series. Ophthalmology. 2011;118(8):1518–1523. Epub 2011 Apr 3.

Miscellaneous Special Forms of Strabismus

Brown Syndrome

Although it is included in most lists of vertical deviations (see Chapter 11), Brown syndrome is best considered a special form of strabismus. The characteristic restriction of elevation in adduction was originally thought to be caused by shortening of the supposed sheath of the superior oblique tendon. It is now attributed to various abnormalities of the tendon–trochlea complex (see Chapter 3), and recent evidence indicates that structural problems within the orbit but remote from the superior oblique tendon, including instability of the lateral rectus pulley, can present an identical clinical picture (pseudo–Brown syndrome). Recent work suggests that congenital Brown syndrome may be a form of CCDD.

Most cases are congenital. Prominent causes of the acquired form include trauma in the region of the trochlea, iatrogenic causes such as scleral buckles and glaucoma drainage devices, orbital tumors, and systemic inflammatory conditions such as rheumatoid arthritis. The latter often result in intermittent Brown syndrome, which may resolve spontaneously. Sinusitis has also led to Brown syndrome; thus, patients with acute-onset presentation of Brown syndrome of undetermined cause should undergo imaging of the orbits and paranasal sinuses to investigate this possibility. The condition is bilateral in approximately 10% of cases. Resolution of congenital Brown syndrome has been thought to be unusual, but a recent report describes spontaneous improvement in 75% of cases, often over many years.

Dawson E, Barry J, Lee J. Spontaneous resolution in patients with congenital Brown syndrome. J AAPOS. 2009;13(2):116– 118. Epub 2008 Dec 12.

Clinical features

Well-recognized clinical features of Brown syndrome include deficient elevation in adduction that improves in abduction but often not completely (Fig 12-5). Several findings differentiate Brown syndrome from inferior oblique muscle paralysis (see Chapter 11, Table 11-3).

Figure 12-5 Brown syndrome, left eye. No elevation of the left eye when adducted; left eye is depressed instead. Elevation is also severely limited in straight-up gaze and moderately so even in up-and-left gaze. Note the characteristic divergence in straight-up gaze and lack of ipsilateral superior oblique overaction. (Courtesy of Edward L. Raab, MD.)

An unequivocally positive forced-duction test demonstrating restricted passive elevation in adduction is essential for the diagnosis. Retropulsion of the globe during this test stretches the superior oblique tendon and accentuates the restriction. In restrictions involving the inferior rectus muscle or its surrounding tissues, by contrast, the limitation of passive elevation is accentuated by forceps-induced proptosis of the eye rather than by retropulsion.

Attempts at elevation straight upward usually cause divergence (V pattern) due to lateral diversion of the globe as it meets resistance from the tight superior oblique tendon (see Fig 12-5). This finding is an important point of distinction from inferior oblique muscle paralysis, which usually exhibits an A pattern (see Chapter 11, Table 11-3). In adduction, the palpebral fissure widens, and a downshoot of the involved eye occurs on gaze to the opposite side in severe cases. The overdepression in adduction seen in Brown syndrome (see Chapter 11, Table 11-2) can be distinguished from that of true superior oblique muscle overaction because downshoot in the latter occurs less abruptly as adduction is increased. In mild Brown syndrome, no hypotropia is present in primary position. Severe cases of Brown syndrome exhibit both a downshoot in adduction and a primary position hypotropia, often accompanied by a chin-up head posture or a head turn away from the affected eye. Moderate cases have findings between these extremes.

Management

Observation alone is appropriate for mild congenital Brown syndrome. When Brown syndrome is secondary to rheumatoid arthritis or other systemic inflammatory diseases, resolution may occur as systemic treatment brings the underlying disease into remission or when corticosteroids are injected near the trochlea.

