The effect of medial versus lateral rectus muscle surgery on distance-near incomitance

For strabismus with distance-near incomitance (unequal distance and near deviations), it is customary to select lateral or medial rectus muscle surgery based on whether the deviation is greater at distance or near. The purpose of this study is to examine how this choice between medial and lateral rectus muscle surgery affects distance-near incomitance.

Preoperative and postoperative distance and near deviations were obtained from a retrospective review of medical records of consecutive patients who underwent bilateral medial or lateral rectus muscle recessions or resections between January 1, 2000, and June 30, 2007.

A total of 626 procedures were identified. After exclusions, initial procedures included 267 medial rectus muscle recessions that produced an average of 9% more exoshift at near and 159 lateral rectus muscle recessions that produced an average of 34% more esoshift at distance. A larger preoperative distance-near incomitance is associated with a greater reduction in distance-near incomitance with surgery, irrespective of which muscles undergo surgery. Recessions for consecutive deviations and resections for residual deviations exhibited a similar pattern.

Esotropia tends to be greater at near and exotropia greater at distance fixation. The apparent greater effect of medial rectus muscle surgery on near deviation and lateral rectus muscle surgery on distance deviation is probably an artifact of this difference in preoperative characteristics. Whether a deviation is greater with distance or near fixation may not be a major consideration in choosing between medial or lateral rectus muscle surgery.