Effectiveness of Inferior Oblique Myectomy in Unilateral Superior Oblique Palsy Depending on Magnitude of Hyperdeviation

Abstract

Purpose: To evaluate surgical outcome and effectiveness of inferior oblique (IO) myectomy on unilateral superior oblique palsy (SOP) as a primary treatment. Methods: This study is a retrospective review of the medical records of 99 patients who had undergone IO myectomy due to SOP as a first-line treatment. Sixty-five patients with hyperdeviation of 15 prism diopters (PD) or less were categorized into group 1, 22 patients with hyperdeviation between 16 PD to 20 PD into group 2, and 12 patients with hyperdeviation higher than 20 PD into group 3. Preoperative hyperdeviation, postoperative hyperdeviation, and improvement of head tilting were then compared between the 3 groups. Surgery was determined to be successful when the post-op residual hyperdeviation is less than 5 PD, or when the improvement of hyperdeviation and head tilting was noted, for the patients who had preoperative deviation less than 5 PD, and without hypercorrection. Results: All groups showed significant improvement of hyperdeviation, and the amount of correction was larger in group with larger preoperative hyperdeviation. 80.3%, 95.0%, and 90.9% of patients showed improvement of head tiling and success rate was 87.7%, 77.3%, and 50.0% in group 1, 2, and 3 respectively. Group 1 and 2, group 2 and 3 had no significant difference in success rate but only group 1 and 3 had significant difference. Conclusions: Considering success rate with improvement of head position, self-titrating and possibility of overcorrection, IO myectomy could be an effective option as a first-line surgical treatment for unilateral SOP with hyperdeviation of 20 PD or less. However, due to a 50% success rate in patients with hyperdeviation larger than 20 PD, a secondary operation must be considered following IO myectomy, or a two-muscle procedure must be considered as a primary treatment.