 
the fusion area." The field of binocular fusion is the 
peculiar kite-shaped area in each retina shown in Fig- 
ure 6 (due to Savage}. 
Hence, in duction tests, when a prism is located be- 
DUCTION TESTS OF THE RECTI MUSCLES. 46 
The Routine of an Eye Examination. 
fore one eye, the fellow eye fixing a definite luminous 
test object at five or six meters distance, and the base 
RIGHT 
Ftg, b 
UE FT 
Figure 6. Fusion Fields of the Recti Muscles. (From 
Savage.) 
of the prism is accurately in, out, up or down, only 
that rectus muscle lying beneath the apex of the prism 
is stimulated into action. All other muscles of both 
eyes remain passive in so far as the prism effects are 
concerned. The independent contractile power or 
range of dissociated action of each rectus may be 
accurately measured and values compared such that, 
in many cases, the origin of the imbalance may be 
determined. 
An accurate and well centered correction for the 
observer's ametropia should be in place during these 
tests. 
To test the adduction, or contractile power of the 
internus, of the right eye, a double rotary prism should 
be placed before this (right) eye and base out turned The Routine of an Eye Examination. 
47 
in the mobile prism until the object is seen double. 
Several tests should be taken and in general averaged. 
The abduction of this same eye may be obtained by 
causing a variable prism value, base in, to be placed 
before the eye until diplopia is obtained. Similar pro- 
cedures are instituted for obtaining the vertical recti 
ductions; for superduction, prism base down should 
be employed and for subduction, base up used until 
doubleness of object occurs vertically. 
To test the ductions of the left eye one proceeds 
in a like manner with the rotary prism before the eye 
to be tested. 
A comparison of the results obtained for the two 
eyes indicates which muscles are lacking in tone, and 
muscle exercise, prismatic corrections or operative 
procedure may then be advised or engaged in with a 
knowledge of the requirements in nearly all instances. 
DUCTION TESTS OF THE OBLIQUE MUSCLES. 
Duction tests upon the oblique muscles may be made 
by means of two Maddox graduated rods placed so as 
to give a vertical band or ribbon of light. One ribbon 
only should be seen; if two are present the lateral im- 
balance should be properly rectified by prisms base in 
or out (in high exophoria or esophoria) and the tests 
then instituted. DeZeng, in his compendium on "The 
Modern Phorometer," says: "To make this test, place 
a Maddox graduated multiple white rod in operative 
position before each eye with the axis of each hori- 
zontal and employ a luminous test object about 10 mm. 
in diameter, located five or six meters distant in the 
dark room and in direct alignment with the phoro- 
meter. Should the observer be either ametropic or 48 
The Routine of an Eye Examination. 
heterophoric, or both, a suitable correction should be 
in place, as no action by the recti is desirable during 
these tests. The observer should see but one band of 
light, Figure 7, and to measure the duction range of 
the superior oblique of the right eye, the rod on the 
corresponding side of the instrument should be ro- 
tated slowly and steadily downward at its nasal end 
until the band of light begins to break, or assume the 
appearance somewhat of the letter X, Figure 8, where- 
upon the position of the indicator with respect to the 
inner scale will denote the degree of right minus cy- 
cloduction. Upon returning the rod to its former posi- 
Fc,. 9. 
Fig. 7. 
Fig. 8. 
Figures 7-9. Illustrating the Images Seen Under Duction 
Tests of the Oblique Muscles. 
tion for a moment and indicator at zero, it may be 
rotated downward at the temporal end until the ver- 
tical band of light breaks in the opposite direction, 
Figure 9, whereupon the position of the indicator with 
respect to the outer scale will denote the duction range The Routine of an Eye Examination. 
49 
of the right inferior oblique, or the degree of right 
plus cycloduction. The plus and minus cycloduction 
of the left eye may be taken in like manner and the 
results obtained in each instance recorded for com- 
parison. The duction range of the oblique muscles 
when taken in this way will average from 5 to 20 
degree of arc. The Maddox rods employed in this 
test should both be white, otherwise the full fusion 
effort of the oblique muscles will not be obtained." 
TONICITY TESTS UPON THE RECTI MUSCLES. 
The Binocular Test. The tests upon the vertical and 
lateral imbalances of a pair of eyes as ordinarily made 
by means of the Maddox multiple rod, giving a band of 
light, before one eye and a distance small luminous 
source or test object at five or six meters being viewed 
by its mate, in reality constitutes a binocular test. This 
is so for the reason that the false image-the band of 
light- has its image thrown within the area of binocu- 
lar fusion of the eye under test, while the true 
object will have its image on the macula of the eye 
not under test. Hence this test may indicate the char- 
acter and approximately correct amount of any exist- 
ing vertical or horizontal imbalance but, due to its 
binocular character, will neither locate the faulty 
image nor the consequently deviating eye. 
Figures 10 to 15 show the relative positions of the 
band of light and the luminous test object when the 
Maddox rod is placed before the left eye. Figure 10 
indicates binocular lateral orthophoria, Figure 11 right 
hyperphoria, Figure 12 left hyperphoria, Figure 13 
binocular vertical orthophoria, Figure 14 esophoria 
and Figure 15 exophoria. 50 
The Routine of an Eye Examination. 
The following simple rule will aid in the mnemon- 
ics of tonicity tests:-According to the law of projec- 
tion the image is referred back into space and is seen 
in the position or the direction from which it should, 
under normal conditions, have proceeded from the 
spatial object. If the retinal image falls to the nasal 
side of the macula it will be projected into space 
Figures 10-15. Illustrating the Images as Seen in the Binoc- 
ular Tests upon The Tonicity of the Recti Muscles. 
through the nodal point of the eye and be seen on the 
temporal side, and so forth; or if the ribbon of light 
falls retinally above the macula it will be seen in space The Routine of an Eye Examination. 
51 
infraly (below). The displacement or equilibrium posi- 
tion of the eye is such that its rotation is in the same 
direction as the retinal image displacement or oppo- 
site to that of the object-image. Hence, in lateral im- 
balances, if the band of light is seen on the same side 
as the eye carrying the Maddox rod, there is a con- 
dition of esophoria; if the images are crossed, exo- 
phoria; if, in vertical imbalances, the streak is seen 
above the light, there is left hypophoria and if seen be- 
low the light, left hyperphoria relatively. 
The writer likewise believes that such tests as the 
Stevenson Muscle Test or the Maddox Tangent 
Scale, carrying a long vertical line to serve as a pointer 
or indicator, (or a line of type with an arrow directly 
below it) and doubleness of image produced by means 
of vertically displacing prisms, are not trustworthy 
in their measurements of exophoria and esophoria, 
since the images of these lines, falling within the 
fusion areas, stimulate fusion. A similar statement 
may be made with reference to these same tests when 
used in any form in investigating hyperphoria and 
cataphoria. The writer hopes soon to publish the re- 
sults of a detailed investigation upon this topic. 
Monocular Tests. Hardly a week goes by that 
someone does not write or ask the author about mono- 
cular tonicity tests. In reply we have generally re- 
ferred the inquirer to Savage's "Ophthalmic Myology" 
-a book which should be read by every eye practi- 
tioner, as well as Stevens' "The Motor Apparatus of 
the Eye." The principle involved is that which we 
have previously stated, namely: The false image 
must fall outside of the fusion area. This is easily 52 
The Routine of an Eye Examination. 
accomplished by putting an 8° prism, base up, before 
one eye in testing lateral imbalances and a 10° to 12° 
prism, base in, before one eye in testing for vertical 
imbalances. These results are shown in Figures 16 to 
21. Figure 16 shows, with the vertical displacing 
prism before the right eye, lateral orthophoria, Figure 
17 right esophoria, Figure 18 right exophoria. Figure 
19, with 12° base in before the right eye, shows no 
vertical heterophoria, Figure 20 shows right hyper- 
phoria and Figure 21 right cataphoria. 
To test, then, the lateral imbalance of the right eye, 
we place a mobile or rotary double prism before this 
(right) eye and rotate the prisms until there is eight 
prism diopters base up. This will displace the test 
object seen by this eye downward beyond the fusion 
Figures 16-21. Illustrating the Images as Seen in the 
Monocular Tonicity Investigations. The Routine of an Eye Examination. 
53 
range and thus produce insuperable diplopia. The 
lower, or false image, is then seen by the right eye, 
while the upper, or true, object is seen by the other. 
The heterophoric or orthophoric condition of the right 
eye is thus under test and the requisite amount of 
prism, base in or out, in cases of exophoria and eso- 
phoria, can be obtained by use of a second prism before 
the left eye. The lateral balance of the left eye can be 
tested in a similar manner, i. e. by putting about eight 
prism diopters base up before it. In testing the verti- 
cal tonicity of the right eye, some twelve prism diop- 
ters, base in, are placed before this (right) eye and 
insuperable horizontal diplopia produced. The right 
eye receives, therefore, the displaced image, and its 
location above or below the horizontal plane of the 
image as seen by the left eye indicates the nature of 
the heterophoria which can be compensated by the use 
of a second rotary prism before the left eye with 
prism, base up or down, as the case may be. 
A discussion of these tonicity tests is included in 
this treatise for the reason that due precautions 
should be taken in order to ensure that fusion, which 
is a dynamic and not static function, shall be elimin- 
ated. 
The rotations in the four cardinal directions are 
those to be studied. The best instrument for these 
tests is the tropometer of Stevens (vide Stevens: 
"The Motor Apparatus of the Eye"). A very satis- 
factory test may, however, be made with the perimeter 
and the small electric lamp of the ophthalmoscope. 
The patient should be placed in front of the perimeter 
VERSION TESTS. 54 
The Routine of an Eye Examination. 
while the eye to be tested must be at the center of the 
perimetric curve. The patient's head should be then 
kept immobile. The extent of the abversion is deter- 
mined by having the subject fix the small electric lamp 
as it is moved behind the perimetric arc or arm toward 
the temporal side of the eye under test. When max- 
imum version has been produced the operator places 
the lamp so that the lamp image occupies the center 
of the rotated cornea and reads the degree mark on 
the perimetric scale opposite the luminous source used. 
The rotation in the opposite direction, or the adver- 
sion, can be obtained in a like manner. With the 
perimeter arms vertical, the extent of the upward and 
downward versions can be determined. Both eyes 
should be thus tested. The extent of the versions 
under normal conditions as given by different authors 
varies somewhat. Landolt gives: Out 46°, in 44°, 
down 50°, up 33°. Stevens' standard, which is prob- 
ably nearer correct, gives: Out 48° to 53°, in 48° 
to 53°, down 50°, up 35°. A muscle that has the 
normal fusion or duction power should also have nor- 
mal verting power and in general, when one is ab- 
normal, the other is likely to be abnormal also. 
We close this chapter and discussion on the dis- 
tance dynamic tests upon duction and version by a 
citation of two illustrative cases. 
Case 6. Mr. A. W. Aet. 25 years. A teacher by 
profession. Has been examined previously and been 
told that there was no accommodative, refractive or 
astigmatic errors. Tests previously made under a 
mydriatic disclosed little spherical correction. Has, 
however, uncomfortable coordination of his eyes. The Routine of an Eye Examination. 
55 
Static retinoscopy disclosed no refractive errors and 
subjective monocular and binocular tests failed to 
elicit comfortable vision under low powered spheres. 
Dynamic skiametry disclosed O. U.-|-1.00 D. S, In 
the prescriptions finally given this young man, one 
involved a reading correction of O. U. -]-0.75 D. S. 
combined with the distance prismatic correction to be 
later disclosed. Binocular tonicity tests showed 5° 
of exophoria and 3° of left hyperphoria. The duction 
tests demonstrated the following:- 
DUCTIONS. 
O. D. 
Abduction 4 to 6° 
Adduction 8 to 10° 
Superduction 1° 
Subduction 4° 
O. S. 
Abduction 8° 
Adduction 12° 
Superduction 4° 
Subduction 1° 
The version tests showed: 
VERSIONS. 
O. D. 
Abversion 48° 
Adversion 42° 
Superversion 27° 
Subversion 55° 
o. s. 
Abversion 50° 
Adversion 46° 
Superversion 35° 
Subversion 48° 
Tests at the reading point, after the manner to be 
described in the next chapter, showed 11° of exophoria 
and 3° of left hyperphoria. The fusional reserve com 
vergence at the reading point was about 10°. The 
data indicates that the interni are both weak duction- 
ally and versionally and that the reserve convergence 
at the reading point is low; these tests also show that 
the abduction and adduction are about normal and 
that the right superior and left inferior are subnormal 56 
The Routine of an Eye Examination. 
in their powers. For distant use we therefore pre- 
scribed : 
O. D. 1° base up 1.5° base in. 
O. S. 1° base down 2 1° base in. 
We likewise instituted prismatic exercises and the 
simple 'toward the nose movement of the finger' in 
order to restore normal lateral equipoise but without 
success. The glasses, according to the prescription 
written above, the patient has worn with perfect com- 
fort and ocular coordination for over three years. 
In the record of the case we find the note that when 
the above corrections (slightly increased, however) 
were worn there was no cyclophoria present but that 
without such corrections several degrees of cyclo- 
phoria were apparently exhibited. 
Case 7. Mr. E. Aged 35 years. History of mel- 
ancholia, uncertainty in gaze and walk, very nervous. 
Severe headaches and so forth. Various tests showed 
that O. D. 4-1.00 D. S. 4-0-50 cyl. ax 75 and O. S. 
4-1.25 D. S. O 4~0.37 cyl. ax. 105 gave normal and 
equal acuity. The binocular tonicity tests showed 
9° exophoria and 4° left hyperphoria. At thirteen 
inches various tests showed 12° exophoria and 4° 
base up O. D. The ductions evidenced: O. D. ab- 
duction 9°, adduction 15° supraduction 1°, infraduc- 
tion 2°; O. S. abduction 11°, adduction 14°, supra- 
duction 2° and infraduction 1°. Version tests did not 
prove out satisfactorily or consistently; adversions ap- 
parently weak in both eyes however. The fusional 
reserve convergence at thirteen inches was approxi- 
mately 5°, but this was erratic in character. Tests 
upon the accommodation disclosed a practical paresis The Routine of an Eye Examination. 
57 
thereof. We were entitled, then, from the above data 
and his history, as well as from other data not here 
recorded, to diagnose an involvement of the third 
nerve and to recommend him to a specialist. This he 
did with the report that the statement had been made 
that his hay-fever of long years standing had ap- 
parently involved the sinuses. To give him as much 
ocular comfort as possible we gave him, in addition 
to the sphero-cylinder corrections both for distance 
and near, the following:- O. D. 2° base in 3 1° base 
up and O. S., 2° base in CP 1° base down. 
Savage. Ophthalmic Myology. Pages 146-179 
Neuro-Myology. Pages 1-54. 
Ocular Muscles. Am. Ency. Ophthalmo- 
logy, Vol. X, pages 7975-7992. 
Laurance. Visual Optics. Pages 152-194. 
Maddox. The Ocular Muscles. Pages 213-251. 
Ophthalmological Prisms. Pages 66-100. 
DeZeng. The Modern Phorometer. 
Worth. Squint. Pages 168-204. 
Eberhardt. Dynamics and Economics of the Bino- 
cular Functions. Optical Journal 1916 
and 1917. 
Sheard. Dynamic Skiametry. Keystone Magazine, 
1916 and 1917. 
Hansell and Reber. Ocular Muscles. Pages 75-123. 
Stevens. The Motor Apparatus of the Eye. Pages 
214-306. 
Thorington. Prisms-Their Use and Equivalents. 
REFERENCES. CHAPTER II. 
Various Subjective Dynamic Methods of Investigating Con- 
vergence as Associated With Accommodation, Fusional 
Convergence, and Their Importance. 
PHYSIOLOGIC EXOPHORIA AND FUSION CONVERGENCE. 
The efforts of convergence and accommodation are 
intimately intersusceptible, so that the smallest impulse 
to either makes a difference in the other, although the 
amount is not necessarily equal in the two cases. 
von Graefe, Maddox and Worth have made rather 
extensive investigations upon tonic, accommodative 
and fusion convergences. These investigations have 
been supplemented by Howe, Theobald, Eberhardt, 
the writer and others. The fundamental conclusions 
obtained from these researches indicate that "if one 
eye be covered while the other is fixing a near object, 
the occluded eye will, in the majority of persons who 
are neither hypermetropic nor presbyopic, deviate out- 
wards 3° to 4°." Normally, therefore, we should not 
expect binocular single vision to be obtained except 
through the supply of some three or four degrees of 
fusion convergence from a source or center wholly 
independent of the accommodation which should not 
be called into play in distant vision. Maddox by means 
of his tangent scale (in America known, in a modified 
form, as the Stevenson's Muscle Test)-carrying an 
arrow at the center of a scale graduated to both the 
right and left thereof and made visually double by the 
use of prisms base up and down before each eye re- 
spectively, the tests being made at 25 centimeters- Accommodative and Fusion Convergence. 
