Does the eye only rotate? : A three-dimensional magnetic resonance imaging study

Abstract

Purpose : To verify the translational movement of the eyeball during horizontal and vertical gazing and to measure the degree of ocular translation using 3-dimensional (3D) magnetic resonance imaging (MRI).

Methods : We enrolled 56 healthy subjects who were 20 to 50 years old. All participants underwent high-resolution T2-weighted MRI of the orbit (Achieva 3.0T; Philips Medical Systems, Best, The Netherlands) in axial planes during central, horizontal, and vertical gazing. Using multilateral 3D reconstruction based on Visual C++, MRI images were processed to analyze eye movements. The distance between the centroid of the eyeball in central gaze and secondary gaze was measured and the direction of centroid movement was evaluated. The correlation between the degree of centroid movement and associated factors was analyzed with Pearson’s correlation.

Results : High-resolution MRI revealed translational movements of eyeball in all gaze directions. Eyeballs were translated in the same direction during horizontal gazing, while translational direction was opposite during vertical gazing. The mean centroid movement lengths were 0.68 ± 0.27 (95% confidence interval [CI]: 0.64– 0.72) mm in horizontal gaze and 0.43 ± 0.21 (95% CI: 0.40–0.47) mm in vertical gaze. The length of centroid movement in horizontal gaze was negatively correlated with axial length and intraocular volume (R= -0.509, -0.405 in axial length and intraocular volume; both p <0.001).

Conclusions : Orbital MRI demonstrated significant translational movement of the eyeball during both horizontal and vertical gazes, and the direction of translation was consistent according to gaze direction. The fact that eye movement is a combination of rotational and translational movement indicates that translational movement should be considered when evaluating eye movement.