Isolated inferior oblique myectomy for vertical deviations of at least 20 prism diopters in the primary position

PurposeTo investigate the efficacy of inferior oblique (IO) myectomy in patients with primary position hyperdeviations ≥20Δ, with unilateral IO overaction and clinically normal or minimally underacting superior oblique ductions, where excyclotorsion was not a barrier to fusion in primary position.MethodsThe medical records of patients who underwent IO myectomy from 1999 to 2014 were retrospectively reviewed to identify those with primary position hyperdeviations of ≥20Δ. Postoperative changes in vertical deviations in primary position and horizontal and vertical planes were analyzed.ResultsA total of 17 patients were included. Mean follow-up was 17.3 months. At last follow-up, the mean hyperdeviation decreased in all five documented positions of gaze by 84% of the initial value, with mean reduction in the primary position vertical deviation from 26.5Δ to 4.1Δ. There was rapid early reduction of deviation in all gaze positions (mean, 53%) at 2-4 weeks' follow-up, with a corresponding mean reduction of vertical deviation to 11.4Δ. There were no overcorrections, but 5 patients (29%) had a postoperative primary position hyperdeviation of >5Δ. Two patients (12%) required further vertical rectus surgery.ConclusionsIn our patient cohort, isolated IO myectomy did not result in symptomatic overcorrections and had a reoperation rate that compares favorably to the traditional primary simultaneous two-muscle approach.