with convergent and divergent squint together
329 cases. Among them:
Visual acuteness to 1/7 239
" less than 1/7 to V. 1/12 19
" " 1/12 to V. 1/36 46
" " 1/36 25
Defective sight of higher degree than 1/7, 27.3 per
cent.
(_b_) In hypermetropia 1 to 3 D., including the few cases
of hypermetropia with divergent squint, 177 cases.
Among them:
Visual acuteness to 1/7 121
" less than 1/7 to V. 1/12 17
" " 1/12 to V. 1/36 27
" " 1/36 12
Defective sight then, 31.6 per cent.
(_c_) In hypermetropia 3 D. and more, 70 cases with convergent
squint, with:
Vision to 1/7 39
V. < 1/7 to V. 1/12 8
V. < 1/12 to V. 1/36 14
V. < 1/36 9
Defective sight then, 44.2 per cent.
This regular increase of defective sight with the increase of the
hypermetropia can be no mere accident, and speaks strongly for the
identity of defective vision in squint with congenital amblyopia. Were
defective vision caused by the squint the various states of refraction
would show no difference in the percentage of defective vision.
Further, the circumstance is worthy of remark that among 198 cases of
periodic squint (convergent and divergent) which are applicable for the
statistics of visual acuteness--
170 possess V. to 1/7.
16 " V. < 1/7 to V. 1/12.
9 " V. < 1/12 to V. 1/36.
3 " V. < 1/36.
14.2 per cent. then of defective vision of considerable degree.
That defective sight on the whole plays an influential part as a cause
of squint is doubted by no one, indeed we see blind eyes lapse into
squint as soon as the conditions necessary to it are supplied by the
muscles. Of all the prevailing causes present defective vision will be
the more decisive in proportion as it is of high degree; for the motive
which despite the presence of favouring circumstances can prevent the
real occurrence of squint, binocular vision, becomes less efficacious as
the defective vision becomes more considerable. As binocular fusion
takes place frequently in periodic squint, for a time at least, that is
as long as proper fixation lasts, one can understand that periodic
squint exists chiefly in cases where the visual faculty of both eyes is
good. Even the highest degrees of congenital amblyopia are not excluded,
for periodic squint appears where the faculty of binocular fusion has
been completely lost. Further, that considerable congenital defective
sight is more frequent with than without squint, may be accounted for
quite simply by the fact that, in extreme degrees of it, binocular
fusion cannot be learnt at all, while in the lesser degrees it is more
easily forgotten again.
If defective vision is undoubtedly one of the causes of squint, we must
seek for the grounds upon which it has been taken to be a consequence of
squint, and described as amblyopia ex anopsia. I will not inquire to
whom the honour of this invention belongs. I do not want to write a
history of mistakes but only to examine the basis of the views now
current. The most complete record of the same may be found in the
well-known journal on the 'Cure of Eye Diseases,' vol. v, p. 1011.
Leber, who does not seem to recognise the existence of congenital
amblyopia, has shown quite a special predilection for amblyopia ex
anopsia.
Amblyopia from want of use, which formerly included all possible
disturbances to vision, great and small, is now only accepted in two
cases, for squint and congenital cataract, if the latter is not operated
on very early in the first or second year of life.
The fact is simply this, that in congenital cataract even the most
successful operation is frequently deceiving as to its issue without
ophthalmoscopic report; this is the more disagreeable as the most exact
reflection test before the operation fails to prove the existence of
this defective sight. But does it follow from this, that congenital
cataract has induced defective sight from want of use? We find the same
defective vision also in congenital defective development of the
transparent lenses (so-called luxation of the lens). On the whole, we
often find several congenital defects in the same individual. The very
circumstance that the cataract is congenital makes it probable that the
defective sight is so also, or are we to take congenital cataract as
being a guarantee against congenital amblyopia?
Von Graefe, who first considered this defective sight to be congenital,
designated it in his later lectures as originating from want of use,
probably in order to advise the earliest possible performance of an
operation. There is no mention of his having brought forward evidence
for this assertion; that the great master himself said it was enough,
and the host of believers felt themselves to be the happy possessors of
a new dogma.
