Spectral sensitivity and color vision tests were performed on a subject who was totally color blind at low photopic luminances, but exhibited hue discrimination at relatively high photopic levels. Chromaticity confusion loci showed that the residual color vision was abnormal; a tritan defect was superimposed on the generalized reduction of cone sensitivity. Although cone function was markedly depressed, a photopic spectral sensitivity curve was obtained for the light-adapted fovea. Dark-adapted foveal measurements, on the other hand, gave a scotopic function almost identical to that of the dark-adapted periphery. However, it was possible to demonstrate objectively that this subject shifts fixation to an eccentric position under scotopic conditions, i.e., the dark-adapted “foveal” results were, in fact, for a para-macular region. Irrespective of the degree of light adaptation, cone function was not detectable in the peripheral measurements.
IRWIN M. SIEGEL, CLARENCE H. GRAHAM, HARRIS RIPPS, and YUN HSIA, "Analysis of Photopic and Scotopic Function in an Incomplete Achromat," J. Opt. Soc. Am. 56, 699-704 (1966)