RODS and CONES are the light-sensitive cells inside the RETINA. They are called photoreceptors. They contain special pigments that are light-sensitive. When these cells detect light coming into the eye, they send a message back to the brain, which, in turn, translates the message into what we see. Rods and cones got their names because of the shape of the cells.
There are approximately 125 million RODS in each eye. Most of the rods are in the peripheral, or side, areas of the retina. They are responsible for gross detection of movement, shapes, light and dark. The vision that we obtain from rods is "black and white". They cannot detect color.
Color vision and detailed vision come from the CONES. There are about 6.5 million cones in each eye. They are concentrated in the center of the retina. At the retina's very center, the fovea, there are 150,000 cones in every square millimeter.
Although the cones provide us with color vision, they are not as light sensitive as the rods. In dim lighting, we rely on our rods for vision. This is one reason why it is hard to tell the color of an object in a darkened area.
PLEASE NOTE: The information contained on this system is not intended to supplant individual professional consultation, but is offered as a community education service. Advice on individual problems should be obtained directly from a professional.
Copyright, 1994. Richard E. Gans, M.D.
Last Modified: August 23, 1996