Report of the Section 
ON 
Ophthalmology, Otology and 
Laryngology. 
A SIMPLE AND VALUABLE 
OPTOMETER. 
By JULIAN J. CHISOLM. M. D., 
Professor of Eye and Ear Diseases in the University 
of Maryland. 
Reprint 
FBOM TRANSACTIONS OF 
IHedical and fthirurgical faculty, 
Of the State of Maryland. 
1887. Reprint from ' ' Transactions of the Medical and Chirurgical Faculty of 
Maryland " for 1887. 
Report of the Section on Ophthalmology, Otology, 
and Laryngology. 
A SIMPLE AND VALUABLE OPTOMETER. 
By Julian J. Chisolm, M. D., 
Professor of Eye and Ear Diseases in the University of Maryland. 
Errors of refraction, faults of accommodation, and diseases of the 
inner eye structures interfering with good vision, are among the most 
numerous of eye affections. Such eye troubles are met with every 
day, and form the majority of cases seen by specialists in office or 
dispensary practice. To facilitate the diagnosis in these many 
patients is a matter of time economy. Each specialist has adopted 
some method by which he can be the more readily guided in the 
direction of the diagnosis, and possibly in the selection of a remedy. 
In many cases some form of spectacle is to do the work of restoration 
to useful vision. 
Ophthalmic surgeons use charts as tests of the strength of eyesight, 
and have in possession a case of trial glasses, in which are found 
lenses of all strengths, convex and concave, spherical and cylindrical. 
From these they seek the special lens which will secure clear and 
easy sight to the patient. The strongest convex lens found in this 
trial case focuses at 1 inch. It is one of extreme strength, seldom 
called for, even when the crystalline lens is removed from the human 
eye, as after cataract extraction, and therefore can never be used in 
supplementing the lens existing within the eye. Still it is the unit 
of strength by which all lenses are measured, and explains why the 
numbers of spectacles are written in fractions. 
The law of optics fixes as the strongest lens the one of greatest 
convexity of surface, and necessarily the one which, by condensing 
light the more rapidly, must have the shortest focus. When we 
accept the lens of one inch focus as the strongest we need in eye-glass 2 
JULIAN J. CHISOLM, M. D. 
adjustment, all others must be weaker in strength, and therefore a 
part only, or a fraction of the stronger one. 
For good clear sight, a sharp image or picture, minute of course, 
must be formed upon the nerve layer of the eye, the retina. A mag- 
nifying lens must do this condensation of light, and it must be so 
adjusted as to focus accurately upon the sensitive layer within the 
eyeball. 
The human eye is about one inch in diameter. The yellow spot, 
the central part of the retina, especially prepared by nature for sharp 
vision, is distanced about one inch from the central portion of the 
cornea, in front of the pupillary opening. The crystalline lens is 
located near the middle of the eye, about f of an inch from the retina, 
and therefore must represent a powerful lens of a little over a I inch 
focus. There are human eyes so very short in this antero-posterior 
diameter that the light condensed by the crystalline lens is obstructed 
by the retina long before the focus of a i inch is reached. Take out 
a cataract lens from such a very flat eye and it may become neces- 
sary to use before it a lens approaching in strength that of one inch 
focus, to produce a clear picture upon the retina of a small object 
held near to it. Hence it is that the very strong convex lens of one 
inch focal power is adopted as the strongest lens required. As the 
eyeball cannot be entered to locate a glass lens near the retina, one 
of greater strength than the inch can never be wanted. 
As we recede from this standard of one inch for extreme focal 
strength, a lens which focuses twice as far, or at two inches, must be 
only half as curved, and necessarily only half as strong. Such a lens 
is called a No. 2 Convex, or as it is usually written £-|-. In like 
manner a lens which focuses sunlight at 10 inches is only as 
thick in its convexity as one which focuses at one inch. It is called 
a No. 10, or as we write it T\y4-. The same rule holds good for 
glasses which focus at any distance. The weakest in the large trial 
cases are those which if held 148 inches from a screen will show a 
feeble condensation of sunlight upon it. These are only the 
strength of the strongest, that of one inch focus. By opticians the 
denomination of the fraction is used to designate the strength of the 
spectacle, and consequently the larger the number used the feebler 
the glass. Persons old enough to require spectacles commence to use 
the largest numbers, which represent the weakest glasses, and as the 
increase of age requires stronger ones, the number of the glass 
diminishes. As the strongest convex glasses are rarely called for, we 
may say the same of the weakest. SECTION ON OPHTHALMOLOGY, OTOLOGY, AND LARYNGOLOGY. 
