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 a.s.sistance. 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 45 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, 45 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 45 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. 15 D., V. 5/9; on the right H. 15 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 gla.s.ses.

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. 35 D., V. 5/9, on the left V. = 1/16 with + 4 D., single words of No. 08 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 gla.s.s 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 gla.s.ses.

CASE 37.--Miss H--, governess, aet. about 30, came under treatment for asthenopic disorders; on both sides hypermetropia 25 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 gla.s.s 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 gla.s.ses in spite of the hypermetropia.

CASE 38.--Bertha W--, aet. 18, reads with the naked eye on the right No.

075 at 10 cm., on the left only 175 at the same distance; hypermetropia of 6 D. is detected with the ophthalmoscope, with + 55 the visual acuteness of the right eye amounts at 1 metre to 1/9 (if the test-letters had contained No. 8 or 75, that would probably have been recognised also), on the left with + 55 D., V. = 1/12, with + 6 D. No.

08 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 a.s.sist 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 gla.s.ses 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 circ.u.mstances 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 ill.u.s.tration 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 gla.s.s, the difference being corrected by a prism of 4, with the base downwards before the right eye; a prism of 4 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. 15 D., V. 10/40 to 10/30, and slight divergent squint on the left side. Crossed diplopia could be produced with a red gla.s.s, 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 eyegla.s.s as well as the spectacles. During the examination I found on the right hypermetropia 55 D., visual acuteness 5/12 to 5/9, on the left with + 55 D., V = 1/12. With convex 6 D. No. 05 was read at 12 inches from the gla.s.s, 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 gla.s.ses, 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 55 D. eyegla.s.s 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 gla.s.s 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 gla.s.s, 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 gla.s.ses 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 gla.s.ses 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.

CASE 42.--Marie S--, aet. 6, came under treatment on November 28th, 1878, for recent superficial marginal kerat.i.tis 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 h.o.m.onymous 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 15 D.; certainly a higher degree was specified when the vision was tested, namely, on the right H. 25 D., V. = 5/12 to 5/9, on the left H.

175 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 pa.s.sed off, the child could see better with the naked eyes than with convex gla.s.ses, 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 gla.s.s 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 a.s.signable causes. It seems to me unquestionable that the permanent use of convex gla.s.ses 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 gla.s.ses; 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 k.n.o.b 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 k.n.o.b 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 pa.s.sed 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 princ.i.p.ally 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 circ.u.mstances 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, princ.i.p.ally 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 a.s.signed 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 princ.i.p.ally 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 circ.u.mstances, 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.