Ординатура / Офтальмология / Английские материалы / Handbook of Pediatric Strabismus and Amblyopia_Wright, Spiegel, Thompson_2006

The surgical plan is to recess the right medial rectus muscle 4.0 to 5.0 mm, as this will match the right medial rectus muscle to its underacting yoke muscle, the left lateral rectus muscle. Weakening the right medial rectus muscle will slightly reduce adduction but will not affect abduction; this reduces the large esotropia in leftgaze without causing an exotropia in rightgaze. Do not recess the left medial rectus muscle because this surgery has little effect in leftgaze where the esotropia is largest and will produce an exo-deviation in rightgaze. Also, avoid a left lateral rectus resection as this will not strengthen the weak lateral rectus. Instead, it will cause a tight lateral rectus muscle that also has little effect in leftgaze where the esotropia is greatest and will cause an exodeviation in rightgaze. For an incomitant esodeviation that is greater than 10 to 15 prism diopters (PD) in primary position and increases in leftgaze, two-muscle surgery will be required to correct the deviation in primary position. Consider asymmetrical bilateral medial rectus recessions, with a larger recession on the right medial rectus muscle.

The Faden operation has also been suggested to reduce incomitance. Adding a Faden to a recession of the medial rectus muscle increases the weakening effect of the recession in adduction and improves the incomitance. The use of the Faden is controversial. If it is used, it is most effective on the medial rectus muscle, as the medial rectus has the shortest arc of contact. Theoretically, the Faden weakens the muscle mostly in the field of action of the muscle, with little effect in primary position; therefore, it may be helpful in reducing incomitance (see Chapter 11). A report on the effect of the Faden procedure on the medial rectus muscles in reducing the AC/A ratio concluded there was a beneficial effect; however, the table of data in this study showed no change of the AC/A ratio. It is likely the Faden procedure has little effect, except in extreme fields of gaze.35

If the limitation is severe, recessing the yoke muscle to match the limitation will not work, as operating on the good eye will not improve the ability of an eye with limited ductions to come to midline. In these cases of moderate to severe limitation of ductions, one must release the restriction or, in the case of a palsy, transpose muscle forces to bring the eye to midline. Recessing the contralateral yoke muscle only works if the limitation is slight, such as a trace to 1 limitation of ductions.

Vertical incomitance can be treated with the same strategy as described previously for horizontal strabismus. One special situation that occurs with Grave’s disease and floor fractures is

that of a patient with orthotropia in primary position and a hypotropia in upgaze secondary to a tight inferior rectus muscle. In this case, recess both inferior rectus muscles, with a larger recession on the side with the restriction. The diagnosis and management of specific types of restrictive and paralytic strabismus follow.

SPECIFIC TYPES OF RESTRICTIVE STRABISMUS

Fat Adherence

Fat adherence is a restrictive form of strabismus occurring after periocular surgery or accidental trauma. Marshall Parks was the first to describe the clinical characteristics and etiology of the fat adherence syndrome or, as it is also called, the adhesive syndrome.84 Normally, Tenon’s capsule and muscle sleeve act as an elastic barrier separating the globe from the surrounding orbital fat. Fat adherence is caused by violation of the posterior Tenon’s capsule, allowing exposure and manipulation of extraconal fat and fascia, which produces an adhesion of these tissues to the sclera. Because the septae within the extraconal fat connect to the periorbita, fibrosis associated with fat adherence can extend from the orbital bone to the sclera (Fig. 10-4). In severe cases, the eye is virtually scarred to the orbital bone, immobilizing ocular rotations. Violation of the muscle sleeve can also result in fat adherence to a rectus muscle causing a tight muscle. Fat adherence most frequently occurs after strabismus surgery involving posterior exposure (especially oblique muscle surgery) and retinal buckle surgery, but can also occur after any periocular surgery, even after blepharoplasty.57,59,134

