Part 9

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.

We rarely have an opportunity of watching the disappearance of squint, still I have observed two cases in which a permanent convergent squint disappeared after about a year. In both cases the squint had arisen in young people (of eight and nineteen years of age) in the course of irido-choroiditis which terminated in blindness, and disappeared with the sight. The fixing eye was emmetropic in one case, in the other the condition of error could not be determined owing to nebulae of the cornea.

We more frequently see periodic squint disappear.

CASE 33.--M--, a boy aet. 10, was first examined by me in April, 1873; the right eye has hypermetropia 4.5 D., and almost full visual acuteness, the left has convergent squint, and recognises No. 6-1/2 (Snellen) with convex 10 D.; V. = 1/18 at 1 metre. (The boy's father also squints with the left eye, which is amblyopic to a high degree (V. = 1/36), right eye has emmetropia, and full visual acuteness). The prescribed spectacles (convex, 4.5 D.) were used for working, but not continually; still three years later, in 1877, the deviation was considerably less and only occurred occasionally. In March, 1880, nothing more was seen of the squint, only slight convergence still recurred on excluding the left eye. Patient now wears convex 4.5 D. constantly.

On account of the importance which the disappearance of squint possesses in hypermetropia I will describe a few more cases which belong here.

CASE 34.--Mrs. B--, aet. 32, has on the left H. 1.5 D., V. 5/9; on the right H. 1.5 D., V. 5/12, binocular vision (H. =.75 D., V. = 5/6 to 5/9). Asthenopic troubles are the cause of her present complaint. She says she squinted with the right eye as a child till her eighth or ninth year; the present position of the eyes is quite normal; ordinary type is read at the usual distance with normal fixation without glasses. Particularly keen fixation is rarely followed by squint, which may be produced by excluding the right eye; the latter then deviates about 5 mm. inwards and slightly upwards; the secondary deviation of the left eye is rather less. Only the left visual field is seen in the stereoscope.

CASE 35.--Mrs. W--, aet. 31, has on the right H. 3.5 D., V. 5/9, on the left V. = 1/16 with + 4 D., single words of No. 0.8 are read (mother and aunt have also congenital weak sight in this eye). Position and movement of the eyes are perfectly normal, exclusion of the left eye is followed by slight relative divergence. In answer to my question whether she had not previously squinted, patient replied that she did not know, it had always been a matter of dispute in her family; as, however, only the right visual field was seen in the stereoscope, we may be sure that squint had been present and that binocular fusion had been lost in consequence.

CASE 36.--Mrs. G--, aet. 49, report in March, 1876: On the right H. 3 D., V. 10/10, on the left H. 4 D., V. 10/40; a previously existing squint had disappeared of itself; the position of the eyes appears perfectly normal, but binocular fusion is not present; with red glass before one eye and a prism deviating in a vertical direction before the other, patient does not see double, but first with one eye and then with the other. The squint as well as its disappearance occurred however, at a time when it would have been regarded as an error to allow children to use convex glasses.

CASE 37.--Miss H--, governess, aet. about 30, came under treatment for asthenopic disorders; on both sides hypermetropia 2.5 D., visual acuteness 5/18. She owns to have squinted as a child,--it had often been remarked when she was at school. The squint gradually disappeared, but still occurred sometimes on keen fixation. The usual position of the eyes appears perfectly normal, and gives no suspicion of squint; convergence occurs on exclusion, sometimes with downward deviation of the right eye. With the aid of a red glass changing fixation is easily produced even without prisms, but never diplopia. At first only the left visual field was seen with the stereoscope; then the right on exclusion of the left eye; never both at the same time. According to this the condition of binocular vision speaks entirely for the fact, that squint had existed long enough to prevent the development of a normal binocular visual act, and the squint had disappeared without the help of convex glasses in spite of the hypermetropia.

