Schweigger on Squint Part 9

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 gla.s.ses to about 070 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 circ.u.mstances; but I have repeatedly a.s.sured 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 gla.s.ses. 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 antic.i.p.ate 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 repet.i.tion 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 pa.s.sed 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 pa.s.sed 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 circ.u.mstance, 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 gla.s.ses, which happens frequently under these circ.u.mstances, the operation offers no further advantages, as the constant use of convex gla.s.ses 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 a.s.serts 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 ill.u.s.tration of the latter observation on account of its rarity.

CASE 44.--Hedw. von L--, aet 10, came under treatment in April, 1874, for convergent squint on the left side which arose in her seventh year, with occasional alternation. Emmetropia, determined with atropine on both sides and good visual acuteness. Diplopia was present at the commencement of the squint. Patient can only be rendered conscious of double images by the help of a red gla.s.s and vertically deviating prisms. Double tenotomy of the internal recti effected a normal position, and at the end of December, 1874, the continuance of the same could be proved as well as binocular fusion with prisms. At the beginning of 1880, I was informed that from time to time periodic squint had occurred with diplopia. In the middle of March, I had an opportunity of seeing the young lady. Myopia 2 D. had meanwhile developed on both sides, visual acuteness almost = 1. The position of the eyes was perfectly good, slight convergence occurred during covering, h.o.m.onymous double images with a red gla.s.s which, at a distance of 5 m., were joined by a prism of 8; stereoscopic fusion was not perfectly certain. A true squint could not be proved. On April 3rd, as patient stopped for a few hours on her journey through, a striking convergent squint of the left eye was seen. The deviation amounted to 4 to 5 mm. Single vision existed at a distance of 15 to 20 cm., then h.o.m.onymous double images appeared, which did not correspond to the objective deviation; the double images were however corrected by a prism of 6 (base outwards) for an object 5 m. distant.

We cannot conclude the consideration of the operative treatment of convergent squint without once more returning to the relation between the line of vision and the position of the cornea. The angle [Greek: a]

still deserves mention in a few thankful words--_hic mihi angulus praeter omnes ridet_--it is a very useful guide in tenotomy. In tenotomy we may count as gain the apparent divergence which it causes in hypermetropes who do not squint. We obtain a perfect cosmetic result, while a convergence, objectively determinable, but not otherwise easily visible, continues to exist. It would be folly to exceed this; and for cases where binocular fusion does not exist, and where diplopia is not present, to wish to remove this covered convergence due to the angle [Greek: a], the cosmetic result would be impaired by it.

Those cases where it is a question of uniting h.o.m.onymous double images are very instructive when considering tenotomy. Only when squint arises after childhood (after the fifteenth year) does it cause troublesome diplopia, this accords naturally with the laws of normal binocular fusion learnt meanwhile. (On the other hand those cases, which sometimes occur after tenotomy, with the double images in a position which does not correspond to the normal physiological laws and which cannot therefore be united by prisms, are naturally unsuitable for the operative removal of diplopia.) Cases in which convergent squint is followed by troublesome double images, appear, with the exception of the hysterical form mentioned on p. 41, chiefly in myopia, more seldom in emmetropia, and very rarely in hypermetropia; for if the conditions contained in the ocular muscles are coincident with hypermetropia, squint usually arises in the course of childhood, before normal binocular vision has become a fixed habit.

As the cases here under consideration are not very common, I will relate a few from which conclusions may be derived as to the effect of tenotomy.

CASE 45.--Miss von B--, aet. 14, came under treatment on May 1st, 1875, for diplopia, which made its appearance about a year previously.

Emmetropia and full visual acuteness exist on both sides. The double images are h.o.m.onymous and further apart on both sides of the visual field. At first single vision existed only to about 075 m.; gradually, however, the area of single vision was extended by practice of the outward movement, supported by the use of prismatic spectacles, so that after a year patient could see singly to a great distance. This improvement was not maintained. At the beginning of 1879, diplopia was again present to a troublesome degree, particularly on looking downwards; on looking straight forwards the left eye showed a slight convergent deviation, amounting at most to 2 mm. During various examinations the distance of the double images was stated to be now less, now greater, a prism of at least 5, at most of 9, was requisite for correction. Diplopia was at once removed by tenotomy of the left internal rectus, with very slight loosening of the conjunctiva, and has not appeared since.

