The Proximate Cause of the 
Transient Form of Myopia 
associated with Iritis. 
With Remarks on Other Forms of 
Symptomatic Ametropia. 
BY 
A. SCHAPRINGER, M. D. 
REPRINTED FROM 
CTfje >3eto Yorit jflSeOical $outnal 
for October 21, 1893. Reprinted from the New York Medical Journal 
for October 21, 1893. 
THE PROXIMATE CAUSE OF 
THE TRANSIENT FORM OF MYOPIA 
ASSOCIATED WITH IRITIS. 
WITH REMARKS ON OTHER FORMS OF SYMPTOMATIC AMETROPIA. * 
A. SCHAPRIXGER, M. D. 
The clinical fact that iritis in a considerable proportion 
of cases is apt to occasion a transitory myopia of low de- 
gree—about 1‘5 D. to 2-0 D.—was first put on record by 
Dr. John Green, of St. Louis, the well-known authority on 
questions connected with refraction. Since the time that he 
read his paper on this subject before the American Ophthal- 
mological Society in 1887 his discovery has been verified 
by a large number of other observers. 
As to the proximate cause of the increase of refraction 
as a symptom of iritis Dr. Green did not offer any specu- 
lations. 
In a paper on Symptomatic Myopia, read before the 
American Ophthalmological Society in 1888, Dr. W. F. 
Mittendorf advanced the theory that this transient increase 
* Read before the Section in Ophthalmology and Otology of the 
New York Academy of Medicine, October 16, 1893. 
Copyright, 1893, by D. Appleton and Company. 2 
TRANSIENT MYOPIA. 
of refraction was the result of an infiltration of the ante- 
rior portion of the vitreous body, increasing the bulk of this 
organ to such a degree as to push the lens system forward 
and with it the posterior principal focus of the eye. This 
theory I do not feel inclined to adopt, because as long as 
the tensile strength of the suspensory ligament of the lens 
remains unimpaired, an increase of pressure in the vitreous 
chamber would have to be very great indeed to displace 
the lens forward. The globe would feel very hard on pal- 
pation, other symptoms consequent upon increase of ten- 
sion would be present, and there would be hardly any 
difference in the clinical pictures of iritis and acute glau- 
coma. 
According to another theory, the increased refraction is 
said to be due to an augmentation in the corneal curvature 
produced by the increased pressure of the lids in conse- 
quence of the great photophobia. The negative results of 
ophthalmometric measurements completely disprove this 
theory. 
Still another hypothesis alleges a spasmodic condition of 
the ciliary muscle as the cause of the symptom in question. 
This hypothetical cause forming the base of certain thera- 
peutical recommendations lately made by Dr. Charles A. 
Oliver, of Philadelphia,* the question of the correctness of 
this hypothesis must henceforth be regarded as not merely 
of theoretical but also of practical interest. 
Dr. Oliver insists that the refraction of the eye should 
be carefully and repeatedly tested in the course of an at- 
tack of iritis, and that instillation of strong mydriatic 
solutions should not be discontinued as long as the in- 
creased refraction persists, even after the pupil has been 
fully dilated. The presence of myopia proves the presence 
* La correction exacte des vices de refraction dans l’iritis plastique. 
Annales d'oculistique, Jan., 1893. TRANSIENT MYOPIA. 
3 
of spasm in the muscle of accommodation, and this being a 
pathological condition, it needs to be combated by the ap- 
propriate means at our disposal. 
Now Dr. Green has already pointed out that the fact 
that the increase of refraction persists for an indefinite 
time after the pupil has fully yielded to the action of 
atropine was a proof militating against the assumption that 
the transient myopia was due to spasm of accommodation. 
Besides this argument advanced by Dr. Green, the sup- 
position that inflammation will cause a spasmodic contrac- 
tion of the ciliary muscle is contrary to all physiological 
experience in regard to analogous conditions elsewhere in 
the human organism. To bring forward only one example, 
let me refer to the behavior of the muscular coat of the 
intestine in peritonitis, where it is anything but contracted. 
