Spatial frequency discrimination in anisometropic and strabismic amblyopia

Spatial-frequency difference thresholds were measured in amblyopes over a wide range of spatial frequencies using a two-alternative forced-choice technique. Four amblyopes, three of whom were anisometropic, exhibited a higher threshold for discrimination at most frequencies in their amblyopic eye. In contrast, three other amblyopes, all of whom were strabismic, exhibited regions of normal discrimination alternating with regions of higher thresholds than found in their dominant eye. These results are discussed in terms of a multiple-spatial-frequency channel model. They suggest that there are different underlying mechanisms for the deficits in the two types of amblyopia: the anisometropic pattern may reflect a failure of normal development of spatial-frequency channels; the strabismic pattern is similar to that shown in the periphery of the retina by normal subjects and may reflect nonfoveal-type function.