Theories of color vision have been founded on behavioral observations of how the human eye distinguishes colors and mixtures of colors. Studies of congenital dyschromatopsias (inherited disorders of color vision) have been important to the development of these theories. Subsequent studies of acquired dyschromatopsias (disorders of color vision caused by disease) were understandably influenced by these concepts. Theories to explain the patterns of color vision impairment found in acquired diseases (for example, preferential hue discrimination defects) have stressed the likelihood of selective damage to specific components of the afferent visual system (photoreceptors, ganglion cells, synaptic elements, axons etc.). More recent evidence suggests, however, that impairment of color vision by diseases of the retina and optic nerve is commonly nonspecific, and not the result of selective impairment of individual neural mechanisms responsible for mediating color vision. Rather, the patterns of acquired dyschromatopsias often appear to be related to a physiologically heterogeneous distribution of color vision in the foveal and perifoveal visual field, coupled with a tendency for the visual field defects caused by acquired diseases to be unevenly distributed in these same areas.