SQUINT.*

BY E. PARDEE BUCKE, M.D., LONDON, ONT.

Mr. President and Gentlemen: I have been asked to prepare a short paper discussing the subject of "Squint." While this is not a subject perhaps directly affecting the general practitioner, for he will not be called upon and would probably not care to undertake the treatment of this condition, it is a subject of which he should possess an intelligent conception in the interests of his clientele, as it is through the early treatment of the case that one expects the ideal result. Too often, perhaps, because of the failure of the family physician to advise wisely, the little victim of a strabismus is, through delayed treatment, doomed to years of ugly deformity, and, what is worse, to the deterioration and practical loss of a formerly good eye. I shall hope, therefore, through the consideration of the subject as it is at present understood to interest you for a few minutes, and perhaps the time required will not be altogether unprofitably spent.

A few words first, by way of introduction, regarding the attitude of the profession on the subject from the earliest times of which we possess a record: Hippocrates makes mention of deviation of the eyes, and considered it a result of epilepsy in childhood. He recognized it as an hereditary condition, but with Celsus, who makes mention of the subject, doesn't offer any suggestion as to treatment. Both evidently considered the deformity as irremediable. It is not until the seventh century that we find a celebrated Greek physician, Paulus Ægineta, suggesting a method for its treatment. He recommended that a mask be applied over the eyes of those afflicted, with two little openings therein, one for each eye to look through. He hoped thus to induce the crooked eyes to become straight.

Ambroise Paré, the pioneer scientific surgeon of France, who lived in the latter half of the sixteenth century, describes the condition and attributes it to the child's turning its eyes toward the light, while lying in its cradle, or to its imitating its nurse, who, perhaps, looked "cross-eyed" to tease or amuse it.

Other theories advanced from this period on included disease or malposition of the lens, influence of visual spirits over the position of the eyes, and defective cornea as being at the basis of the condition.

* Read before the London, Ont., Medical Association.

Erasmus Darwin, in a treatise published in 1801, asserts that squinting is caused by one eye being less perfect than the other, and he recommends that a piece of gauze stretched on a ring of whalebone be placed over the better eye for several hours every day, so as to reduce its vision to an equality with that of the poorer. We have in this suggestion a foreshadowing of the modern method of treatment.

Although as early as 1806 Tenon had published a description of the parts within the orbit, a description which is still classic, and though Sir Charles Bell had published the result of his investigations on the actions of the external ocular muscles in 1823, in which, though he failed in his deductions, the observations were distinctly original and epoch-making, it was not for some years that any operative procedure was undertaken for the correction of deviating eyes. During the first half of the nineteenth century the theory gained ground that squint was due to a contraction of an ocular muscle, and there was instituted then the procedure known as tenotomy. To the Germans we must give the credit of introducing this operation.

It was first described by Stromeyer, of the University of Erlanger, in 1838, and the first operation was performed by Dieffenbach in Berlin the following year. One of the earliest English surgeons to perform Dieffenbach's operation was P. Bennett Lucas, and he describes the procedure (which is a simple tenotomy of the internal rectus, done as close to the scleral attachment as possible), in the Provincial Medical and Surgical Journal of October, 1840. Like many other surgical operations, tenotomy for a few years was much overdone. It came to be a great show operation, the newspapers teemed with descriptions thereof, and surgeons surrounded themselves with admiring crowds to witness the performance of their marvellous "cures." In their enthusiastic desire to obtain astonishing results, the tendon was severed farther and farther back from its anterior attachment, and the muscle itself was very frequently cut through, needless to say, often with very dire results. In many cases the whole four recti were myotomized, and their connective tissue surroundings cut into freely, with an ultimate result such as you can readily appreciate.

From this system of charlatanism the profession was rescued by Von Graefe, who, when the operation was being decried and repudiated by conservative surgeons, restored confidence in it by insisting on a return to the original policy, that of performing the tenotomy as close as possible to the globe.

With the return to more moderate surgical treatment the pre

vention and cure of these cases without operation came to be considered, and it became recognized that the accommodation and refraction of the eyes had some bearing on the etiology of the condition, a theory which was formulated in the dictum of Donders that: 1. Strabismus convergens almost always depends on hypermetropia.

2. Strabismus divergens is usually dependent on myopia; a dictum, which, if it does not embody the whole truth, was a great advance in our conception of the subject, and has paved the way for more recent investigation, and the development of the modern method of treatment, which is sane in its conception and brilliant in its results.

In order to understand the cause and treatment of squint it will first be necessary to consider binocular vision-what it is and how it is accomplished. When the normal eyes are looking at a distant object the rays entering them are practically parallel, and the image of the object is impressed on each retina simultaneously. These images overlap (with the exception of a sector of about 35 per cent. on each temporal side) and are blended in the brain and perceived as one image. This blending of the two separate images constitutes binocular vision, and you will notice that it is purely a psychical act and has nothing whatever to do with refraction. In those cases which do not possess this faculty of binocular vision or who, in other words, do not possess the fusion faculty, either of two conditions must be present: Either the images from both eyes will be perceived separately, that is, diplopia will exist, or else the image of one eye will be suppressed and that of the other only be perceived.