59 
concluded that there was a physiologic exophoria at 
the 10 inch point of about 3° to 5°, measurable and 
corrigible (to place the arrows vertically, one above 
the other) by the use of prisms base in. A modified 
form of this device, due essentially to Eberhardt, for 
near-testing is shown in Figure 26 and will be briefly 
discussed in connection therewith. This divergence 
(physiologic exophoria) does not exist in ordinary vis- 
ion since it is overcome by a visual reflex action, or 
fusion reflex, which affords binocular single vision. 
Hence, the exophoria revealed by such tests shows 
that the association of convergence with accommoda- 
tion is not complete centrally and, therefore, since the 
involuntary desire is to fuse two images into one, sup- 
plementary action is needed. The additional con- 
vergence supply comes through the medium of fusion 
convergence, a function entirely separate from the con- 
vergence as associated with accommodation. 
We have diagrammed in Figure 22 (taken from 
Maddox's "The Clinical Use of Prisms") the three 
grades of convergence in vision at 10 inches. These 
kinds of convergence are tonic, accommodative and 
reflex. 
TONIC CONVERGENCE. 
This has been marked in Figure 22 with a question 
mark (?), since it may be positive, nil, or negative. 
The various methods of testing tonicity at 20 feet 
have been discussed in Chapter I. Exophoria in dis- 
tant vision indicates a deficiency and esophoria an ex- 
cess of tonic convergence. This excess of convergence 
may occur after prolonged near work, in myopes who 
hold their work very near the eyes and yet maintain 60 
Accommodative and Fusion Convergence. 
Fta-ZX. 
Figure 22. Illustrating the Three Grades of Convergence 
in Vision at Ten Inches. (From Maddox.) Accommodative and Fusion Convergence. 
61 
binocular fixation, and in most hyperopes, particularly 
when uncorrected. It may readily cause asthenopia. 
Deficiency of tonic convergence may be due to lack 
of muscular and nerve tone and is quite commonly 
found in myopia. 
In distant vision, when the accommodation is fully 
relieved, two kinds of convergence only are involved, 
namely the tonic and the reflex. In near vision, how- 
ever, there is also the accommodative convergence. 
For we know that an occluded eye will deviate inward 
when its mate changes its gaze from far to near points. 
"As a rule," says Maddox, "each diopter of accom- 
modation is accompanied by about three-quarters of 
a meter-angle of associated convergence, so that in 
a typical emmetrope, not presbyopic, the 4 D. of ac- 
commodation in exercise for vision at a quarter of a 
meter, are accompanied by 3 m. a. of convergence, 
leaving a deficit of 1 m. a. to be made up reflexly" as 
shown in Figure 22. We may make our calculations 
exact by means of the Prentice rule: "Read the 
patient's inter-pupillary distance in centimeters, when 
one-half of it will indicate the prism-dioptries re- 
quired to substitute one meter-angle for each eye." 
If we, then, assume a case of P. D. 60 mms,, and take 
the accommodative-convergence basis laid down by 
Maddox as correct, our calculations would indicate 
that, in order that there be binocular single vision at 
one-third of a meter, approximately 18 prism-diop- 
tries of convergence are required and hence there 
should be demanded and delivered 18x3/4, or 13°, 
ACCOMMODATIVE CONVERGENCE. 62 
Accommodative and Fusion Convergence. 
of convergence as associated with accommodation, 
leaving 5° to be fusionally or reflexly supplied. 
Certain ocular conditions will increase the amount 
of accommodative convergence. They are:-(1) Cy- 
cloplegia from any cause, thus rendering the ciliary 
muscle less responsive to its innervations, demand- 
ing increased impulse to accommodation and thereby 
a proportionate increase of accommodative conver- 
gence. (2) If the object fixed be approached to the 
punctum proximum of accommodation, the effect pro- 
duced in the lens is less than the impulse, so that the 
associated convergence produces an esophoria. (3) 
In hyperopia, without correction, the accommodative 
convergence is generally greater than under em- 
metropic conditions. 
The conditions which lessen accommodative con- 
vergence may be summed up in the one statement that 
anything which renders accommodation easier (where 
1 D of innervation produces more than 1 D of lenti- 
cular change) or any condition which demands less 
than the normal accommodative effort for any speci- 
fied fixation point (myopia) will lessen the accompany- 
ing accommodative convergence. 
FUSION CONVERGENCE. 
Since objects are seen single up to the punctum 
proximum of convergence and since tonicity tests 
prove to us that there may be a divergent or conver- 
gent excess and the best experimentations by authori- 
ties upon these topics indicate that the association of 
convergence with accommodation is not complete cen- 
trally, there must be a fusion or reflex supplementary 
convergence operative in the interests of single vision. Accommodative and Fusion Convergence. 
63 
We should expect, therefore, that fusion convergence 
would involve a greater waste of energy in the pro- 
cesses of coordination than the accommodative con- 
vergence which is associated with the act of accommo- 
dation. The fusion convergence at any fixation point is 
measured by prisms, base out, in testing the maximum 
of positive convergence and prisms, base in, in test- 
ing the maximum of negative or divergent fusion, the 
patient viewing an object such as a line of type. We 
quote the following paragraph from Maddox. "The 
following table shows the fusion range found for vary- 
ing distances in a man 32 with normal refraction * * *. 
The first column (A) gives the refracting angle of 
the highest ( + ), base out, and (-), base in, prism 
he can overcome at the various distances. The second 
column (D) shows the deviation of each eye produced 
by the aforesaid prisms; it is found by calculating the 
deviating angle of each prism, and dividing it between 
the two eyes * * *. The third column (R) gives 
the fusion range for each eye calculated from the 
figures in column (D). It will be noticed that both 
(A) 
Single Prism 
(D) Deflection of 
(R) Fusion 
each axis 
Range 
.6 m. 
16° 
: - 3° 
4.5° : -0.75° 
5.25° 
.1 m. 
18° 
: - 8° 
5.° : -2.° 
7.° 
0.5 m. 
20° 
: -12° 
5.5° : -3.75° 
8.75° 
0.33 m. 
24° 
: -16° 
6.75°: -4.5° 
11.25° 
0.25 m. 
30° 
: -18° 
9.° : -5.° 
14.° 
the positive and negative parts of the range increase 
as vision becomes nearer; also that the positive part 
exceeds the negative, though less so as vision becomes 
nearer." 
The fusion convergence is the element most affected 
by ocular fatigue. We find it involved in so called 64 
Accommodative and Fusion Convergence. 
periodic squint. No squint may appear in the morn- 
ing but as the labors of the day go on, especially if this 
involves much close application of the eyes, the vigor 
of the visual reflex diminishes until the amplitude of 
the reflex becomes less than the squint. If the patient 
is a hyperope with excessive convergent tonicity and 
accommodative convergence it is entirely possible that 
the negative reflex convergence will be able to master 
it in the early hours of the day, but as the excessive 
strain is withstood hour after hour the effort will be 
abandoned, although there may be no squint at dis- 
tance since the demands upon the fusion convergence 
are lessened at that point. 
CLINICAL METHODS OF TESTING THE ACCOMMODATIVE 
CONVERGENCE AND THE RESERVE FUSION CON- 
VERGENCE AT THIRTEEN INCHES. 
Figures 23 and 26 show the forms of two varieties 
of test line which may be used for the testing of the 
convergence as associated with accommodation at any 
near point. We insert these cards in the carrier pro- 
vided with the phoro-optometer and sliding upon the 
rod thereof, or else have the patient hold the card at 
the desired distance from the eyes. This distance 
should preferably be that at which the patient's daily 
close work (occupation and reading distance) is done 
and for which lenticular assistance is chiefly required. 
Invariably, unless there is a reason to the contrary, 
we make the test at thirteen inches. 
One very important feature about these test objects 
is that each shall carry a printed line of type with an 
accompanying indicator point such as the black circle 
in Figure 23 or the arrow in Figure 26. In the ori- Accommodative and Fusion Convergence. 
65 
ginal von Graefe test object, of which the forms now 
presented are but modifications, a single dot or a ruled 
line only was used. Worth (Squint, page 177) pre- 
sents an acceptable form of test card carrying ten let- 
ters of "pearl" type having a large capital O in the 
middle. He likewise recommends the use of a card 
2 feet square in order that the object shall be seen in 
the center of a blank field with no edges near to elicit 
fusion. In this respect the large size of card recom- 
mended may be superior to those used by us which 
have a size of about 5x6 inches. The purpose of the 
line of letters is to bring into play the accommoda- 
tion, the evidence that such is the case being furnished 
the practitioner by having the patient read the letters 
or words. The viewing of a ruled line is an indefinite 
criterion. Hence, the two essential requisites in the 
accommodative convergence tests are: (1) the accom- 
modation must be active and (2) the fusion conver- 
gence and anything which stimulates such a visual re- 
flex must be annulled. 
THE DOT AND LINE TEST CARD. 
Figure 23 shows the form of test objects in which 
a heavy dot and line of type are employed. The Mad- 
dox double prism, consisting of two prisms each of 4° 
ground base to base, is inserted before one eye, the 
patient wearing the full binocular distance correction 
as previously determined upon. The wearing of the 
distance correction is essential as we are desirous of 
knowing whether such corrections are compatible 
with, or in harmony with, the proper co-ordination of 
ocular functions. The double prism being inserted 
with base line horizontal before one eye, its mate being 66 
Accommodative and Fusion Convergence. 
occluded, the position of the prism is so adjusted that 
the two dots as produced by this device are seen in an 
9 Applied Optics-Ohio State University 
pL ^3 
Figure 23. Dot and Line Test Object for Use in the Accom- 
modative Convergence Test 
apparently exact vertical line. We use the word 
"apparent" since the writer has found by making use 
of a considerable number of such prisms that the base 
line of the prisms has to be invariably tilted slightly 
downward temporally or upward nasally before the 
dots appear in a vertical row. A research upon this 
problem has been in progress for some time; we have 
found that there is some difference in the results 
dependent upon whether the card is held in the pri- Accommodative and Fusion Convergence. 
67 
mary position or somewhat as in the general position 
usually assumed in reading and have concluded that 
there is sound physiologic proof of a slight nasal ex- 
torsion above or intorsion below when convergence is 
in vogue. When, therefore, the two dots have been 
aligned vertically, the occluded eye is uncovered, when 
three dots and lines of type (we use No. 2 or No. 3 
Jaeger type for the printed line) should be seen 
normally. The relative positions of these three dots, 
i. e. the position of the middle dot with respect to the 
first and third, constitutes the basis of our test upon 
the accommodative convergence. To be more specific: 
we generally insert the double prism before the left 
eye. The upper and lower lines of Figure 24 will 
♦ Applied Optics-Ohio State University 
• Applied Optics-Ohio State University 
• Applied Optics-Ohio State University 
pty 24. 
Figure 24. Images as Seen under Fusional Dissociation 
Using the Maddox Double Prism. 
then be seen by this (left) eye. The middle line is 
seen by the right eye; the location of the middle dot 
while the line of type is being read gives the clue to 68 
Accommodative and Fusion Convergence. 
the convergence as associated with accommodation. 
Suppose the middle dot is to the left of the upper and 
lower ones; we then have an ocular condition of ex- 
ophoria indicated since the images are crossed and, 
therefore, according to the law of projection, that 
which is received upon the retina to the temporal side 
of the macula is projected into space to the nasal side 
and so on. Suppose that the patient reports that the 
middle dot is toward his left eye and that we find 
that it takes 6° prism, base in, to bring the three dots 
in alignment as nearly as possible. We conclude, then, 
that there are six prism dioptries (i. e. actually 3°) 
of physiologic exophoria. The question is, how much 
convergence is associated with the accommodation? 
Taking the average interpupillary distance of 64 mms., 
with fixation at thirteen inches or one-third of a meter 
and applying the Prentice rule, we find that 19 prism 
dioptries are required for binocular single vision at this 
distance. Since our assumed results on accommoda- 
tive convergence have shown 6 prism dioptries of ex- 
ophoria at this same point we conclude that the accom- 
modative convergence amounts to 13 prism dioptries. 
This is about as it should be under normal conditions, 
since about two-thirds of the total convergence im- 
pulse is supplied by, or associated with, the accom- 
modation. If it takes more than 6° prism, base in, to 
align the dots we should conclude that there was in- 
sufficient accommodative convergence (generally 
found associated with myopia) and if the dots are 
initially in a row or the middle dot is displaced on the 
same side as the 'unprismed' eye we should conclude 
that there was an oversupply of accommodative con- Accommodative and Fusion Convergence. 
69 
vergence and hence generally an abnormal demand 
upon the accommodation. Each case, however, must 
be taken upon its own merits and in the light of the 
remaining data obtained during an examination. 
Hyperphoric Conditions. Two additional tests 
which are of importance in the study of the condi- 
tions of poise of a pair of eyes are made possible under 
the procedure just described. These are: (a) exam- 
inations upon the vertical equipoise and (b) cyclo- 
phoria at near points. If there is a condition of 
vertical orthophoria the middle line will appear cen- 
tered with respect to the other two lines providing 
the double prism is properly placed before one eye and 
the two prisms composing the testing piece are equal 
in power. The test for vertical orthophoria should 
be made while there is before one eye that prism 
which aligns the three dots vertically. The amount of 
prism, base up or down, needed to place the second 
line midway between the first and third denotes the 
amount of hyperphoria or cataphoria present. The 
eye which does not wear the double prism is the one 
under test. When both distant and near-point in- 
vestigations show a degree or more of vertical im- 
balance, at least a partial correction for the same 
should in general be given. It is an open question as 
to the procedure when there is no hyperphoria or 
cataphoria at 20 feet and when there is an appreciable 
amount thereof at the reading point. In presbyopic 
corrections the writer generally incorporates some 
optical assistance in the reading correction looking 
to the alleviation of such an heterophoric condition. 70 
Accommodative and Fusion Convergence. 
Cyclophoric Conditions. The patient should be 
asked the question as to whether or not the three lines 
are parallel. We believe that this test should be made 
with the distance correction (or reading correction in 
cases of presbyopia) before the eyes in addition to 
such prism assistance as will establish strictly orth- 
ophoric conditions at the reading point. There are 
cases in which a cyclophoria will disappear or be 
materially lessened when heterophoric corrections are 
given. These must be indicative of mal-attachments 
of the straight muscles involved. Such a statement as 
this is not contrary to the correct teaching that a cy- 
clophoria per se - in which the oblique muscles are 
involved as in cases of oblique astigmia with diverg- 
ing or converging axes-cannot be relieved by pris- 
matic correction but only by cylinders (vide Savage's 
"Ophthalmic Myology" and "Neuro-Myology"). 
In making the cyclophoric fests at the reading 
point, the double prism may be inserted before the 
left eye. The middle line is then seen by the right 
eye, which is under test. If all three lines are parallel 
no cyclophoria is indicated. If the middle line occu- 
pies the relative position shown in Figure 25 (A), in 
which the middle line dips toward the nose, a weak- 
ness of the right superior oblique, or right plus cyclo- 
phoria, is indicated. In Figure 25 (B) there is dia- 
grammed the positions of the lines when the middle 
line dips toward the temporal side showing right 
minus cyclophoria or weakness of the right inferior 
oblique muscle. The writer believes that, in general, 
these tests at near are of little value unless taken in 
conjunction with tests conducted with fixation at 
twenty feet (see DeZen^s "Modern Phorometer", Accommodative and Fusion Convergence. 
71 
F'ujXS' 
Figure 25. Illustrative of Cyclophoric Tests. 
pages 47-50). The procedure at distance involves the 
use of two Maddox rods so placed as to give two hori- 
zontal streaks when an 8° prism, base up or down, is 
inserted before the eye under test. 
In making the test for cyclophoria at the reading 
point using the double prism method we have found 
the conditions diagrammed in Figure 25 (A) of al- 
most universal occurrence. Tests upon subjects, such 
as engineering students, whose statements are reas- 
onably certain of being trustworthy, indicate about 3° 
to 5° tilting when examined at the reading point. We 
have come, therefore, to regard this condition as prac- 
tically physiologic and the normal condition of affairs 
when accommodation and convergence, with some sub- 
vergence in general, are exercised. As a result we 
give little heed to small amounts of apparent plus cy- 
clophoria but make careful investigations upon the 
obliques when minus cyclophoria is apparently in- 
dicated. 72 
Accommodative and Fusion Convergence. 
THE LINE AND ARROW TEST CARD. 
Figure 26 shows a form of test line carrying a sub- 
joined arrow. In practice a card, bearing these sym- 
bols, is used in the manner and at the distance stated 
in connection with the Dot and Line Test. To pro- 
duce duplicity of images there is ordinarily used a 4° 
Applied Optics-Ohio State University 
Fi^.Zfe 
Figure 26. Line and Arrow Test Object for Use in the 
Accommodative Convergence Test. 
prism, base down, in front of one eye and a like prism, 
but with base up, before the other eye. The two 
images of the test object will be seen in space displaced 
toward the apices of the prisms or away from the base. 
