Effect of inferior oblique muscle belly transposition on versions and vertical alignment in primary position

To evaluate the effect of inferior oblique muscle belly transposition (IOBT) on vertical deviation (VD) in primary position and inferior oblique overaction (IOOA).

Twenty-eight patients who underwent unilateral IOBT for mild hypertropia (≤ 10^△) due to unilateral IOOA were included. Surgical results regarding the correction of hypertropia, IOOA, and fovea disc angle (FDA) were analyzed and compared between groups A (VD ≤ 5^△) and B (5^△ < VD ≤ 10^△).

IOBT showed an overall reduction of 5.86^△ (± 2.24^△) of primary position VD, a mean correction of 1.00 (± 0.27) of IOOA, and an average change of 1.83° (± 3.02°) of FDA. The surgical success rate of IOBT for VD correction and IOOA elimination in all patients was 68% and 71%, respectively. The correction of VD was correlated with preoperative VD significantly (r = 0.86, p < 0.001). Consistently, IOBT demonstrated comparable efficacy in reduction of VD between group A and group B (p = 0.507). Furthermore, the two groups were comparable in the success rates for correcting VD and IOOA (both p > 0.05). None of the patients developed consecutive hypotropia, postoperative contralateral IOOA, or anti-elevation syndrome postoperatively.

IOBT achieved satisfactory outcomes in patients with mild primary position VD (≤ 10^△) that is associated with unilateral IOOA, without any risk of overcorrection of VD and contralateral IOOA for a follow-up period of up to 12 months. This procedure is considered effective and safe alternative for weakening the IO in patients with appropriate surgical indications.