Fat adherence is difficult to surgically correct, as recurrence of fat adherence after removal of adhesions is very common. Once Tenon’s capsule is violated and a scar established, it is almost impossible to reestablish the delicate fascial barrier to prevent recurrence of scarring. Teflon or silicone sheaths have been used as an artificial barrier, but they become encapsulated in scar and often make the restriction worse. Amniotic membrane transplantation has been used to create a barrier separating periocular fat from the sclera, but the technique is difficult, at best, and remains investigational.138 Surgical correction of fat adherence consists of releasing the scar by dissecting close to

FIGURE 10-4A,B. Fat adherence syndrome. (A) Diagram on the right shows the normal anatomy of the periocular fascia with Tenon’s capsule as the barrier separating orbital fat from the sclera and muscle. Diagram to the left shows fat adherence (after violation of Tenon’s capsule) overlying the rectus muscle in an area away from the rectus muscle over sclera. Note that a fibrous scar extends throughout the fat septae attaching periosteum to the muscle and sclera. This scar causes a restrictive leash that limits eye movements. (B) Photograph of fat adherence to the inferior rectus muscle. (Modified from Parks and Mitchell, 1978, with permission.)

sclera and removing the adhesions without repenetrating the orbital fat. (Perform forced ductions after freeing adhesions to evaluate improvement of the restriction.) Dissect carefully with direct visualization, as posterior dissections can be dangerous.

Cases of inadvertent optic nerve transection have occurred, although they are rarely reported. If fat and scar are adherent to a rectus muscle, remove a small amount of the anterior scar, then recess the tight muscle en bloc with the scar rather than trying to dissect all the scar off the muscle. Avoid extensive dissection of scar off the muscle, as this usually results in further fat manipulation and worsening of the adherence. Medical treatment with mitomycin-C has not been effective in reducing postoperative fibrosis and may even increase scarring.17 Injection of peribulbar corticosteroids also fails to prevent postoperative scarring. The best treatment for fat adherence syndrome is prevention: avoid penetration of posterior Tenon’s capsule during the initial surgery. During strabismus surgery, perform minimal dissection of muscle fascia and, when dissecting, dissect close to the muscle to stay away from surrounding orbital fat. If Tenon’s capsule is inadvertently torn so fat is exposed, cover the exposed fat by repairing the Tenon’s tear with 7-0 vicryl suture.

Grave’s Ophthalmopathy

Grave’s ophthalmopathy is an autoimmune disease associated with inflammation of the extraocular muscles. Initially, there is an acute phase during which there is a lymphocytic infiltration of the extraocular muscles, resulting in extraocular muscle enlargement and proptosis. This active phase usually lasts several months to more than a year. Orbital imaging studies show thickened extraocular muscles, especially posteriorly. The second phase is a cicatricial phase with quiescence of inflammation and secondary contracture of the muscles. All muscles are usually involved, but the inferior rectus and medial rectus are most severely affected.91 Strabismus is caused by tight fibrotic muscles and can develop in both phases but is most pronounced in the cicatricial phase. A restrictive hypotropia caused by tight inferior rectus muscles is the most common type of strabismus, followed by esotropia associated with tight medial rectus muscles.

The management of Grave’s ophthalmopathy is careful observation during the acute inflammatory phase. Treatment with systemic steroids and even external beam radiation may be indicated for severe disease; however, radiation therapy is not effective for treatment of the strabismus.126 Orbital decompression is indicated for severe proptosis and visual loss associated

with optic nerve compression from inflamed extraocular muscles. In most cases, it is better to perform strabismus surgery after the active phase has subsided and strabismus measurements have stabilized. A report on eight patients whose eyes were operated on during the active phase of thyroid ophthalmopathy noted that all eight patients achieved successful longterm alignment ( 16 months follow-up); however, half the patients required more than one operation.