CASE 46.--Miss A--, aet. 17, suffered from diplopia for a few weeks, a year and a half ago; for the last half year the diplopia is continuous, and striking squint is stated to be sometimes present. Myopia 2 D. on both sides, visual acuteness = 5/9. On fixation of an object about 4 m.

distant, the left eye deviates inwards at most 2 mm.; h.o.m.onymous double images, with a red gla.s.s and on correction of the myopia, which were united by means of prism 14 at a distance of 5 m., without red gla.s.s (with retinal images alike on both sides) prism 8 sufficed to unite them. If a vertically deviating prism is held before one eye, the double images stand just above one another when looking at an object 20 cm.

off, on nearer approach they are crossed. On May 3rd, 1879, tenotomy of the left internal rectus with small conjunctival wound without loosening of the conjunctiva, and union of the conjunctival wound by a suture. On May 8th, single vision, also with correction of the myopia and with red gla.s.s. Facultative divergence = 2. On May 14th, with correction of the myopia, there was still single vision for distance; however, with red gla.s.s double images occurred again; and at the end of May the condition of the double images was just the same as before the operation. On vertical shifting of one visual field by a weak prism the double images are brought into a vertical line by means of prism 16, with the base outwards. Therefore, on July 1st, the right internal rectus was also divided, with small conjunctival wound without loosening of the conjunctiva and without suture. The evening after the operation slight divergence on covering. On July 24th, binocular single vision is present; with red gla.s.s h.o.m.onymous double images at 5 m., corrected by prism 4. This time the result was final; for in the middle of October, three months after the operation, the report was exactly like the one of July 24th above stated.

CASE 47.--Mrs. A--, aet. 33, has suffered for six months from alternating convergent squint with diplopia, for a short time even a parallel position is still possible. On the right myopia 4 D., V. = 6/12. On the left myopia 4 D., V. 6/9. Single vision occurs to 22 cm., at a greater distance h.o.m.onymous double images, whose mutual distance remains the same when looking to one side. On correction of the myopia a prism of at least 32 is necessary for the union of the double images for an object at 4 m. Two days after tenotomy of the internal recti on both sides, the facultative divergence amounted to 7 (at 4 m.) on correction of the myopia. Single vision was also present when looking strongly to one side, and with differentiation of one retinal image by a red gla.s.s.

CASE 48.--Mr. B--, aet. 32, first observed the occurrence of diplopia at the beginning of April, 1877. Myopia 6 D. is present in both eyes, visual acuteness on the right 1/2, on the left rather more than 1/2 (5/9). The double images are h.o.m.onymous and sometimes (not always) move farther apart at the limits of the visual field. Patient could only decide after two years, in July, 1879, on the operative treatment then proposed. Diplopia continued to exist; single vision was only now and then possible for a short time. On correction of the myopia (if one eye is provided with a red gla.s.s) prism 12 suffices for union of the double images. If one visual field is moved in a vertical direction by a prism of 5 during the trial of convergence, prism 38 is necessary in order to equalize the lateral deviation of the double images, and to place them perpendicularly above one another for an object 5 m. distant. On July 14th, tenotomy of the internal rectus of the left eye; single vision next day on correction of the myopia, prism 6 is overcome by divergence; if, however, double images are produced by a vertically deviating prism of 5 they immediately show h.o.m.onymous lateral deviation, which is corrected by prism 18 at a distance of 5 m.

Two months after the operation the diplopia was certainly better, but by no means removed; squint occurred periodically as before, so that sometimes single vision was possible at 3 to 4 m., sometimes troublesome diplopia was present.

During the test of convergence with prisms deviating in a vertical direction, a prism of 38 was necessary for the equalization of the lateral deviation just as before the operation. Therefore in the middle of October the internal rectus of the right eye was divided, and the conjunctiva loosened as far as the caruncle. Three days afterwards single vision, facultative divergence = prism 5; in the trial of convergence, equalization by means of prism 8. In the middle of October, two months after the operation, diplopia had not appeared again; facultative divergence = 0; h.o.m.onymous double images are produced by a red gla.s.s before one eye, slight convergent deviation on covering it, which in the trial of convergence is equalized by prism 20. The preponderance of the interni was now so far lessened for the ordinary use of the eyes, that permanent binocular single vision was possible.

Notwithstanding the small number of these cases we may conclude from them, that h.o.m.onymous diplopia in typical convergent squint (not paralytic) can only be corrected occasionally by one-sided tenotomy when the deviation is slight. As a rule it is necessary to distribute the operation between the eyes. A result seems attainable by means of simple tenotomy on both sides, which is expressed by prism 20 in the trial of convergence. In future cases it would be desirable to determine during correction of the anomalies of refraction (1) the weakest prism which is able to unite the double images at about 5 m. distant (without red gla.s.s); (2) the distance at which the double images stand apart from one another during the trial of convergence with prisms deviating in a vertical direction; and (3) the prism which brings the double images immediately above one another in the case of objects about 5 m. off.

