o determine the postoperative horizontal alignment changes following different inferior oblique (IO) weakening procedures on cases with IO overaction (IOOA).

In this interventional case series, a total of 40 patients undergoing IO weakening surgery were participated. A comprehensive ophthalmic examination including measurement of the best corrected visual acuity, refractive error, stereopsis, ocular deviation and also assessment of ocular motility as well as anterior and posterior ocular segments evaluation were performed. The grade of IOOA was assessed based on the muscle function in the gaze of elevation in adduction. All study subjects were operated 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.

Our findings showed that all types of IO weakening surgeries improved the postoperative muscle function, hypertopia and V-pattern significantly (P=0.001 for all). Generally, IO weakening surgeries did not effect on the postoperative horizontal alignment and mean exoshift of 0.44pd 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% were shifted away from orthophoria.

Based on our findings, no horizontal alignment change would be expected after weakening procedures of overacted IO. Most of our cases didn’t show any change while a few of them presented eso- or exoshift that was less than 5pd which can be ignored clinically.