De eerste kleurenblindheidsproeven

The first tests for colourblindness Usually Goethe or John Dalton is supposed to have discovered colourblindness. However, the English oculist Joseph Huddart (1776) was the discoverer of this phenomenon. The first physiological explanation of it does come from Goethe. From 1798 onwards he believed that the colourblind missed the faculty to perceive blue. He assumed that green was made up of blue and yellow, with orange being an intensified kind of yellow: whoever wasn't able to see blue, should see green and orange as the same colour. Goethe's colour theory (1810) found its successor in Hering's opponents' theory of colours (1874). In this theory red and green are supposed to be each other's opponent colour, just like blue and yellow. Correspondingly there would be two visual substances: one should give a red sensation if the red-green substance is subject to a katabolic change and a green one if it is subject to an anabolic change, and one should see yellow when katabolism preponderates in the blue-yellow substance and blue when anabolism preponderates in it. So Hering differentiated two kinds of partial colourblindness: red-green blindness (or confusion) when the red-green substance was missing and blue-yellow blindness (or confusion) when the blue-yellow substance was missing. The first and for practical purposes still most important pseudo-isochromatic test of colourblindness (1883) was based on Hering's theory. (Pseudo-isochromatic means: in appearance (but for the colourblind in reality) having the same colour.) It was constructed by the German oculist Jakob Stilling (1842-1915). A colour theory that competed for a long time with Hering's theory, was the three colour theory of Young (1802) and Helmholtz (1855). It explained colourblindness as an absence of one of the three colour sensitive cells in the retina, the so-called cones. According to this theory there are three kinds of colourblindness. Nowadays we explain colour vision with a synthesis of the three colour theory and the opponent' theory. It is rooted in the zonal theory of the Dutch ophthalmologist Franciscus Donders (1818-1889). The former theory is supposed to be valid only for the retina and the latter only for the visual cortex. Like the three colour theory it explains most forms of colourbhndness as an absence of one of the three cones, so that the corresponding double opponent cells in the visual cortex lose their discriminatory function.