Rod cells, or
rods, are
photoreceptor cells in the
retina of the
eye that can function in less intense
light than the other type of visual photoreceptor,
cone cells. Rods are concentrated at the outer edges of the retina and are used in
peripheral vision. On average, there are approximately 90 million rod cells in the human retina. More sensitive than cone cells, rod cells are almost entirely responsible for night vision. However, because they have only one type of light-sensitive pigment, rather than the three types that human cone cells have, rods have little, if any, role in color vision (which is why colors are much less apparent in darkness).