Achromatopsia

Achromatopsia is a medical condition (also called maskun or rod monochromatism) characterized by a low cone cellcount or lack of function in cone cells; these are the light receptors responsible for colour perception. It is endemicon the atoll of Pingelapand was described by Oliver Sacksin Island of the Colourblind. Sacks went there with a Norwegianwho had maskun, and the book narrates his experiences on the island.

People with maskun have difficulty seeing in bright daylight because their rod cells(the receptors responsible for detecting brightness) are saturated. People with normal colour vision do not perceive things in the same way as those with maskun, because they depend on colour more than on luminosityto identify objects and patterns, whereas achromatopics depend almost entirely on luminosity to identify patterns. The closest that normal-sighted persons can come to experiencing maskun-type vision is in the dark, when the rod cells become the predominant receptors for vision due to their sensitivity to variations in brightness. Achromatopsia can vary in its severity from being mild enough that it is not diagnosed to causing near blindness. It is a relatively rare condition requiring two recessive genes(CNGA3 and CNGB3). In the United States, it affects approximately 1 in 33,000 people. The condition is generally stable over the course of one's life. Many achromats function normally with the aid of darkened lenses, while others use guide dogs, canes, and are considered legally blind.

See also

• Color agnosia

External links

• Mapping the geneses:Acromatopsia

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It uses material from the http://en.wikipedia.org/wiki/Achromatopsia Wikipedia article Achromatopsia.