3 
When age creeps on and 40 years is reached, all good eyes begin to 
feel that looking at small print for a length of time is irksome. The aid 
of a weak pair of spectacles of the strength of the very strongest 
one, the No. 60 Convex of the optician, restores former comfort and 
removes altogether the tired feeling. As increasing years continue 
to take away the accommodation properties of the lens, a smaller 
number, stronger spectacle, must be used. The rg-f- gives way to 
these in turn to till in very old 
age even |-|- may be needed to supplement our own i inch crystalline 
lens, to enable the very aged to retain their reading privileges. When 
the crystalline lens becomes opaque, and as a cataract is extracted 
from the interior of the eye, then an entire condensing apparatus 
must be substituted, and the stronger convex lenses, i-|-, i-f-, or |-f-, 
are required. These selections of spectacles are all based upon the 
healthy and perfectly formed eye, and mark the changes which age 
always induces. 
Overwork of the eyes during childhood, too close and long-con- 
tinued study in early school life, keeping up a hyperemic state of the 
organ when the coats of the eye are still soft, yielding and growing, 
permits as it were of an expansion of the organ from within, which 
the recti muscles enveloping the sides, the upper and lower, the 
inner and outer sides, to a certain extent oppose. The result is an 
elongation of the eyeball in the direction of least restraint, antero- 
posteriorly, and this produces the long eye of near-sighted children. 
Once the young eye yields and loses its primitive form, continued 
work forces it to yield the more readily, and progressive myopia is 
established. This is a general weakening of the organ, which in the 
course of time leads to many serious and even destructive diseases. 
The lengthening of the eyeball, usually at the expense of the pos- 
terior wall, carries the retina away from the lens. This elongates the 
focal distance for vision, and necessitates the use of concave glasses 
of various strengths to follow up the retreating retina and secure the 
needful focusing of an image upon its percipient surface which is an 
essential for good sight. 
In the trial cases of glasses each convex lens is matched by a con- 
cave one of corresponding strength, called negative or minus glasses, 
running therefore from 1 inch negative focus to 148 inch focus. 
Sections of cylinders as well as sections of spheres are represented in 
these convex and concave glasses. From the collection of these 
numerous lenses of the trial case, every person with faulty vision from 4 
JULIAN J. CHISOLM, M. D. 
defective shape of the eyeball, whether they be over-sighted or flat- 
eyed, called hyperopic; near-sighted or long-eyed, called myopic; 
old-sighted with flattened lens, called presbyopic ; or irregularities 
in the corneal surface, called astigmatism, can have sight improved. 
In adjusting glasses which advancing age requires, in persons 
whose eyes have always been strong and of proper shape, observation 
has taught us that the natural deterioration in the elasticity of the 
crystalline lens makes itself evident at about 40 years of age, when 
the outline of fine print becomes somewhat blurred; and it steadily 
advances to the end of life. This progress of failing sight is so 
regular that a table indicating the strength of spectacles to suit 
respective ages can be prepared. 
If a good eye at 40 years of age needs a glass to sharpen the 
outline of small printed letters, at the age of 45 a glass will be 
needed. The same eye at 48 years of age requires a and at 50 
years of age a at 55 years a 60 years a ttt+> at 63 a 
l+, at 65 a |-f-, at 70 a 1-, and so on. If all eyes corresponded strictly 
to this normal standard in shape, only such glasses as designated 
would be needed, and the manner of supply would be extremely 
simple. Consult the age of the person and the card for corresponding 
strength of spectacles, and the deteriorating vision is at once made 
sharp by the spectacles selected. Unfortunately, perfectly formed 
eyes may nearly be called the exception among the civilized races. 
The more advanced in mental culture, the more irregular the shape 
of the eyeball. Eye faults, organic in their nature, are creeping 
in with education, and are transmitted with individual peculiarities 
to children. When these faults are present, whether by hereditary 
transmission, or acquired by too much study in very young eyes, they 
stay permanently. Modifications in eye shape, from the typically 
round one-some being long and others flat-break into the simple 
table for adjusting glasses and render these calculations nearly use- 
less. Every eye must be examined for itself, and its individual 
defects corrected. 
