Binocular fixation misalignment measured by border enhancement: a simplified technique

In a previous study, a new method of monitoring binocular fixation performance was presented. The method is based upon the effect of fixation eccentricity on border enhancement: that is, the width of the enhancement band increases consistently with increasing distance of the border stimulation from the foveal center. Unlike the conventional methods of measuring fixation disparity, the procedure is essentially independent of interocular nonius alignment. However, there are some difficulties inherent in the interpretation of measurements of binocularly presented border stimulation, for it is not always clear whether the enhancement band is perceived monocularly or as a binocular average. In this study, we show how this problem can be eliminated by removing a section of the border presented to one eye, the other eye seeing a monocularly presented border segment. A secondary result of the study is a confirmation that convergence-associated accommodation does not significantly influence the enhancement measurements provided an optimum size artificial pupil is used.