That is, if one prism is placed base down before the Accommodative and Fusion Convergence. 
73 
right eye, the upper of the two space images will be 
that viewed by the right eye, and so on. This arrange- 
ment of affairs, exhibiting the normal accommodative 
exophoria, is shown in Figure 27. 
This form of test object is a modification of the 
Maddox Tangent Scale with subjoined arrow or of 
the Stevenson Near Muscle Test. We are positive, 
however, that the results as obtained by these and 
similar devices are inaccurate as a general rule in the 
data which they furnish, for the reason that the head 
Applied Optics-Ohio State University 
Applied Optics-Ohio State University 
*3-^ 
Figure 27. Duplicity of Images under Fusional Dissocia- 
tion by Prisms Base Up and Down before each 
Eye respectively. 74 
Accommodative and Fusion Convergence. 
of one arrow and the tip of the other fall within the 
fusion areas of the eyes and that fusion is thereby 
stimulated. This is certainly true if the fusion area 
measurements of Savage are correct and there is every 
reason to believe that his investigations upon this mat- 
ter are substantiated. How often has the writer had 
the person under this test say: "Why, I can bring the 
arrows over each other or not to suit myself." The 
explanation cannot lie in the presence or absence of 
accommodation and hence of accommodative con- 
vergence since the varying effects can be obtained 
when accommodation is uniformly enforced. The 
results (as yet unpublished) upon about five hundred 
subjects using the two methods-(a) dot and line 
and double prism and (b) line and arrow and prisms 
base up and down respectively before each eye-show 
a greater degree of exophoria as well as a greater 
degree of esophoria by the first method than by the 
second. The great criterion in all tonicity and accom- 
modative convergence tests is that fusion must be 
passive, i. e. one set of images must fall in toto out- 
side of the fusion area. 
We have discussed the fusion range in near vision 
in some detail in previous paragraphs of this chapter, 
and have commented upon the method of measuring 
the negative or divergent fusion by prisms, base in, 
and the positive or convergent fusion by prisms, base 
out, at near points. The table which we quoted from 
Maddox and which is, we believe, in a general way re- 
presentative of the trend of the convergences at vari- 
ous points, clearly demonstrates that both positive 
FUSION CONVERGENCE. Accommodative and Fusion Convergence. 
75 
and negative convergences increase in value as the 
fixation point is approached to the eyes. It is, there- 
fore, evident that a distinction should be made between 
tests for distant vision, which normally involve prac- 
tical parallelism of the visual lines and no accommoda- 
tion, and tests for near vision where the visual axes 
converge to begin with and in which accommodation 
is involved. The writer believes from some experi- 
mentation he has been carrying on that the con- 
vergence as associated with accommodation becomes 
greater (i. e. there is proportionately less physiologic 
exophoria) as the accommodative demands are in- 
creased with approach of the fixation object by virtue 
of the fact that the innervation required to produce 
the last diopter of accommodation is somewhat greater 
than that required for the first diopter, hence giving 
increased accommodative convergence and alleviating 
the demands upon the fusion convergence, thereby 
indicating greater fusion convergence reserves at 
points closer to the eyes. 
Figure 28 shows the form of test object which we 
use in fusion convergence (positive or negative) meas- 
urements at the reading point. It consists of a small 
card printed with a vertical row of letters set in about 
12 point type. This is handed the patient and the 
question asked as to whether one line only is seen. 
The answer will invariably be in the affirmative; if it 
is not, we are at once informed of the existence of 
diplopia at near points which will doubtless have 
Been reported by the patient or else discovered by the 
examiner in his distance tests. The examiner then 
turns in slowly prism power until the maximum power 76 
Accommodative and Fusion Convergence. 
A 
P 
P 
L 
I 
E 
D 
O 
P 
T 
1 
C 
s 
o 
H 
I 
O 
s 
T 
A 
T 
E 
U 
N 
I 
V 
E 
R 
S 
I 
T 
Y 
Figure 28. Test Line for Finding the Amounts of Fusion 
Convergence Reserve at Near Points. 
base out is obtained through which a singleness of 
line of type can just be maintained. In general, the 
positive portion only is tested through the medium of 
prisms base out. Wisdom in these tests seems to lie 
in a testing of the positive fusion convergence when 
tonic exophoria at distance and excessive physiologic 
exophoria, as associated with accommodation, are evi- 
denced at the reading point, whereas the negative por- Accommodative and Fusion Convergence. 
77 
tion should be tried out in cases of high tonic eso- 
phoria and excessive accommodative convergence. 
Such investigations as those we have been describ- 
ing test, in reality, the reserve of fusion convergence. 
The criterion or basis for comfortable vision is taken 
as that laid down by Landolt in which he says that 
not more than one-third or one-fourth of the fusion 
range (amplitude) of convergence can be continuously 
in exercise for comfortable vision. If a line is seen 
single at the thirteen inch point we are then aware that 
the fusion convergence has been able reflexly to take 
care of the deficiency (positive or negative) of tonic 
or accommodative convergence. The adducting or 
abducting prisms which can then be added before a 
pair of eyes, with fixation constant, is a measure of 
the reserve convergence. If our premises as to accom- 
modative convergence and reflex convergence are cor- 
rect, the problem becomes one of simple arithmetic in 
any case as far as data is concerned. What to do in 
the nature of prismatic corrections, prismatic and 
other training exercises, lenticular refractive correc- 
tions and so forth is probably the most difficult prob- 
lem in refraction. Let us assume for illustrative pur- 
poses two simple cases. Suppose that tests demon- 
strate a tonic exophoria of 5° and an accommodative- 
convergence deficiency of 16° of which, allowing 5° 
for the normal physiologic exophoria, 11° represents 
the genuine accommodative-convergence deficiency. 
We are then entitled, we believe, to say that the true 
accommodative convergence is only 6°, allowing 5° 
for the tonic exophoria. However, at least 16° of 
reflex or fusion convergence is demanded in binocular 78 
Accommodative and Fusion Convergence. 
single vision at thirteen inches, while the total demand 
fusionally (including the tonic) and accommodatively 
is about 23°. Let us further assume that the positive 
fusion reserve at thirteen inches is 20°. This means, 
therefore, a total positive convergence amplitude of 
43° of which 16° is demanded reflexly. Vision at 
near points under such circumstances is likely to be 
uncomfortable if engaged in for any length of time. 
As a second case let us assume a tonic esophoria of 
5°, an accommodative convergence of 5° (i. e. 5° over 
and above the physiologic exophoria), and a posi- 
tive reverse convergence of 25° and a negative re- 
serve convergence of 12°. The drain will not, then, 
be upon the positive fusion convergence but upon the 
negative convergence which shows a total fusional 
amplitude of 18° of which 5° is demanded. This it 
is normally able to bear. But the assumed data indi- 
cates that the accommodative convergence is excessive 
in addition to the initial esophoria indicating that the 
accommodative demands need attention. 
The writer agrees with Maddox when he says that 
the view that all squints are due to central fusion de- 
fects only is untenable. "Were it true, all squints 
would date from birth, whereas it is a matter of com- 
mon knowledge that a very large proportion date from 
the age of three years, after binocular vision has been 
enjoyed for some time. Moreover, they generally com- 
mence in near vision only, or when the attention is 
concentrated upon an object." The faculty of fusion 
divergence is not sufficiently developed to conquer the 
strong impulse to convergence which accompanies the 
excessive accommodative impulse in hyperopia. Accommodative and Fusion Convergence. 
79 
THE GREAT OCULAR PROBLEM-THE ECONOMIC CO- 
ORDINATION OF ACCOMMODATION, ACCOMMODATIVE 
CONVERGENCE AND FUSION CONVERGENCE. 
The above caption expresses the view that we have 
been dealing in this chapter with the most vital prob- 
lem in the economy of the ocular regime. When shall 
prisms be prescribed and when not? When are pris- 
matic or natural exercise likely to be of any avail? 
When should maximum or minimum convex or con- 
cave lenses be prescribed? When is operative inter- 
ference necessary? It would take a volume to answer 
these questions: still they would not be solved. In brief, 
we state the following answers. Anatomical defects can 
be altered by operative interference, the tonic position 
by prisms, the accommodative convergence by lenses 
and the fusion convergence by any of these. The 
tonicity may be, however, and generally is, associated 
with accommodative defects and the results under 
proper refractive corrections should be tried and time 
allowed for a re-adjustment before the insertion of 
prisms in the prescription. Suppression or stimulation 
of the accommodation, and thereby the associated ac- 
commodative convergence, should be indulged in 
whenever various tests upon the accommodative re- 
sources, fusion convergence and so on show that the 
function of accommodation is operating under condi- 
tions in which the effort is disproportionate to the 
work. In this group fall accommodative squints and 
cases in which the squint appears only in near vision. 
Prisms can be of no service in the correction of such 
conditions as these per se. Of necessity the burden in 
binocular single vision must fall upon the negative 80 
Accommodative and Fusion Convergence. 
fusion convergence and this may be temporarily aided, 
if deemed best, by the use of prisms base out. The 
writer, however, does not believe in the use of prisms 
for permanent wear in persons under forty except as 
a last resort. The fusion convergence may be altered 
by operation, lenses, or prisms. If the proper accom- 
modation-convergence relations can be re-established 
it will be found that, very frequently, the problem will 
be solved. Attempts at training the fusion converg- 
ence, particularly a weak positive fusion, should al- 
ways be made in persons under thirty-five to forty. 
The simple 'finger toward the nose' exercise over a 
period of some weeks will work marvels in many 
cases; we give an illustrative example in Case 10. The 
difficult problems are those in which the accommoda- 
tive needs, for example, demand that convex lenses be 
prescribed while all the accommodative convergence 
and fusion convergence tests (in particular) show that 
the reflex convergence is low. In such cases we are 
prone to give corrections involving proper lenticular 
assistance coupled with low prisms (1° to 1.5°) base 
in over each eye. The writer feels that prisms base 
in, when indicated, are of much greater ocular service 
than are prisms base out when prescribed. As a gen- 
eral rule prism and other exercises are of little avail 
in persons of middle-age and beyond, hence these very 
important tests should be made and great nicety of 
judgment exercised in the correction given when low 
fusion convergence reserves are found at the reading 
point. 
In concluding this all too brief presentation of this 
very important subject we cite some of the essential 
features of three extremely interesting cases. Accommodative and Fusion Convergence. 
81 
Case 8. Hyperopia with Periodic Squint. Mr. S. 
G. Aet. 21 years. Has frontal and temporal head- 
aches ; eyes sore and burn; print blurs "when he reads 
in a certain way" (probably binocularly) ; has had 
diphtheria and scarlet fever. Static retinoscopic tests 
showed O. D. -0.25 D. S. CL +-50 ax. 90, O. S. -0.50 
D. S. CL +-37 ax. 90. Dynamic skiametry evidenced 
at thirteen inches O. D. -J-1.75 CL +-50 ax. 90 and O. 
S. -|-1.37 CL +-50 ax. 90. Subjectively, O. D. -.37 
D. S. CL +-50 ax. 90 and O. S. -.50 D. S. CL 4~-37 ax. 
90, each eye equally good, did not give better than 
V=8/10 monocularly or V=20/20 with difficulty 
binocularly. With these corrections the patient's 
muscular equipoise at 20 feet showed, under the bino- 
cular tonicity test, 8° of esophoria; cover test, either 
eye, showed a redress of about 1 mm. out. Monocular 
tonicity tests disclosed that the major portions of the 
esophoric tendencies resided in the left eye. The ac- 
commodative-convergence tests evidenced 15° of es- 
ophoria (over and above the allowance for the 6° of 
physiologic exophoria). The various subjective ac- 
commodation tests at 13 inches evidenced about 9 D. 
for each eye. The negative fusion convergence re- 
serve at 13 inches was 6° or relatively nil. The duc- 
tion tests at 20 feet evidenced, for each eye, the fol- 
lowing: abduction 3°, adduction 30°. Our analysis 
of the case is that there is marked evidence of (1) 
anatomical defect, (2) excessive accommodative con- 
vergence, (3) insufficient negative fusion reserve. We 
prescribed the following:-(1) medical examination 
and assistance, (2) abduction exercise recommended 
by Thorington ("Methods of Refraction," pages 275- 
ILLUSTRATIVE CASES. 82 
Accommodative and Fusion Convergence. 
277), (3) reading correction: O. D. -|-1.25 D. S. CD 
4-.50 ax. 90 CD 1-5° base out and O. S. -f-1.12 D. S. DC 
4-.37 ax. 90 CD 2° base out, (4) distance correction, 
O. U. -{-.37 ax. 90 CD 1-5° base out giving V=8/10 (in- 
itially more unsatisfactory to patient than no cylindri- 
cal correction). The patient reports perfect ocular 
comfort over a period of six months. We expect to 
increase the distance correction as soon as feasible. 
Case g. Excessive Accommodative Convergence. 
This case is typical of a set of ocular conditions which 
is occasionally found in practice, in which there is 
apparently either no refractive correction for distance 
or such a weak-powered sphere as to be negligible, but 
in which assistance is demanded when reading and 
working at the usual distance are engaged in. The 
young man in question is a university student, twenty- 
one years of age, a student of law and accustomed to 
long hours of close application to his books. He re- 
ported no symptoms other than an apparent fatigue 
of his eyes. The static skiascopic examination re- 
vealed a neutral shadow condition and at times a 
slightly myopic motion; no convex lenses could be 
added without producing a decided reversal of shadow. 
Subjectively no distance correction was found; mono- 
cularly a quarter of a diopter convex lens was rejected 
as making the twenty foot line unreadable; binocularly 
this line was readable through quarter diopter convex 
spheres. The dynamic skiametric findings with ob- 
servation and fixation at thirteen inches showed a 
decidedly "with" motion and -f-1.25 D. S. before each 
eye was needed in order to produce neutrality. The 
duction tests at twenty feet showed abduction 7°, ad- 
duction 20°, superduction 2° and infraduction 2°, indi- Accommodative and Fusion Convergence. 
83 
eating normal duction or fusion powers at the distance 
for which the test was made. The Maddox rod test 
at twenty feet evidenced no muscular imbalance. But 
the accommodative tests at the reading point, using 4° 
prisms base up and down before each eye respectively 
and the line and arrow card, showed the arrows di- 
rectly over each other, indicating about 6° of esopho- 
ria, while the double prism and dot test showed 10° 
of esophoria with no vertical imbalance or cyclophoria 
at near. The accommodative amplitude was determined 
as 8 D. for each eye by the concave lens method of 
testing this function at thirteen inches. This young 
man was given O. U. -|-1 D. S. for reading, wholly in 
the interest of the proper correlation of accommoda- 
tion and convergence at the reading point. It may be 
pointed out with profit that if the practitioner had de- 
pended solely upon the distance objective and sub- 
jective findings and upon determining the amplitude of 
accommodation by the method commonly in vogue, 
i. e., the distance from the eye at which No. 2 Jaeger 
type can be read both monocularly and binocularly, 
he would have been logically forced to conclude that 
these eyes needed no assistance; but determinations by 
dynamic skiametry and by investigating the conditions 
at the reading point with accommodation active, fu- 
sional convergence passive but accommodative con- 
vergence active, clearly indicated the need of lenticu- 
lar assistance and the reason why. 
Case io. Weak Positive Convergence. This 
extremely interesting case of actual excessive accom- 
modation with a low degree of astigmatism is present- 
ed in some detail as it illustrates that condition of 
affairs, only too frequently found, in which the patient 84 
Accommodative and Fusion Convergence. 
was wearing minus cylinders at axis 180° when plus 
cylinders at axis 90° were really demanded and ulti- 
mately accepted. In this connection read Howe, "Mus- 
cles of the Eye," Vol. II, page 26, et seq. Young lady 
under description came complaining of nausea, head- 
aches and inability to do close work with any comfort. 
She had typhoid fever five years ago and trouble 
dates from that time according to her statement. A 
preliminary ophthalmoscopic examination showed con- 
gestion or hyperesthesia of the retina. The general 
appearance of the patient was anemic. She was put 
under competent medical treatment at once. The ocu- 
lar examination evidenced the following results at the 
first examination. Static retinoscopy, O. U. -0.25 D. 
S. -0.75 cyl. ax. 180. Subjectively this could be 
made O. U. -0.75 cyl. ax. 180 with slightly blurred 
distant vision (V=8/10). Dynamic skiametric tests 
were very erratic but indicated in general O. U. -f-0.75 
cyl. ax. 90. Such a result with dynamic skiametry is 
frequently to be looked for, since the method generally 
indicates increased convex lens power as compared 
with the static skiascopic findings. The tonicity tests 
indicated orthophoric conditions. The accommodative 
convergence, wearing the distance corrections, evi- 
denced 4° of over-stimulation. The accommodative 
tests indicated 9 D. for each eye by the concave-at-near 
method. The positive fusion convergence reserve was 
not in excess of 6°. In fact, as a pencil was approached 
toward the young lady's eyes, she winced and ex- 
claimed : "Do not do that again; it makes me sick." 
