Part 10

CASE 42.--Marie S--, aet. 6, came under treatment on November 28th, 1878, for recent superficial marginal keratitis of the left eye, which was treated first with atropine; a few days later slight blepharitis appeared also. On December 9th, atropine was discontinued; on the 14th, the position of the eyes was still quite normal; on the 19th, permanent convergent squint of the left eye was present. Squint had never been observed in the child before. Double images were voluntarily announced without my having inquired for them, they were homonymous and moved further apart at both sides of the visual field. On December 28th, the squint still remained the same, the double images were, however, scarcely noticed by the child, so quickly do the relations of the corresponding points of the retina change even in the sixth year. Both eyes were atropinised for the better determination of the error, when a slight degree of hypermetropia was shown by the ophthalmoscope, at most 1.5 D.; certainly a higher degree was specified when the vision was tested, namely, on the right H. 2.5 D., V. = 5/12 to 5/9, on the left H. 1.75 D., V. = 5/18, probably, however, the objective determination was more exact than the child's statements. If a child of six knows its letters and figures sufficiently well to undergo a visual test, that is as much as we can expect; in any case, however, the forms of the letters and figures which we use for the visual test are not easy to children, and the more objective the way in which the child comprehends the examination, the less it perplexes itself by guesses, but only names the letters which it really distinctly recognises, the less deficient are the reports as to the visual acuteness; the proportionately larger retinal images are still recognised, even if they are no longer quite distinct, but consist of diffusion circles as a result of over-correction of the hypermetropia. That these observations were right for the case in point, is seen by the fact that eight days later, after the effects of the atropine had passed off, the child could see better with the naked eyes than with convex glasses, and that finally, when it had become accustomed to the forms of the letters and figures employed, V. = 5/9 was announced on the right, and V. = 5/12 on the left.

Mydriasis by atropine had no influence whatever on the squint, therefore, on December 31st, convex spectacles 2 D. were prescribed for permanent use. On January 4th, the linear deviation still amounted to 4 mm.; on January 15th, convergence was no longer discernible for distance, with red glass double images occurred at once; on January 21st, no squint was present, and binocular fusion was again restored; prisms immediately caused double images, the facultative divergence was = 0. I thought it prudent to order the spectacles to be worn till the middle of March, when they were discontinued; squint has not appeared since then.

In this case it is impossible to determine what really induced the squint, certainly not the slight hypermetropia, for the child had already learnt to read without squinting, and was spared any exertion at the time when the squint arose. Neither can we look for the cause in the inflammatory condition for which the child first came under treatment, this was as good as removed before the squint began and no exciting condition worth naming was present. Moreover, most cases of squint arise without directly assignable causes. It seems to me unquestionable that the permanent use of convex glasses made the pathological relation between accommodation and convergence normal, before it had firmly established itself, and before the muscular relations were definitely changed, and that the squint was really thus cured. But if the child had not been under treatment I should scarcely have seen the squint so soon after its first occurrence, and most cases of squint arise at an age which forbids the permanent wearing of spectacles.

If permanent squint has already existed for a long time, nothing can be hoped for from the use of convex glasses; for the conditions of the muscles are then so much changed, that they are no longer influenced by such weak physiological powers. I have been able to convince myself in the case of several squinting persons, who conscientiously wore the spectacles prescribed for them elsewhere, that the squint was concealed by this means; that may suffice in some cases, but if it is a question of young girls we may well ask, which is to be preferred for appearance sake, squint or spectacles.

Tenotomy effects essentially a cosmetic improvement--its object is to restore the correct position of the eyes by equalising the elastic muscular tensions. The means at our disposal are, the simple separation of the tendon of the too-tense muscle from the sclerotic, the distribution of the operation between both eyes, and finally, increasing the strength of the antagonist by moving forwards its insertion.

The method of tenotomy as I carry it out is as follows: The conjunctiva is seized with fine forceps exactly over the insertion of the muscle to be divided, and the fold thus raised cut into with the smallest possible wound. Provided we operate on the right spot we enter this opening with the forceps and immediately seize the tendon close to its insertion on the sclerotic, which is drawn forwards, as was the conjunctiva, and loosened with flat, curved scissors, the points of which must be rounded off. The incision must only be large enough to allow a small hook with a knob to be inserted through it and behind the insertion of the tendon, which is now lifted up and divided with fine pointed scissors close to its insertion into the sclerotic. It is important to make sure that a few threads coming off from the tendon at the ends of the insertion do not remain uncut; we can only consider the operation to be complete when the hook, carried behind the edge of the insertion made clearly visible by the foregoing proceeding, slides up to the margin of the cornea without any interruption.

