When the size of the deviation varies in different gaze positions, the surgical plan should be designed with a goal of making the postoperative alignment more comitant.
When the size of the esodeviation or exodeviation changes significantly between right and left gaze, paresis, paralysis, or restriction is suggested. In general, restrictions must be relieved for surgery to be effective, and the surgical amounts usually used to correct a misalignment of a given size may not be applicable.
When there is no restriction to account for an incomitant deviation, the deviation is treated as if it were caused by a weak muscle, whether from neurologic, traumatic, or other causes. If the weak muscle exhibits little or no force generation, transposition procedures are usually indicated. Otherwise, treatment consists of some combination of resection of the weak muscle (or advancement if it has been previously recessed) and weakening of its direct antagonist or yoke muscle.
In some cases, both restriction and weakness are present, particularly in long-standing paretic or paralytic strabismus, and a combination of treatment strategies is necessary. Forced duction and active force generation testing are helpful in these cases.
Treatment of horizontal distance–near incomitance has classically consisted of medial rectus muscle surgery for deviations greater at near and lateral rectus muscle surgery for deviations greater at distance. Evidence suggests that, regardless of which muscles are operated on, the improvement in distance–near incomitance is similar.
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.