The cause of the inability to do near work and the 
general cause of the ocular discomfort therefor resided 
in this weak fusional convergence. We examined the 
correction she was wearing, prescribed about two years Accommodative and Fusion Convergence. 
85 
previously under a cycloplegic according to her state- 
ment, and found that they exactly incorporated our 
static findings which, by the bye, the writer was cer- 
tain were incorrect. We instituted prismatic exercises 
and had the patient carry out the 'finger toward the 
nose' exercise for a period of a week. Dynamic tests 
then evidenced O. U. -J-1-00 D. S. Q -0.75 cyl- ax. 
180. Subjectively we were able to force on by degrees 
O. D. -f-0.87 D. S. O -0-75 cyl. ax. 180 and O. S. 4" 
0.50 D. S. 3 -0-75 cyl. ax. 180, giving equal visual 
acuity and binocularly affording the patient V=8/10. 
The patient was given O. U. 4~.62 cyl. ax. 90 and the 
exercises continued for a period of two months, when 
the reserve fusion convergence at 13 inches tested up to 
20°. At the present writing she is wearing O. D. -f- 
.37 D. S. S2 4"-?5 cyl. ax. 90 and O. S. 4~-25 D. S. 3 
4-.62 cyl. ax. 90. Tests show no tonic errors at dis- 
tance, proper co-ordination between .accommodation 
and convergence and plentiful fusion convergence. 
She has relief from the symptoms of which complaint 
was made. 
Maddox-The Clinical Use of Prisms. Pages 72-100 
and 158-178. Ocular Muscles. Pages 91-98. 
Worth-Squint. Pages 176-186. 
Prentice- Ophthalmic Lenses and Prisms. Pages 50-58. 
Thorington-Methods of Refraction. Pages 266-290. 
Eberhardt-Dynamics and Economics of the Binocu- 
lar Function. (Optical Journal, 1916 and 1917). 
Sheard-Dynamic Skiametry. (Keystone Magazine, 
1916 and 1917). 
Howe-Muscles of the Eye. Vol. II. 
Hansell and Reber-Ocular Muscles. 
REFERENCES. A Resume of Present Day Methods of Investigating the 
Accommodative Range and Amplitude. 
CHAPTER III. 
There are two principles or methods of procedure 
in common use, which are in theory essentially iden- 
tical, for the determination of the dynamic refraction. 
For we either seek the location of the near point and 
measure its distance from the eye and take the inverse 
of this quantity (expressed as diopters) to represent 
the total dynamic refraction or else we determine upon 
that lens whose refractive power equals that of the 
eye at its maximum of accommodation. 
DETERMINATION OF THE SITUATION OF THE NEAR POINT 
AND THEREBY THE ACCOMMODATIVE AMPLITUDE. 
The common method in vogue is to provide the eye 
under test-this being a monocular procedure-with 
that refractive correction which establishes as nearly 
normal acuity at distance as possible and to then ap- 
proach the test card carrying No. 2 Jaeger type 
(V=0.5 D) until the nearest point is reached at which 
it can still be read or, in other words, until it com- 
mences to become indistinct. A measurement of this 
shortest distance from the cornea is commonly taken 
as the punctum proximum (abbreviated P. P.) or 
near point. If the distance ametropic correction is 
inserted before the patient's eye and this affords nor- 
mal acuity, the eye is rendered artificially and mani- 
festly emmetropic and the near point determination, 
if one accepts the validity of this method, gives the 
true amplitude of accommodation under the condi- Amplitude of Accommodation Tests. 
87 
tions of the test and obviates the arithmetical calcu- 
lations involved in the formula A=P-R. In this 
expression A represents the amplitude of accommoda- 
tion, P the near point in equivalent diopters and R 
the far point in equivalent diopters. The distance 
correction, especially if it includes cylinders, should 
always be inserted before making these tests; by this 
we mean to insist upon the insertion of the proper 
cylindrical correction in all methods of testing accom- 
modative range and amplitude. 
Inaccurate accommodative amplitudes from near 
point determinations are due, we believe, chiefly to the 
following factors:-(1) there is a more rapid in- 
crease of the visual angle under which the test object 
is seen than of the circles of diffusion, hence the size 
of the retinal image increases as the test type is ap- 
proached to the eye and these diffused but larger 
retinal images are more easily interpreted mentally 
than are smaller but sharper images; therefore, the 
person under test is able to read at a point nearer 
than that at which accommodation is proportionately 
enforced: (2) the reduction in the size of the pupil, 
which normally occurs upon the approach of an object 
to an eye and which thereby reduces the sizes of the 
diffusion circles: (3) the effect of closing the lids 
and thus narrowing the palpebral fissure; this narrow- 
ing of the pupillary opening by a narrowing of the 
palpebral fissure is equivalent in action to a stenopaic 
slit and is particularly potent and active in high astig- 
mia, and (4) the size of the test-type or line object 
must bear a certain relation to the visual acuteness of 
the eye under examination: experimentation by objec- 88 
Amplitude of Accommodation Tests. 
tive methods to be disclosed in the succeeding chapter 
shows that there are persons who possess a good range 
of accommodation who cannot read (or will not read) 
fairly fine print at any distance and, again, there are 
those who are able to read such print over a wide 
range whose accommodative amplitude is objectively 
shown to be relatively depleted. 
The reader will, therefore, be appreciative of the 
fact that the writer has never been enthusiastic about 
the value of near point determinations as ordinarily 
made with a tape measure and a few lines of test 
type. And this, in particular, for the reason that our 
near test-cards are printed in fonts of printers' type 
and in nowise observe the scientific standard of a five- 
minute-angle for the distance specified at which the 
reading should be done. 
DETERMINATION OF THE ACCOMMODATIVE AMPLITUDE 
BY ASCERTAINING THE LENS WHOSE REFRACTIVE 
POWER EQUALS THAT OF THE EYE AT ITS MAX- 
IMUM ACCOMMODATION, THE TEST BEING 
MADE MONOCULARLY AT TWENTY 
FEET. 
This test is based upon the fundamental principle 
that for a person whose punctum proximum is situ- 
ated at a finite distance, it amounts to the same thing 
whether he looks at an infinitely distant object through 
a concave lens or without such a lens at an object sit- 
uated at a distance equal to the focal length of the 
lens used. In theory, then, all we need to do is to 
seek the strongest concave lens (equivalent to the dif- 
ference between the strongest plus and the strongest 
minus lenses, or weakest minus and strongest minus Amplitude of Accommodation Tests. 
89 
lenses, dependent upon the ametropia present) 
"through which an eye still sees distinctly at a long 
distance and this lens will give the maximum of 
dynamic refraction of which the eye is susceptible'' 
{Landolt}. Hence the strongest concave or weakest 
convex lens through which an eye can see at a dis- 
tance gives the refraction of that eye when adapted to 
its punctum proximum. The sign of the lens must 
be changed since concave indicates positive and con- 
vex negative refraction. In practice, then, the patient 
is provided with the minimum concave and maximum 
convex lenses, together with the cylinders, which will 
afford as nearly V=20/20 as possible. In this con- 
cave-at-distance method the writer usually selects 
the V=8/10 line as a basis for the distinct-distant- 
vision test. 
There are several vital objections to this method of 
procedure, however. (1) The visual acuteness is con- 
siderably diminished by the use of concave lenses 
which diminish the sizes of the retinal images, 
(2) the term "distinct vision at distance" is indefinite 
and the size of the standard test-object is uncer- 
tain, (3) it is difficult to get an eye to put forth its 
maximum effort of accommodation when looking at 
distance, for accommodation is not thus invited as 
when an object is approached progressively toward an 
eye, and (4) it is a test upon a function made in a 
manner which demands that it be brought into play 
under conditions contrary to those set for it by nature. 
It is certain that the amplitude of accommodation thus 
obtained is smaller than that found from near point 
tests. The reasons are apparent, for the factors, such 90 
Amplitude of Accommodation Tests. 
as increase in the size of the retinal images which are 
likely to give pseudo near-points which are too close 
to the eye, are exactly reversed in their actual physical 
and physiologic actions when viewing a distant test ob- 
ject through concave lenses. It is probable that an 
average of the two amplitudes as determined by these 
two methods will afford a fairly correct estimate of 
the real accommodative amplitude in most cases. Very 
radical differences do, however, arise in the results of 
the two methods and these should form most valuable 
differential and diagnostic data to the practitioner. 
DETERMINATION OF THE AMPLITUDE OF ACCOMMODA- 
TION BY ASCERTAINING THE LENS WHOSE REFRACTIVE 
POWER EQUALS THAT OF THE EYE AT ITS MAX- 
IMUM ACCOMMODATION, THE TESTS BEING 
MADE AT THIRTEEN INCHES. 
We shall refer to this method as the Concave-at- 
near procedure. The normal reading point is about 
twelve to fifteen inches from the eyes; we shall take 
thirteen inches, equivalent dioptrically to 3 D., as a 
normal reading distance. A moment's consideration 
will convince the reader that a very logical procedure 
in investigating the amplitude of accommodation 
would be to find its reserve at the reading point and to 
then add this quantity to the three diopters demanded 
while reading No. 2 Jaeger at thirteen inches. It 
should be accepted as a fundamental principle that 
any ocular function should be investigated under con- 
ditions of activity or quiescence which conform to the 
philosophy of the particular phase of its activity 
under consideration. The normal reading point is at 
a foot from the eyes; it is logical, therefore, to de- Amplitude of Accommodation Tests. 
91 
termine its reserve with respect to the point at which 
this reserve should hold. The thirteen inch or thirty- 
three centimeter point should be ordinarily chosen as 
the point at which the accommodative resources are 
to be investigated, rather than at a nearer or more re- 
mote point, for the reason that nature has ordained 
the establishment of a comfortable convergence point 
(leaving two-thirds to three-fourths of the fusional 
convergence in reserve) and a normal distance of dis- 
tinct vision at about a foot from the eyes. In passing, 
let it be stated that we believe that the function of 
convergence, which normally remains constant in its 
strength, rather than accommodation, which becomes 
depleted with age, is the determining factor in the 
establishment of this normal reading or close work 
distance. 
The method is easily carried out. The test should 
be made monocularly and before each eye should be 
placed the distance correction, particularly the cylin- 
drical element. The spherical element should be the 
maximum convex or minimum concave lens which, 
either alone or in combination with the cylinder as the 
case may be, affords V=20/20 or as nearly the normal 
standard as can be obtained. The writer ordinarily 
uses No. 2 Jaeger type (V=0.50 D.) held at thirteen 
inches; the ciliary must then exert three diopters of 
accommodative action or, at least, produce three diop- 
ters of lenticular action or refractive change if normal- 
ly acting. Minus spheres, beginning in general with 
a -1 or -1.5 diopter glass, are then inserted in the 
trial frame or turned up in the lens battery in con- 
nection with the phoro-optometer until the maximum 92 
Amplitude of Accommodation Tests. 
minus lens has been inserted through which the No. 
2 Jaeger is just barely readable. The available ampli- 
tude of accommodation as thus obtained is the sum of 
the three diopters exerted by the accommodative 
mechanism in order to read at thirteen inches plus the 
amount of concave lens power overcome and expressed 
as a positive quantity. 
There are certain reasons for the insertion of dis- 
tance binocular findings when investigating the accom- 
modative resources at the reading point. These are 
briefly:-(1) The tests upon the total accommoda- 
tive resources and accommodative reserve are made 
under conditions imposed upon them by the optical 
corrections and assistance which the static refractive 
errors have demanded; we are desirous of knowing 
whether or not such a correction will fit in with the 
economic and comfortable operation of accommoda- 
tion and convergence at near points. (2) The accom- 
modative mechanism has been so aided as to permit 
of its meeting most advantageously the normal de- 
mands made upon it as the fixation point is moved 
from twenty feet to near points. (3) The practitioner 
is afforded, when the patient is wearing the binocular 
distance findings, a ready and safe basis for those 
modifications which he may desire to incorporate in 
the prescription that he ultimately gives the patient 
by virtue of the tests upon the accommodative ampli- 
tude and reserve and upon the muscular poise at the 
reading distance. 
Since the effect of concave lenses is to minimize 
the sizes of retinal images and hence the apparent 
sizes of the test-objects, it should be expected that Amplitude of Accommodation Tests. 
93 
the amplitudes of accommodation as determined by 
concave-at-near methods would be less than by 
near-point determination. 
We append a table of amplitudes of accommodation 
as determined by various investigators. 
AMPLITUDE OF ACCOMMODATION. 
Duane. 
Jackson. 
(Concave Lenses. 
Sheard. 
(Monocular 
Age 
Bonders. 
(Near Point) 
Accommodation 
Test Object 
(Near Point) 
Average 
Associated 
at 13 in. 
with 
Concave 
Convergence) 
Lenses) 
10 
14. 
13.5 
14. 
. . . . 
15 
12. 
12.5 
12. 
11.0 
20 
10. 
11.5 
10. 
9.0 
25 
8.5 
10.5 
9. 
7.5 
30 
7.0 
8.9 
8. 
6.5 
35 
5.5 
7.3 
7.0 
5.0 
40 
4.5 
5.9 
5.5 
3.75 
45 
3.5 
3.7 
4. 
50 
2.5 
2.0 
2.5 
55 
1.75 
1.3 
1.25 
60 
1.00 
1.0 
0.5 
ILLUSTRATION. 
Case ii. The writer may be pardoned for reciting 
here his own ocular conditions as illustrative of these 
three subjective methods of determining the amplitude 
of accommodation. The argument for so doing is 
that we are reasonably sure of the results of our own 
personal investigations. With O. D. -1-4.12 CL +-50 
cyl. ax. 90, I am just able to monocularly read the 25 
foot line of letters. With a fairly rapid insertion of 
minus lenses, I am still able to read some of these 
letters and all of the 30 foot letters through a -0.50 
diopter sphere, indicating, by the concave-at-dis- 
tance test, an amplitude of 4.5 D. Binocular tests evi- 
denced from 4.5 to 5.25 D. Provided with my dis- 
tance correction and carrying out the concave-at- 94 
Amplitude of Accommodation Tests. 
near method, I find that 4 D. is the maximum devel- 
opable. The near point determinations show a mono- 
cular near point of 7 inches reading No. 2 Jaeger or 
about 6 diopters of accommodation. 
A case or two illustrative of the value and necessity 
of various subjective tests, other than the near point 
tests, as well as objective tests upon the accommoda- 
tion will be rehearsed in the next chapter. 
REFERENCES. 
Landolt. The Refraction and Accommodation of 
the Eye. Pages 166-184; 275-289. 
Danders. The Accommodation and Refraction of 
the Eye. Pages 28-38 ; 72-79. 
The American Encyclopedia of Ophthalmology, 
Volume I. 
Savage. Ophthalmic Myology. 
Laurance. Visual Optics. Pages 56-63; 68; 84; 89 ; 
107; 111; 128. 
Sheard. Dynamic Skiametry. (Keystone Maga- 
zine, 1916 and 1917.) 
Howe. Muscles of the Eye. Volume I. Pages 
144-148. CHAPTER IV. 
A Resume of Methods of Determining the Relative Range 
and Amplitude of Accommodation and Convergence. 
The reader is referred at the very outset of this 
very brief and meager description of these rather im- 
portant tests upon the relative range of accommodation 
and convergence to that most excellent treatise by 
Howe upon "The Muscles of the Eye" (Volume I, 
pages 309-347). We acknowledge our indebtedness 
to him for the essentials of the following presentation. 
Incidentally we must both acknowledge our indebted- 
ness to that great ophthalmologist, Danders. 
There are upon the market in this country two 
forms of instruments only, insofar as the writer 
knows, which may be used for the tests to be discussed 
in the ensuing paragraphs. These are the devices 
known as the "optometer" due to Howe and the 
"ophthalmodynamometer" due to Gardiner. Howe has 
succeeded in devising by photographic means a near 
test chart constructed on the basis of the minimum 
angle of fifty-five seconds which is adapted for testing 
the vision at each meter-angle from one to twenty. 
The Gardiner instrument is provided with a slide car- 
rying a card printed in several sizes of Gothic type. 
But both methods suffer from the fact that when 
"tests are made on persons whose vision is not per- 
fect, or cannot be brought near to the standard of per- 
fection by suitable glasses, a corresponding allowance 
must be made in the results obtained" (Howe). 96 
Relative Accommodation and Convergence. 
Donders demonstrated that, for nearly all points 
within the range of binocular vision, accommodation 
and convergence are, to a certain extent, independent 
of each other. There are then two fundamental ques- 
tions which may be asked as to the relative range of 
accommodation and convergence. 
