NOTE: This definition was changed in RP-16-17 Addendum 4. Deletions have a strike-through. New text is bold.
Retinal receptors that continue to respond at low levels of luminance, even below the threshold for cones. At these levels there is no basis for perceiving differences in hue and saturation. No rods are found in the fovea.
Retinal receptors that continue to respond at levels of luminance below the threshold for cones, and that provide no ability to discriminate colors. Rods are absent in the center of the fovea.« Back to Definitions Index