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Jay Neitz, Maureen Neitz; Colorblindness confined to one eye. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4298.
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The study of colorblindness has been a guide to the nature of normal color vision and a test for theories of it. A fundamental question is what do colorblind people see? One approach is to study individuals in which dichromacy is confined to one eye. Understanding the underlying cause of the disturbance is important for assessing the validity of one eye representing normal and the other dichromatic vision; however, none have been reported since it has been possible to assess the genetics of the disorder to determine its cause and nature. We examined the genes and color vision of a woman who self-reports having a colorblind father and having normal vision in one eye but being colorblind in the other.
L and M opsin genes were amplified separately and sequenced. The first gene and all downstream opsin genes in the array were separately amplified and sequenced. A MassArray based assay that distinguishes L and M genes and the first gene from downstream genes was used to estimate opsin gene copy number and the proportion of L vs. M genes. Standard tests of color vision were performed. The subject also made comparisons of color appearance between the two eyes.
The subject tested as a protanope with her left eye but showed a very mild color vision deficiency in her right. She had a low proportion of L genes compared to total genes consistent with either a protan defect or a protan-carrier genotype. However, sequence analysis indicated both L and M genes were present indicating protan carrier status. A single nucleotide substitution was detected in the promoter of a subset of her M genes.
This is the first case of protanopic color vision confined to one eye in which its been possible to examine the underlying genetics. There has been speculation that the patchiness of X-inactivation could produce a carrier with one normal and one colorblind eye much like the coat-color of calico cats. However, modern results indicate that the X-inactivation patches of cones are small or non-existent making the occurrence of monocular protanopia by this mechanism unlikely. Moreover, in 300 mothers of colorblind sons (Feig & Ropers, 1978, Hum. Genet. 41:313) monocular disturbances of color vision were not observed. Thus, it appears that a rare combination of genetic changes is required to produce the dramatic difference in color vision between the eyes reported here, providing a rare opportunity to gain insight into the perceptions of the colorblind.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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