Abstract

Several investigators have observed anomalies in the encoding of spatial phase in amblyopic eyes. We adapted the paradigm of Field and Nachmias¹ to examine amblyopic phase encoding in greater detail. Two normal observers and two with anisometropic amblyopia viewed stimuli composed of a fundamental and second harmonic added in various phases. The stimuli were presented foveally. For each eye tested, the spatial frequency of the fundamental was set to the peak of the CSF. The stimuli were Gaussian-damped and presented in a 2IFC discrimination paradigm. When the stimuli were in fact different, they differed only in the polarity of the second harmonic (180° shift). Thresholds were measured by varying the contrast of the second harmonic. Only two mechanisms were required to account for foveal phase discriminations in nonamblyopic eyes. The odd-symmetric mechanisms were slightly less sensitive than the even-symmetric mechanisms. The amblyopic data were also consistent with the two-mechanism model, but the odd-symmetric mechanisms were distinctly less sensitive than the even-symmetric. The difference between odd and even sensitivity was correlated with the depth of the amblyopia. These results suggest that the phase-encoding anomalies observed in the amblyopic central visual field may reflect a diminished sensitivity (or reliability) among odd-symmetric mechanisms. The pattern of results in the amblyopic fovea is similar to that observed in the peripheral visual field of normal obsevers (2). For the two amblyopic eyes, the results were similar to those observed between 20° and 40° eccentric in normal eyes.

© 1986 Optical Society of America