The maximum motor fusion test: a parameter for surgery for acquired esotropia

The purpose of this study was to determine whether surgery for acquired esotropia based on the maximum capacity for motor fusion measured with a prism bar could be used to increase the number of millimeters of bilateral medial rectus recession that could be performed without producing an early overcorrection or a late consecutive exotropia, as a way safely to reduce the need for postoperative wear of glasses or a bifocal.

Category I patients had residual deviations of esotropia (ET) of 12 PD or more with distance fixation, measured after a full hyperopic correction of +1.50 to +3.25 was placed, and had no significant anisometropia or astigmatism. Category II patients had residual deviations of esotropia of less than 11 PD with distance fixation and had residual deviations of esotropia with near fixation (ET') of at least 10 PD more than esotropia with distance fixation ("clinical high AC/A"). Category III patients had had previous bilateral medial rectus muscle recessions and had recurrent esotropia with near fixation of more than 10 PD. For patients in categories I and II, bilateral medial rectus muscle recessions were performed by using a published dose-response table from the national Prism Adaptation Study but with the maximum capacity for motor fusion as the input parameter instead of the prism-adapted angle. Patients in category III received re-recessions of one or both medial rectus muscles, according to a previously published system, with the distance fusional amplitude as the input parameter.

In category I, 24 of 30 (80%) patients needed no glasses after surgery, 1 of 30 had esotropia, and 2 of 30 had exotropia (XT) (10% reoperation rate). In category II, 35 of 36 (98%) patients needed no bifocals after surgery, and 3 of 36 had exotropia (9% reoperation rate). In category III, 10 of 10 patients needed no bifocals, and 2 of 10 had exotropia (20% reoperation rate).

When a postoperative reduction in dependence on continuous wear of an optical appliance is a reasonable goal, the maximum motor fusional capacity, measured with a prism bar, is a good parameter for surgical design.