European Association for Vision and Eye Research

The two most sensitive techniques for assessing congenital colour deficiency and / or acquired changes in chromatic sensitivity involve either measurement of chromatic discrimination thresholds or anomaloscope matches. These techniques also make it possible to quantify the severity of colour vision loss, but the large variability within normal trichromats and the existence of unusual, extreme anomalous matches limit their usefulness. The purpose of this investigation was to examine the factors that cause changes in chromatic sensitivity in order to explain the inherent variability within normal trichromats and the existence of unusual extreme anomaloscope matches.

We measured and compared colour discrimination thresholds and Nagel anomaloscope matches in a large number of “normal” trichromats and a group of colour deficient observers. Genetic analysis was also carried out in a subgroup of subjects to determine the spectral separation between the L and M pigments. We also modelled the Nagel match by considering how changes in wavelength separation, post-receptoral amplification of cone signals and optical density changes affect the parameters of the “yellow” match.

The results define the “normal” statistical limits of chromatic sensitivity and explain and predict the existence of extreme anomaloscope matches.

The parameters of the yellow match can be predicted accurately both within normal trichroimats and in extreme anomalous subjects by a suitable choice of wavelength separation, post-receptoral amplification and cone optical densities.