Variations in cone populations for red–green color vision examined by analysis of mRNA

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IN the central human retina, there are estimated to be nearly two L cone photoreceptors for each M cone. The extent to which this value varies across individuals is unclear and little is known about how the M:L cone ratio might change with retinal location. To address these questions, the ratio of M:L cone pigment mRNA was examined at different locations. For patches of central retina, the average M:L ratio was about 2:3 which decreased to about 1:3 for patches 40°eccentric. There were also large individual differences among the 23 eyes examined. The extremes differed in central M:L mRNA ratio by a factor of > 3. The measured differences in mRNA ratio are proposed to reflect differences in photo-receptor ratio. Such variations provide unique opportunities for understanding how the neural circuitry for color vision is affected by changes in cone ratio.

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