Differential changes in color and motion-onset visual evoked potentials from both eyes in early- and late-onset strabismic amblyopia.

grated in the visual cortex. 1‐4 Cells in the parvocellular pathway respond best to chromatic stimuli of high spatial and low temporal frequencies, whereas cells in the magnocellular pathway respond best to achromatic stimuli of low spatial and high temporal frequency 5‐9 and to motion. 8 Anatomic studies of the effects of monocular visual deprivation on the sizes of cells in the lateral geniculate nucleus (LGN) of nonhuman primates have shown differential effects of visual deprivation on magnoand parvocellular cells, marked changes in LGN cells related to the fellow eye, and major differences in the effects of early- and late-onset monocular visual deprivation. 10,11 Those anatomic findings suggest that color- and motionrelated functions are differently affected in amblyopia. A recent psychophysical study of human subjects with strabismic amblyopia showed a reduction in color-contrast sensitivity in both eyes, with the amblyopic eyes being more affected than fellow eyes, and the color contrast sensitivity in the amblyopic eyes of subjects with late onset being more reduced than in those with early-onset amblyopia. 12 Luminance contrast sensitivity was relatively less affected, so that all eyes showed a reduction in color contrast sensitivity relative to luminance contrast sensitivity. This finding suggested that parvocellular function was reduced relative to magnocellular function in both eyes of subjects with strabismic amblyopia, in keeping with the primate studies. 11 The above findings suggest that color and motion onset VEPs may be differentially affected in amblyopia. It has been suggested on the basis of comparisons between amblyopic and fellow eyes that motion-onset VEPs are relatively spared in amblyopia 13 and one previous study of color VEPs in amblyopia has suggested a relative reduction in parvocellular function. 14 The present study has followed-up the psychophysical study by comparing VEPs to color and motion-onset stimuli in largely the same group of subjects with strabismic amblyopia in whom abnormalities of color and luminance contrast sensitivity were demonstrated. 12