The Effect of Inferior Oblique Muscle Transposition in Primary and Secondary Inferior Oblique Muscle Overaction

Purpose: To evaluate and compare the effect of transposition of inferior oblique muscle in patients with primary inferior oblique muscle overaction and secondary due to superior oblique muscle palsy. Methods: The present study included 41 patients (53 eyes), who appeared to have primary or secondary inferior oblique muscle overaction due to superior oblique muscle palsy and received transposition of inferior oblique muscle with at least 3 months of fol-low-up. Patients were retrospectively analyzed to compare the effect of correction and its prognosis. Inferior oblique muscle over-action was graded as +1 to +4 according to the severity. Successful surgery was defined as postoperative inferior oblique muscle overaction from 0 to +1 and failure as above +2. Hypertropia in primary gaze was also recorded to evaluate the effect of correction. Results: Twenty-six (35 eyes) and 15 (18 eyes) patients with primary and secondary inferior oblique muscle overaction due to superior oblique muscle palsy, respectively, received transposition of inferior oblique muscle. Patients with primary inferior obli-que muscle overaction showed correction of 2.1 ± 0.9 with preoperative inferior oblique muscle overaction of 2.0 ± 0.7. Patients with secondary inferior oblique muscle overaction showed a correction of 2.3 ± 0.9 with preoperative value of 2.3 ± 0.8. Each 3.2 ± 4.1 prism diopters (PD) and 6.5 ± 5.3 PD of hypertropia at primary gaze showed correction of 3.0 ± 7.4 PD and 6.3 ± 5.1 PD, respectively, in each group. Conclusions: Primary and secondary inferior oblique muscle overaction due to superior oblique muscle palsy showed no differ-ence in correction of overaction and hypertropia after transposition of inferior oblique muscle. Except for presence of inferior obli