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 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 tube shunts, orbital tumors, and systemic inflammatory conditions such as rheumatoid arthritis. The latter often results in intermittent Brown syndrome, which may resolve spontaneously. Sinusitis can also lead 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 report by Dawson and colleagues describes spontaneous improvement in 75% of cases, often after many years.
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 11-4).
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 is more likely to exhibit an A pattern. In adduction, the palpebral fissure widens and overdepression in adduction can be observed in severe cases of Brown syndrome (see Chapter 11, Table 11-2). This differs from overdepression in adduction in true superior oblique muscle overaction, which occurs less abruptly with increasing adduction. In mild Brown syndrome, no hypotropia is present in primary position. Severe cases of Brown syndrome with a primary position hypotropia are often accompanied by a chin-up head position or a head turn away from the side of the affected eye.
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.
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.)
Surgery is indicated for more severe congenital cases. Superior oblique tenotomy nasal to the superior rectus muscle is definitive treatment; however, iatrogenic superior oblique muscle paresis occurs in a significant minority of patients after this procedure. Careful handling of the intermuscular septum during surgery can reduce the incidence of this sequela. To reduce the consequences of superior oblique muscle palsy after tenotomy, some surgeons perform simultaneous ipsilateral inferior oblique muscle weakening. Other current options include insertion of an inert spacer or suture between the cut ends of the superior oblique tendon, and split-tendon lengthening of the tendon (see Chapter 14).
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.