Rod cells are one of two types of photoreceptor cells that can be found in the retina of the eyes of humans, as well as other animals. The other type are the cone cells, of which there are about 7 million in the human eye. Rod cells are very sensitive to light. They allow night vision. They are concentrated at the edge of the retina, where they also allow peripheral vision. There are about 125 million of them in the human eye.