Fixation point measurement with an ellipsoid estimation

The fixation point is usually measured with the optic axis of the eye. This method assumes that the relation between the mental direction of view and the direction of the optic axis is mappable with the calibration. In this paper we take up monocular fixation for a static target. In this situation, not only is the relative angle between the visual axis and the optic axis fixed, but also the angle between the visual axis and the mental direction of view are coincident. The accuracy of fixation point measurement would rely on the accuracy of optic axis measurement. We attempted accurate measurement of the optic axis with an ellipsoidal model about the orbit of the pupil center. Consequently, under the condition that the visual field was horizontal 43 and vertical 22 degrees with nine points calibration, the maximum discrepancy between the actual target and estimated fixation point over the field was about 0.7 degrees, which was accurate in comparison with 1.4 degrees which arose from the calibration of the simple plane interpolation method.