CASE 38.--Bertha W--, aet. 18, reads with the naked eye on the right No. 0.75 at 10 cm., on the left only 1.75 at the same distance; hypermetropia of 6 D. is detected with the ophthalmoscope, with + 5.5 the visual acuteness of the right eye amounts at 1 metre to 1/9 (if the test-letters had contained No. 8 or 7.5, that would probably have been recognised also), on the left with + 5.5 D., V. = 1/12, with + 6 D. No. 0.8 is read with difficulty. Patient admits to have squinted as a child; no squint is present now; binocular fusion can be detected with prisms and she only squints now and then on the left side to assist vision, with which, patient states without being questioned, diplopia is combined. Spectacles have not been used till now.

I could cite several more such cases, but they would prove no more than these. At any rate the fact is settled that squint can disappear spontaneously, and without the aid of convex glasses even in high degrees of hypermetropia.

Wecker's announcement that "this spontaneous cure goes hand in hand with the progressive decrease of the accommodation, and depends on the fact that the squinter, on the strength of this progressive decrease, renounces more and more the aid which he finds in the increased convergence during the act of accommodation," only proves to how great an extent one may be prejudiced by theories. A limitation of the accommodation must necessarily increase the claims which are made on it, and can only afford inducement for calling forth all the help possible to support the accommodation.

The fact that squint spontaneously disappears after normal binocular fusion is completely and permanently lost, and in individuals who accommodate without the occurrence of a too strong convergence, notwithstanding their hypermetropia and without the help of the controlling influence of binocular single vision, seems to me quite irreconcilable with Donders' theory. Every motive for the same, hypermetropia, difference of refraction, monocular defective vision, &c., may not only be present without the occurrence of squint, they do not even prevent the spontaneous recurrence of a squint already cured. Of course I will not affirm that the causes made so prominent by Donders exercise no influence on the origin of squint, but will only emphasize the fact, that other causes exist which possess a greater influence, and which we can find only in the ocular muscles.

We have no experience as to whether this spontaneous cure occurs in myopia with divergent squint. This is not to be wondered at, as hypermetropia is present in the great majority of cases of squint, and the observations as to spontaneous cure are also rare in these. But I can vouch for one case where a slight absolute divergent squint, with crossed diplopia, which I treated shortly after its origin in a youthful myope, with prismatic spectacles, soon disappeared, and remained permanently cured.

The inclination to preponderance of the interni appears to be peculiar to youth, while later on circumstances change in favour of the externi, and that seems to me the chief ground for the spontaneous cure of convergent squint. The cure is not always complete; deviation still occurs on exclusion, or on particularly keen fixation; sometimes, however, also under conditions which can only be put down to a change in the elastic tensions of the muscles. The following is an interesting illustration of this:

CASE 39.--Miss S--, aet. 20, states that she squinted frequently as a child from her fifth to her tenth year; the squint gradually disappeared, but returned again from time to time during the last half year without apparent cause. The examination showed normal position of the eyes, slight convergence only on exclusion. Visual acuteness on the right 5/6, with atropine ophthalmoscopic and functional emmetropia, the visual acuteness is lowered to 5/12 by convex 1 D.; on the left hypermetropia 7 D., visual acuteness 5/18; the same degree of hypermetropia is found with the ophthalmoscope.

Crossed diplopia with a difference in height is distinguished with the aid of a red glass, the difference being corrected by a prism of 4 deg., with the base downwards before the right eye; a prism of 4 deg. with the base inwards suffices to place the double images immediately above one another. Spontaneous diplopia does not take place; only the right visual field is seen in the stereoscope. As patient lived in Brandenburg and only came to consult me occasionally I never had an opportunity of seeing the squint till she decided to stay here for some time. It was then seen that a peculiar oscillating deviation of the left eye of about 4 mm. inwards often occurred. As the previous spontaneous disappearance of the squint and the crossed diplopia made one fear that tenotomy of the internus might be followed by divergence, instillations were used in order to make a more exact measurement of the deviation,--by this means the condition was so improved in the course of a few weeks, that deviation no longer occurred even on exclusion of the right eye.

The spontaneous cure of squint may, however, be quite complete; indeed I have seen one case where convergent squint became divergent.