Surgery is indicated for more severe congenital cases. Sheathectomy, originally advocated by Harold Brown, has been abandoned in favor of ipsilateral superior oblique tenotomy nasal to the superior rectus muscle. However, iatrogenic superior oblique muscle paresis occurs in a significant minority of patients after this procedure. Careful handling of the intermuscular septum during surgery and avoidance of complete tenotomy as a sole procedure can reduce the incidence of this sequela. Options used currently include insertion of an inert spacer or suture between the cut ends of the superior oblique tendon, a Z-plasty of the tendon on the medial side, and partial (80%) tenectomy of the posterior portion of the tendon on the temporal side. Using any of these procedures, the surgeon should repair the intermuscular septum to prevent contact of the spacer or suture with nearby structures and therefore avoid a downgaze restriction due to adhesions to the upper nasal quadrant of the globe. To reduce the consequences of superior oblique muscle palsy after tenotomy, some surgeons perform simultaneous ipsilateral inferior oblique muscle weakening.

Wright KW. Brown’s syndrome: diagnosis and management. Trans Am Ophthalmol Soc. 1999; 97:1023–1109.

Third Nerve Palsy

In children, third nerve palsy can be congenital (40%–50% of cases) or can be caused by conditions such as trauma, inflammation, or viral infection. It can also occur as a manifestation of ophthalmoplegic migraine, after vaccination, or (infrequently) as a result of a neoplastic lesion. In adults, the usual causes are intracranial aneurysm, microvascular infarction, inflammation, trauma, infection, or tumor. See BCSC Section 5, Neuro-Ophthalmology, for detailed discussion of the causes and manifestations of third nerve palsy. This section is concerned primarily with the principles of treatment of the disturbed motility.

Clinical features

The location of the lesion along the central and peripheral pathway of the third cranial nerve determines the presenting features. Ischemic causes may spare the pupil, whereas compressive lesions, such as tumors or aneurysms, typically cause mydriasis. Complete paralysis results in limited adduction, elevation, and depression of the eye, causing exotropia and often hypotropia. These findings are expected because the remaining unopposed muscles are the lateral rectus (abductor) and the superior oblique (abductor and depressor), except when the cause of the paralysis involves the nerves supplying these muscles as well. Upper eyelid ptosis is usually present, often with pseudoptosis due to the depressed position of the involved eye (Fig 12-6).

Figure 12-6 Third nerve palsy, right eye, with ptosis (bottom photo) and limited adduction, elevation, and depression (upper eyelid elevated manually in top 9 photos). (Courtesy of Edward L. Raab, MD.)

The clinical findings and treatment may be complicated by misdirection (aberrant regeneration) of the damaged nerve, presenting as anomalous eyelid elevation, pupil constriction, or vertical excursion of the globe—any or all of which can occur on attempted rotation into the field of action of the EOMs supplied by the injured nerve. A miotic pupil is sometimes seen in congenital cases, irrespective of whether there is aberrant regeneration. Affected adults report incapacitating diplopia unless the involved eye is occluded by ptosis or other means.

Management

Except in congenital cases, it is advisable to wait at least 6 months, and even up to 12 months, for spontaneous recovery before proceeding with surgical correction. Patients with at least partial recovery are much better candidates for good functional and cosmetic results. Because the visual system is still developing in pediatric patients, amblyopia is a common finding that must be treated

aggressively.

Surgical elevation of the upper eyelid and incomplete realignment without useful single binocular fields may reinforce the incapacitating diplopia in adult patients with previously good binocular visual function. Prism adaptation testing has shown that adult patients who can achieve single binocular vision with prisms of any power before surgery are most likely to do well. The incidence of diplopia in patients younger than 8 years is low because of suppression (see Chapter 6).

Third nerve palsy presents difficult surgical challenges because multiple EOMs, including the levator muscle, are involved. Replacing all of the lost rotational forces on the globe is impossible; therefore, the goal of surgery is adequate alignment for binocular function in primary position and in slight downgaze for reading.