Regarding the timing of surgery, strabismus surgery is usually performed after orbital decompression surgery, because orbital surgery can alter eye alignment.21,75 The strategy for the treatment of Grave’s ophthalmopathy strabismus is to release the restriction from the tight rectus muscle, with a rectus muscle recession being the procedure of choice. It is not advisable to use rectus muscle resections, as this tightens an already stiff, inelastic muscle. A right hypotropia less than 15 PD with a tight right inferior rectus muscle can be surgically addressed with a right inferior rectus recession, with or without an adjustable suture technique (Fig. 10-5).8,68 If the deviation in primary position is greater than 18 to 20 PD with severe restriction, recess the tight inferior rectus muscle more than 5.0 mm and add a recession of the contralateral superior rectus muscle. As a rule, expect 3 PD of vertical correction for each millimeter of vertical rectus muscle recession.135

One common problem with correcting thyroid strabismus has been late overcorrection after inferior rectus recession, which occurs in up to 50% of cases.24,56,80 Initially after surgery, there is a successful result. Then, at 4 to 6 weeks after the inferior rectus recession, a consecutive hypertropia on the side of the recession occurs, with underaction of the recessed inferior rectus muscle and ipsilateral lower eyelid retraction.132 R. Friedman suggested that performing asymmetrical bilateral inferior rectus recessions avoids late overcorrection. A report by Cruz and Davitt on eight patients who underwent asymmetrical bilateral inferior rectus recessions showed no overcorrections; however, 25% of these patients were undercorrected.24 Ludwig has suggested that a stretched scar at the new insertion is the cause of the overcorrection. It is hypothesized that, at 4 to 6 weeks after surgery, the absorbable suture loses its strength. The muscle–scleral attachment stretches and causes the tight muscle to retract posteriorly. This author has now switched to nonabsorbable sutures (6-0 Mersiline), and preliminary results have been good, even when using an adjustable suture.

Congenital Fibrosis of the Extraocular Muscles

Congenital fibrosis of the extraocular muscles (CFEOM) is an autosomal dominant, nonprogressive disorder usually characterized by bilateral congenital ptosis and restrictive external ophthalmoplegia48,49; however, rare unilateral cases have been described (CFEOM 8, 21, 26, 29, 30, 31).28,51 Systemic diseases reported to be associated with CFEOM include Prader–Willi syndrome (CFEOM 25),60 Joubert syndrome (CFEOM 23),3 and cortical and basal ganglia dysplasia (CFEOM 2).123 CFEOM has been mapped to chromosomes 12, 11, and 16 (CFEOM 3, 5, 6, 7, 9, 18, 16).26,51 There can be significant phenotypic heterogeneity with a variety of subtypes of CFEOM found in the same family (CFEOM 6 and 8).96,118

The clinical features of CFEOM have been classified into five groups: (1) generalized fibrosis syndrome,4 (2) fibrosis of inferior rectus with blepharophimosis, (3) strabismus fixus,

(4) vertical retraction syndrome,39 and (5) unilateral fibrosis blepharoptosis and enophthalmos (CFEOM 17).32,34,51 The medial rectus muscle is one of the most commonly involved, causing a strabismus fixus esotropia with extreme restriction to abduction (Fig. 10-6). Strabismus fixus is a term for an eye that is fixed and cannot move, usually secondary to severe restriction or a combination of restriction and paresis. The strabismus associated with CFEOM is mostly caused by tight fibrotic muscles, but a component of paresis can also be a factor. As with thyroidrelated strabismus, the surgical procedure of choice is a recession of the tight rectus muscle. Resections should be avoided. These CFEOM cases can be technically difficult because exposure of the muscle is limited, especially in cases with a fibrotic medial rectus muscle.