CASE 40.--A young lady, slightly over twenty years of age, showed on the right M. .75 D., V = 10/10, on the left H. 1.5 D., V. 10/40 to 10/30, and slight divergent squint on the left side. Crossed diplopia could be produced with a red glass, tenotomy of the left abducens sufficed to correct it. I had not concealed my doubts as to her statement that she had previously squinted inwards, but they were quite dispelled by a photograph taken about twelve years before, in which decided right convergent squint could not be mistaken. There is something to be said for the fact that it may have been a periodic squint, which occurred during the taking of the picture, as the photographer would have taken pains to hide a permanent squint in some way.

Conscious suppression of squint happens now and then, although very rarely.

CASE 41.--Miss A. L--, aet. 27, is stated to have commenced to squint in her first year, until at the age of eighteen she took pains to cure the habit, and with perfect success as far as regards the position of the eyes; the only disagreeable symptom was that she could no longer read with the naked eye. Spectacles were therefore prescribed for her, convex 5 D., but even they did not quite remove the trouble in reading; it was now a disagreeable, painful sensation to have recourse to squint in order to see more clearly. It was easiest to read with greatly lowered field of vision and with the help of a convex eyeglass as well as the spectacles. During the examination I found on the right hypermetropia 5.5 D., visual acuteness 5/12 to 5/9, on the left with + 5.5 D., V = 1/12. With convex 6 D. No. 0.5 was read at 12 inches from the glass, but not nearer, with normal fixation on both sides. The binocular near point (if we may employ this expression in the absence of normal binocular fusion) was considerably removed without the existence of paresis of the accommodation, despite the over-correction of the hypermetropia. It was rather a question of the same disposition of the relative amplitude of accommodation as I have previously described in a similar case. By methodical practice of binocular vision, I had taught an intelligent boy to fix binocularly, not only for distance, but also for near objects, but here again the relative amplitude for accommodation was diminished, so that with correct binocular fixation he could only read with convex glasses, which greatly over-corrected the hypermetropia. Finally, the normal amplitude of accommodation was restored by tenotomy of the left internal rectus, and when I saw the patient twelve years later I was able to satisfy myself that both were perfectly preserved. In the case of Miss L--, I believed I ought to give up all thoughts of an operation; the position of the eyes could not be improved, convex 5.5 D. eyeglass perfectly sufficed for distance, and convex 7 D. spectacles for reading. It seemed to me senseless to perform tenotomy merely to enable her to use the same glass for distance and for near objects, without any possibility of a cosmetic improvement. Moreover the condition of binocular vision quite confirmed the statements as to the previous squint. Diplopia could only be produced now and then with the help of prisms and red glass, at first the right visual field only was seen in the stereoscope, on closer observation also the left, but without binocular fusion.

Besides, the proved decrease of the relative power of accommodation in both these cases, marked by a voluntary suppression of the squint, does not appear in those cases where squint disappears of itself, the state of the accommodation, therefore, shows nothing unusual.

The spontaneous cure of squint teaches us two important facts, firstly, that the conditions of tension of the ocular muscles may change in the course of time, and secondly, that normal binocular fusion of the retinal images is not necessary for a correct position of the eyes; neither the spontaneous nor the operative cure of squint presupposes the presence or the restoration of a normal binocular fusion. If this were the case the operation for squint would not be of much use.

Observation of these cases further teaches, that treatment with convex glasses has prospects of success, particularly in periodic squint with hypermetropia, if squint can disappear spontaneously even without correction of the hypermetropia. At the same time, however, it appears that we need not form hasty conclusions about it. Periodic squint frequently arises during the earliest years of life, and everyone (perhaps with the exception of a few ophthalmologists) will at once reject the idea of allowing children of two to three years old to wear spectacles; constant wearing of spectacles even by older children seems to me not to be without risk as long as there is any chance of their falling when running, playing, &c., in which case the eyes as well as the spectacles would be in danger. As a rule I only order children to wear convex spectacles when they are distinctly indicated, and then only during sedentary occupations, when working and eating. Of course, exceptions may be made according to the individuality of the child, and the care with which it is looked after at home.

We are more rarely able to remove permanent convergent squint by means of convex glasses than the periodic form; that it is possible, however, I should like to show by an account of a patient, who offers, besides, other interesting peculiarities.