First. "Convergence remaining the same, by how 
many diopters can accommodation be increased or di- 
minished ?" 
Second. "Accommodation remaining unchanged, by 
how many meter angles can convergence be increased 
and diminished?" 
THE MEASUREMENT OF RELATIVE ACCOMMODATION FOR 
CLINICAL PURPOSES. 
We have, in these tests, to determine the positive 
side and the negative side of the relative range of ac- 
commodation at any given fixation point. The first of 
these is determined by concave lenses and the second 
by convex lenses. We proceed somewhat as follows: 
The subject looks at the standard test line and the 
maximum negative and maximum positive lenses, held 
before both eyes, are ascertained. These values give 
us, in turn, the powers in diopters of the positive and 
negative sides of the relative accommodation with 
visual axes parallel, i. e., convergence nil. Then, using 
the Howe or Gardiner apparatus with appropriate test 
objects, the fixation point is made at 50 centimeters. 
This demands an accommodation of 2 D. and a con- 
vergence of 2 M. A. (about 7° or the equivalent of 
about 13 prism diopters). By placing negative lenses 
in the holders, we find the strongest concave lenses 
with which the line previously read without glasses Relative Accommodation and Convergence. 
97 
can be read. The power of these lenses in diopters 
will indicate the positive side of the relative range 
of accommodation at 50 centimeters. Without chang- 
ing the fixation point, the maximum convex lenses 
under similar conditions of visual acuity as those speci- 
fied in the above sentence, give the negative range of 
accommodation. These tests can be continued until the 
binocular punctum proximum is reached when the 
patient can no longer read through any negative lenses, 
showing that the limit of the positive accommodation 
has been reached. Generally, however, the patient 
can still read through positive lenses indicating that 
the negative range of relative accommodation is still 
operative. If desired, the tests may be continued in- 
side of the binocular punctum proximum until the 
absolute punctum proximum is found at which point 
the positive lenses necessary to enable the patient to 
read the type are the only ones with which it can be 
read. From this data thus obtained most interesting 
and valuable curves can be plotted using convergence 
in meter-angles as the X axis or abscissa and the posi- 
tive and negative dioptric values of the maximum 
lenses overcome as the Y axis or ordinate. (SeeHowe: 
Muscles of the Eye, Volume I, pages 324-328; Dan- 
ders: Accommodation and Refraction of the Eye, 
pages 110-125; Landolt: Refraction and Accommoda- 
tion of the Eye, pages 190-218.) 
In ametropia the normal relationship between ac- 
commodation and convergence does not exist and in 
consequence the problem becomes more complicated. 
In myopia we know that convergence is always in ex- 
cess of accommodation and in hyperopia the reverse 98 
Relative Accommodation and Convergence. 
is true. The technique for measuring the relative range 
of accommodation and convergence in ametropia does 
not differ from that outlined for emmetropia, but the 
altered relations between the functions must always 
be taken into account. A most excellent method, to 
my mind, is the insertion of the apparent static correc- 
tion as determined in the light of all distance tests 
and to then proceed on the basis of semi-normally 
restored ocular conditions. Particularly is this true 
of the cylindrical corrections; spherical ametropic 
errors are easily taken into account. 
Clinically or in office practice the above procedure 
would be too technical and laborious. As a matter of 
practice, two points suffice, namely 6 meters, or 20 
feet and 33 cms., or 13 inches. "Naturally we wish 
to ascertain if there is any hypermetropia and in so 
doing we use convex glasses in gradually increasing 
strength. If no convex lenses are accepted at 20 feet 
fixation we know there is no negative part of the rela- 
tive accommodation. If convex lenses are accepted 
there is hyperopia and the maximum lenses give the 
measure of the negative part of the relative accommo- 
dation. We then place minus glasses before the eyes 
-about minus 3 D. if he is an emmetrope, or if he is 
an ametrope varying their strength proportionately. 
This gives us at once the positive part of the relative 
accommodation with parallel visual axes or the sum of 
the two is the total range. * * * It is sufficient to de- 
termine at once the amount of relative accommodation 
with convergence at three meters, namely at about 
the reading distance. For that purpose the test types 
which the normal eye can see at one-third of a meter Relative Accommodation and Convergence. 
99 
are given to the patient, and having made sure that 
the distance at which they are held is about thirty- 
three centimeters, we place before each eye the strong- 
est concave glass with which the patient can still read 
that print readily. This gives the positive part of the 
relative accommodation, understanding that we must 
subtract in that case three diopters from the strength 
of the lens, because convergence at one-third of a 
meter itself necessitates for the normal eye an accom- 
modation of three diopters. In a similar way, by 
placing convex glasses before the eye while the print 
is still held at one-third of a meter, and by ascertain- 
ing what is the strongest convex glass through which 
that print is seen, and again making a corresponding 
correction, we have the negative part of the relative 
accommodation with convergence at three meter 
angles." (Howe). 
Donders stated the important principle that "the 
accommodation can be maintained only for a distance 
at zvhich, in reference to the negative part, the positive 
part of the relative range of the accommodation is 
relatively great." Howe says: "In our studies of the 
conditions of the muscles we shall find that the most 
important and apparently the most frequent anomolies 
are those involving the ciliary muscle. It is desirable 
to determine whether the action of that muscle is 
normal, or excessive, or insufficient. At least a general 
idea as to this power of the ciliary is shown simply 
by placing a minus 3 D. glass before each eye and ask- 
ing the patient to read again the distant test type. I 
have learned to regard this as one of our most im- 
portant tests * * *. If the person cannot overcome 100 
Relative Accommodation and Convergence. 
these or weaker minus glasses in proportion to his 
age or in proportion to his ametropia, then we at once 
suspect some insufficient power of the ciliary muscles 
* * *. Ordinarily, if the positive part of the relative 
accommodation is insufficient with parallel axes and 
also with convergence at one-third of a meter and 
if discomfort and headache do exist, then that clue 
should be followed up." 
To illustrate this method let us apply it to a case 
of actual excessive accommodation commonly called 
"Spasm of Accommodation." This is a condition quite 
common in school children and cases of actual excess- 
ive accommodation with a low degree of astigmatism 
are frequent. (1) The range of accommodation is not 
normal. The near point, as determined by the tape 
measure and closeness of reading of fine print, is too 
near the eye. There may be at distance an apparent 
myopia (say -0.50 D.) and when a low power con- 
cave lens is offered the patient may be able to read 
20/20. (2) The relative accommodation is altered, 
for the positive part of the relative accommodation is 
increased. The negative part of the relative accom- 
modation is abnormally small. With convergence at 
three or four meters the minus glass which can be 
overcome is stronger than usual. The causes may in- 
clude: (a) Excessive effort of accommodation for a 
considerable time-professional men, bookkeepers and 
so forth-undoubtedly tends to produce this condition, 
(b) Glare of strong lights may cause it. (c) General 
causes, among which may be named primary diseases 
of the nervous system, reflexes from the stomach or 
elsewhere and (d) toxemias. In the matter of treat- Relative Accommodation and Convergence. 
101 
ment the so called ''blurring" plan is of decided ad- 
vantage ; by this we mean nothing more or less than 
constant over-correction with convex glasses. Bifocal 
glasses are often of great assistance; if efforts at ac- 
commodation become difficult this may be necessary. 
These methods on the measurement of the relative 
binocular amplitude of accommodation are here called 
attention to for the reason that they seem to be some- 
what of a closed book to the average ocular practi- 
tioner. As a matter of fact they are not difficult and 
the information acquired is often most valuable. It 
will be noted, however, that this is a binocular test, 
whereas it seems to me more logical to engage in 
monocular tests, as described in Chapter III, for the 
two eyes may be distinctly different in their accom- 
modative range and resources. It likewise seems a 
much more logical procedure to absolutely eliminate 
convergence from accommodative tests (if the occlu- 
sion of one eye does so) and to investigate the ac- 
commodation monocularly and to then, under the 
fusional dissociation tests outlined in Chapter II, in- 
vestigate the convergence as associated with the ac- 
commodation. However, both methods are most valu- 
able and either one practiced consistently will lead to 
much more scientific work in ministering to the needs 
of the ocular economy. The analysis should be made, in 
so far as possible, upon each function separately and 
then in co-ordination. 
These methods have been presented for a further 
reason and that is this: Dynamic skiametry is, in 
part at least, an objective method of testing the rela- 
tion of accommodation to convergence since it is one 102 
Relative Accommodation and Convergence. 
method of supplying that lens assistance which will 
make the relative positive and negative portions of 
accommodation that which they should be in em- 
metropia. But we believe that dynamic skiametry is 
more than this; but if not, it serves as a most valuable 
test if it quickly and objectively reveals the needed 
lenticular assistance in the interest of proper accom- 
modative balance at the reading point. 
THE MEASUREMENT OF THE RELATIVE CONVERGENCE 
FOR CLINICAL PURPOSES. 
To measure the relative range of convergence similar 
operations to those described in preceding paragraphs 
are carried out except that prisms are substituted for 
spherical lenses. The test chart is placed at various 
points representing roughly integral meter-angles and 
prisms are placed before the eyes, base out to measure 
the positive, and base in to measure the negative, por- 
tions of relative convergence. For the average base 
line (64. mms.) the simplest way to convert degrees 
into meter angles (approximately) is to divide the 
number of the prism degrees by 7. The test object is 
a line, or better a line of coarse type. In the ordinary 
routine the amount of abduction and adduction are ob- 
tained at the far point; this may be considered as the 
relative range with relaxed accommodation. We then 
proceed to the relative convergence and divergence at 
thirteen inches, accommodation being exerted at one- 
third of a meter. If these tests at the reading point 
fit in in agreement with those at six meters, ordinarily 
no further regard need be given them; but in cases of 
exophoria and esophoria they are most valuable. We 
have discussed them under fusional convergence in Relative Accommodation and Convergence. 
103 
Chapter III. We note again, in closing this chapter, 
that normally about two-thirds of the convergence is 
associated with the accommodation at any point fixed 
upon. If, therefore, when reading at thirteen inches, 
accommodation and its associate convergence are 
normal, about 12° of convergence will be associated 
with the 3 D. of accommodation and since, assuming 
an interpupillary distance of 64 mms., some 18° of 
convergence is required, approximately 6° of fusional 
or positive convergence is demanded for binocular 
single vision. If the supplementary fusional con- 
vergence at 13 inches turns out to 18°, we may draw 
two conclusions:-(1) that the abduction at 20 feet 
is approximately 24° or about the normally accepted 
standard, and (2) that Landolt's criterion is fulfilled, 
namely, that not more than one-third of the total 
fusional convergence is called into action at the read- 
ing point. 
Howe-Muscles of the Eye. 
Vol. I pages 308-349. 
Vol. II, pages 1-90. 
Landolt-Refraction and Accommodation of the Eye. 
Pages 166-218 and 501-516. 
Danders-Accommodation and Refraction of the Eye. 
Pages 28-37; 110-126. 
Sheard-Physiologic Optics. 
(Essay from American Encyclopaedia of 
Ophthalmology. To be reprinted later.) 
REFERENCES. CHAPTER V. 
An Objective Method of Determining the Monocular 
Amplitude and Range of Accommodation. 
All subjective tests should be supplementary to in- 
vestigations by objective methods. Whenever possible 
objective methods should be devised and used even 
though they may fail to agree in toto with various sub- 
jective tests and even though they may have their 
probable or apparent inherent source of error. Static 
retinoscopy is a striking example. Up to the present 
writing, in so far as the writer is aware, no one has 
presented an objective method for the examination of 
the accommodative resources. If such is not the case 
and the method to be described has been antedated or 
surpassed, we shall have served with pleasure in em- 
phasizing the simplicity of the method and the value 
of the data thus obtained to the ocular practitioner. 
The description of the monocular objective test will be 
supplemented by its applications to binocular investi- 
gations upon the accommodation in the succeeding 
chapter. 
Figures 29, 30 and 31 show diagramatically the gen- 
eral modus operandi in the monocular method. Each 
eye should be, in turn, occluded and its accommodative 
range investigated, since some of the most interesting 
and important cases from the ocular economic stand- 
point are those involving marked differences between 
the accommodative resources of the two eyes. 
In practice we so arrange matters that the object 
viewed (Figure 29) shall be reasonably illuminated. Objective Monocular Accommodative Test. 
105 
The flooding of the room with artificial light is not 
objectionable except from the operator's standpoint. 
With experience, however, one can use retinoscopic 
methods and follow the reflexes with ease and ac- 
curacy under almost any subdued luminous sur- 
roundings. 
A 
P 
P 
L 
1 
E 
D 
O 
P 
T 
I 
C 
S 
o 
H 
I 
O 
s 
T 
A 
T 
E 
U 
N 
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Figure 29. Fixation Test Object for Use in Obtaining the 
Objective Value of the Monocular or Binocular Accom- 
modative Amplitude. 106 
Objective Monocular Accommodative Test. 
The patient is given a line of type printed in large 
letters (12 to 16 point) upon a card about one-half 
inch wide and fastened to some convenient holder such 
as illustrated in Figure 29. Or a single line ruled on 
a card or a pencil will serve satisfactorily as a fixation 
object, but there is not the incentive to full accommo- 
dation as when reading is demanded. The full mono- 
cular distance finding, affording as nearly V=20/20 
as possible, is inserted before the eye to be tested. The 
patient is then given the test object-which he holds 
initially at about 13 inches-and told to read the let- 
ters. In general we have the patient hold the card 
slightly to the nasal side during the examination of 
either eye while we proceed to examine retinoscopic- 
ally from the temporal side and as close to the visual 
line as possible. 
In Figure 30 we have represented the optical and 
ocular conditions when the retina and the object 
viewed are conjugate points and the exact or requisite 
number of diopters of accommodation demanded for 
the point fixed are supplied. Under these conditions, 
therefore, with the accommodative point kept con- 
stant at F and the mirror A in the same plane a neu- 
tral shadow condition should obtain and by moving 
the retinoscope to C-an inch nearer the eye-a hy- 
peropic condition would be revealed or by withdraw- 
ing an inch further from the eye, as at B, a myopic 
condition would be evidenced. By then moving or 
having the patient move the test-object nearer the eye 
the actual near point will be found as soon as the reti- 
noscopic mirror has to be operated in a plane back of 
the fixation point in order to obtain a neutral shadow. Objective Monocular Accommodative Test. 
107 
These are ideal conditions in that we are assuming the 
presence of a true or artifically produced emmetropia 
and a perfectly innervated and functioning ciliary 
and lenticular action. 
Ftq 3O- 
Figure 30. Illustrating the Optical Principles Involved in 
the Objective Monocular Test upon Accommodative 
Amplitude. 
In general we find that when the patient, wearing 
the full distance correction, reads monocularly the 
letters (which, by the bye, may be as small as the 
patient can see), there is a "with" or hyperopic motion 
indicating that the point conjugate to the retina in an 
eye optically statically perfect is not at the position of 
the object viewed but at a position somewhat in front 
of that point, i. e. further from the eye. Three valu- 
able tests may be made. First, with monocular fixa- 
tion and observation retinoscopically at any point de- 
sired the operator can find that convex lens power 
which must be added in order that the monocular ac- 
commodative demands, in the interest of conjugacy of 108 
Objective Monocular Accommodative Test. 
retina and object viewed, may be met. This would be 
shown by the additional lens power needed to give a 
neutral Yetinoscopic reflex. Suppose that 1 D. is thus 
demanded when both fixation and observation points 
are at thirteen inches: our interpretation would be that 
objectively an assistance to the accommodation, over 
and above the assistance (or burden in cases of over- 
corrected myopia) afforded by the static finding given 
the eye, is required to relieve the accommodation of an 
extra burden. Notice that we specify minimum 
amount of additional lens power to produce neutraliza- 
tion skiascopically; more assistance might be and gen- 
erally would be accepted under the method of proce- 
dure we have disclosed. Second, observation may be 
kept constant at any distance specified and the test- 
object drawn closer to the eye until a neutral shadow is 
obtained. In Figure 31, let F be the point viewed and A 
the position of the operator's mirror. If a certain test 
shows that D F is 10 inches (4 D.) and DA is 13 
inches (3 D.) we should conclude that the accommoda- 
tion actually available at ten inches is sufficient only 
for optical conjugacy at 13 inches, hence indicating 
the need of a diopter of lenticular assistance. Third, 
by approaching the object closed and closer to the eye 
a point will finally be found such that no nearer ap- 
proach to the eye changes the neutral condition of re- 
flex as retinoscopically observed at the closest point to 
the eye. In testing, therefore, for the near point ob- 
jectively we proceed as follows: The patient draws 
the test object as near the eye as will still permit of its 
reading. To the observer at thirteen inches the retino- 
scopic reflex will show an "against" or myopic condi- Objective Monocular Accommodative Test. 
