[WITH THE WRITER’S COMPLIMENTS 
I. 
A REPORT ON THE PERCENTAGE OF NEAR-SIGHT 
FOUND TO EXIST IN THE CLASS OF 1880 AT HARVARD COLLEGE, WITH SOME 
ACCOUNT OF SIMILAR INVESTIGATIONS. 
ii. 
AN ACCOUNT OF THE PHAKOMETER OF SNELLEN. 
By HASKET DERBY, M. D. 
[Reprinted from The Boston Medical and Surgical Journal, March 22 and 29, 1877.] 
CAMBRIDGE : 
$rinte& at tfjc ilitosidc 
1877. A REPORT ON THE PERCENTAGE OF NEAR-SIGHT FOUND 
TO EXIST IN THE CLASS OF 1880 AT HARVARD COL- 
LEGE, WITH SOME ACCOUNT OF SIMILAR INVESTIGA- 
TIONS. 
Charles W. Eliot, LL. D., President of Harvard College: 
Sir, — I present herewith the results of an examination of the eyes 
of the present freshman class, made in the month of January, 1877, 
and undertaken with the view of determining the percentage of near- 
sightedness in the class on entering college as compared with the per- 
centage of near-sight that would be found to exist at the termination 
of the under-graduate course. 
Near-sight, or myopia, is by no means the innocent affection that 
ordinary text-books on physiology have so long represented it. Perhaps 
no idea concerning the organ of vision is more firmly grounded in the 
popular mind than that a near-sighted eye is a strong eye, the difficulty 
depending on an undue convexity of the crystalline lens or of the 
cornea, and likely to be corrected in after-life by the flattening of one 
or the other. This is wholly false. Near-sightedness depends on a 
change in shape, an elongation of the eyeball; its progress, on an 
increase of that elongation; its dangers, on that elongation being 
pressed beyond the power of endurance of the tissues of which the 
organ of sight is composed. 
Near-sight is either stationary or progressive. The former variety 
is, unfortunately, comparatively rare. Having remained at the same 
point up to about the fortieth year, it may afterwards even slightly 
decrease, as the crystalline lens flattens and the pupil contracts, thus 
neutralizing to some extent the unnatural length of the globe. 
This state of things is, however, the exception ; progression is the 
rule. The words in which this is described by Bonders have, for 
years, been classical: “When the increase in length of the eye has 
reached a certain point, its layers become so thin and their power of 
resistance so much diminished that the stretching process can no longer 
remain stationary, especially as the pressure in the interior of the my- 
opic eye is generally somewhat heightened. The progressive stretch- 
ing and the progressive myopia go hand in hand, and here we have a 
true disease of the eye. I unhesitatingly proclaim a myopic eye to be a 
diseased eye. High degrees of myopia are much less likely to remain 
stationary than slight degrees; even in advanced age they are liable to 
increase. Nearly all myopia is progressive in the young, its increase 2 
The Percentage of Near-Sight. 
being often coupled with symptoms of irritation. This time of life 
is the critical one, for the myopic eye; if, during its continuance, 
the myopia does not appreciably increase, it may become stationary. 
If, however, it considerably advances, it will ultimately become more 
difficult to limit its progress. This is therefore the time when special 
efforts must be made to guard against injurious influences. On this 
point I can hardly lay sufficient stress. Apprehension must be enter- 
tained with regard to the future of every case of progressive myopia. 
For, if it constantly progresses, distressing symptoms soon arise, inter- 
fering with the usefulness of the eve. And, not infrequently, at the 
age of fifty or sixty, in some cases even earlier, vision may be irretriev- 
ably destroyed. Such an issue may be due to retinal separation, to 
hcemorrhage, or finally to atrophy (suspension of nutrition) and degen- 
eration of the macula (the most sensitive portion of the retina).” 
Modern science has fortunately provided the surgeon with a means 
of accurately measuring and expressing the amount of myopia present 
in any eye, and has also given him a formula for indicating the amount 
of vision inherent in that eve when furnished with the glass neutral- 
izing its near-sight. Thus the myopia and the vision being measured 
and stated in simple figures, a subsequent examination would easily 
ascertain whether the myopia has progressed or the vision degenerated, 
and express it in the same simple manner. The difference between 
the first and second sets of figures would show the extent of the in- 
crease, the amount of the degeneration. 
Such examinations have, for some years, been made on the conti- 
nent of Europe, and recently in this country. A brief reference to 
their results will clearly demonstrate their utility. 
