To determine the efficacy of isolated inferior oblique myectomy on hypertropia in primary position, side gazes, and tilts, and its effect on comitancy and abnormal head posture in unilateral superior oblique palsy.

Thirty-nine patients with unilateral superior oblique palsy who had inferior oblique overaction underwent inferior oblique myectomy. The hypertropia was measured in primary position, side gazes, and tilts preoperatively and postoperatively. Abnormal head posture was also assessed. Success was defined as primary position hypertropia of 5 prism diopters (PD) or less.

The mean distance hypertropia was 15.7 ± 7.7 PD (range: 3 to 30 PD) preoperatively and 1.5 ± 3.3 PD (range: 0 to 16 PD) postoperatively (P < .001). The mean reduction of distance hypertropia postoperatively was 14.2 ± 7.8 PD (range: 3 to 30 PD). The contralateral gaze hypertropia decreased from 21.7 ± 9.0 PD (range: 5 to 45 PD) preoperatively to 3.6 ± 5.1 PD postoperatively (range: 0 to 20 PD) and ipsilateral head tilt hypertropia decreased from 21.9 ± 8.4 PD (range: 8 to 40 PD) preoperatively to 5.0 ± 5.9 PD (range: 0 to 24 PD) postoperatively (P < .000 for both). Incomitance (contralateralipsilateral gaze hypertropia) decreased from 15.0 ± 7.4 PD (range: 3 to 35 PD) preoperatively to 2.8 ± 4.1 PD (range: 0 to 16 PD) postoperatively (P < .001). The success rate between the two groups of patients who had hypertropia of 15 PD or less and greater than 15 PD in primary position was not statistically different (94.7% vs 85%). Two patients underwent a second operation for residual hypertropia. There was no overcorrection. Thirty-two patients had abnormal head posture, which resolved postoperatively in 29 cases.

Isolated inferior oblique myectomy is an effective procedure in resolving hypertropia up to 30 PD due to unilateral superior oblique palsy, with a minimal risk of overcorrection and low risk of undercorrection. It decreases incomitancy, is a self-titrating procedure, and resolves abnormal head posture efficiently. [J Pediatr Ophthalmol Strabismus. 2019;56(1):23-27.]. Copyright 2018, SLACK Incorporated.