For small, symptomatic deviations that lack a prominent torsional component—especially those that have become comitant—prisms that compensate for the hyperdeviation in primary position may be used to overcome diplopia. Abnormal head position, significant vertical deviation, diplopia, and asthenopia are indications for surgery. Common operative strategies are discussed in the following sections (see Chapter 14 for details of the procedures and for related videos).
Unilateral superior oblique muscle palsy
There are many options for surgical treatment of a unilateral palsy. Any of the 4 cyclovertical muscles in each eye could potentially be operated on to correct the hypertropia. Some surgeons use a uniform approach and weaken the ipsilateral antagonist inferior oblique muscle. For other surgeons, the surgical plan is informed by superior oblique tendon laxity. Tendon laxity is assessed at the time of surgery by forced duction testing, in which the globe is pushed (translated) posteriorly into the orbit while it is simultaneously extorted, thus placing the superior oblique tendon on stretch (Video 11-1). If the tendon is lax, they perform a superior oblique tightening procedure; if it is not, they usually perform an inferior oblique weakening procedure. Other ophthalmologists use tendon laxity only as diagnostic confirmation of superior oblique palsy.
Oblique muscle forced duction testing.
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Many surgeons take a tailored approach, reflecting the variety of hypertropia patterns that may occur with superior oblique palsy. For example, if underaction of an affected right superior oblique muscle is the most prominent feature, then the deviation will be greatest in down-left gaze. Another patient, by contrast, may predominantly exhibit overaction of the antagonist inferior oblique muscle, with the greatest deviation in up-left gaze. Because each of the 8 cyclovertical muscles has a somewhat different field of action, surgery involving some muscles will be more appropriate than others, depending on the field of gaze in which the deviation is largest (Table 11-3). In addition, some surgeons believe that superior oblique tightening is the most effective procedure for addressing a marked head tilt in children with congenital superior oblique palsy. Extorsion in unilateral superior oblique palsy rarely produces symptoms, but when it does, it can be corrected with a Harada-Ito procedure.
If the hyperdeviation is greater than 15 prism diopters (Δ) in primary position, surgery usually involves at least 2 muscles. Ipsilateral inferior oblique weakening and superior oblique tightening represent a particularly powerful combination but carry an increased risk of problematic iatrogenic Brown syndrome or overcorrection. In the unusually severe case with a vertical deviation greater than 35Δ in primary position, 3-muscle surgery is usually required.
Whatever the approach, it is important to avoid overcorrection of a long-standing unilateral superior oblique muscle palsy. Because there are often no sensory or motor adaptations to hypertropia in the opposite direction, disabling diplopia can result.
Bilateral superior oblique muscle palsy
Surgical planning for treatment of bilateral superior oblique muscle palsy can be complex. If the paresis is asymmetric, hypertropia in primary position may be present and require many of the same considerations as hypertropia in unilateral palsy. In addition, there is often symptomatic extorsion or a V pattern that needs to be addressed.
If the palsies are symmetric (minimal hypertropia in primary position), both inferior oblique muscles can be weakened if they are overacting and hypertropia is present in side gaze. Bilateral superior oblique muscle tightening should be performed when hypertropia in side gaze is accompanied by V-pattern esotropia or symptomatic extorsion, especially in downgaze. If there is symptomatic extorsion but minimal hypertropia in side gaze, bilateral Harada-Ito procedures can be performed. Other, less commonly used approaches, such as bilateral inferior rectus muscle recessions, serve to add extra innervational drive on downgaze to help overcome the superior oblique deficits.
Table 11-3 Surgical Treatment of Unilateral Superior Oblique Palsy
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.