The point they illustrate is the progress of myopia, due to the mod- 
ern system of education. 
The end in view is the elimination, as far as possible, of the special 
exciting cause or causes, when they are once ascertained. 
About the year 1867, Dr. Cohn, of Breslau, examined the eyes of 
10,060 school children and pupils. His results may be summarized as 
follows : — 
In no village school was myopia found among children who had not 
yet completed their first half year of work. In these schools, taken as 
a whole, there was found 1.4 per cent, of myopia. 
Taking all schools together, and following the scholars, at successive 
intervals, from the first half year to the fourteenth year of school life, 
the percentage of myopia was found to be the following: — 
1st Half 
Year. 
2d Half Year 
to 2d Year. 
3d and 4th 
Years. 
5th and 6th 
Years. 
7th and 8'h_ 
Years. 
9th and 10th 
Years. 
11th and 12th 
Years. 
13th and 14th 
Years. 
0.4 
4.8 
8.6 
7.9 
11.3 
24.1 
49.5 
63.6 The Percentage of Near-Sight. 
In 1871, Dr. Erismann published the results of his investigations of 
the condition of the eyes of 4358 scholars at various educational estab- 
lishments in St. Petersburg. The pupils were aged from eight to 
twenty. Taking the classes in order, the fifth being the most advanced, 
the following results were obtained : — 
Class. 
Percentage of Myopia. 
Class. 
Percentage of Myopia. 
Preparatory 
13.6 
Ill 
30.7 
I 
15.8 
IY 
38.4 
II 
22.4 
Y 
41.3 
In 1874 and 1875, Dr. Conrad examined the eyes of 3036 school 
children in Konmsbero:. 
He found the percentage of myopia to rise as follows : — 
Class. 
Percentage of. Myopia. 
Class. 
Percentage of Myopia 
VIII. (youngest) 
11.1 
IV 
28.44 
VII 
15.8 
Ill 
44.39 
VI 
20.5 
II 
54.59 
V 
21.8 
I 
62.10 
In 1872, 1878, and 1875, Dr. Reuss examined 1050 pupils at the 
gymnasia of Vienna. 
His results are here shown : — 
■ Class. 
Percentage of Myopia. 
Class. 
Percentage of Myopia. 
I 
33.4 
V 
43.5 
II 
39.4 
VI 
47.7 
Ill 
47 
VII 
61.4 
IV 
48.2 
VIII 
59.6 
After one year Dr. Reuss found forty-one per cent, of the myopic 
eyes unchanged, while the difficulty had increased in 47.T per cent. 
In the third year 28.4 per cent, only remained unchanged, while sixty- 
one per cent, had grown more near-sighted. 
In 1876, Dr. Pfliiger published the result of his investigations in the 
schools of Lucerne, 1846 pupils being examined. 
Myopia was found to be present in the following percentage, accord- 
ing to age : — 
Year of Life. 
Percentage of Myopia. 
Year of Life. 
Percentage of Myopia. 
7 
0 
15 
26 
8 
2 
16 
30 
9 
3 
17 
43 
10 
6 
18 
55 
11 
6.5 
19 
56 
12 
6 
20 
40 
13 
10 
21 
61.5 
14 
14.5 
* 4 
The Percentage of Near-Sight. 
In our own country, Dr. Agnew, of New York, has instituted ex- 
aminations of the eyes of 1479 school children and advanced pupils in 
Cincinnati, New York, and Brooklyn. His results were published dur- 
ing the present year. They are as follows : — 
Cincinnati. 
School. Percentage of Myopia. 
District • 10 
Intermediate 14 
High 16 
New York College. 
Class. Percentage of Myopia. 
Introductory 29 
Freshman 40 
Sophomore 35 
Junior 53 
Senior 37 
Brooklyn Polytechnic. 
Department. , Percentage of Myopia. 
Academic 10 
Collegiate 28 
From the foregoing figures the influence of study on the develop- 
ment and advance of near-sight may readily be appreciated. The facts 
speak for themselves. 
It has occurred to me that by following the same class through its 
school or collegiate course, and noting the different phases that myopia 
assumes in the same individual at different periods of his career, results 
of much practical importance might be attained. A study of the cases 
where myopia most progressed might add to our knowledge of its 
cause, and increase our means of prevention. 
