Purpose: To investigate translatory movement during the lateral gaze in patients with horizontal strabismus using magnetic resonance imaging.
Methods: Patients with esotropia or exotropia and normal controls underwent orbital magnetic resonance imaging during the central gaze and lateral gaze at 40°. The position of the static tissues was superimposed three-dimensionally for all gazes using a self-developed software, allowing the analysis of the net eyeball movement. Then, the eyeball centroid coordinates were extracted for each gaze, and the distance and direction of centroid movement from the central to lateral gaze were calculated.
Results: The mean distance ± standard deviation of the centroid movement was 1.0 ± 0.5 mm during abduction in the exotropia group, which was significantly longer than that in the esotropia (0.6 ± 0.3 mm; P = 0.003) and control (0.7 ± 0.2 mm; P = 0.002) groups. Conversely, the centroid moved farther in the esotropia group (0.9 ± 0.3 mm) than the exotropia (0.6 ± 0.3 mm; P = 0.005) and control (0.7 ± 0.2 mm; P = 0.023) groups during adduction. Posterior translation during abduction was longer in the exotropia group (-0.8 ± 0.3 mm) compared with the esotropia (-0.5 ± 0.3 mm; P = 0.017) and control (-0.4 ± 0.3 mm; P = 0.001) groups, whereas that during adduction was longer in the esotropia group (-0.4 ± 0.4 mm) than the exotropia (-0.1 ± 0.2 mm; P = 0.033) and control (-0.1 ± 0.2 mm; P = 0.026) groups.
Conclusions: During abduction, more translatory movement occurred in the exotropia group, whereas the centroid moved farther in the esotropia group during adduction. The translatory movement difference between both strabismus groups implies that there is a difference in biomechanics among the types of strabismus.