Transverse rotation of the eyeball affected by fixation distance

The video eye-tracker can measure the direction of the visual axis of the eye based on the calibration, which creates a relationship between the displacement of a feature on the eyeball and the direction of the visual axis. However, this calibration method takes no account of the distance from the subject to the target. Version displacement of the pupil center was measured when the subject is fixating on stationary targets on the planes stood at different distances from the subject. As a result, the small transverse movement of the pupil center was observed when the subject had a version movement of the eyes for the targets on the near plane. The relationship between the distance and the amount of transverse movement was conspicuous in the dominant eye.