I commenced in the fall of 1875 with Amherst College, and contin- 
ued the investigation last autumn. The classes of 1879 and 1880 were 
required to report to me for examination, and were furnished time for 
that purpose. Twenty-eight per cent, of the former class were, in the 
fall of 1875, found to be myopic. One year later fifty per cent, of 
these had grown more near-sighted. Twenty-seven per cent, of the 
latter class were found, early in their freshman year, to be myopic. 
The kindness of the faculty of Harvard College enabled me to exam- 
ine volunteers from the class of 1880, in January of the present year. 
One hundred and twenty-two presented themselves for that purpose. 
Of these, 29.5 per cent, were found to be myopic. 
The accompanying printed forms are filled in with the name and 
age of each individual, the state of each of his eyes as separately tested 
by glasses and the ophthalmoscope, the amount of his vision, and re- 
marks on his previous history and family peculiarities in this regard. 
Blanks are left for a similar examination at the close of the senior 
year. Only a little over half of the class presented themselves. The 
percentage of near-sight corresponds to a remarkable degree with that 
obtained by Dr. Agnew in New York and Brooklyn, and by myself at The Percentage of Near-Sight ' 
5 
Amherst. It is worthy of remark that twenty-two per cent, of the near- 
sighted members of the Harvard class of 1880 had, up to the time of 
the examination, supposed their vision to be normal. 
The advantages of such examinations to the college student are mani- 
fest. He is enabled at no further outlay to himself than a trifling ex- 
penditure of time and trouble to obtain, at the outset of his collegiate 
career, important information in regard to the state of his eyes, their 
availability for study, and the course he must pursue to maintain their 
integrity or keep existing evils from increasing. At the termination of 
his under-graduate course he learns the effect of his four years of study, 
and is thereby enabled to form pr modify his future plans; and in after 
life he can at any time, by consulting the college records, learn to what 
extent his eyes have varied from the condition they were in, and to 
what extent his vision has altered from the amount he possessed when 
he was an under-graduate. 
But such examinations, to be reliable and truly valuable, require the 
attendance of the whole class. And I would respectfully submit to 
the consideration of the proper authorities whether, in view of the 
reasons now alleged for making and following up such investigations, 
it may not be found expedient to insist on every member of the fresh- 
man class passing this trifling ordeal on the occasion of his admission 
to college, and on his submitting to it once more just previous to the 
termination of his senior year. 
I would here express mv deep obligation to Professor Wolcott Gibbs, 
who took pains to arrange his lecture room and laboratory for my ex- 
aminations, and placed them for several days at my disposal at consid- 
erable inconvenience to himself. Also to Dr. Wm. S. Dennett, of 
Boston, who materially lightened my labors by undertaking the ophthal- 
moscopic examination of every case, and furnished me with two hun- 
dred and forty-four (244) separate estimates of refraction. 
In conclusion I would direct the attention of the faculty to the fol- 
lowing points : First. Myopia is probably not, as commonly supposed, 
congenital. It is admitted that a tendency to the disease may be and 
is frequently inherited. Second, it has been shown by the very nu- 
merous examinations above cited that it occurs among school children 
at first in a very small proportion of the whole number, and that it 
increases with the course of study till, in many cases, not less than 
sixty per cent, of the graduates of European colleges and high schools 
are found to be myopic. 
It is only by a most careful and thorough study of the disease, as 
prevalent in schools and colleges, that we can hope to devise means of 
preventing its extension and its progress in individuals. 
[Note. As an appendix to the foregoing, I will briefly report a calse 
that illustrates two points I have alluded to: first, the development of The Percentage of Near-Sight. 
6 
myopia in a person born emmetropic, bnt inheriting strong tendencies 
in the direction of near-sight; second, the rapid and alarming progress 
of unchecked myopia. 
March 11, 1868. Saw this'day for the first time Master M., aged ten. 
His father is quite near-sighted, and has for many years used concave 
glasses, what number I am unable to ascertain. His mother has in the 
right eye a myopia of 5.75 dioptrics, left M. 4.5. The lad himself has 
right emmetropia, left M. 0.75. Interni strong; each fundus normal. 
He comes for slight asthenopic symptoms, and the refraction is merely 
noted incidentally. Vision of each eye normal. 
November 1, 1870, M. 0.75 in each eye. 
June 20, 1878, right M. 2.25, left M. 2.75. Patient is on his way to 
Europe. A course of atropine treatment is advised on his return in 
the fall. 