The common mode of doing this is to place the person to be exam- 
ined at a fixed distance before a card upon which graded letters are 
arranged, of a size and dimensions mathematically determined upon, 
the basis of vision being that belonging to an emmetropic or per- 
fectly formed eye. If, standing 20 feet from this card, a person can 
readily read letters designed to be seen only by a perfectly formed 
eye at the given distance, then such a person has perfect distant 5 
SECTION ON OPHTHALMOLOGY, OTOLOGY, AND LARYNGOLOGY. 
vision. Should the person examined only see from the distance of 
20 feet letters which should be read at 30, 40, 60, 80, 100, or even 
200 feet, such eyes are deemed faulty to these various degrees, and 
are classified as ametropic. To determine whether the faulty seeing 
is caused by a flattened or an elongated condition of the eyeball, a 
weak concave and a weak convex glass are taken from the trial case 
and placed alternately before the eye. The one which improves the 
vision shows the direction in which the search is to be made. By 
following up the examination with stronger lenses, the one which 
gives the most perfect vision or permits the reading of the letters 
designed to be read at 20 feet, from a 20-foot distance, is the one to 
be selected. This successive changing of lenses requires time-an 
item of value to a busy physician. 
To have some quicker guide to direct us to the glass wanted is 
most desirable. Many specialists have recourse to the ophthalmoscope, 
whiph, while revealing the error of refraction, also enables the eye 
to be explored for any diseased condition which may exist. This 
requires special knowledge. The general physician, however skillful 
he may be in the diagnosis of disease, could not make this ophthal- 
moscopic examination. Even the specialist in eye diseases often 
desires a more rapid method; hence optometers-instruments for 
the measuring of eyesight-have been devised. 
They consist of a convex lens attached to one end of a metallic rod. 
Upon this rod slides a small plate or card, upon which letters are 
printed. On the sides of the rod are marks with figures attached, 
which figures represent the strength of a glass that the person read- 
ing at such distances requires. This is the method used by jewelers 
in adjusting spectacles, and gives them all the data they possess for 
carrying on their traffic. Even this crude instrument, with care- 
lessly ground lenses, has its advantages. The more elaborate and 
expensive optometers are similar to it in construction. 
When a student at the Royal Ophthalmic Hospital in London, 
many years ago, I found in constant use in the dispensary a simple 
form of optometer. It seemed to solve promptly many eye problems. 
On my return home I took up the instrument, determined to get out 
of it all that it was capable of doing, and for many years have made 
it my daily companion in office and dispensary work. I am sure that 
I can get out of it more information in a short time than by any 
other method of research, and I am in the habit of appealing to it 
quite early for information in the examination of an eye. 6 
JULIAN J. CHISOLM, M. D. 
This optometer consists of a two-foot rule in a single piece, as if it 
were two-thirds the length of a yard-stick, split through the middle, 
to diminish its bulk, and retaining all the inch-marks. To one end of 
this graduated stick is secured a carefully ground lens of 10 inches 
focus. On the stick is a sliding ferrule, with an upright support, 
holding a printed card containing three sizes of letters, some of them 
very small. The lens of 10 inches is preferred because the decimal 
facilitates calculations. When the printed matter is placed 10 inches 
from the lens it is at the focus of the lens. As the lens is a fixture, 
any movement of the printed card to or from the lens is equivalent 
to a change in the focal strength of the lens. The range of the 
sliding card, 24 inches on the stick, permits this simple instrument 
to represent nearly the entire trial case of lenses, from the very 
strongest concave to strong convex ones. 
If a patient can be made to see to read by any glass, there must be 
a position on this stick at which some of the letters on the card can 
be made out. As we all know, the external appearance of an eye 
gives no index of its visual power. Some of the very brightest, as fax* 
as cornea and pupil can express a healthy organ, have neither retina 
nor optic nerve worthy of the name. The brightest of eyes, to all 
outward appearance, may have no visual properties whatever. In a 
very few seconds the optometer will show not only if a glass can be 
beneficial, but what lens to select. 
