[Reprinted from The Medical News, July 8, 1893.] 
A NEW EYE-MODEL ( A N A K L A S / M ET E Rl) FOR 
DETERMINING THE REFRACTION 
BY OPHTHALMOSCOPY AND 
RETINOSCOPY. 
By CARL WEILAND,m.D., 
CLINICAL ASSISTANT, EYE DEPARTMENT, JEFFERSON MEDICAL 
COLLEGE HOSPITAL, PHILADELPHIA. 
That an accurate and inexpensive apparatus for 
practice with the refraction-ophthalmoscope is a 
desideratum will be conceded by all that have en- 
deavored to avail themselves of this most valuable 
aid of ophthalmology. The tyro, especially, who 
has to learn the use of the ophthalmoscope and 
who must endeavor to relax his accommodation, is 
very much in need of an instrument that will allow 
him to accurately observe how far he has succeeded 
in his efforts; or, if he cannot relax his ciliary 
muscle wholly, how much accommodation he still 
employs in his observations. 
It is for this reason that I have constructed a lit- 
tle model of the eye, which by axial changes per- 
mits the accurate determination of all refractive 
conditions from —10 to +10 dioptries, with or 
1 From the Greek f] avan/iacug, the refraction, and to fierpov, 
the measure. The usual word, refractomeier, a compound of 
Latin and Greek stems, seems rather barbarous, and has there- 
fore been avoided. ; A 2 
without astigmatism, in gradations of 0.50 dioptry, 
if wanted. The little apparatus consists essentially 
of a blackened tube, A (diagram), about one inch 
Half of actual size. 
in diameter and three and one-half inches in length, 
and closed at either extremity by metal discs, C and 
B, the anterior disk, B, having a central opening 
of about one-half inch, which contains a lens of 
-(-20 D power. Near the bottom of the instru- 
ment is a screw, D, which extends along the whole 
length of the tube and has at the back a little han- 
dle, E, which projects from the posterior disc and 
allows the screw to be turned. Along this screw 
there slides on a nut a plate, F, representing the 
retina, the position of which is indicated on the 
outside of the tube by a pointer, G. I he number 
to which the pointer is directed indicates the refrac- 
tive condition of the eye, the white m mbers apply- 
ing to the degree of hypermetropia and the red 
ones to the degree of myopia. From the anterior 
part of the tube projects a metal plate, H, which sup- 
ports the ophthalmoscope and is so constructed that 
if the ophthalmoscope rests against it the lenses of 
the latter are exactly fifteen millimeters from the 3 
lens of the eye-model. In order to produce an 
astigmatic eye three little hooks are attached to the 
anterior plate, B, so that a —2D cylinder can 
be slipped in and turned to any desired angle. 
As, of course, the eye of the completely relaxed 
emmetropic observer is only adapted for parallel 
rays, it will only see the objects on the artificial 
retina distinctly if the rays coming from the eye- 
model have been made parallel by the lens of the 
ophthalmoscope. The numerical value of these 
lenses for the different positions of the retina can 
be easily calculated as follows: If /is the focal dis- 
tance of the lens of the eye model and d the dis- 
tance of the artificial retina from this lens, then, 
by the known laws of refraction, b, or the distance 
of the image of the retina from this lens, will be 
111 
determined by means of the formula: = 
from which we find that b = J——. This equa- 
d-f 4 
tion shows that b is positive as long as d is greater 
than f i. e., the image of the retina falls in front 
of the lens, and we have therefore to do with 
myopia. The ophthalmoscopic lens is 15 mm. in 
front of the lens of the model, or b—15 mm. from 
the retinal image; it is therefore necessary to find 
a minus lens that has a focal distance of b—15 mm., 
so that the rays that would come to a focus 
b—15 mm. behind the ophthalmoscope are made 
parallel after their passage through this lens. The 
focal distance of this required lens must then be 
b — 15 mm. = —15 ; or, in dioptries, its re- 
d—J 4 
fractive power D must be 1000 = 1000— = D 
b—15 fd 
d=y-'s 
From this we find that d =■ (1000 ~^_l 5_P 
1000 — (/—i5)D 
This value for d shows us how far from the lens of 
the model we have to place our artificial retina in 
order to obtain a given number of (D) dioptries of 
myopia. In the same way we would find for hyper- 
metropia that d — (IOO° J . (It must 
1000 + (/— i5)I) 
be remembered that the D’s have to be taken with 
their absolute values only, without regard to the 
sign.) In this way the following two tables were 
found: 
Myopia. 
d = 50.00 mm. gives a myopia of o. D. 
d = 52.59 " " “ “ 1. D. 
d = 55.37 *' “ " “ 2. D. 
d = 58.38 “ " “ “ 3. D. 
d = 61.62 “ “ “ " 4. D, etc. 
Hypermetropia. 
d = 50.0 mm. gives a hypermetropia of o. D. 
d = 47.5 » “ “ ** I. D. 
d = 45.3 “ " “ “ 2. D. 
d = 43.2 " “ “ " 3. D. 
d = 41.2 “ '* “ " 4. D, etc. 
In accordance with these two tables the scale of 
the instrument has been so constructed that all 
refractive conditions from —10 D to -j-10 D can 
be accurately determined. Practically all that is 
necessary is to take the model in one hand and the 
ophthalmoscope in the other hand, and then, after 
bringing the ophthalmoscope in contact with the 5 
rest, to find the highest plus or the lowest minus lens 
with which accurate and sharp definition of the de- 
tails of the image can be obtained; and finally, to 
compare the number of the ophthalmoscope with 
that of the model. Perfect agreement shows perfect 
relaxation of the emmetropic eye; a plus lens in 
the ophthalmoscope too low or a minus lens too 
high by a certain number of dioptries shows just so 
many dioptries of accommodation used by the em- 
metropic observer. If the observer is not emme- 
tropic, and if his refraction is not perfectly cor- 
rected, he has, of course, to make allowance for 
this in the reading of his ophthalmoscope. 
If we place the cylinder of —2 D in its proper 
position in front of the -[-20 D lens we have then 
a sphero-cylindrical combination of +20 D in one 
and -f-18 D in the other main meridian. For the 
first meridian the former scale remains therefore the 
same, but for the —{— 18 D lens a new scale is given 
below the other, so that the value of each meridian 
can be read off directly. Let, e.g., the retina be 
at 85.7 mm. from the lens, then we find the pointer 
indicating a myopia of —7 D in one and of 
—4.5 D in the other. 
How the instrument may also be used for retin- 
oscopy will be clear from the foregoing description, 
and needs no further remarks. Of course, there are 
a good many contrivances that one might feel 
tempted to add, e.g., a stand for the whole instru- 
ment, a changeable iris and a lens-holder in front 
of the rest for the ophthalmoscope, in order to get 
a point of reversal of 1 meter by using the lenses 
of the trial-case in this holder. The aim, however, 6 
has been simply to furnish a reliable and inexpensive 
means for the yvufli oeavrbv of the ophthalmologist 
and to omit all unnecessary accessories, which can 
be added, if desired. I am under great obligations 
to Mr. D. V. Brown, 740 Sansom Street, Philadel- 
phia, for the elegance and accuracy with which the 
little apparatus has been constructed, and which is 
sold for $3.50. 
315 North Sixth Street.