Selection of the surgical procedure is dictated by the number and condition of the involved muscles and the presence or absence of noticeable paradoxical rotations. In a case of incomplete paralysis, a large recession-resection of the horizontal rectus muscles to correct the exodeviation, with supraplacement of both to correct the hypotropia, is effective. For complete paralysis, a large lateral rectus muscle recession combined with fixation of the globe to the nasal orbital periosteum is one suggested approach. Disinsertion of the lateral rectus muscle and reattachment to the lateral orbital periosteum can maximize inactivation of the muscle. Some surgeons correct hypotropia with concurrent superior oblique tenotomy. Transfer of the superior oblique tendon to the upper nasal quadrant of the globe also has been employed; however, anomalous eye movements can result from this procedure. Most surgeons reserve correction of ptosis for a subsequent procedure, which allows for more accurate positioning of the upper eyelid.

Sixth Nerve Palsy

Paralysis of the sixth cranial (abducens) nerve is less common in children than in adults. This entity is discussed in Chapter 8. See BCSC Section 5, Neuro-Ophthalmology, for additional discussion.

Thyroid Eye Disease

Thyroid eye disease affects the eye and the orbit in a variety of ways. Only motility disturbances are covered in this volume.

Edema, inflammation, and fibrosis of the EOMs due to lymphocytic infiltration occur in this disease. Not only do these pathologies restrict motility, but the massively enlarged muscles can cause compressive optic neuropathy. Detection of muscle enlargement by orbital imaging helps confirm the diagnosis.

The myopathy is not caused by thyroid dysfunction. Rather, both conditions probably result from a common autoimmune disease. Thyroid-stimulating immunoglobulins (TSIs) likely mediate thyroid eye disease and may be regarded as a functional biomarker for this condition. Some patients also have myasthenia gravis (discussed later in this chapter), complicating the clinical findings. An association between severity of thyroid eye disease and smoking has recently become apparent; the hazard ratio for strabismus surgery is almost double in patients with thyroid disease who smoke.

Clinical features

The muscles affected in thyroid eye disease, in decreasing order of severity and frequency, are the inferior rectus, medial rectus, superior rectus, and lateral rectus. The condition is most often bilateral and is often asymmetric. Forced-duction test results are almost always positive in one or more directions.

Most often, the patient presents with some degree of upper eyelid retraction, proptosis, hypotropia,

and esotropia (Fig 12-7). Thyroid eye disease is a common cause of acquired vertical deviation in adults (see Chapter 11), especially women, but it is rare in children.

Figure 12-7 Thyroid eye disease. Note right upper eyelid retraction and restrictive right hypotropia with very limited elevation. Other rotations are not affected.

Management

Diplopia and abnormal head position are the principal indications for strabismus surgery. The operation may eliminate diplopia in primary gaze but rarely restores normal motility because of the restrictive myopathy, the need for large recessions in some cases to place the eye in primary position, and the ongoing underlying disease.

It is best to perform surgery after strabismus measurements and thyroid function tests have stabilized; waiting for at least 6 months and even 12 months is recommended. In the meantime, prisms may alleviate diplopia. Botulinum toxin may reduce the severity of fibrosis when injected into tight muscles in the acute phase. Performance of surgery before stability is achieved has been studied in patients with severe head positions. The results were favorable, but half the patients required further surgery.

Recession of the affected muscles is the preferred surgical treatment, addressing the tight muscles in 1 or both eyes. Strengthening procedures usually worsen restriction, but in carefully selected cases they may be helpful as part of the surgical plan. Adjustable sutures can be helpful in these difficult cases. Slight initial undercorrection is desirable, because late progressive overcorrection is common, especially with large inferior rectus muscle recessions. Limited depression of the eyes after inferior rectus muscle recessions can interfere with patients’ bifocal use. Proptosis can become worse after EOM recessions.

If the need for orbital decompression is foreseeable, it is usually preferable to postpone strabismus