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 125 million rod cells in the human retina. More sensitive than cone cells, rod cells are almost entirely responsible for night vision.
Rods are a little longer and leaner than cones but have the same structural basis. The pigment is on the outer side, lying on the pigment epithelium, completing the cell's homeostasis. This epithelium end contains many stacked disks. Rods have a high area for visual pigment and thus substantial efficiency of light absorption. Because they have light-sensitive pigment, rather than the three types that human cone cells have, rods have little, if any, role in colored vision.
Like cones, rod cells have a synaptic terminal, an inner segment, and an outer segment. The synaptic terminal forms a synapse with another neuron, for example a bipolar cell. The inner and outer segments are connected by acilium, which lines the distal segment.The inner segment contains organelles and the cell's nucleus, while the rod outer segment (abbreviated to ROS), which is pointed toward the back of the eye, contains the light-absorbing materials.