Purpose To compare inferior oblique (IO) myectomy with recession for the treatment of superior oblique (SO) palsy.

Methods A retrospective review of medical records identified all patients with SO palsy who underwent IO weakening procedures. Patients were excluded if IO muscle surgery was bilateral, combined with other vertical muscle surgery and if follow up was less than 4 weeks. Good outcome parameters were: improvement of deviation in primary gaze, resolution of diplopia in primary and reading gazes and correction of head tilt to the contralateral side. We analysed subsets of subjects with large preoperative vertical deviations (>15Δ) and those with small-moderate deviations (≤15Δ). Comparisons were made using Wilcoxon rank sum and Fisher's exact tests.

Results Eighty-five patients met the study criteria. Forty-three eyes underwent myectomy, and 42 underwent recession of the IO. Those patients who underwent myectomy compared with recession had less postoperative hypertropia (HT) in primary gaze (p<0.001) and were more likely to meet criteria for success as measured by ≤4Δ residual HT (p=0.056). This difference was pronounced (p=0.005) in patients with preoperative small-moderate deviations, but statistical significance was lost in patients with large preoperative deviations. There was no difference between the two groups with respect to resolution of diplopia or anomalous head tilt.

Conclusions IO weakening procedures, including both recession and myectomy, are effective in the treatment of SO palsy. While the two procedures were similar in treatment of diplopia and abnormal head tilt, our findings support myectomy as slightly more effective than recession in improving HT in primary gaze; this difference is more pronounced in individuals with small-moderate preoperative hyperdeviations.