In using the optometer the examination is made by closing one 
eye, and requiring the patient to look through the lens placed before 
the open eye; the end of the stick with lens attached resting upon 
the cheek near the inferior orbital ridge. The printed card is placed 
near the lens, and is slowly withdrawn. Should the patient not be 
able to read the text at some point on the stick, the conclusion surely 
drawn is that no relief can come from glasses. In the minute that 
is required to draw the printed card the length of the rod you have 
presented before the eye of the patient every concave lens, from the 
strongest of two-inch focus to the weakest of 148-inch focus; also every 
convex lens, from the weakest of 148-inch focus to the strong one of 
six inches focus, a range which must supply every eye capable of 
being benefited by spectacles. Should no reading point be found, 
the case becomes one for ophthalmoscopic investigation to discover 
the diseased condition which has destroyed useful vision. 
An eye properly formed must possess good distant vision; that 
is to say, light coming from distant objects must be clearly SECTION ON OPHTHALMOLOGY, OTOLOGY, AND LARYNGOLOGY. 
7 
focused on the retina. Rays of light coming from distant objects 
are practically considered equivalent to parallel rays, or such as come 
from the sun. The focal power of a lens is the concentration of 
sunlight to a point. A 10-inch convex glass is one which will focus 
sunlight, our standard for parallel rays, at just 10 inches from the 
centre of the lens. This also means that if a brilliant point of light 
be put 10 inches from a convex lens of 10-inch focal power, the rays 
of light diverging from that source and passing through the trans- 
parent lens must be so changed in direction as to go out from the 
opposite surface of the lens as parallel rays. If now a normally 
shaped eye be put behind this lens to concentrate these parallel rays 
by its own crystalline lens, a perfect point of light would be reformed 
on the retina, similar to the source from which it started. Such an 
eye, having focused diverging rays of light made paralled by passing 
them through a lens, can focus parallel rays coming from any dis- 
tance, and therefore such an eye must have good distant vision. Any 
eye that can readily read fine print through a 10-inch convex lens at 
10 inches distant, must also possess the property of focusing perfectly 
parallel rays of light from distant objects, and consequently must 
have perfect distant vision. There is no need of taking such a 
person to the door and asking him to read a distant sign. He has 
already read the specially prepared card on the optometer, and can 
as a matter of course see any distant object that any one else can see. 
When a normally shaped eye looks at distant objects, the muscular 
apparatus within the eye, which influences the lens in reading, is not 
at work. A well established law of optics is, that rays of light from 
an approaching object necessarily become more and more divergent. 
As these diverging rays pass through a convex lens they must 
lengthen the focus of said lens, and therefore it is necessary for the 
screen receiving the focused rays to be moved back from the lens in 
the same proportion to the moving forward of the source of illumi- 
nation. The newly acquired foci are called conjugate foci, in con- 
tradistinction to the true focus of the lens for distant rays of light. 
If it be desired to focus on a fixed screen which cannot be moved 
backwards, then the lens must be made stronger for every advance of 
the illuminated object; Our retina, the normal sensitive screen 
placed in the back of the eye chamber, is fixed, and nature has so 
intended it that it cannot be moved, as a healthy condition. If near 
and far objects are to be equally seen by the human eye, there must 
be some apparatus within the eyeball which will adapt the focus for 
these varying distances. 8 
JULIAN J. CHISOLM, M. D. 
The living crystalline lens is a marvel of creative ingenuity. It is 
a clear, very elastic mass, of great condensing power, capable of 
changing its shape through muscular agency. These inner eye 
muscles comprise the accommodating apparatus. To understand the 
working of the young, vigorous crystalline lens, we may liken it to an 
elastic ball across the front of which a resisting band is firmly drawn, 
flattening it. If the pressure of this band be relaxed, the inherent 
elasticity renders more convex the surface of the ball. There is just 
such a compressing band, the Zonula of Zinn, tightly drawn across 
the anterior face of our living crystalline lens, with muscles arranged 
in such a way that when they contract the pressure of the band is 
lifted. The surface of the elastic crystalline lens then becomes more 
convex, and with necessarily an increase of focal power. When an 
object approaches a good eye from a distance, these muscles com- 
mence to act; increasing in activity with each step of progress, till 
with a very near object the whole energy of the muscles is required 
to release the lens from all pressure and bring out its whole elastic 
and consequently full focal power. This is called the range of 
accommodation. Soon after the lens matures it commences to lose 
some of this elastic property. When one attains 60 years of age the 
elastic properties of the lens are nearly gone, so that in the aged the 
muscles afford no longer help in seeing. Even should the band be 
lifted the lens now remains flat. Convex spectacles are required to 
make this old eye do its former work. This is no fault of the nervous 
machinery. The retina, ever ready, only needs a properly focused 
image. Spectacles, if properly selected for advancing age, enable our 
weakening lens to secure this essential focusing for good vision. 
