Dose-response relationship in inferior oblique muscle recession

Recession of the inferior oblique muscle is a widely applied operation in the treatment of strabismus sursoadductorius. In this retrospective study, the dose-response relationship of this procedure was determined in order to improve surgical outcomes. In particular, the effect of an additional anteroposition of the operated muscle was analysed, as well as differences between short and long term results.

This retrospective study included 37 patients. Inclusion criteria were unilateral strabismus sursoadductorius and normal retinal correspondence. Exclusion criteria comprised previous ocular muscle surgery and any ocular or orbital disease. Nineteen patients had received an additional anteroposition of the muscle. Patients were examined at a tangent screen pre-operatively and 1 day post-operatively (short-term effect). Sixteen patients underwent an additional examination 3 months post-operatively (long-term effect). Changes of vertical, torsional and horizontal deviations, measured in different positions of gaze, were related to the surgical dose in order to calculate the dose-response relationship by linear regression analysis.

Surgery always reduced preoperative deviations. The short-term vertical dose-response without/with anteroposition was 0.6 degrees /0.5 degrees per mm in primary gaze and 1.2 degrees /1.1 degrees per mm in adduction. The short-term torsional dose-response without/with anteroposition was 0.8 degrees /0.5 degrees per mm in primary gaze. Three months later, the vertical effect had remained constant, whereas the torsional effect had decreased to 0.6 degrees /0.1 degrees per mm. Variance was high, e.g. the standard deviation of the short-term effect for the vertical deviation in adduction was 2.5 degrees .

Despite the large variation of effects, a dose-response relationship could be established, facilitating surgical planning. Large vertical deviations with small excyclodeviation are an indication for additional anteropositioning. The torsional effect of inferior oblique muscle recessions can diminish over time.