A number of children appeared in my practice, in whom congenital
cataract was needled by von Graefe in the first or second year of life
with recovery of transparent media, who showed, however, the extremest
degrees of defective vision when they were sufficiently intelligent to
have their vision tested. Whoever is interested in this can find a
number of such cases in the Royal Institution for the Blind at Steglitz,
which I am accustomed to visit several times a year by request of the
committee. On p. 91 I have related a case of monocular congenital
defective sight in congenital cataract of both eyes.
Everywhere then the principle holds good, that whoever makes an
assertion must be prepared to verify it; amblyopia from non-use is
denoted as an inherited trouble, and still not a single observation
exists which furnishes proof that an eye of previously ascertained good
visual acuteness has become amblyopic in consequence of disuse, a fact I
drew attention to ten years ago. Leber replies to this, he remembers "to
have seen patients with complete amblyopia in the squinting eye, who
stated that its visual faculty had been found to be good during an
examination instituted years before." Is this intended as an
observation? By that I mean is it a proof of facts, for the
trustworthiness of which he holds himself responsible: in the handling
of scientific questions I do not place the least reliance on the dim
recollections of unnamed individuals. Even in personally conducted
examinations we must be on our guard to avoid mistakes, and now we are
confronted with mere recollections of tests of vision!
By means of the above observations the theory that "the peculiar variety
of monocular amblyopia which is so frequent in monocular squint is
hardly observed without squint" is sufficiently disproved.
Leber seeks to enfeeble Alfred Graefe's statement that the presence of
extremely defective vision may sometimes be proved at a very early age,
in children who have only squinted a short time (the rapid development
of amblyopia in consequence of the squint really appears incredible), by
the assertion "that just at the earliest age, when the activity of the
optic nerve is not yet sufficiently strengthened by use, the conditions
for producing amblyopia from non-use are most favorable with complete
exclusion of one eye," but complete exclusion of the squinting eye does
not take place even in extremely defective sight, as can easily be seen
by the mirror test (p. 66) I described fourteen years ago. Which
activities of the optic nerve apparatus are strengthened then by use?
Perhaps visual acuteness? The physiological conditions of this are only
to be sought in the anatomical structure, and the physiological
arrangements of the retina or the visual organs, which cannot be changed
much by use. What we can learn from the visual act relates solely to the
conclusions which we are able to draw from sensual impressions; but
visual acuteness, _i. e._ the faculty for the recognition of distinct
points, is an anatomical, physiological gift, and not a thing to be
acquired.
The opposing observation, that squint, even of monolateral character
dating from earliest childhood, continued to the middle and later years
of life, can still exist with very good visual faculty, may easily be
explained by alternation from time to time. If that is so indeed, if
squint begins during the presence of good visual acuteness, and nothing
further is necessary to its maintenance than alternation from time to
time, why should defective vision from non-use ever be developed? With
good visual faculty on both sides alternations also occur from time to
time.
Still more convincing are those cases which are numerous where the
visual acuteness of the squinting eye only amounts to about 1/7 to 1/12,
and where, on this account, there is no alternation. Were this defective
sight acquired through non-use it must of necessity be progressive; it
must exist in proportion to the duration of the squint. A moderate
experience will suffice to show that this is not the case. And further,
defective sight must continue progressive even after removal of the
squint by operation, for by the operation nothing is changed in the
relations of the binocular vision present in squint, which are dismissed
with the one word, "suppression," by the advocates of defective vision
from non-use.
Moreover, suppression may exist for years without the slightest
disadvantage to the visual faculty.
CASE 32.--In November, 1873, I operated on Fritz F-- for a slight
divergent squint of the left eye. Slight hypermetropia was present on
both sides, and nearly full visual acuteness. In October, 1880,
perfectly normal position of the eyes showed itself with the same visual
acuity and emmetropia in both eyes; at the same time, however, the boy
affirmed that when reading he could never see with his left eye but only
with the right; in reality only the right visual field was perceived in
the stereoscope.