Human eyes, although they should be of fixed dimensions, vary 
much in depth. Often the retina is approached too near to the crys- 
talline lens, as in flat or hyperopic eyes, necessitating stronger lens 
work for the shorter focus. In another class of eyes, the near-sighted 
or myopic, the retina is too far off, making the lens too strong for 
distant vision. The focus of parallel rays from distant objects is made 
before the retina is reached. To make such eyes see well distant 
objects, some of the strength of the lens must be taken away so as to 
lengthen the focus. Concave glasses will do this work, and hence 
they are worn by near-sighted persons. 
The change which a good eye requires in its lens to enable it to 
see near small objects as well as it does distant ones, is equal to a lens 
of 10-inch focal power added to the passive crystalline lens. If a SECTION ON OPHTHALMOLOGY, OTOLOGY, AND LARYNGOLOGY. 
9 
solution of atropia be put in such a well formed eye, it temporarily 
paralyses the accommodation for all near seeing, but does not interfere 
with the clear seeing of distant objects. If a 10-inch convex lens be 
placed before such an atropenized eye, the ability to see fine print is 
at once regained. With the optometer a good eye reads the fine print 
on the trial card 10 inches from the lens, and as the slide is moved 
inwards continues to read with equal clearness till it reaches 5 inches. 
The halving of the distance on this graduated rod from 10 inches to 
5 is equivalent to the doubling of the strength of the 10-inch lens. 
It represents a lens of 10 inches focal strength added to our crystalline 
lens, and marks our useful and needful accommodation. It is an 
indication of the proper functioning of the accommodating muscles. 
With this optometer therefore, any eye which can clearly read the 
test card at 10 inches must have perfect distant vision. If the eye 
continues clearly to read the test as it is advanced till it reaches 
5 inches, the index of perfect near vision, it clearly shows that the 
eye is capable of seeing at all distances, near and far, without help, 
and needs therefore no glasses. 
Often young eyes can still see clearly the card letters as it is 
advanced within the 5 inches to 4 and even to 3 inches. This indi- 
cates a superabundance of accommodation, an amount of elasticity to 
spare, which all young lenses possess, and which age up to 40 will 
gradually use up. The 5-inch point on the optometer is equivalent 
to holding a finely printed book at 12 inches from the eyes in read- 
ing. Young eyes may see the page with equal clearness at 10, 8, or 
even 6 inches, but this is uncalled for, and if kept up for a long time 
would annoy. It is the equivalent of reading through the 10-inch 
optometer at 4 and 3 inches. 
To be sure, we have Test Types that mean the same thing and will 
give the same results as the optometer does-types prepared to be 
read by good eyes at various distances, from one foot to two hundred. 
These are necessarily of graduated sizes made to correspond with 
an angle of 5 minutes, which means that two diverging lines starting 
from a point in the centre of the crystalline lens and moving 
backward to the retina, measuring at the angle of divergence 5 minutes 
or of one degree, will by the time they touch the retina form an 
image of light sufficiently large to impress the retinal elements and 
establish perception, or the recognition of an object. Continue these 
lines from the point of contact in the lens outward through the pupil 
and cornea, divergingas they go into space, any letter sufficiently large 10 
JULIAN J. CHISOLM, M. D. 
to touch these diverging lines at any point of their course can be 
clearly seen. 