On the contrary, it is completely paralyzed, and by its 
paralysis causes two of the main symptoms of the disease, 
tympanites and constipation. The contraction of the 
pupil in iritis is not due to spasm of the sphincter iridis 
muscle, but is only dependent on the swelling of the tissue 
of the iris in consequence of hyperaemia and infiltration. 
It is also a very significant fact in connection with the 
question here discussed that in the insidious forms of sym- 
pathetic iridocyclitis the first sign of impending trouble is 
the diminution of the power of accommodation, causing 
recession of the near point. 
Having dismissed all the theories hitherto enumerated 
as unsatisfactory, it behooves me to substitute one against 
which no valid objections could be raised. I think that 
the transient myopia of iritis can be best explained by a 
temporary increase of the refractive index of the aqueous 
humor. That the composition of the contents of the ante- 
rior chamber in iritis differs from that in the normal state 
is not a hypothesis, but a fact. The formed particles sus- 4 
TRANSIENT MYOPIA. 
pended in the aqueous humor, rendering its aspect turbid, 
will, of course, have no influence upon the refraction of 
the eye. We are here concerned only about the trans- 
parent part of the liquid. Judging from the deposits, 
among other substances, of fibrin upon the walls of the 
anterior chamber, nothing would seem more plausible than 
to assume that in iritis the aqueous humor contains this 
substance in more than the normal quantity. If this is 
the case, it follows from physical laws that its index of re- 
fraction must be increased. A higher index of refraction 
of the aqueous will produce myopia, because the beams, of 
light which receive an inclination toward the optical axis, 
when refracted at the anterior corneal surface, will receive 
an additional inclination toward this axis at the posterior 
corneal surface. In the normal state there- is no refraction 
at this surface, because then there is no difference between 
the refractive indices of the cornea and of the aqueous 
humor. The posterior wall of the cornea in iritis repre- 
sents a convex refracting surface with a medium of higher 
refrangibility behind it than before. Consequently the op- 
tical conditions present at this surface will be the same in 
kind, though not in degree, as those present at the ante- 
rior surface. 
If the refractive index of the aqueous humor of an em- 
metropic eye were lessened instead of increased, the incli- 
nation of the rays of light toward the optical axis would be 
diminished and the eye therefore rendered hypermetropic. 
The question now presents itself, How much must the 
index of refraction of the aqueous be increased in order to 
produce a given degree of myopia ? 
In order to solve this problem, we have to take into 
consideration the factors coming into play at the refraction 
by the posterior corneal surface. The relation of the con- 
stants is expressed by the well known formula— TRANSIENT MYOPIA. 
5 
p _ n2r 
n2— nt 
We wish to calculate the value of n2, which represents 
the index of refraction of the aqueous humor : 
FoW, 
n~ ~ iv^v 
F2 represents the second principal focal distance of our 
refractive system, consisting of corneal substance, posterior 
corneal surface, and iritic aqueous, or, in other words, the 
collective power of this system. This collective power is 
measured by the concave glass placed before the eye, neu- 
tralizing the collective power by its dispersive power. In 
substituting the reciprocal value of this glass, we have to 
deduct the distance of the correcting glass from the poste- 
rior corneal surface. 
stands for the refractive index of the corneal sub- 
stance, which is 1‘3365 according to Helmholtz. 
r represents the radius of curvature of the posterior 
wall of the cornea, which, following Tscherning, we will 
put down as six millimetres. 
Carrying out the calculation for different degrees of 
myopia as met with in iritis, we find the following values 
of n2: 
Degree of myopia. 
Index of refraction of aqueous. 
1-0 I) 
1-345 
1-5 D 
1-349 
2-0 D 
1-353 
The increase from the normal—which is l-336—not being 
considerable, the figures at least do not speak against the 
plausibility of our hypothesis. 