The method of performing advancement is as follows: An incision is made in the conjunctiva over the tendon of the muscle to be brought forward and just at the outer bend of the latter, then loosened together with the subconjunctival tissue to the corneal margin; it is desirable to carry out this loosening close to the sclerotic, as the flap of the conjunctiva thus formed must afford sufficient support to the muscle to be brought forward. Then the capsule of Tenon is cut into at one edge of the insertion, a flat, curved, blunt hook without a knob is carried between muscle and sclerotic, and out again at the other edge of the insertion. We must be careful to get the muscle as clean as possible on the hook in the whole width of its insertion, that is without the capsule of Tenon, for the suture put in ought only to enclose the muscle, without at the same time dragging the capsule of Tenon. For the suture I always use fine catgut which is provided at both ends with curved needles; needles of slightly different form may be chosen in order that the threads may be easily distinguished from one another. A needle is carried behind the hook from each thread, one through the upper, the other through the lower edge of the muscle, between it and the sclerotic, then the thread is tied in a knot on the muscle to make sure that it does not slip back through the loop of the thread after its separation from the sclerotic. Then the threads are knotted on the muscle, and the insertion is separated from the sclerotic. As the edge of the insertion is now exposed we can see how the land lies, and can carry the threads exactly in the direction of the muscle under the conjunctiva to the corneal margin, where they are passed through, and ends tied in a knot. By this means the muscle is drawn forwards precisely in its normal direction and stretched tighter. The wound in the conjunctiva is closed by a suture.

It is desirable to slightly stretch the muscle that is to be brought forward in both the above operations while the eye is rolled towards the opposite side with forceps. Further, as I always operate under chloroform, I dispense with the usual test of the immediate effect of the operation; such tests have no value before the effects of the narcotic have completely disappeared, and one must be sure in the way above described that no single fibres are left undivided. I lay special stress on the fact that the operation is so performed, that it is able to bring about the desired mechanical effect.

The immediate mechanical effects of simple tenotomy may be easily deduced; the divided muscle retracts as far as its elasticity and its relations with the surrounding tissues permit. With reference to the internal and external rectus with which strabotomy specially has to do, those relations come principally under observation which the front part of the muscle enters into with the conjunctival tissues; the greater the extent to which we loosen these relations, the farther the muscle can retract. If it is a question of obtaining a greater effect, I am accustomed to loosen the subconjunctival tissue at the front part of the muscle behind the lachrymal caruncle to a greater extent--this offers the additional advantage that the distorting sinking in of the caruncle is avoided.

By dividing one rectus its antagonist gains in proportion and rolls the eye towards it as far as its own elastic tension and the powers still present on the other side permit. The improvement in position which we strive to obtain is brought about by the elastic power of the antagonist, and not by the tenotomy itself, and it is seen by this then, that the term strabotomy simply, does not quite express the circumstances of the case. Tenotomy is nothing more than the means for procuring a preponderance of the elastic power of the antagonist, therefore the effect attainable on the position of the eye does not depend solely on the division of the muscle, but to a great extent on the elasticity of the antagonist, and may be nullified at once, if the antagonist does not perform what we expect from it, and that may happen without our being able to foresee it. For example:

CASE 43.--Julie B--, aet. 21, is stated to have squinted inwards since her third year, principally with the right eye, but with occasional alternation. The deviation amounts to 5 mm., the outward movement of both eyes is perfectly normal. Hypermetropia 2 D., visual acuteness 5/18 on both sides. Ophthalmoscopically with atropine the same degree of hypermetropia. Tenotomy of both interni on March 7th, 1879. On March 14th, deviation 5 mm., just as before. Then renewed division of the internal rectus and shortening of the external rectus of the right eye; but still the result was insufficient. Therefore, on March 21st, the left eye was dealt with in the same way. By this means a normal position of the eye was obtained, which was perfectly preserved when I saw the patient again a year and a half later. Everything led me to suppose beforehand that simple tenotomy of both internal recti would perfectly suffice to remove the squint, yet it was of no use, but had to be supplemented by shortening both external recti. In such cases I would not advise repeated tenotomies, but for the correction of the insufficient result as soon as possible by advancement of the antagonist.

