Longitudinal changes in binocular coordination of smooth pursuit in patients with intermittent exotropia after strabismus surgery

Purpose: To observe the change in horizontal smooth pursuit in patients with intermittent exotropia before and after strabismus surgery. Methods: The smooth pursuit of patients with intermittent exotropia was recorded using a video eye-tracker before and 1 week, and 1, 3, and 6 months after strabismus surgery. Subjects were asked to track a step-ramp target moving at ±6.1°/sec horizontally as accurately as possible under binocular viewing. The differences in gain (eye velocity divided by target velocity) and amplitude of smooth pursuit between right and left eyes before and after surgery were compared. Results: A total of 9 patients (mean age, 22.2 ± 13.9 years) were included. Mean preoperative ocular alignment at near was 59.1^Δ ± 34.7^Δ. The difference in gain between the left and right eyes before surgery was 0.23 ± 0.1; in amplitude, 3.0° ± 3.7°. These values were improved at 1 week after surgery (gain, 0.08 ± 0.06; amplitude, 0.9° ± 0.65°) and continued to improve for 6 months after surgery; however, ocular alignment at near reverted from 5.9^Δ ± 10.5^Δ to 18.9^Δ ± 17.5^Δ by 6 months after surgery. Conclusions: In this small patient cohort, surgical correction of ocular alignment improved binocular coordination of smooth pursuit in intermittent exotropia. In the long term, the improvement of the binocular coordination of smooth pursuit tended to remain, although the eye position partially reverted to the presurgical state.