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Elise W Dees, Maureen Neitz, Rigmor Baraas; Variation in chromatic discrimination predicted by polymorphisms at specific amino acid residues in L- and M-pigment genes. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4541.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate whether chromatic contrast sensitivity and discrimination is predicted by polymorphisms at specific amino acid residues that are known to affect spectral tuning.
Normal male and female trichromatic subjects, carriers of protan and deutan color vision deficiencies (20-45 yrs) were included in the study. Subjects were healthy with no known ocular abnormalities. Color vision discrimination was assessed with several color vision tests, including Cambridge Colour Test (CCT), Medmont C-100 and Rayleigh anomaloscopy. Chromatic contrast sensitivity was tested with 9-16 spatial frequencies ranging from 0.3-6.0 c/deg using a pseudo-isochromatic grating stimulus. The color of the grating was varied along either the L- or M-cone axis in the CIE 1931 chromaticity diagram. Whole blood or saliva samples were collected from all subjects, and the genes encoding the L- (OPN1LW) and M- (OPN1MW) opsins were amplified using long distance polymerase chain reactions (PCR). The PCR product was further used to amplify the specific regions exon 2, 3 and 4 for the OPN1LW and OPN1MW, and the nucleotide sequence of each exon was determined by direct fluorescent sequencing. A matrix-assisted laser-desorption/ionization time-of-flight (MALDI-TOF) mass spectrometer-based instrument was also used for genotyping.
Polymorphisms at position 180 and 230 of the OPN1LW were found to influence chromatic discrimination and sensitivity, irrespective of sex and carrier status. As shown previously for males, presence of serine (Ser) at position 180 results in a shift in peak sensitivity of the L-cone pigment towards longer wavelength and a green-shift in Rayleigh matching midpoints. Subjects with Ser at 180 also exhibited increased sensitivity on CCT (lower error score on trivector test along protan axis and shorter length on the ellipse) and higher chromatic contrast sensitivity. Presence of isoleucine (Ile) at position 230 results in a green shift in peak sensitivity of the L-cone pigment, and significantly predicted the subjects’ null point settings on Medmont C-100. Subjects with Ile at 230 exhibited reduced chromatic contrast sensitivity.
Polymorphisms at specific amino acid residues were found to influence not only the subjects’ color discrimination, but also to predict their sensitivity to chromatic spatial patterns.
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