Influences of monocular image degradation on the monocular components of fixation disparity

The monocular components of the forced vergence fixation disparity curve were evaluated for equal retinal images and for two kinds of monocular retinal image degradation. Computer-generated nonius lines were used to measure the fixation disparity curve components. Monocular defocus was obtained by placing convex lenses before one eye. In the second instance monocular image degradation was achieved by placing light-scattering filters before one eye. A small percentage of subjects displayed unequal distribution of the monocular components of fixation disparity with no image degradation. For both conditions of monocular image degradation, the distribution of the monocular components was found to be biased in favor of the clear image. However, defocus, which affects the high spatial frequencies relatively more than scatter, was found to have a greater effect on the distribution of the monocular components of fixation disparity than scatter.