The second reason brought forward is, that the variety of amblyopia from
non-use is quite a peculiar one; "it consists of a functional
disturbance of those parts of the retina whose images belong to the
common V. F., and are suppressed in squint in order to render vision
distinct--the macula and the temporal and only a part of the nasal
halves of the retina." Does this hold good for all cases of amblyopia in
squint, or do those cases only belong to amblyopia from non-use where
excentric fixation takes place with an inward deviating visual axis? It
would be difficult to draw the line. I have seen a case in which the
squinting eye possessed a visual acuteness of 5/36 together with
excentric fixation and nystagmus; however, I attach no value to isolated
cases. We frequently find excentric fixation with a visual acuteness of
1/12 to 1/36. Further, those cases cannot possibly be regarded as
results of squint, which possess unsteady oscillating fixation or
rapidly trembling nystagmus, which occurs as soon as the squinting eye
fixes. But this conclusion is false, even for the excentric fixation
with visual axis deviating inwards; if it were right the angle at which
the eye deviates inwards on fixation in convergent squint would always
be greater than the squint angle. Those cases are, of course, more
remarkable where this is not the case; however, on close investigation
those cases are more frequent where the angle of deviation is about the
same size or smaller than the squint angle, and is fixed with a part of
the retina which undoubtedly belongs to the common visual field.
On p. 91 I have described two cases of excentric fixation in children
who had never squinted, and it is only necessary to take a little
trouble to repeat the mirror test which I described, to be convinced
that squinting eyes have not lost the power "of using those parts of the
retina," even if they are amblyopic to an extreme degree; without the
slightest doubt the reflection is perceived as soon as it falls on the
retina.
Value is attached to the improvement produced by the separate use of the
squinting eye. According to my experience no higher visual acuity can be
attained by use of the amblyopic eye, than that which is best detected
by the aid of eserine in the first examination, if it is only carried
out thoroughly enough. No doubt if we proceed otherwise, and rest
content with whatever statements the patient likes to make, without
giving ourselves any more trouble, we may expect the most superficial
diagnoses to show the most astonishing therapeutic results, as, indeed,
often happens. And now, talking of strychnine injections! When two
celebrated ophthalmologists occupy themselves simultaneously with the
therapeutics of strychnine, one of whom obtains the most astonishing
results in atrophic troubles of the optic nerves, but, on the other
hand, obtains no real improvement in "amblyopia from non-use," while the
other can show brilliant success in the last-named form of defective
vision, and, on the other hand, none in atrophy of the optic nerves, we
may perhaps conclude that both are right, if even really on the negative
side, and that the circumstances are the same in the tests of vision.
Again, we must examine more closely some of the cases, in which
strychnine injections showed a brilliant result. (Anyone interested in
the original work can read up the 'Vienna Weekly Medical News' for the
year 1873.)
"1. Wilhelm H--, a strong healthy boy, aet. 12, complains of defective
vision. Right eye has nothing abnormal in its outward appearance, and
just as little in the fundus. V. 16/100, H. 2.5 D., Snellen IV-I/II; is
the smallest type he reads at 3 to 7 inches. With + 10, I-I/II is read
at 4 to 6 inches. Left eye V. 16/70. H. 2.75 D. II-I smallest type
legible at 3 to 12 inches. With + 4 D. I-I/II is read at 4 to 6 inches.
On March 14th, 1872, first injection of strychnine with 0.002 gr. in the
temples. An hour later V. of right eye 16/70, left unchanged. On March
23rd, 1872, after one injection daily, V. of each eye is 16/50."
Patient shows then in the right eye visual acuity 16/100, with manifest
hypermetropia 2.5 D.; in all probability the total hypermetropia really
present was higher, and was scarcely corrected by means of convex 4 D.
