Diagnosis and genetics of defective colour vision / by H. Kalmus.

  • Kalmus, H. (Hans), 1906-1988.
Date:
[1965]
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Diagnosis and genetics of defective colour vision / by H. Kalmus. Source: Wellcome Collection.

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    I б DEFECTIVE COLOUR VISION (see p. 4). Table 2 presents this classification in its most usual form. Table 2. Simple types of defective colour vision (followingWright, 1957) While a fuller understanding of this system can only be gained by an appreciation of the diagnostic methods described in Chapter VII, it is useful at this point to explain the technical terms of the table and the principles of the classification. The main (physical) subdivision concerns the number of suitably chosen primary stimuli, for instance a red, a green and a blue monochromatic Hght, v\^hich suitably mixed are necessary to match all colour sensations of a person. Normal people (= normal trichromats), about 92 per cent of males and 99 per cent of females, need in general all three components for a colour match and there is Httle difference betv^een such individuals concerning the relative intensities of these components. Other people (anomalous trichromats) may also need the three components for a general match, but the intensity of these components differs greatly from the intensity necessary for the normal trichromats. There are three kinds of these anomalous trichromats, namely protanomalous people who require more red stimulation, deuteranomalous people who require more green stimulation for their matches, and tritanomalous individuals who require more blue. Dichromats need only two primary stimuli to effect all their colour matches. Their deficiency is more severe and it is said that they lack one of the fundamental sensations altogether. However, some people are dichromatic when matching small test areas, but are anomalous trichromats when matching larger fields (Jaeger and Kroker, 1952).* There are again three kinds of dichromats, namely the protanopes lacking a red sensation, the deuteranopes lacking separate red and green sensations, seeing yellow in place of both, and tritanopes lacking the blue sensation. * To some extent this reflects differences between central and peripheral colour perception.