Quantitative Analysis of Eyeball Rotation During Lateral Gaze in Intermittent Exotropia: A Magnetic Resonance Imaging Study

PURPOSE: To evaluate the eyeball rotation during lateral gaze in patients with intermittent exotropia (IXT) using three-dimensional magnetic resonance imaging (MRI). METHODS: In this prospective observational study, patients with IXT (n = 29) underwent orbital MRI during central, right, and left gazes. Fixation targets were placed at a 40° angle for lateral gaze. After acquisition of MR images, the position of the static tissues other than the eyeball in the MR images were matched three-dimensionally. The optical axis was defined as the perpendicular line to its lens passing through the corneal vertex. The rotation angle was measured as the angle between optical axes in central gaze and lateral gaze using ImageJ. A difference of 3° or more in the rotational angle between both eyes was considered a significant difference. RESULTS: Eight patients (26.7%) had a larger adduction angle than the abduction angle of the fellow eye and six patients (20.0%) showed a smaller adduction angle during lateral gaze on at least one side. There was no significant factor associated with the pattern of rotation. CONCLUSIONS: Almost one-half of the patients with IXT had significant difference in the rotation angle between both eyes during lateral gaze. Measurement of the rotation angle during lateral gaze using MRI showed that IXT is not a perfectly comitant disturbance of gaze in some subjects. TRANSLATIONAL RELEVANCE: Quantitative analysis for eye movements using MRI can provide useful information for physiologic mechanism and proper surgical planning in patients with IXT.