color blindness
the inability to discriminate between colors and to perceive color hues. Color blindness may be caused by disease, drugs, or brain injury (see acquired color blindness), but most often it is an inherited trait (congenital color blindness) that affects about 10% of men (it is rare in women). The most widely used classification of the different types of color blindness is based on the trichromatic nature of normal color perception, using prefixes to indicate the three primary colors: proto- (red), deutero- (green), and trit- (blue). The type of deficiency is indicated by suffixes: -anomaly for partial inability to perceive one or more of the primary colors and -anopia for complete inability to do this. The most common form of the disorder involves the green or red receptors of the cone cells in the retina, causing a red–green confusion (see deuteranopia; protanopia). Total
color blindness is rare, affecting about 3 individuals out of 1 million (see achromatism). See also dichromatism; monochromatism; trichromatism.