I now lost sight of him for more than two years, during which time 
he was preparing himself for the examination to enter college. No- 
vember 26, 1875, I found M. 4.50 in each eye, also in each a progress- 
ive posterior staphyloma. Atropine treatment and entire rest were 
again earnestly advised, but not concurred in by the parents. 
The course of study has, notwithstanding all this, been steadily per- 
severed in. At his last visit, March 1, 1877, Mr. M. had M. 5.50 in 
each eve by sight-test and ophthalmoscope, and each staphyloma was 
becoming marked. No suggestions with regard to rest or treatment 
were heeded. 
Here is a progressive change, ranging in nine years from emmetro- 
pia in one eye and M. 0.75 in the other to M. 5.50 in each (M. to 
M. \ of the former series). I suppose it would have been perfectly 
possible to have arrested the myopia at any time during this period; in 
the outset, indeed, to have prevented it altogether. If the present use 
of the eyes be persisted in, the preparation for college completed, and 
college itself passed through, the chances are that the myopia will go 
on increasing, and possibly an amount of structural change be brought 
about incompatible with the integrity of the eye through life.] 
Boston, February 28, 1877. THE PHAKOMETER, FOR THE DETERMINATION OF THE 
FOCUS AND CENTRE OF SPECTACLE LENSES.1 
In this little pamphlet Dr. Snellen, of Utrecht, gives us a description of a 
new and ingenious instrument he has contrived for the above purpose. The 
accompanying wood-cut is copied from the one given by him. 
The new numeration of spectacle lenses consequent on the introduction of 
the metric system is rapidly winning its way into favor in this country, and 
daily gaining adherents. The ophthalmic surgeon, adapting and working with 
metric glasses, abundantly realizes the truth of the claim made by Donders at 
Heidelberg in 1875, that this system would be found the most convenient, the 
quickest of application, and the most exact. A few months’ experience with 
it brings a vivid sense of the difficulties and complexities of the old inch scale. 
At first the glasses of the former trial-case had to be used, their metric 
values being ascertained by means of the table published by Snellen and 
appended to his “ Optotypi,” or test types. Subsequently, Roulot, Nachet, 
and Cretes, of Paris, began to furnish trial-cases of glasses, ground according 
to the new scale. Such glasses, in the possession of the surgeon, would serve 
as standards with which to compare the ordinary lenses of commerce. 
For an accurate determination, however, we must have an accurate stand- 
ard. This is particularly necessary at the present time, when the tools by 
which glasses are fashioned are undergoing a change of shape to correspond 
with the new required numbers. The old standards have to be discarded and 
new ones provided. , 
The strength of a convex standard lens can be found directly by allowing 
parallel rays, falling upon it along the line of its principal axis, to form an 
image on a screen placed behind it, the distance between the lens and the 
image being its focal length. In practice this method can be successfully em- 
ployed only with the stronger lenses, the weaker forming a diffuse and faint 
image at a more or less considerable distance, rendering accuracy of measure- 
ment very difficult. 
Donders has described a method of measuring the strength of a lens by 
means of the ophthalmometer. There are certain difficulties in the way of 
applying this method, not the least of which is the fact that an ophthalmome- 
ter is possessed by comparatively few. 
Dr. Snellen has recently invented an instrument by means of which the 
metric strength of any convex lens, spherical or cylindrical, can be immedi- 
ately and accurately read off, and at the same time its centre determined. It 
is called a “ phakometer,” and is based on the principle that when an object 
and its image formed by a convex lens are of equal size, object and image are 
equidistant from the lens, and such distance is twice the focal length of the lens. 
In describing the instrument I will, as far as possible, follow Dr. Snellen’s 
own words. A reference to the wood-cut will render the explanation easy to 
follow. The luminous object (B) and the screen (D) on which the object is 
formed are moved by the same mechanism, being simultaneously moved 
1 De Phakometer, ter bepaling van focus en centrum van brilglazen. Door Dr. Herman 
Snellen. The Phakometer. 
towards or made to recede from the lens, placed midway between them, at an 
equal rate. Each is affixed to the extremity of a thin, very flexible, steel 
ribbon, running along the track on which object and screen move, and de- 
scending side by side into the upright on which the track or flooring of the 
instrument is supported. Passing down this upright support they are secured 
each to the same movable button (E). Pushing the button upwards causes 
the distal extremities of the steel band to pass in opposite directions along the 
track; pulling it down brings them again nearly together in its centre, followed 
of course by the object and the screen. 
