colour vision deficiency

The colour vision deficiency -  Any abnormality in colour vision that causes a person to have difficulty in distinguishing between certain colours.

TYPES:
The most common type of colour vision deficiency is the reduced ability to discriminate between red and green. Most cases of red–green colour vision deficiency are the result of defects in the light-sensitive cells in the retina. These defects are usually inherited, and tend to be sex-linked (see genetic disorders); the majority of sufferers are male, while females are unaffected, but they can pass on the disorder to their children.

Occasionally, defects may be acquired as a result of diseases of the retina or the optic nerve, or they are caused by injury. There are two forms of red–green deficiency. A person with a severe green deficiency has difficulty in distinguishing between oranges, greens, browns, and pale reds. A severe red deficiency causes all shades of red to appear dull.

A much rarer colour vision deficiency exists in which blue cannot be distinguished. This condition may be inherited, or it may be due to degeneration of the retina or the optic nerve. Monochromatism (the total absence of colour vision) also exists, but this deficiency is very rare.