Colour-blindness

Colour-blindness is the inability to perceive particular colours. It was sometimes called Daltonism after the english chemist John Dalton, who in 1794 published the first scientific paper on the subject, Extraordinary facts relating to the vision of colours, after his realisation that he could not see all the colours that other people could distinguish.

The condition usually has a genetic cause; the most common types are sex-linked, being far more common in males than females. Another, very rare cause of colour blindness is the result of brain damage, whether by injury or stroke, in which the eyes are normal, but the part of the brain that interprets colour is no longer functioning. Full color blindness is rare with the most common form of color-blindness being the inability to distinguish between red and green.

Colour blindness is tested using the Ishihara colour test which consists of a series of pictures of coloured spots. A figure (usually a number) is embedded in the picture as a number of spots in a slighly different colour, and can be seen with normal colour vision, but not with a particlar colour defect. The full set of tests have a variety of figure/background colour combinations, and enable diagnosis of which particular visual defect is present.

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needs: types of colour blindness, frequency of each