Next to the cases above discussed stand those where convergent squint remains after paralysis of the abducens; at the same time slightly defective mobility and a distinct moving apart of the double images towards the affected side can usually be detected. In a few such cases I could restrict myself to tenotomy of the internal rectus of the affected eye, but in those cases which I was able to attend to more particularly, double tenotomy was necessary, and did not always suffice. Here also the advancement of the external rectus is suitably applied, which I should like to ill.u.s.trate by means of a few examples.

CASE 49.--Mr. B--, aet. 20, was seized by paralysis of the abducens of the right eye in November, 1877. In April, 1878, convergent squint was still present, and as it continued patient decided on an operation in February, 1879. Both eyes are emmetropic and possess full visual acuteness.

Immediately before the operation the double images were united at 4 to 5 m. in the horizontal plane by a prism of 39; towards the right their deviation rather increased. The measurable deviation amounted to 4 mm.

in the right eye, the secondary deviation of the left to 5 mm. In order to proceed carefully, I confined myself at first to tenotomy of the internal rectus of the right eye. After the s.p.a.ce of a week single vision was present at the distance of 1 metre in the middle line and at the height of the eyes; at about 5 m. h.o.m.onymous double images corrected by prism 12, together with slight difference in height (= prism 4, base upwards before the right eye). The area of double vision extended from the limit of the right visual field to about 20 the other side of the middle line.

This result would have sufficed perfectly for a cosmetic tenotomy where binocular fusion did not exist; the annoyance caused to patient by diplopia, however, was only slightly relieved. I decided, therefore, on a second operation, not without fearing an excessive result, and performed tenotomy of the left internal rectus with a very small conjunctival wound and by closing the wound by means of a suture. The result was by no means excessive, for it was perfectly _nil_, apparently even negative at first, for a few days after the operation the area of single vision approached the eye to less than 05 m. and at 4 to 5 m. a prism of 20 was requisite for correction; however, eighteen days after the tenotomy of the left internus everything was as before. Single vision to 1 m. while prism 12 corrected for a distance of 4 to 5 m. The tenotomy then had no effect at all on the position of the eye; however, the restriction of movement dependent on it, a.s.serted itself in that the double images were crossed on the limit of the right visual field (about 45 towards the right). On the supposition that this insufficient result might be caused by the suture of the conjunctival wound I decided to repeat the separation of the internal rectus. The agglutination of the muscle with the sclerotic is so slight for two to three weeks after the operation that the strabismus hook perfectly suffices to sever the connection; no suture was put in, but the result again was _nil_, and on the day after the operation single vision was only present to 05 m. in the middle line, just as after the previous tenotomy of the left internal rectus. It was now clear that the result with respect to the position of the eye was only unsuccessful because the antagonist did not do its duty. I shortened the abducens (without touching the internus again). The immediate effect, during the chloroform narcosis, was a terrible divergence, but on the same evening it was less, and twenty-four hours after the operation with a red gla.s.s, h.o.m.onymous double images were present close together at a distance of 4 m. Ten days afterwards binocular single vision was insured, facultative divergence = 3 at 4 m., crossed double images towards the limits of both visual fields, but only on moving the eyes in a lateral direction; no practical use was made of this. If one could have diagnosed beforehand the insufficiency of the externi a.s.suredly present here, which was probably the reason for the development of squint on the healing of the paralysis of the abducens, one would have been able to combine shortening of the right abducens with tenotomy of the internus in the first operation, whereas the necessity for the advancement was only shown by the abnormally slight effect of the tenotomy on the left side. According to accounts received by letter the favorable result has continued.

We obtain a result more quickly by the immediate advancement of the abducens. For example:

CASE 50.--Mr. K--, aet. 29, suffered from paresis of the right abducens in the autumn of 1877. In December, 1878, convergent squint is present, linear deviation 5 mm. (scarcely more on the left than on the right).

The defect of movement towards the side of the right abducens amounts to about 2 or 3 mm. Diplopia is present in the whole visual field with increase of the deviation towards the right. Emmetropia and full visual acuteness on both sides. Tenotomy of the internal rectus and advancement of the abducens of the right eye at the end of December. Three weeks later single vision is present in the middle line; on the left limit of the visual field crossed double images, on the right side h.o.m.onymous ones, beginning about 20 from the middle line. The result was by no means excessive.

