To examine changes in vertical deviation and improvement in head tilt after graded inferior oblique (IO) recession surgery in patients with congenital unilateral superior oblique palsy (SOP). Frequency of inferior oblique overaction (IOOA) or bilateral SOP in the contralateral eye after surgery was also investigated.

We retrospectively reviewed medical records of 65 patients who had undergone graded IO recession surgery in unilateral congenital SOP with at least 1 year of postoperative follow-up. Postoperative vertical deviation was classified as excellent (under 3 prism diopters, PD), good (4-7 PD) or poor (over 8 PD). The occurrence of IOOA was considered if more than 2 IOOAs were observed in the contralateral eye after surgery.

Forty-five of the 65 patients (69%) obtained excellent results and 67.3% had improvement in head tilt after surgery. IOOA in the contralateral eye was not observed in any patients before surgery. Postoperative IOOA in the contralateral eye occurred in 9 patients (13.8%) and a diagnosis of masked bilateral SOP was made in 1 patient (1.5%).

The graded IO recession procedures are considered to be an effective surgical method for the treatment of unilateral congenital SOP. However, IOOA or masked bilateral SOP occurring in the contralateral eye was observed in 15.3% of the patients undergoing surgery.