Assessing chromatic discrimination in individuals varying in iris color and ethnic origin

This study aimed to investigate how variation in iris color, along with ethnic origin, affects color vision. For color vision deficiency screening, the Ishihara, D-15, and D-15d tests were employed. Chromatic discrimination was assessed in normal trichromats using the Cambridge Colour Test (CCT). Three groups were tested: light-eyed White (N = 30), hazel-eyed White (N = 30), and brown-eyed Black (N = 29). Black observers revealed significantly higher CCT measures-protan and tritan thresholds (Trivector) and Ellipse measures (major axis, axis ratio, and angle); no significant differences were found between the two White observer groups. We attribute Black observers' subtle tritan-type impairment to prereceptoral factors, in particular, the higher optical density of the macular pigment, which filters out short-wavelength light, affecting S-cone-mediated chromatic discrimination, and, also, is likely to reduce retinal illuminance. The elevated protan thresholds are discussed in relation to the receptoral level; considered are possible causes of genetically determined L-cone characteristics in observers of African descent.