Abstract
Purpose: Previous studies have concluded that the packing arrangement of foveal L and M cones is not distinguishable from random in most eyes. However, these measurements have been confined to retinal eccentricities of only about 1 deg from the foveal center. Here, we measured the packing arrangement in extrafoveal retina.
Methods: We classified the L, M, and S cones in a deutan carrier and a color-normal male subjects with adaptive optics imaging combined with retinal densitometry at 1.25, 4, and 10 deg in the temporal retina. We evaluated the packing arrangement of the 3 cone classes by comparing the frequencies of distances between all cones of the same type with those expected based on a random pigment assignment rule.
Results: Peripheral L and M cones of the deutan carrier exhibited significant clumping at 4 deg whereas those at 1.25 deg did not. The arrangement in the carrier at 10 deg had a tendency toward clumping but was not significant. The arrangement of the normal male was not significantly different from random both in the parafovea and in the periphery.
Conclusions: The organization of L and M cones outside the fovea, in a deutan carrier, shows a tendency toward clumping of cones of like type, as expected from X chromosome inactivation. This clumping may have implications for the strength of red-green color vision in peripheral retina since it increases the probability that peripheral midget cell centers will be driven by predominantly one class of cone.
Supported by NIH EY04367, NIH EY01319, NIH EY07551 and the NSF Science and Technology Center for Adaptive Optics (cooperative agreement no.: AST-9876783 with UCSC). Genetic data: courtesy of Dr. Maureen Neitz, Medical College of Wisconsin.