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.