If the patient now reads No. I-I/II Snellen with + 4 D. at 6 inches,
this proves a visual acuity of 1/3 during the first investigation before
the strychnine injection, and shows that the estimate of 16/100 was
inaccurate. At the close of the treatment, only a visual acuity of 16/50
(almost exactly 1/3) is specified for distance. The result seems to me,
then, to be this, that the patient during repeated examinations has
gradually learned to make more accurate statements, indeed, with a boy
twelve years old one can scarcely expect it to be otherwise.
"4. Paul A--, aet. 18, was operated on ten years ago for internal squint
of the right eye, and dismissed with + 2 D. for distance, and + 6.6 D.
for near use. He now complains of decrease of his visual acuity. The
eyes are normal externally and internally. Hyperopic formation in a high
degree. Right eye V. 1/20, with and without convex glasses, without
glass only VIII-I/II with difficulty, with + 6 V-I/II the smallest. Left
eye appears emmetropic, but is decidedly hyperopic. V. 5/4. Glasses are
rejected; I-I/II is read fluently at 6 to 12 inches. After one injection
the right eye recognises III-I/II with + 6, after the second II-I/II,
after the eighteenth I-I/II with difficulty. The visual acuity, however,
remains at 1/20, and is not changed after six months, although latterly
patient daily practised with + 3 D."
Visual acuity of 1/20 suffices to read III-I/II at 2.5 inches, II-I/II
at 1.5 inches, and I-I/II at about 1 inch; clear, retinal images are
then scarcely obtainable, but we know what hypermetropes can do in that
case; besides this, if the patient is examined for weeks by Snellen's
method, he may get so far as to realise fairly well "the strange fate of
that man" of I-I/II, despite larger diffusion circles; in any case
vision remained at 1/20, despite strychnine and separate use.
In extremely defective vision little importance should be paid to the
fact of slight diversity in the statements, as where visual acuity
amounts only to about 1/36, or where fingers are counted at a distance
of 1 to 2 metres, it is quite immaterial, as far as the usefulness of
the eyes is concerned, whether fingers are counted at a half or a whole
metre, and we ought never to forget that all conclusions which we draw
from the state of the visual acuity, are unreliable in proportion as the
latter is lowered. Indeed, on repeated examination of such cases we
frequently find considerable fluctuation in the statements of the
patients, therefore we ought not to expect accurate statements for very
inexact sensual impressions.
By separate use, even in extremely defective vision, no improvement in
visual acuteness is developed, but only a more complete acquirement of
the power of deducing right conclusions from imperfect sensual
impressions. That which has been most unscientifically designated as
"suppression of diffusion circles," depends solely on this method of
use. As with indistinct retinal images so with facial impressions which
are insufficient, one can never learn to recognise larger objects
aright.
We must never forget that vision is a conclusive act acquired by
practice; whoever sees well with one eye, and is weak sighted with the
other, acquires this end only for the sensual impressions of the better
eye, and must first collect experience for the defective eye, before he
can use it.
Leber has recently joined those cases which are described as blindness
through blepharospasm, to amblyopia from disuse. First, I wish to
observe that blepharospasm is not a necessary cause; I have seen the
same disturbance of vision follow severe double blenorrhoea, which
destroyed one eye but left the other uninjured. These children are
always of an age which renders any trial of vision impossible, and we
are therefore obliged to draw conclusions as to visual power from the
movements of the body. If children move as though they were blind, it
need not necessarily follow that they are so in the common meaning of
the word. The art of vision is a difficult one, the acquisition of which
begins with the earliest days of life; we do not call every person blind
who does not see what is before his eyes, because he does not understand
how to see it. A child who has only imperfectly learnt the conclusive
act of vision, and forgotten it again during a continued disuse of both
eyes, will not know how to use perfect visual acuity, and will move like
a blind person till he again learns to estimate the relations between
his retinal images and the things of the material world, which happens
in a very short time.