If we accept this hypothesis as the true explanation 
of the myopia occasioned by iritis, we shall refrain from 
continuing the instillations of atropine after the pupil 
has fully yielded to its action and the congestion has 6 
TRANSIENT MYOPIA. 
subsided, although the myopia may still be present. Our 
theory furnishes a contraindication against the persistent 
employment of atropine under these circumstances, inas- 
much as a dilated pupil means an obstructed iris angle, and 
this means interference with the drainage of the anterior 
chamber. We shall not feel inclined to do anything to 
keep the morbid aqueous humor longer in the anterior 
chamber than necessary. Our hypothesis furthermore 
does not impose upon us the obligation of carefully and 
repeatedly testing the refraction of eyes affected with 
iritis, of which release we shall avail ourselves with avidity 
and earn the thanks of our patients. 
If the myopia persists for some time after the subsi- 
dence of the inflammatory symptoms and we should feel 
called upon to hasten the work of Nature, massage of the 
eyeball would offer itself as a local therapeutic measure in 
consonance with our theory. 
The two recognized varieties of myopia in general are 
axial myopia, which is the most common form, and myopia 
of curvature. If our theory as to the causation of the tran- 
sient nearsightedness occasioned by iritis is verified, we 
shall have “ index myopia ” as a third type of this error of 
refraction. 
To test the merits of the theory here propounded, very 
accurate measurements with instruments of precision rarely 
met with in the possession of practitioners will be neces- 
sary. Those who have a Helmholtz ophthalmometer, or, 
what seems to be a still more suitable instrument for the 
purpose, a Tscherning ophthalmophakometer at their dis- 
posal, will deserve the thanks of the profession by taking- 
up this problem. The shortest way to determine the re- 
fractive index of iritic aqueous would be to tap the anterior 
chamber and test the liquid obtained by means of an Abbe 
refractometer; but the clinical indication for paracentesis TRANSIENT MYOPIA. 
7 
of the cornea hardly ever arises in the course of plastic 
iritis. 
Since we are discussing the subject of index ametropia, 
the question naturally suggests itself, What would become 
of an emmetropic eye if the index of refraction of the 
vitreous body be increased ? 
The answer to this question will be found in the fol- 
lowing consideration : 
The beams of light, striking the concave anterior sur- 
face of the vitreous, are deflected toward the optical axis 
to join it at the place of the retina. The strength of the 
deflection depends upon the difference of the refractive 
indices of the crystalline body and the vitreous. The 
index of the vitreous being the lesser quantity, we will, 
by increasing it, lessen the difference between it and 
the crystalline index, or, in other words, lessen the incli- 
nation of the rays of light toward the optical axis. This 
means that the emmetropic eye is being rendered hyper- 
metropic. 
A change in the refractive index of the vitreous will 
therefore have the opposite effect from that which is pro- 
duced by the same kind of Change in the aqueous. 
In the intervals between the prodromic attacks preced- 
ing an outbreak of inflammatory glaucoma the patients 
usually complain of being compelled to use increasingly 
strong convex glasses in rapid succession for reading pur- 
poses. This is usually explained as the result of a rapid 
diminution in the power of accommodation, but it seems to 
me not improbable that this symptom may have something 
to do with an increase in the refractive index of the vitre- 
ous body. Such an increase, as said before, will render an 
emmetropic eye hypermetropic, and a hypermetropic eye 
still more hypermetropic. I have met nowhere with the 
distinct statement from any observer that, while the near 8 
TRANSIENT MYOPIA. 
point of the glaucomatous eye thus rapidly receded, the far 
point was found to remain stationary. 
