COLOR-VISION IN 2 OBSERVERS WITH HIGHLY BIASED LWS MWS CONE RATIOS/

Two sisters, heterozygous carriers for congenital X-linked protanopia, were diagnosed as normal trichromats by the Rayleigh match on the ano maloscope. The heterozygous state was established by molecular analysi s of their visual pigment genes. The normal color match establishes th at the spectral sensitivities of their long-wavelength-sensitive (LWS) and middle-wavelength-sensitive (MWS) cone visual photopigments are w ithin normal variability. Their FM 100-hue test error scores were low, demonstrating superior chromatic discrimination, Heterochromatic flic ker photometric (HFP) spectral sensitivities were like those of protan opes. The estimated LWS/MWS cone ratios from the HFP data were 0.09/1 and 0.03/1, compared with ratios in the range of 0.6/1 to 10/1 for typ ical normal trichromats. Measurements of chromatic grating acuity on c hromatically selective backgrounds were performed to study the cone mo saic. The data were consistent with a sparsity of LWS cones. Both prot an carriers showed normal spectral sensitivities for all three cone ty pes under cone isolating chromatic adaptation and normal three-peaked curves for increment thresholds on a white pedestal. Hue estimation, r un on one carrier was normal. The equilibrium yellow locus was measure d in the other carrier and was in the range of normal trichromats. The data indicate that normal color vision can occur even when the LWS/MW S cone ratio is quite abnormal. (C) 1998 Elsevier Science Ltd. All rig hts reserved.