daltonism

   Daltonism is also known as deuteranopia, deutan colour blindness, and deutan colour deficiency. All four terms are used to denote a colour vision deficiency of the green-red type. The eponym Daltonism refers to the British chemist and physicist John Dalton (1766-1844), who in 1794 published an account of his own colour vision deficiency. As Dalton remarks in this paper, "My yellow comprehends the red, orange, yellow.and green of others; and my blue and purple coincide with theirs. That part of the image which others call red appears to me little more than a shade, or defect of light; after that the orange, yellow and green seem one colour, which descends pretty uniformly from an intense to a rare yellow, making what I should call different shades of yellow." In addition to his own colour vision deficiency, Dalton also described those of his brother and 28 other males. He initially referred to his own condition as 'red-blindness'. However, a genetic analysis of the tissue preserved from his eyes, carried out some 150 years after his death, indicates that it was actually of the green-red type. Dalton was not the first to publish on this type of colour vision deficiency. As early as 1777 it was described by the British hydrographer and engineer Joseph Huddart (1741-1816). Today Daltonism is the most prevalent form of colour vision deficiency. Attributed to an X-linked autosomal condition, it affects 6% of all men, but very few women. The fact that the prevalence of the condition is higher in men than in women was already noted by Dalton. Daltonism can be subdivided into a dichromatic form, called 'green' for short, in which the retina's medium-wavelength cones (M-cones) are missing, and an anomalous trichromatic form, referred to as 'green weak', in which the M-cones are present, but in which the peak of the sensitivity for light is displaced towards the red-sensitive cones. Daltonism is commonly classified as an * entoptic phenomenon. In the past the term Daltonism has also been used as a synonym for the (now obsolete) term * colour blindness.

   References

   Dalton, J. (1794). Extraordinary facts relating to the vision of colours: With observations. Memoirs and Proceedings of the Manchester Literary and Philosophical Society, 5, 28-45.

   Huddart, J. (1777). An account of a person who could not distinguish colours. Philosophical Transactions ofthe Royal Society, 67, 260-265.

   McIntyre, D. (2002). Colour blindness. Causes and effects. Chester: Dalton Publishing.