The myopia caused by diabetes is a form of myopia to 
which Hirschberg has called attention and which is proba- 
bly also a type of index ametropia. I have myself re- 
cently met with two cases of this kind in succession—one 
of them in a lady sixty-one years old, referred to me by the 
kindness of Dr. S. J. Meltzer, of this city. The acquired 
myopia in both cases was of considerable degree, being 
more than 6 D. An increased curvature of the front sur- 
face of the lens I can hardly deem accountable for this, 
since the depth of the anterior chamber, at least as far as 
could be made out without the use of the instruments of 
precision mentioned before, seemed perfectly normal in 
both cases. A decrease in the refractive index of the cor- 
tical substance of the lens will, I think, best account for 
this type of myopia, if the myopia is to be accounted for by 
a change in this organ. Such a decrease will increase the 
refractive power of the lens system as a whole and thereby 
bring the posterior principal focus of the eye in front of 
the retina. It may sound paradoxical at first dhat the col- 
lecting power of a biconvex lens like the crystalline body 
should be increased by a decrease in the refractive index 
of one of its constituent parts. But it must be remem- 
bered that the cortical substance represents a system of 
concave or dispersive lenses which neutralize the over- 
strong collective power of the globular nucleus. By lower- 
ing the refractive index of the cortex we lessen its disper- 
sive power, and the result will be a preponderance of the 
collecting power of the nucleus; the principal focus of 
the eye is thereby brought forward and the eye made 
myopic. 
Since writing the foregoing my attention has been 
drawn to a paper, On the Presence of Sugar within the Eye TRANSIENT MYOPIA. 
9 
in Experimental Diabetes,* by the brothers Cavazzani, an 
abstract of which has recently appeared in the Centralblatt 
fur prakt. Augenheilkunde (supplement for 1892, p. 496). 
Having made experimental researches on the functions of 
the pancreas, these authors report the results of the chemi- 
cal analysis of the refracting media of two dogs which 
were afflicted with a permanent form of diabetes in conse- 
quence of the extirpation of the pancreas. The animals 
were killed in due season and their eyeballs enucleated. In 
the first dog the aqueous humor contained 0'386 per cent, 
of sugar. In the peripheric layers of the lens very little of 
this substance was found, and none at all in the nuclear por- 
tion of the lens and the vitreous body. In the second dog 
sugar in the proportion of somewhat less than 0-05 per 
cent, was found in the aqueous humor and none at all in 
the other refracting media.f The lenses were completely 
transparent and anatomically normal in every respect. The 
fact that the lens, at least of one of the animals, contained 
sugar, speaks against the theory enunciated by Deutsch- 
mann,J which says that no sugar can diffuse into the sub- 
stance of the lens as long as the epithelial layer of the lens 
capsule remairfs intact. 
In the investigations of the Italian experimenters, at 
least as far as they are reported in the Centralblatt, no at- 
tention was paid to the refraction of the eyes during life or 
to the refractive index of the media subjected to chemical 
examination. I hope that in future investigations of the 
same kind these matters will not be lost sight of. The re- 
sults of the chemical analysis make it probable that the 
* This is a portion of a larger work, Le funzioni del pancreas ed i 
loro rapporti colla patogenesi del diabete. Venezia, 1892. 
f From the marked difference in the chemical behavior of the aque- 
ous and the vitreous the authors draw the conclusion that the sources 
of nutrition of these two substances must be entirely distinct. 
\ V. Graefe’s Arch. f. Ophthalm., 1887, p. 229. 10 
TRANSIENT MYOPIA. 
aqueous humor at all events plays an important part in the 
production of diabetic myopia. Future investigations will 
have to show whether the peripheric layers of the lens are 
also concerned in this change of refraction and how far. 
It is very characteristic that the vitreous body of the dia- 
betic dogs was found absolutely free from sugar. This is 
in remarkable harmony with what was pointed out before 
on theoretical grounds—viz., that the degree of myopia 
produced by an increase of the refractive index of the 
aqueous humor will not become further increased by an in- 
crease of the refractive index of the vitreous body, but, on 
the contrary, an increase of the refractive index of the vit- 
reous would neutralize, more or less, any myopia caused by 
a change of index of the aqueous humor. 
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