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This paper considers the substantial variation among anomalous trichromats, even among those within a discrete subtype such as simple deuteranomalous trichromacy. First, theoretical calculations show that relatively small individual differences in wavelengths of peak sensitivity of pigments and/or in optical densities can substantially affect Rayleigh matching, which is the procedure typically used to diagnose different types of anomalous trichromacy. Second, an ensemble of colour matches is introduced as a technique to assess individual differences in peak wavelength and density. Finally, results are reported from simple deuteranomals, two of whom are shown to have pigments with different peak wavelengths and two of whom are shown to have pigments with different optical densities. We argue that the standard classifications of anomalous trichromacy are too broad to relate phenotypes to genotypes

The Rayleigh match typically is used to assess whether an individual has normal or red/green-defective color vision. There is substantial variation, however, in the Rayleigh matches of color-normal observers, and even differences in the matches from the left eye and right eye of a single observer. We confirmed this interocular difference in two independent samples of normals, and measured additional color matches to seek the cause of the difference. Color matches that varied the wavelength in the mixture field or the field size (i) fail to provide any evidence of an interocular difference in the wavelength of peak sensitivity of photopigment (Xmax) and (ii) suggest the difference often is due to effective optical density of photopigment. We conclude that an interocular difference in Rayleigh-match midpoint (but not range) is common, and due to effective optical density and/or pre-receptoral spectrally selective filtering.

The Rayleigh match, a color match between 589 nm spectral light and an admixture of 545 and 670 nm lights, traditionally has been used as a test of defective color vision. Among normal trichromats, however, there is considerable variation in the range and midpoint of the Rayleigh match. The variation in normals’ Rayleigh matches was studied by measuring the matches of 20 observers on three repeated occasions. The left eye and right eye of each observer were tested at each session. These results assess the importance of five factors that might contribute to variation in normals’ matches: (1) differences among people in the match midpoint, (2) differences among people in the match width, (3) differences between the two eyes of the same person in the match midpoint, (4) differences between the two eyes of the same person in the match width, and (5) measurement error. The first three factors are shown to contribute significantly to differences in the matches of normal trichromats. The first factor accounts for most of the normal variation.