Part 12

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, æt. 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--, æt. 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.