In convergent squint with congenital paresis of the abducens, not much can be attained without shortening the abducens. Of course only the squint can be removed, not the paralysis, but if once a correct position is attained for the middle line, cosmetic demands are satisfied; the outward movement, which is absent, must be replaced by turning the head.

The chief method for absolute divergent squint is the combination of shortening with tenotomy of the externus. If the impulse for convergence is once lost, so that an a.s.sociated movement occurs in place of an accommodative one on fixation of a point situated on the middle line, a removal of the squint cannot be obtained by simple tenotomy of the externi--another proof that a change of position of the eye is by no means a necessary result of tenotomy.

Moreover, this slight aid given by tenotomy has its ground not solely in the condition of the opposing recti muscles. In other practices I have seen cases enough in which tenotomy of the externi, performed on account of relative divergence, was followed by convergent squint, just as injudicious division of the interni may induce divergent squint. It is probable, therefore, that the faulty effect of simple tenotomy in permanent absolute divergent squint depends on other causes, which, in my opinion, are to be found in the obliques. The loop formed by the obliques round the posterior circ.u.mference of the eye is most stretched, when the visual line falls in with the muscular plane of the obliques in a medial direction of the eyes. On the whole, then, it is proved that the obliques are extended on turning the eyes inwards, but shortened on turning the eyes outwards by means of their muscular action. In divergent squint, if the movement inwards occurs but seldom or not at all, the obliques consequently are not extended in a normal way--it follows then that they lose in ductility, offer greater resistance to the inward movement, and by means of their elastic tension continually draw the posterior pole of the eye inwards and the cornea outwards. As in strabotomy we cannot get at the obliques, it seems all the more desirable to offer them stronger resistance by greater tension of the internus by means of advancement. Certainly tenotomy of the external rectus of the fixing eye is as a rule also necessary. A sufficient result is usually thus obtained at once; if it is much lessened in the course of one or two months there is nothing to prevent the repet.i.tion of the tenotomy of one or the other external rectus.

The innervation for the movement of convergence is not always perfectly lost; it withdraws itself from the influence of binocular fusion because this is gradually forgotten while a convergence, even if an insufficient one, unites itself with the effort of accommodation. If we ask such patients to fix a large object lying near, a pencil, for example, they cannot usually converge upon it, whilst if we ask them to read at the same distance, a distinct convergent movement occurs; large objects are sufficiently clearly recognised, even without distinct retinal images, and the supposition that an effort of accommodation is present is only justified if we employ sufficiently small objects at the examination, in order to distinguish which, clear retinal images are necessary. Of course we must have regard to the condition of refraction; myopes, who use their far point for reading, want no accommodation, therefore no convergent movement occurs, even if the impulse of innervation for it, is not yet quite lost. However, the innervation for convergence may be lost, without the internal recti losing in elastic tension. The operative importance of this relation may be ill.u.s.trated by an example.

CASE 51.--Bertha K--, aet. 10, has myopia 5 D. on both sides, visual acuteness 12/20, and divergent strabismus. At 4 mm. the crossed diplopia is corrected by prism 23; a convergent movement is no longer attained, at most parallelism of the visual axes. Tenotomy of both interni on October 2nd, 1873. The immediate result was convergent squint, with a defect in movement outwards amounting to 4 to 5 mm. in both eyes. On October 9th prism 37 was still necessary to unite the h.o.m.onymous double images at a distance of 4 m.; single vision existed only to about 20 cm.

The area of single vision gradually extended itself; at the end of October it was restored for distance also, facultative divergence _nil_; however, relative divergence was present for near objects.

Naturally this was not the result of muscular weakness of the interni, for they had proved their capabilities by a convergent squint, fortunately only temporary, which made one anxious, but was solely the result of a faulty innervation. The further course was also interesting.

After three years, in October, 1876, the myopia of the left eye amounted to 8 D., that of the right 7 D., visual acuteness 1/2 on the right, on the left 3/4 of the normal; a posterior staphyloma measuring about 1/3 of the diameter of the optic disc was present. The left eye was used for near objects with relative divergence of the right and the occasional occurrence of diplopia; there was convergence only to about 15 cm.

Facultative divergence _nil_.

We very frequently have the opportunity of seeing, that myopia increases even after tenotomy of the externus, and if von Graefe's a.s.sertion that the progress of myopia would be brought to a standstill by means of tenotomy still finds believers, I should like to cite one example which offers proof to the contrary.