109 
tion indicating that he is outside of the optical ocular 
far point dynamically considered. The practitioner 
then moves forward until he obtains the neutral 
shadow position. The test-object is then to be carried 
still closer to the eye (blurred image makes no differ- 
Fig. BL 
Figure 31. Illustrating the Optical Principles Involved in 
the Objective Monocular Test upon Accommodative 
Amplitude. 
ence) and the nearest point of neutral shadow found 
and measured. This gives the apparent near point 
under whatever ocular conditions the test is made 
(ordinarily when wearing the distance correction) and 
from it the range and amplitude of accommodation are 
easily determined. We measure the distance D A 
(Figure 31) and not F D. We occasionally vary this 
test, and with observation and fixation at thirteen inch- 
es, produce neutralization of shadow and then proceed 
as outlined above. We are, however, partial to the 
test in which the static finding is worn. 
The method is certainly very simple and quickly 
carried out. The question is, are there any inherent 110 
Objective Monocular Accommodative Test. 
errors? Yes; those of observation and optical imper- 
fections, lack of response on the part of the person 
under test, and the difficulties of making accurate 
measurements of distances. For this latter purpose 
we use a light-weight, narrow tape-measure, one end 
fastened to the trial frame with due allowance for 
distance from the cornea, and the other end weighted, 
the tape when in use being carried between the finger 
and thumb of the hand holding the retinoscope. 
These tests must certainly suggest themselves to the 
reader as being most valuable, especially in finding the 
range and amplitude of accommodation in children 
(one can employ small colored pictures pasted on the 
rear side of the test-object shown in Figure 29), in 
presbyopia, in subnormal accommodation, in excessive 
accommodation, in amblyopia when we are uncertain 
of whether or not accommodation is still active be- 
cause of the uncertainty of subjective tests by virtue 
of the reduced visual acuity. 
Likewise, we are provided with an objective method 
which tells us whether or not accommodation is pro- 
portionately enforced in those rather frequent cases, 
mentioned in Chapter III, in which the patient, usually 
young in years, is not able to read fine print at four- 
teen inches but can read it when brought up very 
close to the eye. Our answer is that these tests demon- 
strate the universality of lack of proportionate accom- 
modative action and that such type is read at points 
abnormally close to the eye because of increased sizes 
of retinal images, constriction of pupil and narrowing 
of palpebral fissure. 
Furthermore, these objective tests show that the Objective Monocular Accommodative Test. 
111 
amplitudes of accommodation are in closer agreement 
with the results tabulated in Chapter III under the 
concave-at-near method than they are with monocular 
near point and binocular concave-at-distance methods. 
We close the chapter with a few illustrative cases. 
Case 12. Normal Monocular Accommodative Range. 
Miss E. N. Aet. 25 years. Static Skiametry, O. U. + 
1.00 D. S., Dynamic Skiametry, O. U. +1.50 D. S., 
Subjective, O. U.+1.25 D. S., Objective monocular 
accommodation, each eye, 6 inches or 7 D.; binocular 
objective accommodation 5 inches or 8 D. Monocular 
near point, reading No. 2 Jaeger through distance cor- 
rection, showed punctum proximum at 4.5 inches. All 
accommodative convergence tests showed 3° esophoria 
at near, 1° esophoria at distance, wearing subjective 
findings. Concave-at-near test at thirteen inches de- 
monstrated that each eye was possessed of 8 D. accom- 
modation. 
Case 13. Unequal Binocular Amplitude of Ac- 
commodation. Mr. E. P. B., Aet. 21 years; headaches; 
dryness of eyes; cannot read for any length of time; 
sensitive to light. Distance correction, acuity equally 
good, O. D. +.50 D. S. -0.37 ax. 180. O. S. +.87 D. S. 
-0.37 ax. 180. Monocular objective accommodation 
with distance correction, O D. 5 inches or 8 D. and O. 
S. 4 inches or 10 D. Binocular objective accommoda- 
tion point at 4 inches. Concave-at-near methods dem- 
onstrated O. D. 8 D., O. S. 10 D. With distance cor- 
rection before the eyes the following facts were dis- 
closed; binocular tonicity test 9° exophoria; ductions, 
O. D. abduction 8°, adduction 14°, O. S. abduction 7°, 
SOME ILLUSTRATIVE CASES. 112 
Objective Monocular Accommodative Test. 
adduction 13°. Accommodative-convergence tests at 
13 inches, with fusional convergence passive, showed 
by one test 4° base in or 2° exophoria (assuming a 
physiologic exophoria of 6°) and by another test 2° 
base in or 4° exophoria. The reserve convergence was 
found to be 23° or more. The binocular near point 
subjectively determined was 3.5 inches. The concave- 
at-near monocular tests on accommodation showed O. 
D. 8 D. and O. S. 10 D. These tests then demonstrate: 
(1) that the convergence as associated with the ac- 
commodation is overly taxed, probably in the interest 
of relieving the fusional convergence. (2) that the 
reserve convergence is amply able, except under peri- 
ods of strain at near work, to overcome the tonic di- 
vergence but that the burden upon it is excessive, 
(3) that the amplitude of accommodation of the right 
eye is greater than of the left. We prescribed O. D. 
4*-37 cyl. ax. 90, 1° base in and O. S. -.37 cyl. ax. 
180, 1° base in, chiefly for distant use. 
Case 14. Amblyopia. In a particular case of a man, 
aged 30, the static retinoscopic findings were O. D. 
4*3.00 D. S., O. S. -j-5.00 D. S. Dynamic skiametry 
showed O. D. 4*3.50 D. S., O. S. 4*6-50 D. S. Static 
subjective tests gave O. D. 4*2-50, V-20/20 and O. S. 
4-4.00, V less than 1/10 which could not be improved 
upon. The monocular objective accommodative test 
showed that the right eye had 4 D. of accommodation 
but that the near point accommodatively for the left 
eye was 15 inches or 2.5 D. Some 8° of esophoria 
was elicited at distance. We are satisfied that little 
can be done for the left eye for it has very low visual Objective Monocular Accommodative Test. 
113 
acuity and practically little amplitude of accommoda- 
tion. 
Case 15. Anisometropia with Good Range of Ac- 
commodation. Young girl, aged 10 years. Static 
retinoscopic test showed O. D. 4-3.00 D. S. CG -5-00 
ax. 10; O. S. 4-0-37 C 4~-50 ax- Subjectively, O. 
D. -2.25 3 4~4.75 ax. 100 gave V-8/10 while the 
static finding for the left eye gave V=10/10. The 
monocular objective accommodation, wearing the 
above correction, showed O. D., 5 D. and O. S., 8 D. 
Distance muscle tests evidenced 4° exophoria and 
tests at 13 inches demonstrated 10° base in and 12° in, 
or approximately 6° of exophoria. The maximum re- 
serve convergence at 13 inches was 16°. We gave the 
subjective finding for constant wear with advice to 
use the pencil method (a drawing of the finger or a 
pencil toward the eye until diplopia ensues) for de- 
veloping additional convergence reserve and to cover 
the left eye for short periods of time several times a 
day and to exercise the right eye by reading coarse 
print. This has been done with the result that after 
six months her accommodation in the right eye has 
developed an additional diopter and her reserve con- 
vergence some 5° more strength. 
Case 16. Presbyopia. The subjective findings, in 
good agreement with the static retinoscopic results, 
gave in the case of a woman 58 years of age normal 
acuity under O. D. 4-1.75 D. S. O' -1.25 ax. 30 and 
O. S. 4-2.00 D. S. O -1-00 ax. 165. Dynamic ski- 
ametric tests at 16 inches (where she desired to read) 
gave O. U. 4~T00 D. S. 3 -1.25 ax. 180. The ob- 
jective accommodative test, the patient wearing the 114 
Objective Monocular Accommodative Test. 
distance correction, demonstrated a monocular near 
point of 20 inches or 2 D. while the binocular test 
showed 17 inches or 2.37 D. Therefore, for reading 
purposes at 16 inches (equals 2.5 D.) and allowing her 
to retain one-half her available amplitude of accom- 
modation in reserve, we gave her an additional -|-1.75 
D. S. binocularly. The interesting part of this case 
is the following: 1° exophoria at distance; at the 
reading point some 20° base in or 16° exophoria under 
the accommodative-convergence test wearing the read- 
ing correction; a reserve convergence of about 12°. 
We gave this patient 1.5° prisms, base in, incorporated 
in her reading glasses and did nothing further since 
she has been for years and is now under medical treat- 
ment "for her nerves." We hope we will not be mis- 
understood when we say that the woman is enjoying 
her life as she has not for years, for she came wear- 
ing a correction which she had worn for six years in- 
volving cylinders which I am positive never had their 
corresponding neutralizers in her eyes. CHAPTER VI. 
An Objective Method of Determining The Binocular Range 
and Amplitude of Accommodation and the Effects 
Which Lateral Muscular Imbalances Have 
Upon the Same. 
This chapter presents the monocular objective 
method of determining the range and amplitude of 
accommodation as made applicable to binocular inves- 
tigations upon the functions of accommodation in 
each eye as correlated with that of convergence. The 
one very vital factor which enters into these binocular 
tests and which is, presumably, absent from monocu- 
lar investigations when the eye not under examina- 
tion is occluded, is that of convergence. For this term 
convergence we ought properly to write binocular 
single vision. As a result there is ostensibly less like- 
lihood of a true analysis of ocular conditions being 
made and less likelihood of an ability to interpret the 
data obtained when two functions, not wholly in- 
dependent neither wholly dependent one upon the 
other, are investigated under conditions in which they 
are co-ordinated in some manner such as will give 
binocular single vision (convergence) and distinctness 
of vision (accommodation), than there is when each 
function is investigated, insofar as possible, by itself. 
The methods and tests have been presented in the fore- 
going chapters. 
But the binocular methods to be described are most 
valuable in many cases and as a well-known American 
ophthalmologist and an authority on ocular muscles 
said to me: "We are still guessing these optical puzz- 
les" ; hence that which is of value even in a small 116 
Objective Binocular Accommodative Test. 
percentage of cases is worth preservation and use. 
Marked departures in the values of the objectively 
obtained binocular and monocular near-points are 
nearly always indicative of disturbances in the extrin- 
sic muscles or their innervations or the supplementary 
convergence. Excessively close binocular near-points 
as compared with the monocular tests usually accom- 
pany conditions of over-convergence or relatively ex- 
cessive accommodation, while in those circumstances 
in which the binocular accommodative near-point is 
farther from the eyes than is the monocular objectively 
determined punctum proximum, weakness of con- 
vergence or abnormal divergence is present. 
In determining the binocular range of accommoda- 
tion we employ a test object such as that shown in 
Figure 29. The subject approaches this toward his 
eyes while the practitioner follows behind with his re- 
tinoscope until he has determined the closest position 
at which he can obtain a neutral shadow even though 
the test object may be approached still nearer the eye. 
We have diagrammed in Figure 32 the ideal conditions 
of convergence and accommodation and the determina- 
tion of the binocular near point and have shown in 
Figure 33 the ordinarily found arrangement of fixa- 
tion and position of the observer when the closest 
neutral shadow position is obtained. For if, as in 
Figure 32, we have a pair of eyes in which the monocu- 
lar accommodations are so perfectly regulated that one 
diopter of innervation produces one diopter of actual 
accommodative or refractive change and if the accom- 
modation as associated with convergence is so per- 
fectly adjusted that, in conjunction with the supple- Objective Binocular Accommodative Test. 
117 
mentary or fusional convergence, the commonly ac- 
cepted standard relation of three to one (this ratio 
being dependent upon the value of the meter-angle) 
between convergence and accommodation obtains so 
Figure 32. Illustrating the Optical Principles and Proce- 
dure in the Binocular Accommodative Amplitude 
Tests. 
that the convergence and accommodative fixation 
points are one and the same, then the fixation point F 
and the observation point A will remain one and the 
same until the binocular near point is reached. A 
further approach to the eyes will, however, give a 
"with" motion (when the plane mirror is used) since 
the accommodation can no longer keep up with the 
convergence, i. e. an object would be seen single but 
indistinctly or double but distinctly, and the binocular 
dynamic far-point (or subjective near-point) would be 
back of the fixation point. 118 
Objective Binocular Accommodative Test. 
In the majority of cases we find the conditions as 
shown in Figure 33 in which the fixation point B is 
nearer the eye than the neutralization of the retino- 
scopic shadow position at 0 when the same has been 
determined at its closest position to the eyes. That 
the binocular near point is ordinarily, either by sub- 
jective or objective methods, nearer the eyes than is 
the monocular near point argues for a greater activity 
on the part of accommodation when associated with 
convergence than when not so associated and especial- 
ly under the impetus of overconvergence when the 
Fea- 33. 
Figure 33. Illustrating the Optical Principles and Pro- 
cedure in the Binocular Accommodative Amplitude 
Tests. 
convergence punctum proximum and binocular accom- 
modative near point approximate each other. This is, Objective Binocular Accommodative Test. 
119 
however, one of the intricate ocular problems and, 
insofar as we are aware, it is rather commonly ac- 
cepted that "whatever may be true of other associated 
brain-centers, it appears that the center of the ciliary 
muscles and the third conjugate innervation center 
(the one to converge both eyes) can have the associat- 
ed impulse to run in only one direction; that is, from 
the former to the latter." (Savage). Such a statement 
is probably correct when we have reference to the 
convergence as associated with the accommodation but 
it does not necessarily follow that the third member 
which enters into binocular single vision, namely the 
fusion convergence, may not alter the convergence 
associated with certain accommodative conditions and 
thereby make available greater accommodative possi- 
bilities. In fact, the proof is conclusive that the fusion 
convergence serves as the correlating medium between 
accommodation and convergence in order that fixation 
may be one and the same accommodatively and con- 
vergently when possible. 
We may well ask with Howe: "Of what clinical im- 
portance is the difference between the binocular and 
monocular near point?" To my mind the answer lies in 
the process of convergence or as the result of the act 
of convergence. For if the eye is tested as to its 
accommodative resources in its straight-away, parallel- 
axis position (as when looking at twenty feet) no 
convergence is involved, hence we should expect to 
experimentally obtain the minimum value of the ac- 
commodative resources when this function is investi- 
gated at 20 feet. When the tests are made monocular- 
ly, either by objective or subjective methods, only that 120 
Objective Binocular Accommodative Test. 
convergence which is associated with the act of accom- 
modation is in operation. This accommodative con- 
vergence we believe to be, under standard conditions, 
less than the amount demanded for binocular single 
vision at any given near point. Hence this must be 
supplemented by fusion convergence. We likewise 
have reason to believe that the portion of the con- 
vergence demands met by the accommodation in- 
creases as the fixation point is approached toward the 
eyes, since the fusion convergence increases at points 
closer to the types as shown by such investigations as 
those recorded by Maddox and given in Chapter II. 
The accommodative and convergence functions are in 
part independent of each other and in part interde- 
pendent ; we should, therefore, expect the monocular 
accommodative tests to indicate greater values of the 
accommodation when associated with accommodative 
convergence than when tested at points involving no 
such convergence and less, in turn, than the results 
shown by tests upon the binocular accommodative re- 
sources. There must, therefore, be an interplay of 
accommodative and fusional convergence, not neces- 
sarily through physiological or anatomical channels, 
however, whereby the convergence makes possible a 
slightly greater dynamic refractive change under a 
given delivery of innervation to the accommodative 
mechanism. Under excessive positive convergence 
tendencies or in which the positive fusion convergence 
is extraordinarily large we should expect a greater 
binocular than monocular range of accommodation. 
A binocular amplitude of accommodation which is in 
excess of the monocular amplitude by a diopter or Objective Binocular Accommodative Test. 
121 
more is, in general, indicative of an associated positive 
overconvergence or a subnormal accommodation. 
When the reverse conditions exist, and the binocular 
accommodative near point is farther from the eyes 
than is the monocular, we may conclude that there is 
a deficiency in either the accommodative convergence 
or the positive fusion convergence or both. 
In the clinical use of the binocular test we supply 
the eyes with the full distance binocular findings (the 
same, however, as used in the monocular method) and 
determine the nearest point at which the shadow stays 
neutral. For, if we are outside of the accommodative 
far-point, the shadow or reflex will move "against" 
the mirror motion (using the plane mirror) and if in- 
side, it will move "with." There is evidently one posi- 
tion of the observer's mirror in which, with a con- 
stant approach of the test object to the eyes, it will be 
at the closest point possible for a neutral shadow. 
It may be claimed that this method is similar to, or 
the same as, that known by the name of "dynamic ski- 
ametry." It is, in part, a modification of this system 
and when the dynamic skiametric tests, with fixation 
and observation at the customary reading distances, 
are being carried out, these monocular and binocular 
range of accommodation tests can be readily made. 
But the nature and purpose of these tests are entirely 
different from those involved in dynamic skiametry. 
