Ipsilateral gaze deviation as a risk factor for surgical overcorrection in two-muscle surgery for unilateral superior oblique palsy

Abstract

To investigate the angle of deviation in various gaze positions as a risk factor for overcorrection of moderate-angle unilateral trochlear nerve palsies treated with two-muscle surgery. The medical records of consecutive patients with presumed unilateral moderate-angle trochlear nerve palsy who underwent two-muscle surgery were retrospectively reviewed. Patients with overcorrection, defined as reversal of hyperdeviation by prism alternate cover testing at distance (straight ahead) or near measured at 6weeks, were compared to non-overcorrected patients for their preoperative torsion and ocular alignment at near and distance. A total of 45 patients (age range, 12-77years; 24 [53%] males) with deviation ranging from 14Δ to 25Δ in primary position underwent two-muscle surgery, of whom 8 (18%) experienced surgical overcorrection by 6weeks' follow-up. The preoperative angle of deviation was similar between overcorrected and non-overcorrected patients for eight of nine cardinal distance positions and near gaze; however, patients with smaller deviations in ipsilateral gaze were more likely to be overcorrected with two-muscle surgery (8.5 vs 16.0 [P=0.029]). Cut point analysis determined that an ipsilateral gaze of ≤9Δ was significantly associated with overcorrection. Greater lateral incomitance also trended toward overcorrection (15.0 vs 9.0 [P=0.059]). Torsion was not a clinically significant indicator of overcorrection (3.5 vs 6 [P=0.083]). A preoperative ipsilateral angle of ≤9Δ was associated with overcorrection in patients undergoing two-muscle surgery for moderate angle unilateral trochlear nerve palsies.