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achromatopsia (s) (noun), achromatopsias )pl)
A rare form of color vision impairment in which the world is seen only in black, white, and shades of gray.
This hereditary disorder of sight is the result of a lack of cone vision; that type of vision which is provided by the cone photoreceptors in the retina.
In the normal human eye, it is estimated that there are about six million cone photoreceptors that are located largely in the center of the retina.
Lacking cone photoreceptors, people with achromatopsia must rely on their rod photoreceptors. There are approximately 100 million rod photoreceptors which are located mainly around the periphery of the retina.
Rods saturate at higher levels of illumination and do not provide color vision or good detail vision.