The effect of inferior oblique muscle weakening on horizontal alignment

PURPOSE: To determine the postoperative horizontal alignment changes following different inferior oblique (IO) weakening procedures on cases with IO overaction (IOOA). METHODS: A total of 40 patients undergoing IO weakening surgery participated in this prospective interventional case series. A comprehensive ophthalmic examination was performed on all patients. The grade of IOOA was assessed based on the muscle function in the gaze of elevation in adduction. All study subjects were operated on by one of the IO weakening procedures including recession, myectomy, or anteriorization, and all were followed up for at least three months after the surgery. Postoperative change of the horizontal alignment in primary position was the main outcome measure. RESULTS: Our findings showed that all types of IO weakening surgeries improved the postoperative muscle function, hypertopia, and V-pattern significantly (P = 0.001). Generally, IO weakening surgeries had no effect on the postoperative horizontal alignment, and mean exoshift of 0.44 ± 6.2 prism diopters (PD) was observed in all study subjects, specifically. It was found that 70% of cases had no postoperative horizontal changes, 15% showed improvement toward orthophoria, and 15% shifted away from orthophoria. CONCLUSIONS: Based on our findings, no horizontal alignment change would be expected in the majority of cases undergoing weakening procedures of overacted IO. Most of our cases did not show any change while a few of them presented eso- or exoshift less than 5 pd which can be clinically ignored.