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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    CHAPTER VI THE DETECTION OF DEFECTIVE COLOUR VISION In spite of a great deal of work, no single instrument or test has as yet been proved infallible in the detection of defective colour vision. Even less can a single procedure scale its degree or determine its special kind. Several methods must be used according to the circumstances as in other clinical investigations and it is the main justification for this little book to enable the reader to select the most useful methods and to apply them properly. objective tests To date, the only objective difference between normal and one class of colour-defective people is that discovered by Rushton (1955, 1958), who showed that light reflected from the normal eye fundus indicated the presence of two foveal cone pigments.* Reflected Hght from the protanopic and the severely protanomalous fundus showed abnormal absorption (Fig. 12). Partial bleaching with intense red or blue light gave identical difference spectra in protan eyes, but different spectra in normal eyes, indicating the absence of one cone pigment in the former. No similar difference can be shown for deuteranopic or deuteranomalous eyes. Microspectrometric measurements on single cones (see p. 4) in the retina of a colour-blind person have as yet not been made. An interesting half-objective method for the demonstration of dichromasy (protanopia and deuteranopia) has been invented by Finch a m (1953); using an optometer he could show that the accom¬ modation of the lens when an observer looks at a small object depends on the colour of the hght used. This depends on the difference of refraction of monochromatic hght of different wavelength and the reaction is actuated by colour fringes at the edge of the retinal image * The fovea centralis of the normal eye is tritanopic, lacking blue receptors (see p. 21). 28