Advancement very frequently gives us an opportunity of seeing with our own eyes the insufficiency of the antagonist and its faulty anatomical development. We may suppose this to be the case if the mobility towards the side of the antagonist is faulty, however that is no proof; considerable insufficiency may co-exist with perfectly normal mobility. If limitation of movement is present, to which insufficiency of the antagonist may be assigned as the cause, or if it is desirable to obtain the greatest possible result by means of an operation on the squinting eye, we must combine tenotomy of the deviating muscle with advancement of the antagonist. The same is stretched tighter, and rolls the eye more strongly to its side, and we can regulate the degree of shortening of the muscle, by the distance behind the insertion at which we place the threads in the muscle, also by the distance from the corneal margin at which we place our anterior sutures, although the rapidly increasing ductility of the conjunctiva makes it desirable that we should not go far from the corneal margin.

The exact rules for the application of the methods of operation differ according to the nature of the case under consideration. If we contemplate first the largest group, that of the ordinary permanent convergent squint, the choice of the method is principally determined by the average degree of deviation, the condition of error, and the visual power, lastly by the mobility, particularly the outward movement of the eyes. If the visual power of both eyes is nearly the same, or if the squinting eye possesses such a visual acuteness that it can be used in fixation, it is advisable as a rule to arrange the relations of the muscles as equally as possible in both eyes--simple division of the internal recti is therefore, as a rule, to be performed in both eyes. If, on the other hand, the vision of the squinting eye is in a high degree defective, so that only the better one is used, it is generally advisable to confine the operation as far as possible to the squinting eye; in that case, tenotomy of the internal rectus and advancement of the external rectus is usually indicated in the squinting eye, and frequently suffices.

Deviations which are so slight, that the careful division of both interni without loosening the conjunctiva at the front part of the muscle makes us fear an excessive result, are seldom the subject of operative treatment; if the deviation is slight but still a disfigurement, if it amounts to 3 to 4 mm., distribution between both eyes is suitable, because, when the squinting eye possesses requisite visual acuteness it is put into fixation more frequently after the operation than before. Under these circumstances, if the operation is confined to the squinting eye, and a sufficient result is thereby obtained, as soon as this eye is used for fixation a remarkable secondary deviation of the other eye occurs, which is not the case if the tensions of the muscles have been balanced by an operation on both sides.

A deviation of 5 to 6 mm. may usually be balanced by means of simple double tenotomy if the conjunctiva is considerably loosened behind the caruncle; not unfrequently, however, we must be careful to strengthen the result by means of the after-treatment. Commonly, during the first twenty-four hours, the result appears to be quite satisfactory, whilst on the second or third day troublesome convergence again sets in. By practice of the outward movement we then usually obtain at once a perceptible improvement of the position. Both eyes are repeatedly turned as far as possible to the right and left, by which means is obtained on the one hand, exercise of the external recti, on the other, increase of the effect of the tenotomy of the internal recti. I order these exercises to be begun on the day after the operation.

Besides this, however, in the relation between accommodation and convergence of the visual axes there is a very essential cause which is able to lessen the immediate effect of the operation. Persons who squint inwards, even if emmetropic, have the habit of combining accommodation for near objects with excessive convergence of the visual axes, thus the immediate effect of the operation is diminished as soon as they begin to use their eyes again. This happens, not by a lessening of the effect of the tenotomy, which could, indeed, only be increased by exertion of the internal recti, but in that sufficient time is not given for the external rectus to regain its normal elastic tension. Nothing is changed at first by the operation in the customary relation between accommodation and innervation of the internal recti--it is a question, then, of avoiding every exertion of the accommodation for some time, in order that no inducement for strong convergence should be given. I am accustomed, therefore, even in the case of emmetropes, to paralyse the accommodation by means of atropine twenty-four hours after the operation, and to remove the far-point by convex glasses to about 0.70 m.; the spectacles must, of course, be worn constantly, for only by that means can we be sure that they are always used for near objects. After a few weeks the spectacles are discontinued, first for distance, then for near objects also. This after-treatment is not necessary under all circumstances; but I have repeatedly assured myself that an originally sufficient result which perceptibly diminished after a few days, could by this means be restored and permanently maintained even in emmetropes.

In the case of hypermetropes, we more often meet with the same experience; in permanent convergent squint it is by no means necessary to neutralise the hypermetropia permanently after the operation, but it happens here more often than in emmetropia, that a perfectly good immediate effect is lost within the first week after the operation, and can be restored again by permanently wearing the correcting convex glasses. In such cases also, I am accustomed after a few months to discontinue the spectacles for distance as an experiment, while they are still used for working.

