- colour vision deficiency
- Also known as colour blindness and anomalous colour vision. All three terms refer to the inability or diminished ability to distinguish between at least two colours. Although this group of visual deficiencies is traditionally known as colour blindness, true colour blindness (i.e. * achromatopsia) is extremely rare. What is generally signified by the term colour blindness is one of a group of colour vision deficiencies. As a consequence, the term colour vision deficiency is the preferred term to denote any of these conditions. Because the human optical system is trichromatic (as opposed to some animal systems which are quadrichromatic), persons with normal colour vision are called normal trichromats. Colour vision deficiencies in humans present in the form of *monochromatism, *dichromatism, or * anomalous trichromatism. Usually both eyes are affected, but rare cases of unilateral colour vision deficiency have also been described. Individuals with monochromatism are unable to discriminate differences in hue. In dichromatism, the affected individual is able to detect differences in hue, except for those between two primary colours. There are three basic varieties of dichromatism, called *protanopia, or red-green colour vision deficiency; *deuteranopia, or green-red colour vision deficiency; and * tritanopia, or blue-yellow colour vision deficiency. Etiologi-cally, all three conditions are associated primarily with specific chromosomal deficits. Pathophysio-logically, colour vision deficiencies are attributed to the absence or diminished function of the long-, medium-, or short-wavelength cones within the retina. As a consequence, colour vision deficiencies have traditionally been labelled as * entoptic phenomena. They have an estimated lifetime prevalence of 8% in men and 0.5% in women. Colour vision deficiencies may be either congenital (i.e. hereditary), or acquired through trauma or disease. Etiological factors in acquired colour vision deficiencies include multiple sclerosis, optic neuritis, anaemia, leukaemia, vitamin B1 deficiency, carbon disulphide intoxication, lead poisoning, thallium poisoning, nicotine poisoning, and chronic alcohol abuse. The correlations between the transmission of colour vision deficiencies, genes, and sex linkage were first established by the American zoologist and geneticist Edmund Beecher Wilson (1856-1939). Colour vision deficiencies should not be confused with * chromatopsia and the group of *colour-processing deficits.ReferencesBrewster, D. (1826). On the invisibility of certain colours to certain eyes. Edinburgh Journal of Science, 4, 85-87.Hsia, Y., Graham, C.H. (1965). Color blindness. In: Vision and visual perception.Editedby Graham, C.H. New York, NY: John Wiley & Sons.McIntyre, D. (2002). Colour blindness. Causes and effects. Chester: Dalton Publishing.
Dictionary of Hallucinations. J.D. Blom. 2010.