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James A Kuchenbecker, Jay Neitz, Maureen Neitz; Ethnic variation in the ratio of long- to middle-wavelength sensitive cones. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4539.
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The ratio of long (L) to middle (M) wavelength-sensitive cones in Caucasian males is widely variable, averaging about 2 L cones for each M cone. Here we examined the ratio of L to M cones in a larger sample and extended the analysis to more ethnic groups.
Spectral sensitivity functions were measured using the ERG in 579 males with normal color vision. L and M opsin genes were sequenced. Amino acids specified at spectral tuning sites were used to estimate the peak sensitivities for the L and M cones, and this was used to calculate the cone ratios from the spectral sensitivity functions. Subjects self-reported their ethnicities as follows: 138 African American, 362 Caucasian, 19 Chinese, 5 Japanese, 17 Korean, 6 Taiwanese, 7 Vietnamese, 8 Filipino, and 18 Native American. Variation in the ratio of L to M cones as a function of ethnicity was evaluated with a single factor ANOVA.
Variation in mean cone ratios across ethnic groups was greater than predicted by chance (p = 1.16x10-19). Combining Chinese, Japanese, Korean, Taiwanese, Vietnamese and Filipino into an “Asian” group and reanalyzing with a non-parametric ANOVA reveal significant variation in median cone ratio with ethnicity (p<0.0001). Dunn’s Multiple comparison test indicates significant differences for African American versus Caucasian (p<0.001), Asian versus Caucasian (p<0.001), and Caucasian versus Native American (p<0.05). The mean cone ratio for each ethnic group was near 1 L to 1 M cone, except for Caucasians where the mean ratio in this sample was 1.9 L to 1 M cone ratio. The ratios across the other ethnic groups ranged from 0.8 L for every M cone to 1.3 L for every M cone.
There are significant variations in certain vision disorders with ethnicity, notably, myopia. Ethnic differences in L to M cone ratio coupled with variability in the amino acid sequences of L and M opsins may contribute to ethnic differences in susceptibility to vision disorders.
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