Outcomes of Asymmetric Primary Inferior Oblique Muscle Overaction Managed by Bilateral Myectomy and Tucking of Proximal Muscle End: A Cohort Study

BACKGROUND: We present the outcomes of bilateral myectomy and tucking of the proximal end of the muscle for the treatment of asymmetric primary inferior oblique (IO) overaction. METHODS: This was a one-armed prospective cohort study. An ophthalmologist and orthoptist evaluated cases of primary IO muscle overaction presenting between January 2010 and December 2013. All eyes underwent bilateral myectomy and tucking of the proximal end of the IO muscle. Data were collected on ocular motility, the angle of deviation, postoperative complications, and status of hypertropia at 6 months postoperatively. The 95% confidence intervals (CI) were calculated. The statistical significance was indicated by P < 0.05. RESULTS: The patient cohort was comprised of 51 patients with primary IO muscle overaction. Preoperatively, all eyes had +2 or greater overaction of the IO muscle except one patient with +1 and +3 overaction in the right and left eyes, respectively. At 6 months postoperatively, the reduction in the angle of deviation for distance and near was 32.6 prism diopters (PD) ([95% CI 30.3–34.9], P < 0.001) and 32.6 PD ([95% CI: 29.8–35.3], P < 0.001), respectively. There was no significant difference in the postoperative variation of the reduction in the angle of deviation based on gender, right or left eye, and type of horizontal strabismus. There were no cases of “A” or “V” patterns, clinically a significant IO underaction or “adherence syndrome” postoperatively. CONCLUSION: Bilateral myectomy and tucking of the proximal end of the muscle is likely an effective method of treating asymmetric primary IO muscle overaction.