Test types are prepared in accordance with this mathematical 
formula. Each letter makes a picture upon the retina equivalent to a 
space covered by this 5-minute shadow', and each arm of the letter 
must cover -1 of the whole space. The letters of the Baltimore Sun, 
our daily newspaper, notoriously of very fine type, w'ould touch 
these lines at about one foot from the eye, and may be used as a 
coarse test for near seeing. In the back of most works on eye diseases 
are test type plates for these investigations. The larger type, such 
as would measure the distance between these diverging lines at 10, 
15, 20, 30, 40, 60, 80, 100 and 200 feet, are printed upon a heavy 
card and are suspended from the office wall. Should a person sitting 
on the opposite side of the room, say 15 feet off, read promptly and 
correctly the letters or numbers designed to be seen by a good eye at 
15 feet, we can also say that such an one has good distant vision, 
because if we extend these mathematically adjusted diverging lines 
far enough, at 500 feet they will take in a large sign, at i of a mile a 
man, and at 2 miles a church steeple. With the wall letters on the 
one hand, aided by the finely printed matter in book form, the trial 
for accommodation is soon tested. 
Up to this point the optometer has shown no superiority over the 
graded test types. Should the individuals see clearly the near fine 
print and not the distant wall letters, the presumption is that they 
are near-sighted, and we must go to the trial case of glasses to find 
out, by testing one after another, what concave glass will be needed to 
make distant vision good. Should on the contrary the ■wall print be 
readily read and the fine near print not, the persons, if old enough, 
that is over forty, may be deemed presbyopic, if under that age 
hyperopic, and we experiment with convex glasses to find out what 
magnifier they will require to read with comfort. It is in these 
adjustments that the optometer shows its very marked superiority over 
the arbitrary method of selecting an unknown lens from the many 
dozens of the trial case until the proper one is secured. With the 
optometer the selection of the glass is promptly secured; and here is 
the working of it. 
We have already seen that- any eye which can read the printed 
matter on the optometer test card at from 10 inches to 5 inches 
possesses all that good vision requires. If at the same time it can 
read at four and three inches, this we call a superabundance of 11 
accommodation. Should an eye reading clearly fine print up to the 
10-inch mark, indicating good distant sight, not read clearly also at 
the 5 inch, but possibly at the 6 or 7 or 8 or 9 inch only, then such an 
eye is old or flat, presbyopic or hyperopic, and does not possess the 
reading power for books or near fine work. To restore this power it 
will be necessary to bring back the vision to the 5-inch point of the 
optometer, the ]ooint of good near sight, and the fraction which 
marks the difference between the | or 5-inch point for near reading 
and the | of | at which the eye actually reads, will indicate 
the glass needed. If reading is only clear at the point, the 
difference between | and | is T-|- glass, | - - to -11 
at the |-inoh point, the difference between 4-inch point and 
point is | l - - reduced to y1 or T7-|-, throwing out 
the parts of a fraction. If between the £-inch point and the J- point, 
i -| = reduced to or and so 011 • These 
calculations can be made as quickly as the eye records its visual 
powers. By this method it is seen that glasses needed by good eyes 
in advancing years can be determined in a very few seconds. So 
much for presbyopia of every grade. 
Now let us take the flat eye, or hyperopic, a very numerous class of 
congenital defects, and also an acquisition in very advanced age, 
over 60. We have seen that a well shaped eye with a good lens 
focuses parallel rays of light from a distance without the aid of the 
eye muscles, and that the 10-inch point of the optometer is its 
equivalent. A flat eye with retina too near the lens, requiring a great 
shortening of its focus, is not able to do this without muscular aid. 
Such an eye is using up its accommodative powers for distant vision, 
as expressed when it is reading fine print through the 10-inch opto- 
meter lens at 10 inches. Give the muscles a chance to relax, by draw- 
ing away the reading matter from the 10-inch point to 11, 12, 13,14, 
16 or 18 inches. If reading is still clear, it is an evidence of the 
amount of muscular power required to read at 10 inches. When an 
eye has only a certain amount of accommodation and uses one-half 
of it for distant vision, it has but little left for near and continued 
work. The difference between the distance at which the individual 
can see on the rod and the distant point, 10 inches, for good distant 
vision, will indicate the glass needful to permit distant seeing without 
calling upon the eye muscles for aid. If an eye that should not be 
able to read beyond 10 inches can see clearly the fine letters as far 
out as 15 inches, the difference between the y and y (yff-yy - 
SECTION ON OPHTHALMOLOGY, OTOLOGY, AND LARYNGOLOGY. 12 
JULIAN J. CHISOLM, M. D. 
Tyy- -vo-Tihr, reduced t° -/q-4-) is the glass needed for constant 
nse to rest the eye when viewing distant objects, or to aid the eye 
when used for reading, sewing, or writing. 
