and Cone Densities
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
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.
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.
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.