The etiology of CFEOM is unknown, but the syndrome is associated with atrophic and fibrotic changes of the extraocular muscles.33 Light and electron microscopy demonstrated replacement of normal muscle with collagen, dense fibrous tissue, and areas of degenerated skeletal muscle (CFEOM 29, 30, 31).125 Research suggests that the cause of congenital fibrosis of the extraocular muscles is an abnormality in the development of the extraocular muscle lower motor neurons, with agenesis of the third nerve being most common (CFEOM 1, 14, 11, 10).109 Nakano et al. reported finding three mutations in ARIX gene (also known as PHOX2A) in four pedigrees of congenital fibrosis of the extraocular muscles type 2 (CFEOM 2).79,123 ARIX

FIGURE 10-6. Patient with congenital fibrosis syndrome and a large angle esotropia. There was severe limitation to abduction, bilaterally, and forced ductions at the time of surgery show severe restriction to abduction in both eyes. Bilateral medial rectus recessions (7.0 mm) resulted in good alignment with improved abduction.

encodes a homeodomain transcription factor protein shown to be required for development of cranial nerves III and IV in mouse and zebrafish. These findings confirm the hypothesis that CFEOM 2 results from the abnormal development of cranial nerves III and IV and emphasize a critical role for ARIX in the development of these midbrain motor nuclei.37,79

Double Elevator Palsy or Monocular Elevation Deficit Syndrome

Double elevator palsy is classically defined as a congenital inability to elevate one eye, with the limitation occurring in adduction and abduction (Fig. 10-7). One might question why double elevator palsy is included under restrictive strabismus. The term double elevator palsy is a misnomer because, in most cases, the cause for the limited elevation is not a palsy of both elevators but is a tight inferior rectus muscle. Studies using saccadic velocity measurements and forced ductions showed that approximately 70% of patients diagnosed as having a double elevator palsy actually had limited elevation as a result of inferior rectus restriction, not a palsy of the superior rectus and inferior

oblique muscles.73,106 A more descriptive term now used is monocular elevation deficit syndrome (MED). MED may be mistaken for Brown’s syndrome, although the limited elevation is worse in adduction than abduction in the latter. Patients with MED present with a hypotropia, a chin elevation, and, often, an ipsilateral ptosis. True congenital ptosis is present in 25% of cases whereas pseudo-ptosis may occur in almost all patients with a large hypotropia.2 In those cases with a true double elevator palsy and a lack of an upgaze saccade, forced ductions at time of surgery usually reveal a tight inferior rectus muscle coexisting with the superior rectus palsy.

An interesting finding in approximately 25% of patients with double elevator palsy and congenital ptosis is the Marcus Gunn jaw-winking phenomenon.133 This association indicates a congenital misdirection syndrome involving the oculomotor nerve. It is possible that, as with congenital fibrosis syndrome, the cause of the tight inferior rectus and, in some cases, superior rectus and inferior oblique palsy, is abnormal development of cranial nerves (including the oculomotor nerve) with secondary muscle fibrosis.

Surgery for MED is indicated if a significant hypotropia is present in primary position with an associated chin elevation. The type of surgery depends on the cause of the elevation deficit (Table 10-3). If the etiology is a tight inferior rectus muscle and the upgaze saccade is normal, recess the ipsilateral inferior rectus muscle, usually around 5 to 6 mm depending on the size of the hypotropia. It is important to evaluate preoperatively for the presence of an upgaze saccade and to perform forced ductions at the time of surgery to make the correct procedural choice. Lack of upgaze saccades, combined with a weak superior rectus muscle on forced generation testing, indicates a true

A B C

FIGURE 10-7A–C. Double elevator palsy (monocular deficit syndrome). Child has had limited elevation of the right eye since birth. Note that elevation of right eye is worse in abduction (A) than it is in adduction (C). Patient is fixing with the involved right eye so the left eye is hypertropic as per Hering’s law of yoke muscles (B). Preoperatively, this patient had intact upgaze saccades and a tight inferior rectus muscle on forcedduction testing at the time of surgery. The elevation deficit was successfully treated with a right inferior rectus muscle recession of 6.5 mm.