Why strabismus surgery works: the legend of the dose-response curve

The dose-response relationship has historically been regarded as an important approach to improve the success of strabismus surgery. The purpose of this study was to explore the role of preoperative deviation, in addition to the amount of surgery, as a predictor of the response to strabismus surgery.

Dose-response data from a variety of sources are analyzed in a multiple linear regression model with both preoperative deviation and surgical dose as independent variables. P values and partial correlations from these regressions are used to investigate the relative contribution of each factor.

These analyses consistently show that preoperative deviation is statistically a better predictor of the response to surgery than the amount of surgery. In data sets where one factor is constant, preoperative deviation alone accounts for 78%, and the amount of surgery alone accounts for 46% of the variance of the surgical response.

The importance of preoperative deviation as an independent variable implies a biologic response to strabismus surgery that tends to produce more change in alignment when the deviation is large and less when it is small. The strong association of amount of surgery with surgical outcome in bivariate analysis studies may be an artifact of making the amount of surgery a strict function of the preoperative deviation. Because of its lesser role as a predictor, accuracy of preoperative deviation measurement upon which the amount of surgery is based, refinement of the dose-response curve, or use of adjustable sutures may have less potential to improve surgical outcome than generally believed.