Effect of superior oblique weakening on vertical alignment and horizontal and vertical incomitance in patients with A-pattern strabismus.

Objective: To determine the relationship between the magnitude of preoperative A pattern and the correction of vertical alignment and horizontal and vertical incomitance in patients treated with superior oblique muscle-weakening procedures for A-pattern strabismus.

Methods: The records of consecutive patients who underwent surgery for A-pattern strabismus between 1997 and 2008 were retrospectively reviewed. Both horizontal (from up- to downgaze) and vertical (from right to left gaze) incomitance were assessed.

Results: Twenty-six patients were treated with superior oblique muscle-weakening procedures (either tendon spacer or nasal or posterior 7/8 temporal tenotomy, with or without simultaneous rectus muscle surgery). In these patients, the A pattern improved from 36Δ preoperatively (range, 15Δ-75Δ) to 6Δ postoperatively (range, 0Δ-16Δ). The magnitude of the reduction in A pattern correlated strongly with the size of preoperative A pattern (r=0.92), whereas the reduction in the magnitude of the vertical incomitance correlated weakly with the magnitude of the preoperative deviation (r=0.56). There was no significant correlation between the magnitude of the A pattern and the vertical incomitance (r=0.25). Of the 9 patients with preexisting primary position vertical deviation≥6Δ, 5 required additional vertical rectus muscle surgery.

Conclusions: Superior oblique muscle-weakening surgery improved the A pattern but did not reliably improve the primary position vertical deviation and lateral gaze vertical incomitance. Patients with associated primary position vertical deviations of >6Δ preoperatively tended to have a greater likelihood of requiring additional strabismus surgery.