Foveal cone mosaic and visual pigment density in dichromats

Abstract

1. Optical reflectance spectra of the fovea were measured in ten subjects with normal colour vision, ten protanopes and seven deuteranopes. Four conditions were used: perpendicular and oblique angle of incident and reflected light on the retina, both in a dark-adapted and a fully bleached state. 2. The spectra were analysed to assess the effects of dichromacy on the cone mosaic. A replacement model, i.e. one where the total number of cones remains unchanged and all cones are filled with a single type of pigment, was found to fit our data best. 3. The analysis of the spectral fundus reflectance also provided estimates for densities of photo-labile and photo-stable retinal pigments and fraction of long wavelength-sensitive (LWS) cones. Visual pigment density was 0.39 for protanopes and 0.42 for deuteranopes, significantly lower than the 0.57 found for colour normals. Macular pigment density was 0.54 for colour normals, 0.46 for protanopes and 0.42 for deuteranopes. 4. For colour normals the LWS cone fraction was 0.56, in agreement with psychophysical literature. The LWS cone fraction for protanopes was -0.04, and for deuteranopes 0.96, consistent with their Rayleigh matches.