Abstract: PURPOSE: To assess whether there is an interocular delay in anisomyopia and myopia and whether optical correction can reduce the delay
METHODS: 15 emmetropes, 18 anisomyopes, and 17 myopes participated in the study. Viewing a psychophysical paradigm that shows a rotating cylinder, subjects were asked to report their perception of rotation. The interocular delay could be measured from ambiguous perception. The stimuli were shown at three spatial frequencies (0.5, 1 and 2 c/deg). To investigate whether optical correction could reduce the delay in observers with myopia or anisomyopia, we also measured their delay using the same visual task after they were been optically corrected with contact lenses. Axial length, which is an anatomical marker of myopia, was also measured in the two patient groups to determine whether there would be a relationship between their interocular delay and axial length.
RESULTS: The absolute value of the interocular delay was found to be larger in the myopic and anisomyopic observers than that of the emmetropic controls at 1 and 2 c/deg when there was no optical correction. We didn't find a significant correlation between ratio of absolute interocular delay with and without correction and ocular features (e.g., spherical equivalent difference, axial length difference and corneal curvature difference). However, we found that optical correction relieved the delay in the two patient groups.
CONCLUSIONS: We show that there is an interocular delay in anisomyopia and myopia in the range of low spatial frequencies. Our data do not support the premise that interocular differences in refractive error or other clinical characteristics induce the Pulfrich phenomenon. Moreover, when these differences are resolved, interocular delay is still present. This indicates that the absence or presence of naturally-occurring delay in individuals with normal or abnormal vision is not related to the anatomical differences of the two eyes; instead, we speculate that the cause might originate from the visual cortex.

Key words: Anisomyopia, interocular delay, Pulfrich phenomenon, optical correction, binocular parallax