Underacting inferior oblique muscle following myectomy or recession for unilateral inferior oblique overaction.

PURPOSE To assess the incidence and investigate the functional impact of postoperative overcorrection following primary unilateral inferior oblique muscle recession and myectomy for inferior oblique overaction. METHODS A retrospective study of 79 consecutive patients undergoing inferior oblique myectomy (43) or recession (36) with a minimum 6 months of postoperative follow-up. All underwent ocular motility examinations preoperatively and postoperatively at approximately 2 weeks and 6 months. The vertical deviation in primary position and on contralateral gaze and inferior oblique versions and ductions on contralateral elevation were analyzed. RESULTS At 6 months, 51 patients had no inferior oblique underaction (group 1), 23 of 28 who had developed inferior oblique underaction were asymptomatic (group 2), and the remaining 5 were symptomatic (group 3). The mean preoperative hyperdeviation was 12.9 (group 1), 13.1 (group 2), and 15 (group 3) prism diopters (PD) in primary position. Postoperatively, these measured 3.8 (group 1), 3.8 (group 2), and -7.8 (group 3) PD (- indicates deviation reversal). The mean preoperative and postoperative inferior oblique versions for these three groups were +2.7, +2.2, +2.2 units and +0.9, -1.0, -1.4 units, respectively. CONCLUSION Inferior oblique underaction was common (28 patients, 35.4%), generally mild, persistent, and usually asymptomatic 6 months following surgery. Although uncommon (5 patients, 6.3%), symptomatic inferior oblique underaction required further surgery with a successful outcome. They included 2 patients with a history of head or orbital trauma and one with masked and one with highly asymmetric bilateral inferior oblique overaction.