NBEO Histology Practice Test

Rods dominate the peripheral retina, while cones are concentrated in the central retina (especially the fovea). Photoreceptors are the rods and cones, and the light-detecting parts are their outer segments. In the periphery, the rod outer segments are far more numerous than cone outer segments, so the layer that is richest in photoreceptors there corresponds to the rod outer segments. The outer nuclear layer holds photoreceptor cell bodies, but the regional abundance of photoreceptors in the periphery specifically reflects the rod outer segments.