The fusion faculty varies in its intensity in different persons. In the highest expression of it we have the sense of perspective, which is, happily, the prevalent condition, but there are cases in which it is very feeble, and, indeed, occasionally, entirely wanting.

It is normally a development of the first few years of life. Within two or three weeks after birth one notices that the infant has some feeble power of fixation. He is able to "fix" for a few moments only with one or other eye, but does not employ both in unison until he is about six weeks of age. These facts are simply demonstrated by reflecting a candle light into the child's eyes by means of an ophthalmoscopic mirror. The baby is readily attracted by this light, and as he looks at it you will notice a bright spot on the cornea, a reflection from the mirror. If the eye is "fixing" or engaging the light this "reflex" is seen practically in the centre of the pupil-as a matter of fact, it is slightly to the

nasal side of the centre, due, of course, to the fact that the true axis and the visual axis of an eye are not identical.

As I have just said, it can be readily demonstrated that in a normal case there is some power of binocular vision as early as the sixth week. It is necessarily very feeble, and the faculty is indeed quite unstable during the first few months of life. No doubt we have all noticed a young child squint on occasions, often due to a trifling disorder of the stomach and bowels.

However, while this faculty of fusion is absent at birth, it comes into evidence, as I have said, quite early in life, and gradually increases in intensity for months; indeed, it does not come to its highest development, and, therefore, its most stable condition, until about the sixth year.

Now this faculty, while it is a normal possession of the race, is wanting or deficient in a certain small minority of persons. It is this lack of the fusion sense that is the basic cause of squint. In those cases of alternating refractive errors, especially hypermetropia, may contribute to produce squint, but they are never essential to its appearance. In those cases of alternating strabismus in which we find sometimes one eye turning in and sometimes the other, it is quite usual to find the refraction of the eyes normal, and each eye being used in turn, the vision of each is preserved and is usually normal also. These cases are, however, much the worst from the standpoint of treatment, as it is in them that the fusion sense is quite wanting and incapable of development.

Because constant convergent squint greatly preponderates over the other varieties, I think it will be well to devote the most of our time to a consideration of its phenomena, causes and treatment. We will thereby avoid confusion, and the main purpose of our paper will be served if we succeed in obtaining a clear conception of this condition.

The term squint implies, besides the deviation of the eye (which is only the outward and visible sign of the anomaly), four other factors as being present, namely:

2. Deficiency of the fusion sense, as already mentioned.

3. Suppression of vision of the squinting eye.

4. Greatly diminished vision of this squinting eye; and

5. There is usually present a refractive error, hypermetropia most often, which is present in both eyes.

Let us first consider the deficiency of the fusion faculty. The instrument employed for the investigation and treatment of this anomaly is known as the amblyoscope, and was devised by Claud Worth, of Moorfields Eye Hospital, London.

It is essentially a stereoscope made in the form of two tubes of about an inch and a half diameter, which are hinged at the proximal end and supplied with convex lenses, to render unnecessary any effort of accommodation in order to focus the image in the objectslides, which are at the distal end of the tubes. These tubes, instead of being straight, are in reality composed of a very short tube at the proximal end joined at an angle of 120 degrees with a longer tube, and at the junction of the two is situated a mirror.

Now, if a person with normal fusion faculty looks into this instrument and suitable object-slides be placed in position, it will be found by adjusting the direction of the tubes that a position will readily be found in which he can fuse the two images, seen separately with either eye. Moreover, it will be found that the tubes can be approximated and separated to the extent of several degrees, while fusion is still maintained. In a case of developing squint, however, it will be found that the degree to which the direction of the tubes can be changed is extremely limited. This is a very short sketch of the method employed, but will probably be sufficient to give you an idea of it. Worth has found by this means that in all his cases of squint the faculty of fusion is limited. Moreover, another point which is very convincing as to the causal retention. of this defect. He was enabled to examine a considerable number of younger brothers and sisters of his squinting patients, and in some of these was able to observe their cases at later periods. Of 157 children he found the fusion faculty well developed in 106. None of these have subsequently squinted. Of 37 cases which he considered doubtful, 6 have since squinted, and of 41 whom he considered very deficient 9 afterwards developed squint. Which data goes strongly to show the importance of the relation of deficiency of fusion sense to squint.

Now as to the rationale of the development of the inward deviation:

If we look at a distant object, the rays entering are parallel and the axes of our eyes are straight ahead, our accommodation being at rest. If, however, we now fix our gaze on a near object, say a book at reading distance, we have to make use of our accommodation, and at the same time we have to converge our visual axes. These two functions of accommodation and convergence have been always so closely associated that they are practically indissoluble, and it is next to impossible to perform either act without the other.

This effort of accommodation, which is equal to 3 dioptres in a case with natural refraction, means, of course, a stronger effort in hypermetropes.