After this digression let us turn again to amblyopia from disuse, and to
the last trump which is played for it. "Those cases are very remarkable
where an immediate improvement occurs after tenotomy in amblyopia of
high degree, which according to this is certainly produced and
maintained by the squint." As proof a case is cited by Knapp, who
describes it in the following words:--"The improvement in visual power
varied very much. In many cases it was indefinable, in others very
pronounced; for example, in one case, where it was very great before the
operation, only No. 16 Jaeger could be read at 1 inch, while after it
No. 2 was read at 8 to 9 inches."
And we are to believe wonders on the strength of this scanty
communication! It is an every-day experience that a person who squints,
who has just asserted his inability to read the largest type,
immediately afterwards reads smaller and the smallest type, and it would
at least first have to be determined that all endeavours to produce a
better visual result before tenotomy were unsuccessful; but as the
communication stands, the conclusion as to the effect of tenotomy is
quite a superficial _post hoc ergo propter hoc_. Moreover, I had this
case in view when I spoke on this matter in the first edition of my
'Handbook:'--"The frequently repeated assertion that a considerable
improvement of vision may occur as a direct result of tenotomy, is so
little in accordance with all the laws of physiology, that inquiries
must be instituted _ad hoc_, and carried out with the most perfect
exactitude. Only trials of vision which are carefully carried out and
repeated several times before the operation, and which have regard to
visual acuteness for distance as well as for near objects, the latter
indeed by the aid of convex glasses or Calabar extract, can be
recognised as proving anything in face of such a perfectly improbable
assertion. In the course of examinations so instituted I have not myself
found that tenotomy exercises any direct influence on visual acuity."
I would not have given so much space to this explanation had not a
principle been in question. The occurrence of amblyopia as a result of
non-use has been deductively constructed and is not inductively proved
by observation. It is just an article of faith, and in science we cannot
rely on such things; we must not depart from the inductive method.
ON THE CURE OF SQUINT.
Therapeutic investigations have their safest and most instructive basis
in observation of the course of a disease as it appears without
complications, and with no unusual symptoms; we can only arrive at a
certain decision as to the extent of our therapeutics when we know
exactly what will happen without skilled assistance. When squint is once
present it is seldom complicated by fresh symptoms; on the other hand,
spontaneous cures unquestionably take place. We must certainly not rely
simply on the statements of patients themselves. On p. 1 we have seen
what mistakes occur, even when it is a question of whether squint is
present or not. How little such vague statements are worth is seen by
the fact, that the question as to the direction of the previous squint
very seldom finds a satisfactory answer; as a rule it is impossible to
determine whether periodic or permanent squint has been present.
If we undertake the task of converting the statements of patients as to
previous squint into observations, in order to confirm the statements
from the objective material, we must first prove whether the squint
cannot by some means be still produced (by excluding the eye or by
raising or lowering the eyes). Thus the condition of binocular vision
offers us valuable guides. If we find that binocular fusion does not
exist with available power of vision on both sides, but that the same
conditions of sight appear in the eyes as we have learnt to attribute to
squint, there is no reason for doubting the statements about a
previously existing squint. It is otherwise in those cases of extreme
amblyopia where normal binocular vision is never expected, or at least
cannot be proved on account of the enormous difference between the two
eyes.
If we discover the existence of normal binocular fusion, squint may
nevertheless have been present at a former time, for in many cases, of
periodic squint particularly, the habit of binocular fusion is never
quite lost.
That squint can disappear of itself is unquestionable; how often this
happens it is difficult to say. The fact that in ophthalmic practice we
see many more squinting children than adults is best explained by
this,--that squinting children are brought to us by their parents, while
adults who still squint have usually given up any desire for a cosmetic
improvement, and only come under treatment accidentally or on account of
other ailments; lastly, a considerable number of cases are cured by
operation. If the squint has disappeared we only discover by accident
that it was ever present. The fact of its previous existence may usually
be determined by other signs more positive than mere statements from
memory; with reference, however, to the age at which the spontaneous
cure takes place we are left to depend almost entirely on the patient's
statement. As far as I have been able to determine, the period from the
ninth or tenth up to the sixteenth year seems to offer the most
favorable conditions.