Examining cone cells from above
This image shows an aerial view of cone photoreceptor cells, which are one of two types of light-sensitive nerve cells in the eye's retinal tissue. Photoreceptor cells convert light energy into electrical signals that are communicated to other nerve cells involved in the visual system. Cones allow humans to see in color and in brightly lit environments, while rod photoreceptor cells permit night vision.
This photo reveals the mosaic pattern that cone cells form in the retina of a ground squirrel, which looks similar to the central area of the retina in humans. NEI scientists use this type of image to study pathways in the eye that control color vision.
Within this mosaic are two types of cones that respond to different wavelengths of light. The cells outlined in blue are known as S-cones, which are most sensitive to shorter wavelengths of light, such as blue light. The remaining grey-colored cones in this image are M-cones, which are most sensitive to medium wavelengths of light, such as green light. Humans also have a third type of cone, L-cones, which are more responsive to longer wavelengths of light, such as red light.
Even though they are essential for color vision, individual cones are actually "blind" to color. Because they respond to both the brightness of light and the color of light, they may have the same response to a dim blue light and a bright green light, for example. Therefore, individual cones transmit general information about color to other nerve cells, which interpret information gathered from all cones to generate specific color vision.
Image of ground squirrel retinal tissue courtesy of Wei Li, Ph.D., chief of the NEI Unit on Retinal Neurophysiology.