Simple tenotomy of both internal recti does not, as a rule, suffice for deviations of more than 7 mm.; therefore, even if both eyes possess good visual power, we must still decide on tenotomy of both internal recti together with advancement of the external rectus of the squinting eye, or anticipate repeated tenotomies of the internal recti, or seek to obtain the greatest possible effect by means of slight modification of the method of procedure.

Provided that the muscle was completely divided, and sufficiently loosened from the conjunctiva during the first operation, a repetition of the tenotomy can only aim at an increase of the effect if the elastic tension of the antagonist has improved in the meantime. I very rarely therefore carry out repeated tenotomies; it seems to me much more desirable to obtain a sufficient result at one operation whenever that is possible.

In some cases where there is a deviation of 7 to 9 mm., the effect of the tenotomy may be increased by inducing a strong divergence immediately after the tenotomy of the internal recti, which is maintained for 6 to 8 hours. For this a thread is passed through the conjunctiva at the outer edge of the cornea about 4 mm. above the horizontal meridian, and out again about 2 mm. below the horizontal meridian, then from below upwards in the same way, so that the conjunctiva is contained in a loop. The needle is then passed through the external canthus from the conjunctival surface and fastened by tying it over a roll of paper. This procedure is only to be recommended in exceptional cases; a greater effect on the internal recti is thus obtained, while with reference to the position the result depends on the elastic tension of the external rectus just as in simple tenotomy.

If the squinting eye has only an unavailable visual acuteness, a combination of tenotomy of the internal rectus with shortening of the external rectus is the best procedure. As a rule, simple tenotomy of the internal rectus of the squinting eye is of very little use in such cases, as the abducens, weakened by continual extension and wanting practice, places too slight an opposing power in the balance. The chief effect of the operation then devolves on the other solely available eye, which is not a desirable circumstance, and is also frequently insufficient. On the other hand, the combination of tenotomy of the internal rectus with advancement of the external rectus enables us successfully to change the opposing muscular tensions. As a rule, the operation may be confined to the squinting, weak-sighted eye, as that suffices to obtain a correction of 5 to 6 mm.

If the result is seen to be insufficient, it may be supplemented by tenotomy of the internal rectus of the other eye; in the case of deviations of more than 7 mm. it is advisable to divide the operation between the eyes in this way.

The suture has a special use in so-called artificial strabismus; that is, in those cases where convergent is converted into divergent squint through unskilful treatment, or where tenotomy of the abducens, performed on account of "insufficiency of the internal recti," is followed by convergent strabismus. I have not found confirmation of the fear expressed by Arlt, that the method proposed by me could be scarcely practicable if it is a case of the advancement of a muscle too far forward, and I have corrected a large number of such cases in other practices. It is seldom profitable to take up things in which others have been unsuccessful, but it bring its own reward in the case of artificial squint.

Periodic convergent squint offers a less certain ground for the operation. The change between normal position and a very considerable squint gives rise to the fear that an operation which would be able to remove the convergence might finally induce divergent strabismus. This fear is certainly not groundless, but at the same time it must be remembered that, with the exception perhaps of a few cases of clearly accommodative deviation, elastic preponderance of the internal recti or insufficiency of the external recti is generally the cause of periodic squint also. I have frequently, in periodic squint, performed double tenotomy of the internal recti with the slightest possible loosening of the conjunctiva. I have also attempted to confine the operation to the shortening of the external rectus without loosening the internal recti and with success, but not frequently enough to be able to deliver a certain opinion upon it.

In periodic squint, the first care must always be to determine the condition of refraction, if possible with atropine, and to neutralise or over-correct hypermetropia if present. If squint is absent during the use of convex glasses, which happens frequently under these circumstances, the operation offers no further advantages, as the constant use of convex glasses afterwards can hardly be avoided. If the periodic deviation continues to exist, the operation can be carried out according to the above rules and so as to cause a slight effect.

The final result is usually attained after two to three weeks in convergent squint; it is better to allow a slight degree of convergence to exist, as divergence, however slight, existing at this time, brings with it the fear of a gradual increase. It happens occasionally, that after years, convergence asserts itself again; I have observed it in spontaneous (see Case 39) as well as in operative cure of squint; still, this is so unusual, that I should like to give an illustration of the latter observation on account of its rarity.