CHAPTER VI

OPERATIONS UPON THE EXTRA-OCULAR MUSCLES

SQUINT OPERATIONS

=Indications.= Operations upon eyes with concomitant squint are undertaken for two purposes:--

(i) For cosmetic reasons, to remedy a deformity due to a squinting eye which is amblyopic.

(ii) To rectify the muscular equilibrium in alternating or latent squints, so that binocular vision may be regained.

When the operation is performed for the latter reason the adjustment will naturally have to be much more accurate than for the former, so as to bring about the superimposition of the images falling on each macula. The muscular balance is interfered with by the administration of a general anæsthetic, and therefore the results cannot be gauged accurately. Thus it is desirable that operations upon the ocular muscles should be performed under local anæsthesia. This is usually possible, except in the case of very small children.

During and after the operation muscular equilibrium is tested by means of an electric light fixed to the ceiling immediately over the head of the patient (see Fig. 74). The room is darkened and the patient is made to look at the light. In a case with an amblyopic eye the reflection of the light should appear in the middle of each cornea if the eye be properly adjusted. In cases where good vision is present in both eyes the Maddox rod test should be used, the rod being placed before the eye not being operated on; the bar of light produced by the rod should pass through or within a few inches of the light if the adjustment has been performed accurately.

The tendons of the recti muscles are inserted into the globe at the following distances from the corneo-sclerotic junction: internal, 5 mm.; inferior, 6 mm.; external, 7 mm.; superior, 8 mm. Each muscle is held in place by expansions on either side of the tendon as well as by the tendinous insertions. Division of these expansions allows a greater retraction of the muscle and is, therefore, to be undertaken when a considerable degree of squint has to be overcome. On the other hand, there will be a danger that the muscle may not regain a proper attachment to the globe if division be too freely performed, and a squint in the opposite direction may result; proptosis also may be caused thereby. It is, therefore, better to combine tenotomy with advancement in high degrees of squint over twenty degrees convergent and in all cases of constant divergence. This is usually better than performing a tenotomy in the other eye, as there still remains the muscle of the other eye in reserve to tenotomize if necessary, if the advancement be insufficient to correct the squint. Further, it is much easier to rectify a muscular error by accurate tenotomy than by advancement. Division of the tendon of the internal rectus only, without its expansion, will usually rectify cases of latent convergent strabismus with a deviation of about 12° prism (Maddox test). Cases of latent divergent strabismus of about 8° prism (Maddox test) require complete division of the tendon of the external rectus, and, in some cases, of the expansion as well. Tenotomy of the superior rectus for hyperphoria should only be undertaken in bad cases; that is to say, of over 12° prism, any lateral deviation being first corrected, as occasionally the correction of the lateral deviation, especially when this is due to the faulty insertion of a muscle, will sometimes correct the hyperphoria present.

Partial tenotomies are performed by some surgeons for the correction of latent muscular errors, but the experience of most in this country is that little benefit is gained unless the tendon be completely divided. Tendon-lengthening by various methods has been performed, but has not come into general use.

After all operations upon the ocular muscles both eyes should be occluded to keep the eyes at rest whilst the muscle is gaining its fresh attachment to the globe; this usually takes about seven days, after which time both eyes should be uncovered, and if there is a tendency to convergence atropine should be used. Glasses correcting any error of refraction should be worn.

TENOTOMY

Tenotomy may be performed by (1) the open, or (2) the subconjunctival method.

=Instruments.= Speculum, straight blunt-pointed scissors, strabismus hook, needle and silk, needle-holder.

=Operation.= The operation is performed under adrenalin and cocaine.

1. _By the open method._ The surgeon stands on the right side facing the patient when dividing the right external or the left internal rectus, but at the head of the table when dividing the right internal or the left external rectus.

_First step._ The speculum is inserted and the patient is made to look away from the muscle to be divided. The conjunctiva is freely divided vertically with scissors directly over the insertion of the tendon into the globe (see Fig. 130) and dissected backwards.

_Second step._ The tendon of the muscle is then seized with fixation forceps and button-holed about its centre as close to the globe as possible (Fig. 131). The lower blade of the scissors is then passed through the hole in the tendon, and the rest of the tendon and its expansions are divided upwards and downwards to the extent required to bring the eye straight as tested by its appearance or by the Maddox rod test. The strabismus hook may be inserted, both upwards and downwards, to see that the tendon is properly divided, but all pulling on the muscle with a hook should be avoided, as it is painful and disturbs the muscular equilibrium. The conjunctiva is then brought together with a fine silk suture. If the squint be over-corrected by the tenotomy, a deep hold should be taken with the stitch so as to draw the eye back into position.

2. _By the subconjunctival method._ This is unsatisfactory in that accurate adjustment by division of the expansion of Tenon’s capsule is not possible. It is painful, and is sometimes followed by a troublesome hæmorrhage into the capsule of Tenon. Occasionally it may be of use in some cases of amblyopic eyes where a small wound is desirable. The conjunctiva is button-holed below the tendon, and separated from the surface of the muscle. The capsule of Tenon is then opened below the tendon, a strabismus hook is passed through the opening with its concavity against the globe, and is then rotated upwards beneath the tendon, which is subsequently divided between the hook and the globe.

=Complications.= These may be immediate or remote.

=Immediate.= 1. _Hæmorrhage into the capsule of Tenon_, leading to intense proptosis, only occurs when the subconjunctival method is adopted. As a rule the hæmorrhage ceases on the application of pressure, but occasionally it may be necessary to open up the wound and turn out the blood-clot.

2. _Perforation of the globe_ has been known to occur during the division of a tendon in an obstreperous patient. It should be treated as a wound of the sclerotic (see p. 235).