When such an eye gets older it may lose the power of reading at 
5 inches, representing a loss of near vision, but it may still read 
from I inch to TV inch of the optometer. Distant seeing will then 
require a magnifying glass the difference between y and TV=:T|T, 
or which glass will be too weak to read with, because he can 
only make out fine print through the 10 inch optometer at 8 inches 
when he should do so at 5. The difference between | and i is y% or 
magnifying glass, the one needful for reading, nearly three times 
as strong as the one used for walking. 
We often see old persons who have not only lost all power of 
accommodating for near work, but the crystalline lens has become so 
hard, dried and flat that it can no longer focus at even 10 inches. 
Its very best work is to see fine print at 13, 15, or 17 inches of the 
optometer, with no range at all. Under such conditions the old eye 
cannot read any print, and has lost also the ability to see distant 
objects clearly. Such persons live in a smoke or fog all the time 
unless they use glasses for all purposes. If such an eye can be made 
to see at any point of the optometer, say 15 inches, not clearly further 
off or nearer to, the glasses needful to restore to it most of its former 
privileges are soon determined. For distant glasses y what the eye 
ought to do to see clearly distant objects, what the eye does =T|y 
or t;1o4~ removes all the mist from distant objects. A what the eye 
ought to do to read, y- the only point a£ which it can now read, 
1- yh- gives 44 or vx4~ f°r reading fine print, so that spectacles to 
suit such a case would be f°r aY use> magnifying 
glasses for reading, sewing, or writing, or what is still better, have 
them set in a frame as i glasses for constant wear-Franklin glasses, 
as they are called. 
Now for the near-sighted or myopic eye, an error of refraction con- 
stantly met with. The 10 inch point of this optometer must ever be 
our reference for good distant vision. An eye reads at 5 inches, the 
index of good near vision, but cannot read clearly beyond 6 or 7 or 8 or 9 
inches. This condition marks near-sightedness. The difference 
between the 10 inches at which the patient ought to read, and 6 
inches, the most distant point at which he can read, |-A:=H 
- - K4ff, reduced to , clearly indicates the concave glass which 
will give good distant vision. In the very near-sighted even the five SECTION ON OPHTHALMOLOGY, OTOLOGY, AND LARYNGOLOGY. 
13 
inch point cannot be reached on the optometer. With some the 4 inch, 
3 inch, or even 2 inches from the 10 inch lens is the very best that the 
patient can do for distant vision. Such persons can only see printed 
matter when held very close to the face: in sewing, an uncomfortable 
and even dangerous proximity. They will need weak concave glasses for 
seeing near things, and much stronger ones for walking or seeing dis- 
tant objects. If we will keep in mind that it is best to bring all near 
sight up to the 5 inch point of this optometer, and all far sight up to 
the 10 inch point, the glasses needed for both purposes are quickly 
determined. The patient ought to read at 5 inches to be able to read 
at a comfortable distance without glasses, the patient can only read 
at 3 inches,^-- -vx? or 7-> the concave glass 
for all near work; | - A== w- iV -reduced to or |-, 
the near-sighted lens which will give the best distant vision. 
As one becomes more familiar with the ranges of accommodation 
as exhibited by the optometer, slight changes or greater deviations 
from standard measurements will be significant in expressing not only 
the various degrees of refractive errors, but also the irregularities of 
visual construction, so that astigmatism, whether hyperopic, myopic, 
or mixed, can also be foreshadowed, not however to the degree of 
selecting glasses for their correction. It will thus be seen that 
when one understands the use of a 10 inch optometer it becomes 
a simple instrument of great value, by which can be promptly 
determined whether a given case of defective vision can be bene- 
fited by glasses or not; also, if glasses can help to restore sight, 
what strength of spectacle is the necessary one for near-sighted, 
old-sighted, or over-sighted persons. To a general practitioner, who 
is so circumstanced that he will be consulted by eye patients, and 
who is not disposed to invest in an expensive trial case, this opto- 
meter, prepared at a very small cost, will enable him to administer 
much comfort to such of his patients as are not able to consult a 
specialist in eye diseases. It will also enable him to prove to a number 
of his patients that his knowledge of certain eye faults is correct, 
even when compared to the diagnosis and prognosis of the ophthalmic 
surgeon who is afterwards consulted.