In the former we are testing for the maximum avail- 
able amplitude of accommodation, while in the latter 
it is presumed that there will be objectively indicated 
that lenticular assistance at any given fixation point 
such that accommodation and convergence will be 
harmoniously correlated at the point of test. 122 
Objective Binocular Accommodative Test. 
We close the chapter by a citation of two cases 
illustrative of the points we have been discussing. 
ILLUSTRATIVE CASES. 
Case 17. The Binocular Amplitude of Accommoda- 
tion as Objectively Determined Greater than the 
Monocular Amplitude. Miss E. K. Aet. 12 years. 
Complains of frontal headaches and inability to read 
in the late afternoons or evenings. Static retinoscopic 
tests evidenced O. U. 4~ 1-25 D. S. Dynamic skiametry, 
the patient wearing the distance correction, fixation 
and observation being made at 13 inches, disclosed a 
decided "with" motion requiring O. U. 4-3.00 D. S. 
in toto to neutralize. Binocularly, under subjective 
tests, O. U. 4-1.00 D. S. was accepted giving V=8/10 
to 10/10. The accommodative convergence tests 
showed 7° esophoria, the tonicity tests at 20 feet evi- 
dencing 4° esophoria, the patient wearing the dis- 
tance findings. The objective monocular accommoda- 
tive amplitude test showed 3.5 D.; the binocular test 
5 D. The subjective accommodative tests disclosed 
the fact that the patient could not monocularly read 
No. 2 Jaeger at 13 inches and that the same was read- 
able binocularly with great difficulty. 
With a reading correction of O. U. 4-2-00 D. S. No. 
2 Jaeger could be read but not closer than 10 inches. 
From the nature of the case and the child's nervous 
condition we prescribed O. U. 4~ 1-25 D. S. for constant 
wear and forbade the use of the eyes for reading or 
any other close work. 
Case 18. The Binocular Amplitude of Accommoda- 
tion as Objectively Determined Less Than The Mono- 
cular Amplitude. Mr. J. W. Aged 25 years. Suffered Objective Binocular Accommodative Test. 
123 
a nervous breakdown two years ago and is still under 
his physician's care. His eyes have troubled him a 
great deal; has worn glasses for years. Static retino- 
scopy showed O. D. -f-0.62 D. S. 3 4-1.12 ax. 90, O. 
S. 4~0-62 D. S. O 4~l-50 ax. 90. Dynamic skiametry 
disclosed practically the same findings; if anything a 
trifle less spherical power. Subjectively it was found 
that the static retinoscopic findings afforded satisfact- 
ory vision. The monocular objective accommodative 
test, wearing the distance corrections, showed near 
points of 8 inches, equivalent to 5 D.; the binocular 
test disclosed a near point of 12 inches or 3.3 D. of 
accommodation as the maximum that could be used 
(not developed, however) in binocular single vision. 
The reason why these conditions existed is evident 
from the following statements: (1) a tonic exophoria 
of 4°, (2) an accommodative convergence deficiency 
of 14°, requiring 20° base in at the reading distance to 
bring the test objects in alignment and (3) a positive 
fusional convergence reserve of 8°. We may say, in 
conclusion, that we ordered two pairs of glasses for 
this young man, one for distance wear and with no 
prisms incorporated and another pair for reading in- 
cluding in the prescription therefor 2° base in O. U. CHAPTER VII. 
The Principles and Methods of Dynamic Skiametry. 
A rather brief presentation of some of the essential 
principles and methods of a system known as 'Dynamic 
Skiametry' must suffice in the closing paragraphs of 
this rubric on various dynamic tests. The reader who 
is specially interested in this system of ocular refrac- 
tion will find considerable that is of value with refer- 
ence to the same in the book entitled "Dynamic Ski- 
ametry in Theory and Practice," by A. J. Cross, and 
in the writings upon this subject by the author of this 
compendium. 
The procedure as commonly adopted in this method 
is to initially obtain by static retinoscopy those refrac- 
tive findings which put the eyes, monocularly, in an 
optical condition such that the retina and the distant 
point, presumably passively fixed, are conjugate points. 
The distance corrections are then inserted before the 
eyes under test and the patient is told to read aloud a 
series of letters indiscriminately arranged or count a 
number of fairly large dots upon a test card attached 
to the retinoscope. The test is a binocular one, for 
both eyes are involved, hence convergence and accom- 
modation are both demanded in order that binocular 
single vision may ensue. While the patient is reading 
the letters or counting the dots the examiner takes note 
of the character of the reflex or shadow in each eye, 
one after the other. Should he find a "with" motion, 
using a plane mirror or the Cross form of dynamic 
skiascope, the practitioner then proceeds, according to 
the method generally advocated, to add such convex Dynamic Skiametry. 
125 
lenses as will give a slight over-correction binocularly 
as evidenced by the "against" character of the retino- 
scopically obtained shadows. We believe that this 
statement covers, in essentials, the mechanical proced- 
ure, unless we add to these remarks the further 
statement that, should an "against" motion be obtained 
with fixation and observation at any given point, con- 
cave lenses are added until a neutral shadow is found 
in both eyes. The fixation point, when fixation and 
skiascopic observation are made at one and the same 
position, may be varied to suit the practitioner. Com- 
monly chosen points vary from ten to twenty inches 
from the eyes. This method, which we may describe 
as the simultaneous-fixation-observation procedure, 
may be modified, as has been suggested by Cross, and 
fixation may be demanded at any desired point through 
the medium of a suitable chart or test object, while 
the reversal of skiascopic shadows is sought at another 
point. For example, fixation may be made at 40 inches 
and the reversal sought and found at 26 inches. This 
procedure is analogous to that which may be used in 
myopic cases under static retinoscopic methods in 
which the points or positions of retinoscopic reversal 
may be located. For our own part we rarely use either 
of these static or dynamic 'determination of reversal 
point' methods, for the reason that measurements of 
distances are likely to be too inaccurate to be of value 
from an exact refractive standpoint. This 'measure- 
ment' method of finding the skiascopic neutralizing 
lens quantity is, however, very rapid and satisfactory 
for obtaining the order and magnitude of the error, 
in either static or dynamic procedures, particularly 
in cases where the reversal point is within a one-meter 126 
Dynamic Skiametry. 
distance. The 'fixation-at-one-point and observation- 
at-another-point' method of operation in dynamic ski- 
ametry has been criticized by many on the basis that 
it is impossible for the patient to read the letters on a 
chart and still have an observational reversal point at 
another position. This criticism is unwarranted pro- 
vided there is not instituted a change of lenses before 
the patient's eyes to bring the skiascopic reversal at 
any specified point. For 'ray values' have their equiva- 
lent lenticular counterparts. If fixation should be 
made at 20 inches, for example, and the operator 
should find a neutral point at one meter (equivalent 
to 1 D.), then, under the procedure as we shall outline 
it, we have evidence that -f-l D. lenses are required in 
order that the positive range of relative accommoda- 
tion, the negative range of relative accommodation, 
and convergence, may be properly correlated. But, 
more of this in the succeeding paragraphs! 
Cross recommends the use of his own peculiar form 
of skiascope which carries a light frame attached to the 
mirror support in such a manner that one fixation card 
is slightly behind and the other slightly in front of 
the operator's nodal point. The fundamental notion 
underlying this device is that when full correction has 
been approximated with fixation at the card more re- 
mote from the subject's eye, a quick change to the 
slightly nearer fixation object is made possible and 
that, if there is then a reversal of shadow, a correct 
refractive finding as to the needs of a pair of eyes 
at the point fixed, in order that the accommodative and 
convergence relations may be properly correlated, has 
been found. The writer differs from Cross as to his 
notions of just what this dynamic test means and, Dynamic Skiametry. 
127 
therefore, in his modus operandi, and uses the simple 
form of plane retinoscope with a small card attached 
thereto and printed in heavy-face six point type. In 
passing, let it be stated that the card which serves as 
the test object should be sufficiently illuminated; we 
carry out such tests in a room well-lighted artificially. 
In his presentation of the theory of dynamic ski- 
ametry Cross writes: "While the static method of 
practicing skiametry is one where the ciliary muscle 
of an eye is at rest, the dynamic method is the exact 
reverse of this, and is made while the accommodation 
is exerting itself sufficiently to readily accept refractive 
assistance up to a point where its relation with con- 
vergence is interfered with * * * . So in dynamic 
skiametry a call is made for a pronounced increase of 
the accommodation by having the patient read a series 
of test letters placed on the observer's brow," (the 
writer then gives other methods), "then varying this 
tension as judgment teaches, and by being able to 
easily supply required artificial lens power, the accom- 
modation is reduced to its normal relationship with 
convergence. And most eyes, no matter what the 
age of the patient may be, will only surrender the ac- 
commodative excess which has been required to main- 
tain near-vision * * *. The relationship between ac- 
commodation and convergence, if roughly stated, is 
found to be in about the proportion of one to three 
for the two eyes." The writer's interpretation of 
Cross's statements are that he (Cross) believes that 
the accommodative excess will be surrendered only to 
the extent of the establishment of a normal "one to 
three" ratio between accommodation and convergence. 
We are not entirely in accord with the theory of 128 
Dynamic Skiametry. 
Cross as quoted or as amplified in his book. We are, 
however, in agreement with the statement that tests 
can be made to determine when the accommodation is 
reduced to its normal relationship with the conditions 
of convergence as demanded at any fixation point. But 
our procedure and interpretation are somewhat differ- 
ent. In Chapter IV we have given a summary of 
methods of obtaining the relative range of accommoda- 
tion (i. e., by how many diopters it can be increased 
or decreased) when convergence is constant. When, 
therefore, fixation is made at any point a definite con- 
vergence is involved. By the Gardiner or Howe ap- 
paratus we should then proceed to find out how much 
convex lens can be added until the test type can no 
longer be read. This gives the negative range of 
relative accommodation. Is not, then, dynamic ski- 
ametry, when practiced with fixation and observation 
points identical, and convex lens power added until 
reversal occurs, simply and purely an objective method 
of determining the negative range of accommodation? 
We believe it is, and if so it is a most valuable asset 
in investigations upon ocular conditions. A citation 
from Cross (which can be repeated by anyone in al- 
most any case of hyperopia) supports this view. He 
writes: Case I. Fixation, 40 inches ; observation 39 
inches. Shadow with the mirror. Can add plus 1 D. 
before reversal occurs. But with fixation and observa- 
tion at sixteen inches, a total of plus 1.50 D. can be 
added before reversal takes place. Same result is 
obtained with fixation and observation at thirteen 
inches." These results are in accord with an affirma- 
tive answer to our question, for relative accommoda- 
tion-convergence curves show, except in exceptional Dynamic Skiametry. 
129 
cases, a decrease in the positive range (through con- 
cave lenses) and an increase (through convex lenses) 
of the relative amplitudes as the fixation and hence 
convergence are changed. The writer believes that a 
careful study of a few cases by both relative range of 
accommodation and convergence subjective methods 
and by dynamic skiametric tests as explained above 
will substantiate this explanation. 
The question may, therefore, be very properly 
raised at this juncture: Is there any objective method 
of procedure whereby one can determine the lenticular 
assistance needed in binocular single vision at any 
given reading point such that the proper relations be- 
tween positive and negative ranges of relative accom- 
modation and the convergence may be met so as to 
establish normal or balanced conditions? We again 
answer in the affirmative and say that there should be 
placed before the eyes, for any given fixation and 
observation distances, the maximum convex or mini- 
mum concave lenses which will just give a neutral 
shadow and that we should not proceed to the point 
of adding such less quantities as will produce reversal. 
The distance binocular findings may be inserted pre- 
vious to this test and they may be made the basis of 
further lenticular changes under this proposed system 
of dynamic skiametry until neutrality of shadow 
arises. To illustrate: We found in a certain case 
just previous to our writing these sentences the fol- 
lowing:-static retinoscopy, O. U. -|-1.00 D. S.; dyna- 
mic skiametry, as advocated above, at 13 inches, 4" 
2.00 D. S., and for reversal 4-3.00 D. S. The positive 
range of relative accommodation at 13 inches was 
found to be 3 diopters and the negative range 3 D. 130 
Dynamic Skiametry. 
Such data shows that the positive part of the relative 
accommodation in this case was abnormally taxed by 
the hyperopia and that by its alleviation to the extent 
of 2 D. a balanced condition between accommodation 
and convergence was established. As Donders stated, 
"The accommodation can be maintained only for a 
distance at which, in reference to the negative 
part, the positive part of the relative range of the 
accommodation is relatively large." The foregoing 
data shows that such was not the case. We believe, 
therefore, that dynamic skiametry, when properly 
practiced, will afford a quick and accurate method, in 
general, of finding that lenticular assistance needed 
at the reading point to re-establish normal relations 
between the positive range of accommodation, the 
negative range of accommodation and the convergence. 
The most animated discussions have arisen as to 
whether or not the dynamic skiametric findings can 
be worn for distant use. In other terms, the claim is 
made by some that the dynamic findings indicate the 
lenticular assistance really (or ultimately) demanded 
by a pair of eyes, and that this method operates (from 
the accommodative strain rather than the total re- 
laxation of strain method of attack) to the same pur- 
pose as does a cycloplegic-namely, the determination 
of the full refractive demands. Hence the two 
methods, although radically different in method and 
in action, look toward the same sort of an indicated 
answer. The static finding without cycloplegics or 
without fogging, and the dynamic findings at near- 
points constitute the two extreme sets of findings be- 
tween which the final prescription given is to be de- 
termined upon by reason of other dynamic ocular Dynamic Skiametry. 
131 
tests at distant and near points in particular. Other 
investigators claim that the findings as made by dyna- 
mic skiametry are those suitable for proper correla- 
tion of accommodation and convergence at the point 
fixed. They claim that the method affords a reading 
correction only. From a strictly scientific basis the 
writer believes that the latter view is, in general, the 
only one which can be substantiated. Hence, if a 
practitioner prescribes under all conditions that which 
leaves the visual acuity at or nearly normal, then no 
dynamic methods will be of any service to him. The 
static findings taken in conjunction with the dynamic 
objective and subjective tests will lead to the accumu- 
lation of that data from which the practitioner, in the 
light of his training, his experience and his scientific 
study, can formulate those lens prescriptions which 
will serve the real demands of the ocular regime and 
not simple cater to V=20/20 acuity tests. The ques- 
tion, "Would you prescribe from dynamic skiametric 
findings ?" we would emphatically answer in the nega- 
tive and say that we would prescribe from the results 
of no particular method but from the analyzed results 
of all the methods and data obtained. And, in passing, 
let it be said that a scientific study of a pair of eyes 
cannot be made in fifteen or twenty minutes. 
The dynamic skiametric test is easily made by any- 
one familiar with the practices of retinoscopy. If you 
have never tried this system, take the findings at the 
fifteen inch fixation and observation points in the 
manner we have outlined and make an intensive study 
of fifteen or twenty cases by all tests possible. This 
will be of more value to the reader than many, many 
pages of written description. 132 
Dynamic Skiametry. 
We have cited the dynamic skiametric findings in 
the rehearsal of a number of illustrative cases in the 
foregoing pages. It appears, therefore, unnecessary 
to supplement this closing chapter with many practical 
examples, but we may be pardoned the addition of a 
few characteristic cases and a few rather exceptional 
ocular conditions in which dynamic skiametry has 
been a valuable aid in the solutions to which we have 
finally arrived. 
Case ip. Simulated Myopia. Young lady, aged 23 
years. Complained of frontal headaches, eye burn, 
photophobia and the usual train of accommodative 
strain symptoms. Static retinoscopic tests showed O. 
U. -0.62 D. S. Dynamic skiametry, with observation 
and fixation at 15 inches, gave O. U. -|-0.50 D. S. for 
neutralization and + 1.50 D. S. for reversal of shadow. 
Subjective binocular tests showed that O. U. -0.25 D. 
S. gave normal acuity and that O. U. +0.50 D. S. re- 
duced it to not better than 7/10. The tonicity tests 
gave 2° esophoria and the accommodative convergence 
test evidenced 7° esophoria. These latter investiga- 
tions were made without any lenses before the patient's 
eyes. We gave O. U. +0.50 D. S. which relieved the 
symptoms and after a few weeks' time gave practi- 
cally normal acuity as well as comfort. 
Case 20. Hyperopia with High Esophoria. A 
young man, a chemist, who had suffered great ocular 
discomfort for years, presented himself and gave an 
interesting history of all kinds of ocular treatment. 
The observations on this case have covered a couple 
of years and cannot all be given here. The 
initial examination (as well as the last one for that 
ILLUSTRATIVE CASES. Dynamic Skiametry. 
133 
matter) evidenced through static retinoscopy O. U. 
4-1.00 D. S. Ci 4~0-50 cyl. ax. 90. Dynamic skiametry 
showed that -J-2.50 D. S. Ci 4~0-$0 cyl. ax. 90 gave 
neutral shadows at 13 inches. Without correction of 
any character, the tonicity tests showed 10° esophoria 
and the accommodative convergence measurement 
some 13° esophoria. Subjectively, O. U. -j-1-25 D. S. 
