Unilateral anterior transposition of the inferior oblique muscle for correction of hypertropia in primary position.

PURPOSE To evaluate the correction of hypertropia in primary position with unilateral inferior oblique (IO) anterior transposition (IOAT). METHODS Ten patients with idiopathic (nonparalytic, restrictive, or dissociated vertical deviation) hypertropia with marked IO overaction, who underwent unilateral IOAT, were prospectively evaluated to observe the correction of the hypertropia in primary position. No previous ocular muscle surgery had been performed. Four patients had esotropia and two had exotropia. In addition to the proposed surgery, horizontal procedures were performed to correct horizontal deviation, but no vertical transposition of horizontal muscles was done. Four patients had hypertropia and IO overaction, without horizontal strabismus, and IOAT was the only procedure performed. The IO muscle was reinserted 1 mm laterally to the lateral extremity of the inferior rectus muscle insertion using only one suture. The statistical analysis was performed by Wilcoxon rank sum test. RESULTS The mean absolute correction in primary position was 18.1 prism diopters (PD) (range, 4 to 33), directly proportional to the size of the hypertropia before surgery. Nine of the 10 patients had a residual vertical deviation of </=6 PD. After surgery, 4 patients (40%) presented limited elevation in adduction (-2) in the field of the operated IO, presumably caused by the antielevator effect of the transposed muscle, which did not improve during the follow-up period (range, 2 to 79 months). CONCLUSION Unilateral IOAT is an effective technique for correction of large hypertropia associated with marked unilateral IO overaction. Some lower lid curvature deformity and some limitation of elevation were observed in forced upgaze in some patients, but this was of no cosmetic importance.