Rod and Cone Densities

Rods and cones are differently distributed in the retina. Only cones are present in the fovea. Cone density decreases rapidly outside the fovea and then falls to a fairly even density in the peripheral retina.

The highest density of "M" and "L" cones, but the lowest density of "S" cones are found in the fovea. S-cones form only 3-5% of the cones in the fovea. There are no "S" cones in the center of the fovea, the fovea centralis, where visual acuity is highest. The maximum density of "S" cones,15%, is found 1 degree from the fovea. The remainder are dispersed unevenly throughout the retina where they make up 8% of the cones.

The small number of cones sensitive to blue, the "S" cones, in the fovea and in the rest of the retina is why pure blue should not be used for small text, lines, or symbols. Blue also has little perceived brightness which is why it should not be used against black or a darker shade of blue as background.

This figure shows the relative density of rods and cones in the retina. There are no rods in the fovea where vision is most acute. Rods are most dense in the periphery of the retina; cones are most dense in the fovea.