The luminous object consists of a black metal screen pierced with several 
fine openings arranged in the form of a cross, and covered with ground glass. 
It is illumined by parallel rays proceeding from a lamp placed in the focus of 
a lens (A), and on a projecting shelf attached to the phakometer. The 
screen on which the image is formed consists of ground glass, and has on it 
black dots, corresponding accurately to the little openings on the screen but 
of course in reversed position. 
The lens to be examined is held in a clip (C) consisting of two metallic 
rings placed in the centre of the apparatus, midway between the luminous 
object and the screen. One of these rings has an upright spur projecting 
from it, designed to point out the true centre of the lens under examination. 
An auxiliary lens of 2.75 dioptrics is placed on either side of the clip (repre- 
sented by 1 and 2 on the diagram). The distance between these lenses is 
fifty millimeters. 
The whole length of the apparatus is eighty-six centimeters, its height fifty- 
three centimeters. The luminous object and the screen can be separated 
777.94 millimeters from each other. At this distance a sharp image of the 
luminous points is formed on the screen, and here the zero point of the scale 
begins. This scale is engraved on a strip of metal, running parallel to the 
track along which the screen moves. Its divisions correspond with the metric 
lenses from 0.25 up to twenty. A small pointer projects from the screen for 
the purpose of denoting the division of the scale opposite which it stops. 
The lens the value of which is to be ascertained is placed in the central 
clip, and object and screen are moved from or brought toward each other 
until a sharp image of the luminous points is formed on the screen. The 
division of the scale opposite the point of arrest of the screen shows the value 
of the lens in dioptrics. If the luminous points do not exactly coincide with 
the dots on the screen, already described, the lens is improperly centred, and 
must be moved until correspondence is secured. The true centre of the lens 
is then indicated by the pointer attached to the clip. 
The values of cylindrical lenses can easily be found in like manner, lines 
instead of points being formed on the screen. Approximate determinations 
of concave spherical and cylindrical lenses can also be made by combining 
them with stronger convex glasses. Lenses with one face spherical and one 
cylindrical can be analyzed easily and with considerable correctness. Abso- 
lute accuracy can however only be predicated of symmetrical biconvex lenses 
for which the scale is meant. For these the instrument will be found correct 
within 0.05 of a dioptric, a lens having a focal length of twenty meters. The Phakometer. 
The advantages of the phakometer may be briefly summarized: First and 
foremost it establishes the accuracy or want of accuracy of our new test lenses. 
Further, it enables us to convert our former inch glasses into dioptrics, tells 
us what dioptric a patient is wearing, and informs us whether the optician 
has furnished the glass designated in our prescription ; all this more rapidly, 
easily, and correctly than by the old method of comparison. Finally, we dis- 
cover whether glasses are properly centred. 
In connection with this account of the instrument I have been urged to 
publish the results of my examination of Nachet’s trial-case of metric glasses, 
and to give the errors I found. These measurements were made with the 
utmost care, and repeated several times. 
SPHERICAL. 
No. of 
Dioptric. 
Error 
No. of 
Dioptric. 
Error. 
0.25 
0 
5.50 
0 
0.50 
0 
6 
0 
0.75 
0 
7 
0 
1 
0 
8 
0 
1.25 
0 
9 
0 
1.50 
0 
10 
+0.15 
1.75 
0 
2 
0 
11 
0 
2.25 
0 
12 
0 
2.50 
0 
13 
0 
2.75 
—0.05 
14 
0 
3 
0 
15 
0 
3.50 
0 
16 
—0.27 
4 
0 
18 
—0.22 
4.50 
0 
20 
—0.12 
5 
0 
No. of 
Dioptric. 
Error. 
No. of 
Dioptric. 
Error. 
0.25 
0 
2.75 
0 
0.50 
0 
3 
0 
0.75 
0 
3.50 
+0.12 
1 
+0.05 
4 
0 
1.25 
+0.05 
4.50 
+0.05 
1.50 
+0.15 
5 
0 
1.75 
+0.20 
5.50 
0 
2 
+0.15 
6 
0 
2.25 
0 
7 
+0.15 
2.50 
+0.1 
CYLINDRICAL. 
[Note. I am under much obligation to Dr. Charles H. Williams, of Bos- 
ton, who was kind enough to lend me his phakometer while I was awaiting 
the arrival of my own.]