3. _Tenonitis_ very rarely occurs, but may lead to matting down of all the extra-ocular muscles and defective movements of the globe. Panophthalmitis has been known to follow this condition.

=Remote.= 1. _Failure to correct the muscular error._ If the error be large it must be rectified by tenotomy of the corresponding muscle of the other eye or by the advancement of the opposing muscle of the same eye. This should not be undertaken until five or six weeks have elapsed since the previous operation.

2. _Over-correction of the muscular error at the time of the operation_ may be remedied by stitching the tenotomized muscle forward to the extent required to bring the eye straight. Advancement of the tenotomized muscle should be performed if the over-correction be only discovered after the operation. In cases with binocular vision lesser degrees of deviation may be corrected with prisms if they are causing symptoms, while small errors of over-correction, of about 3° prism, often disappear after the first few weeks.

3. _Defective movement in the tenotomized muscle_ is usually present for the first week or two after the operation, but recovery usually takes place after the muscle has regained its attachment to the globe; it may persist, however, to a slight extent; this is most liable to occur after free division of the tendon and its expansion (more especially in the case of the external rectus), or because the tendon has not been divided close enough to the globe. In patients with previous binocular vision diplopia is present after the operation on turning the eyes towards the same side as the tenotomized muscle, but this usually disappears.

4. _A granulation_ may form at the site of the tenotomy wound. It may be due to a tag hanging from the wound or to a portion of a stitch that has been imperfectly removed. It should be snipped off with scissors and the conjunctiva drawn together over its base.

5. _Proptosis_ may result from too free a division of a tendon.

6. _Retraction of the caruncle_ is best avoided by closing the conjunctival wound with a stitch, and thus pulling the caruncle forward.

ADVANCEMENT

Advancement is an operation undertaken to rectify a squint by forming a fresh attachment for one of the ocular muscles nearer the cornea, and at the same time shortening it. There are three main types of operation performed:--

1. The capsulo-muscular, in which the tendon, together with the attachment of the capsule of Tenon to it, is advanced.

2. The tendon only is isolated, shortened, and advanced.

3. The tendon is shortened by folding it upon itself.

The first operation is by far the most satisfactory of these, owing to the fact that a broader new insertion of the muscle is obtained, which is less likely to yield subsequently; it is the operation usually performed in this country.

The chief cause of unsatisfactory results after advancement operations is the cutting through of the sutures holding the tendon in position. The various operations, which are some fourteen in number and have mostly their respective surgeon’s name attached, differ principally in the method of insertion of these sutures. Whichever method of inserting sutures be used, the main factors which aim at preventing the stitches from cutting out are (1) that the stitches should take a good hold in the scleral and episcleral tissues on the corneal side of the wound, for the passing of which it is most essential that the needles should be sharp; (2) that complete rest of the muscles should be ensured by bandaging both eyes for the first seven days after the operation; (3) that the opposing muscle should be tenotomized so as to prevent traction on the sutures.

Of the many operations that have been devised the capsulo-muscular advancement or some modification of it is most frequently used.

=Instruments.= Speculum, straight scissors, fixation forceps, Prince’s advancement forceps (Fig. 132), four sharp needles and strong silk, needle-holder.

=Operation.= Under adrenalin and cocaine. _First step._ The patient is made to look away from the side on which is the muscle to be advanced, and the conjunctiva over the muscle is freely divided with scissors, by a curved incision with the convexity towards the cornea, and dissected back.

_Second step._ The capsule of Tenon is button-holed by a small incision well above or below the tendon. A tenotomy hook is passed beneath the tendon and its expansion and brought out through a small hole in Tenon’s capsule on the opposite side of the tendon. The smooth blade of Prince’s forceps is then inserted in place of the hook, and the tendon with its expansion is grasped between the blades. The forceps are given to an assistant, who should avoid all traction on the muscle. The eye is then rotated in the direction of the muscle to be advanced, and tenotomy of the opposing muscle is performed by the open method.

_Third step._ The muscle to be advanced and its expansion, which are clamped between the blades of Prince’s forceps, are separated from the globe with the scissors and given again to the assistant to hold. Three strong silk sutures are passed in the following order, middle, upper, and lower, first through the conjunctival and episcleral tissue on the corneal side of the wound and then as far back as possible through the muscle and out through the conjunctiva near the cut margin on the other side of the wound (Fig. 133). Care should be taken that the middle stitch is passed through the episcleral tissue exactly opposite the horizontal plane of the cornea and the central portion of the tendon. The portion of the tendon and capsule within the grasp of the forceps is then removed with scissors by cutting close to the blades of the Prince’s forceps, taking care not to cut the sutures.

_Fourth step._ The middle suture should be first tightened to the extent required to bring the eye straight. The upper and lower sutures are then tied.

If, on testing with the Maddox rod, the error be found to be slightly over-corrected by the advancement, the eye can be drawn back by taking a firm hold with the conjunctival stitch over the tenotomy wound. The conjunctival stitch may be removed on the fourth day, but the stitches holding the advanced muscle in position should not be removed till after the tenth day. Atropine in both eyes is desirable, especially when there is any tendency to convergence. Glasses should be worn on uncovering the eyes.

=Complications.= 1. _The eyes may not be straight after the operation._ No further operation for rectification should be undertaken for at least two or three months. If there be a tendency to convergence, glasses should be worn and atropine used. Small latent errors may be corrected by prisms. _If the muscular error be insufficiently corrected_ tenotomy may be performed on the other eye. _If the muscular error be over-corrected_ it may also require tenotomy on the other eye, the adjustment by tenotomy being more accurate than that by advancement.

2. _Thickening over the site of the advanced muscle_ usually disappears in a few months.

Other complications as described under tenotomy may occur (see p. 250).