Clinical Outcomes of Inferior Oblique Myectomy in Patients with Unilateral Superior Oblique Palsy

Abstract

Background – Unilateral superior oblique palsy (SOP) is the most common isolated cranial nerve palsy. This report looks at the results and safety of inferior oblique (IO) myectomy for SOP. Methods – A retrospective chart review of patients with fusional ability who underwent IO myectomy for unilateral SOP over a 15-year period, at one of our university-associated health care centers. Primary outcomes were distance hypertropia and excyclotropia in primary position, and inferior oblique overaction (IOOA). A secondary outcome was the correlation between the age at surgery and the residual distance hypertropia. Results – A total of 73 patients with unilateral SOP who underwent IO myectomy were included in the analysis. Mean pre-operative values were: distance hypertropia: 15.41 ± 6.8 Prism Diopters (range 4–30 PD), IOOA: +2.2 ± 0.7 (range 0-3.5) and excyclotropia:+5.34 ± 3.6° (range 0–12°). Mean post-operative values were: distance hypertropia: 3.7 ± 3.4PD [0-14PD], IOOA: -0.1 ± 0.8 [(-2)-2] and excyclotropia: +1.1 ± 2.3°[(-5)-10]. The younger age group (0–20 years old) had a trend toward smaller preoperative distance hypertropia (P = 0.051), and a significantly smaller distance hypertropia post-operatively (p = 0.007). There was no case of over-correction or ocular complication. Conclusion - On average, IO myectomy results in a 11.7PD reduction of the distance hypertropia, and 4° reduction of excyclotropia, with an effective reduction of IOOA. While these results are comparable to other surgical methods reported in the literature, they underline an efficacy without the risks of complications such as anti-elevation syndrome and possible scleral perforation. The younger age group had a trend toward smaller preoperative deviation, and better outcomes compared to the older age group.