Rod Health Dictionary

One of the 2 specialized types of nerve cell within the retina of the eye that convert light energy into nerve impulses. The rods are very sensitive and can respond to very dim light. (See also cone.)

n. one of the two types of light-sensitive cells in the *retina of the eye (compare cone). The human eye contains about 125 million rods, which are necessary for seeing in dim light. They contain a pigment, *rhodopsin (or visual purple), which is broken down (bleached) in the light and regenerated in the dark. Breakdown of visual purple gives rise to nerve impulses; when all the pigment is bleached (i.e. in bright light) the rods no longer function. See also dark adaptation; light adaptation.