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.