In permanent divergent squint we shall have, as a rule, to combine shortening of the internus of the squinting eye with tenotomy of both externi, even if the convergent movement is still possible to a slight degree. The result thus obtained differs somewhat; sometimes it suffices at once, sometimes a repet.i.tion of the separation of the externi is necessary later on. Two examples may ill.u.s.trate this.

CASE 52.--Miss Marie M--, aet. 22, has squinted on the left side since her third year, nominally after a kerat.i.tis, which left behind in the left eye a nebula of the cornea of small circ.u.mference. The deviation amounts to 8 mm. The visual power is much worse than the opacity of the cornea leads us to suppose, with visual axes deviating inwards fingers were only counted at a distance of about 1 m.

On the right myopia 1 D., V. = 4/5. A slight convergent movement is still practicable. At the end of May, 1879, shortening of the left internal rectus, tenotomy of both externi. The next day slight convergence on viewing distant objects, correct position after four days. In January, 1880, correct position of the eyes, convergence possible to about 20 cm. While a correction of 8 mm. was immediately obtained here, the same operation does not always permanently suffice for slighter deviations.

CASE 53.--Ernest Sp--, aet. 11-1/2; divergent squint had been observed as early as his second year. The deviation amounts to 5 or 6 mm., is sometimes alternating, generally the left eye deviates. No convergent movement on fixing a pencil about 25 cm. distant; the right eye is then used for reading, the left one makes a distinct, but not a sufficient, movement inwards. Emmetropia on both sides, visual acuteness nearly perfect on the right, on the left 2/3 of the normal. Even with red gla.s.s and prisms deviating in a vertical direction, double images not perceived. On October 2nd, 1879, shortening of the left internal rectus, tenotomy of both externi. A week later divergence was no longer present.

When reading, the left eye makes a distinct, perhaps rather too great, movement of convergence, and yet six weeks after the operation, distinct divergent squint was again present, even if to a slighter degree than before; the left eye deviates 3 to 4 mm., the right 2 to 3 mm. outwards.

The result obtained amounted then to not more than about 3 mm. In the middle of December the tenotomy of both externi was therefore repeated.

A week after the operation convergent squint of 2 mm. is present with h.o.m.onymous diplopia. A pencil made to approach on the middle line is seen double to about 20 cm., on approaching nearer, double images are not perceived in spite of distinct relative divergence. Double images at a distance of 4 m. are corrected by prism 25; as, however, normal binocular vision is not present, the value of this statement is very questionable. Three weeks after the second operation the position of the eyes was normal, and the slightest convergence was perceived only on close investigation. Double images are no longer observed, however they may still be brought to view.

In periodic divergent squint, if the deviation is considerable and frequent, if at the same time the normal near point of convergence is only attained with difficulty or not at all, we can hardly combine shortening of the internus with tenotomy of the externus; more often indeed, additional tenotomy of the externus of the other eye is necessary in order to obtain a permanent cure. In exceptional cases (when it seemed to me as if the squint depended more on insufficiency of the internus than on preponderance of the externus) I have confined myself to shortening the internus without separating the externus; I will quote just one example of this.

CASE 54.--Ida K--, aet. 11. On the right, hypermetropia 3 D. with the ophthalmoscope, visual acuteness 5/24. No. 03 is read with difficulty.

On the left, with the ophthalmoscope hypermetropia 45 D. with asymmetric meridian. Single letters of 30 m. are recognised with convex 65 D. Fingers are counted at about 1-1/2 m. The choroid is slightly and unequally pigmented, no ophthalmoscopically a.s.signable reason exists for the considerable visual defect. The left eye frequently deviates outwards, convergence is attainable to 15 cm. On May 2nd, 1877, shortening of the internus (without tenotomy of the externus). Two weeks later slight convergent squint was present; in November, 1877, six months after the operation, the position of the left eye was perfectly normal.

Tenotomy of the externi suffices when the divergent deviation is inconsiderable and does not occur often, if the normal near point of convergence can still be reached, and binocular fusion is possible.

If we want to increase the effect of simple tenotomy of the externi, this may be done just as well by practice of the a.s.sociated movements of the eyes as by practice of the convergence, of course for a short time only after the operation. As long as the detached tendon of the external rectus is not re-attached firmly with the sclerotic, all these movements of the eyes help to strengthen the result of the tenotomy. In order to practise convergence we can bring a suitable fixed point on to a mirror and so make it possible for the patient himself to see the position of his eyes, of course only in cases where binocular fusion is no longer present. He who possesses a normal binocular vision is troubled in these exercises by diplopia; but this is not the case in the suppression of binocular fusion so frequent as a result of squint.