Analysis of Convergence and Divergence Using an Eye Tracker in Acquired Comitant Esotropia

Abstract

Purpose To quantitatively evaluate vergence-related eye movements in acquired comitant esotropia (ACE) using video-based eye tracking and to characterize abnormal movement patterns and their postoperative changes. Methods We studied 46 patients with ACE (mean age, 24.3 years) who underwent unilateral or bilateral medial rectus recession. Binocular gaze was recorded at 300 Hz (Tobii Pro Spectrum) while participants alternately fixated every 5 seconds on a near target (30 cm) and a far target (60 cm). Stable amplitude was the difference between the mean near- and far-target gaze angles in the 3- to 4-second period after each target step. Eye movements were classified as conjugate or vergence according to the direction of stable amplitude in each eye. Saccadic onset, offset, and postsaccadic stabilization metrics were extracted. Statistical analyses included logistic regression and Wilcoxon signed-rank tests. Results Despite vergence stimulation, 26 patients (56.5%) exhibited conjugate movements, whereas 20 patients (43.5%) showed vergence movements. Conjugate movements were associated with a larger absolute stable amplitude of the fixating eye, larger absolute saccadic amplitudes in both eyes, and a smaller interocular difference in saccadic amplitude (fixating – non-fixating; all P < 0.05). In addition, interocular differences were observed in stabilization time and amplitude, particularly in the vergence group. Postoperatively, conjugate movements decreased markedly, as 81.8% of patients (18/22) demonstrated vergence movements at 1 month, and 92.3% (12/13) at ≥3 months. Conclusions Video-based eye tracking revealed frequent conjugate movements during vergence stimulation in ACE. After medial rectus recession surgery, vergence responses increased substantially, suggesting restoration of coordinated binocular motor control.