Surgical Dose-Effect Relationship in Single Muscle Advancement in the Treatment of Consecutive Strabismus

Abstract

To evaluate the dose-effect relationship for single muscle advancement in consecutive esotropia and consecutive exotropia. Medical records from 22 patients with consecutive esotropia (n = 11) or exotropia (n = 11) were retrospectively reviewed. All patients had undergone either single lateral rectus or medial rectus advancement surgery. The alterations in muscle position and the angle deviation were measured in millimeters and prism diopters (PD) and the change in deviation was determined by subtracting the postoperative angle of deviation at 1 week from the preoperative angle. To quantify the clinical effect of muscle advancement, the ratio of the change in muscle position to the change in visual angle deviation was calculated (ie, the surgical dose-effect relationship). The mean deviation was 25.5 ± 10.4 PD preoperatively and 0 ± 6.9 PD at 1 week postoperatively. The success rate was 82% in the consecutive esotropia group and 91% in the consecutive exotropia group. The average correction ratio was 4.31 ± 0.96 PD/mm. In multiple regression analysis of total patients with consecutive strabismus and the consecutive esotropia group, the amount of muscle advancement and preoperative angle deviation were positively correlated with the correction ratio. In the consecutive exotropia group, there was no significant relationship between variables. Single muscle advancement generally provides enough correction for most consecutive strabismus cases. Surgical dose-effect relationship increases with preoperative angle deviation and amount of muscle advancement. Surgeons should consider reducing the amount of muscle advancement in patients with larger angle deviations, especially patients with consecutive esotropia.