Dose-effect relationship of medial rectus muscle advancement for consecutive exotropia

To evaluate the dose-effect relationship for medial rectus muscle advancement in patients with consecutive exotropia.

Pre- and postoperative deviations 1 day and 6 months after surgery were measured by linear strabismometric method. The change in deviation (difference between preoperative and postoperative deviation at 6 months) was correlated to the surgical dose (dose-effect relationship) and the preoperative distance deviation by multiple regression analysis. Multivariate regression analysis was performed with three and two independent variables (preoperative distance deviation, millimeters of advancement, intraoperative muscle stretch test), with change in deviation as a dependent variable.

Twenty-four patients (mean age, 33 years; range, 18-60 years) were included. The mean preoperative deviation was 32(∆), the mean postoperative deviation was 0(∆) at day 1, and 9(∆) 6 months after surgery. The mean dose-effect relationship was 5(∆)/mm at day 1 and 4(∆)/mm 6 months after surgery. Mean exodrift 6 months after surgery was 9(∆). The univariate model was statistically significant for each variable (P < 0.05). The multivariate model was statistically significant for preoperative distance deviation and millimeters of advancement (P < 0.05) but not for intraoperative muscle stretch test (P = 0.1519).

The dose-effect relationship at 6 months after advancement of the medial rectus muscle for consecutive exotropia could be a useful guide for planning surgical correction, even considering the expected exodrift.