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.

    50/134 (page 34)
    DEFECTIVE COLOUR VISION arabio numerals used in the West: they v\rrite, for instance, o for our numeral 5, and something very much like 5 and 7 for our 2 and 6, while only i and 9 are really similar in both Euro¬ pean and Arab numerals. Until special charts are printed for the Arab people European confusion charts must obviously be apphed with great care. lUiterate people and children can be tested with the aid of patterns as, for instance, in the Ishihara and Stilling charts which do not depend on reading but can be traced. Numerals, of course, may also be traced by ilHterates. Illumination is very important in chart tests (see p. 39). The various pigments of a chart may differ in their gloss so that a colour- defective person may get clues from strongly oblique light; diffuse light or light impinging perpendicularly on the charts from the direction of the observer must therefore be used. The most important source of error in the use of confusion charts is a wrong choice of illuminant. Chart tests must never be under¬ taken in direct sunlight, nor during dawn or dusk, nor in rooms with strongly coloured walls. Most important of all the charts must not be used in artificial light except as specified below. Waaler (1928) noted, for instance, that adult deuteranopes could more correctly read a greater number of Stilling charts under incandes¬ cent light than under daylight; similar observations have often been made since. Though dayhght varies considerably (Famsworth and Reed, 1943), diffuse dayhght of sufficient brightness is in practice almost invariably used and for genetical purposes chart readings in the open either in the shade or under an overcast sky will seldom be misleading; nor will be reading in a room where the subject has its back to a north window (in the Northern Hemisphere). If more stringent conditions are desired, for instance in comparative studies or if testing in the above daylight conditions is impossible, artificial standard illuminants must be used. The most important characteristic of these is colour temperature, that is the absolute temperature of a radiant black body which would produce light corresponding to the illuminant's spectral composition. It should be mentioned that a high colour temperature corresponds to cold (greenish-bluish) Hght, while a low colour temperature produces a warm (yellow-reddish) illumination. Standard illuminants may be produced by combinations of incandescent lamps with filters or by fluorescent Hght.