Ci 4-0.50 cyl. ax. 90 in the first examination did not 
give better than 8/10. We gave this young man O. U. 
4-1.37 D. S. SS 4-0-50 cyl. ax. 90 for constant wear. 
He became accustomed in a little time to the "blur- 
ring" caused by these. We prescribed for him a year 
and a half later the full dynamic skiametric findings. 
These he wears with comfort and efficiency in his 
work but with an acuity not quite equal to 8/10. The 
criterion of normal visual acuity is a poor one in many 
cases, especially in those conditions similar to the one 
we have just described. 
Case 21. Peculiar Condition of Monocular Astig- 
matic Requirements at Reading and Distant Points. In 
a particular case seen recently static retinoscopy in- 
dicated O. D. -1.25 D. S. Ci 4-4.50 cyl. ax. 100 and 
O. S. -0.75 D. S. Ci 4-3.50 cyl. ax. 80. With slight 
modification these gave normal acuity conditions under 
the minimum possible binocular concave lenses. Tonic- 
ity tests gave 4° exophoria and accommodative con- 
vergence investigations showed 8° exophoria. The 
fusion convergence reserve at thirteen inches indicated 
22°. The monocular objective accommodative method 
gave O. D. 5 D. and O. S. 6 D., while the binocular test 
indicated about the same. Dynamic skiametry gave, 
under a neutral shadow method, O. D. -0.75 D. S. Ci 
4-6.50 cyl. ax. 100 and O. S. -0.25 D. S. Ci 4-4.00 134 
Dynamic Skiametry. 
cyl. ax. 80. The marked difference between the dyna- 
mic and static values for the right eye is worthy of 
comment. Under occlusion, it was found that the 
patient could not read with her right eye No. 3 Jaeger 
type (V=0.75 D.) through the distance correction but 
that, with the dynamically determined cylindrical cor- 
rection, she could read No. 1 Jaeger as close as 10 
inches. Other corroborative tests of a nature similar 
to those outlined in this brochure were carried out and 
the patient was given the following prescriptions: For 
distance, O. D. -1.00 D. S. + +4.50 cyl. ax. 100, O. 
S. -0.62 D. S. U +3.62 cyl. ax. 80; for reading, O. 
D. -0.87 D. S. + +6.00 cyl. ax. 100 and O. S.-0.50 
D. S. + +4.00 cyl. ax. 80 The old glasses, given her 
after an examination under a mydriatic, were O. D. - 
1.00 D. S. + +4.50 cyl. ax. 100 and O. S. -0.75 D. S. 
+ +4.50 ax. 80. With the reading glasses as pre- 
scribed she has done near work in comfort by the 
hour-a procedure impossible before. 
Case 22. A Case of Divergent Strabismus Coupled 
With Autonomic Control of the Refractive Status of 
the Eyes. An article dealing with a most interesting 
case in which all monocular static methods gave a 
hyperopic correction, but in which dynamic skiametric 
methods and all dynamic tests indicated the advisa- 
bility of the use of concave lenses, was reported by the 
writer in the Ophthalmic Record, August, 1916 and 
reprinted in The Keystone Magazine and The Optical 
Journal during September, 1916. Space forbids our 
giving this case in detail; the reader is referred to these 
journals for this as well as other valuable papers along 
the line of refraction. We quote from this article the 
following paragraph: Dynamic Skiametry. 
135 
"The data thus elicited clearly evidenced the follow- 
ing facts: (1) the refractive error of each eye, axially 
considered and dissociated from its mate, was hyper- 
opic ; the eyes when in this condition or when corrected 
for this defect were decidedly negatively convergent, 
(2) when the fusion faculty was exercised and suffi- 
cient innervation supplied through the proper centers 
to give the proper or necessary positive convergence 
and thus correlate the eyes from this standpoint, the 
ciliary through the third nerve innervation also re- 
sponded and caused a lenticular change such as to pro- 
duce a myopically refractive condition. The logical 
line of reasoning seemed, therefore, to be somewhat 
as follows:-the wearing of minus lenses by this hy- 
perope would force the supply of necessary innerva- 
tion to accommodatively overcome the correction given 
and thus supply the necessary innervation to produce 
positive convergence." 
Elsewhere (The Keystone Magazine, January, 1917) 
the writer has given a summary of some of the main 
conclusions relative to dynamic skiametry and its ser- 
vice in ocular refraction. We quote these at length. 
(1) Data of value accrues to the practitioner 
through investigations by dynamic skiametry in which 
tests upon the co-ordination of convergence and ac- 
commodation to the enhancement of ocular comfort 
and economy are made possible; the fact that static 
and dynamic results are not in agreement furnishes a 
basis for the determination of the proper assistance 
to be furnished in the interests of all the ocular func- 
tions concerned and enables the practitioner to inhibit 
excessive innervation, relief weaknesses or to economi- 
CONCLUSIONS RELATIVE TO DYNAMIC SKIAMETRY. 136 
Dynamic Skiametry. 
cally draw upon functions, which are in strength, to 
the relief of those which are in weakness through 
the medium of the lenses which he prescribes. 
(2) Dynamic skiametric findings, taken at the read- 
ing point, indicate increased convex lens corrections as 
compared with the static retinoscopic findings and 
subjective acuity findings when esophoric, subnormal 
accommodative, or latent hyperopic conditions exist. 
Such findings also indicate the need of lens assistance 
in near work when convergence dissociation tests at 
thirteen inches show the existence of an over-con- 
vergence associated with accommodation in cases 
where no refractive errors or muscular imbalances 
exist at distance. 
(3) The dynamic skiametric findings in myopia 
generally indicate lesser concave lens findings at the 
reading (thirteen inch) point than at twenty feet, be- 
cause the deficiency in convergence, or exophoria, 
usually associated with myopia is supplied by the fu- 
sional convergence, since the decreased accommodative 
demands in such cases elicit a corresponding decrease 
in the convergence associated with accommodation. 
It is probable, therefore, in cases of myopia in which 
fixation and observation points are outside of the 
patient's far-point that dynamic skiametry will indi- 
cate findings in fair agreement with those which would 
statically result if the patient's far-point were to be 
left at the point at which observations are made. If 
such results accrue, it is evidence that full distance 
corrections should not be ordinarily prescribed for 
general use and especially for near work, since a too 
radical readjustment of the relations between accom- 
modative convergence, fusional convergence and the Dynamic Skiametry. 
137 
accommodation is not desirable. The history of the 
case, the symptoms of which complaint is made, the 
previous ocular corrections worn, or the absence of 
any previous refractive attention, must aid the prac- 
titioner in the judgments which he forms and pre- 
scriptions which he finally gives. In cases where the 
reserve fusional convergence is too heavily taxed, this 
deficiency in convergence may be supplied by addi- 
tional accommodative convergence through an over- 
stimulation of accommodation, thereby indicating to 
the dynamic skiametrist as great, or greater, concave 
lens corrections at near as at distance. The demand 
for definiteness of fixation is met by increased accom- 
modative convergence. Or, again, cases may arise in 
which greater degrees of myopia are indicated at the 
reading point as compared with the data furnished by 
the static findings, when conditions of functional ex- 
ophoria, as detected at the reading point, and the total 
amplitude of accommodation available at this point 
indicate that less than one diopter of innervation ac- 
complishes the act of one diopter of accommodation. 
(4) The dynamic skiametric findings, in which hy- 
peropic conditions are apparently found existent at 
near-points, while static methods evidence low-valued 
myopic conditions at distance demand careful investi- 
gation. Such findings are commonly found to exist in 
connection with spasms of accommodation and in cases 
in which there is an over-stimulation of the interni by 
virtue of the convergence associated with the innerva- 
tion delivered in the interests of accommodation, in- 
dicating esophoric conditions at the reading point. 
(5) All retinoscopic and subjective findings must 
be supplemented by tests upon the amplitude of ac- 138 
Dynamic Skiametry. 
commodation, the reserve convergence and investiga- 
tions upon the convergence associated with the accom- 
modation, while fusional convergence is passive, at 
the normal reading and near-work point. Such tests 
enable the practitioner to correctly diagnose his cases 
and analyze his findings and to know why and in the 
interests of what functions his final prescription is to 
be given. 
(6) No single test is to be given preference over 
any other tests and none is to be assumed as giving an 
accurate finding; all data is to be taken and analyzed 
and from it all a logical conclusion drawn as to what 
should be prescribed in the interests of ocular economy 
and of the conservation of vision and all the functions 
therein involved. 
In conclusion, we hope that a perusal of these pages 
may induce the reader to institute a systematic study of 
these most important ocular problems from the re- 
fractive standpoint. We hope that this compendium 
may serve to stimulate many to a reading of such 
standard works on ocular muscles as those by Howe, 
Savage, Stevens and others whose names and works 
are listed in the appended table, as well as to stimulate 
original investigations along these and similar lines. 
NOTE. The writer will be pleased to furnish test 
cards corresponding to Figures 23, 25 and 28 to any 
who desire them. 
Cross-Dynamic Skiametry in Theory and Practice. 
Sheard-Dynamic Skiametry. 
REFERENCES. BOOKS FOR REFERENCE AND STUDY. 
139 
American Encyclopedia of Ophthalmology. 
Cross-Dynamic Skiametry in Theory and Practice. 
DeZeng-The Modern Phorometer. 
Donders-The Accommodation and Refraction of the 
Eye. 
Eberhardt-Dynamics and Economics of the Binocu- 
lar Function. (Optical Journal). 
Hansell and Reber-Ocular Muscles. 
Howe-The Muscles of the Eye. Vols. I and II. 
Javal-Manuel de Strabisme. 
Landolt-The Refraction and Accommodation of the 
Eye. 
Laurance-Visual Optics. 
Maddox-The Clinical Use of Prisms. 
The Ocular Muscles. 
Prentice-Ophthalmic Lenses. 
Ophthalmic Lenses and Prisms. (Reprinted from 
Vol X. of the American Encyclopedia of Ophthal- 
mology. ) 
Savage-Ophthalmic Myology. 
Ophthalmic Neuro-Myology. 
Ocular Muscles. (Vol. X American Encyclopedia 
of Ophthalmology.) 
Sheard-Physiologic Optics (To be reprinted from 
Am. Encyl. of Oph. when issued). 
Dynamic Skiametry. (Keystone Magazine.) 
Stevens-Motor Apparatus of the Eyes. 
Thorington-Methods of Refraction. 
Retinoscopy. 
Tscherning-Physiologic Optics. 
Valk-Strabismus or Squint. 
Wiseman-Blood Pressure in Ocular Work. 
Worth-Squint. INDEX 
Abduction, Tests for 47 
Accommodative Convergence 43, 61 
Clinical Methods of Testing 64 
Accommodation, Spasm of 100 
Objectively Determined 109 
Relative, Measurement of 96 
Acuity, Tests upon 36-41 
Adduction, Tests for 47 
Amplitude of Accommodation- 
Near-point Method 86 
Concave Lenses at 20 ft 88 
Concave Lenses at 13 inches 90 
Inaccuracies in Near-point Method 86 
Table of, by Various Authors 93 
Apparent Near-point 109 
B 
Binocular Tests 49 
Accommodative Tests, Objective 115-123 
Blood Pressure in Ocular Work 10 
c 
Ciliary Relaxation 17 
Clinical Methods of Testing- 
Accommodative Convergence 64 
Binocular Accommodation ; 121 
Relative Accommodation and Convergence 98 
Relative Convergence 102 
Reserve Convergence 64 
Skiametry, Dynamic in 124-138 
Comparison Tests- 
At Distance 33 
At the Reading Point 36 
Conclusions Relative to- 
Dynamic Skiametry 135 
Ophthalmometry 32 
Conditions Affecting Accommodative Convergence 62 
Contrast, Immediate 33 
Convergence- 
Accommodative 43, 61 
Clinical Methods 64 
Fusion 43, 58, 62, 74, 80 
Fusional Dissociation 67 
Relative, Measurement of 102 
Table of 63 
Tonic 59 
Weak Positive (Case) 83 
Cross 124-128 
Dynamic Skiametric Method 125 
Skiascope 126 
Cycloduction 48 
Cyclophoria 15, 22, 70 
Tests at near for 70 
Cylinders for Distance and Reading 15, 23 
D 
DeZeng 47, 70 
Ponders 93, 95, 96, 97, 130 
Rule Relative to Accommodation 96, 99 
Dot and Line Test 65 
140 Duction Tests- 
Oblique Muscles 48 
Recti Muscles 45 
Cases Illustrative of 54-57 
Duane 93 
Dynamic Far-point 117 
Dynamic Skiametry 13, 14, 55 
81. 82, 84, 101, 111, 112, 121, 122, 123, 124-138 
Cross Method 125 
Author's Method and Interpretation 129 
E 
Eberhardt 19, 22, 26, 58 
Equality of Acuity Tests 36-41 
Essential Dynamic Tests 41-57 
Exophoria, Physiologic 38, 58 
Extrinsic Muscles, Essential Tests upon 41 
F 
Fixation, Necessity of Definite 17 
Fusion Area 42, 46, 51, 52 
Fusional Convergence 43, 58, 62, 74, 80 
Fusional Dissociation- 
Lateral Tests upon 67 
G 
Gardiner, Ophthalmodynamometer 95, 96 
Graefe, von 58, 65 
II 
History of a Case : 8 
Howe 38, 58, 95, 97, 99, 119 
Method of Testing Acc. and Con 95, 96 
Hyperphoria- 
Alternate Occlusion Test for 35 
Tests at Near for 69 
Hypophoria 35 
I 
Insertion of Binocular Findings in- 
Accommodative Tests 92 
Acuity Tests 36 
Muscle Tests : 46 
Irregular Refraction 18 
J 
Jackson 93 
L 
Landolt 44, 54, 89, 97 
On Convergence 44, 77 
Laurance 26 
Line and Arrow Test 72 
M 
Mascular Reflectoscope 19 
Refraction 19-21 
Maddox 38, 43, 51, 58, 59, 61, 63, 65, 74, 78, 120 
Tangent scale 51, 73 
Table of Convergences 63 
141 Measurement, Binocular Objective Accommodation 115-123 
Accommodative Amplitude 85-95 
Cyclophoria 22, 70 
Duction 45-48 
Fusion Convergence 43, 58, 62, 74, 80 
Monocular Obj. Acc 104-114 
Relative Accommodation 96 
Relative Convergence 102 
Monocular, Objective Accommodation 104-114 
Tonicity Tests 44, 51 
N 
Near-point Determinations 86 
O 
Objective Monocular Accommodation 104-114 
Binocular Accommodation 114-123 
Oblique Muscles, Duction Tests of 47 
Ophthalmometric Examination 11, 13 
Conclusions Relative to 32 
Illustrative Cases 12-16 
Ophthalmoscopic Examination 10, 13 
Optical Principles in- 
Objective Monocular Acc. Test 106-110 
Binocular Accommodation Test 117-118 
Orderliness, Necessity of 7 
Outline of Eye Examination Routine 8 
Periodic Squint 64 
Hyperopia with 81 
Peripheral Refraction 18 
Phorometric Tests 42-54 
Physiologic Exophoria 38, 58 
Prentice Prism Rule 61, 68 
Presbyopia 40, 113 
R 
Record Card 7 
Reflectoscope, Macular 19 
Refraction, Irregular and Peripheral 18 
Retinal Sensitiveness as- 
Affecting Retinoscopic Findings 18 
Retinoscopy, Scissors Movement in 23 
Illustrative Cases 29-31 
Recti Muscles- 
Tests upon Duction 45-47 
Tests upon Tonicity : 49-54 
Routine of Eye Examination 8 
s 
Savage 16, 41, 45, 46, 52, 70, 74, 119 
Scissor Movement in Retinoscopy 23 
Conclusions Relative to 32 
Illustrative Cases 29-31 
Shift of Cylindrical Axes 14-16 
Skiametry, Dynamic 13, 14, 55, 
81, 82, 84, 101, 111, 112, 121, 122, 123, 124-138 
Cross Method 125 
Author's Method and Interpretation 129 
Squint, Periodic - 64 
142 Static Retinoscopic Tests .. 17 
Steele Rules 16 
Stevens 38, 52, 54 
Stevenson Muscle Test 51, 58, 73 
T 
Test Object for-- 
Accommodative Convergence 66, 72 
Esophoria and Exophoria 66, 72 
Fusion Convergence / 76 
Monocular Objective Accommodation 105 
Theobald 58 
Thorington 25, 26, 28 
Tonic Convergence 59 
Tonicity Tests 44 
Tonicity Tests on Recti Muscles- 
Binocular Tests 49 
Monocular Tests 52 
Treatment of Muscular Imbalances 79 
Version Tests 54 
w 
Weak Positive Convergence. 83 
Wiseman 10 
Worth 38, 58, 65 
143