Photoreceptors

These are light-sensitive sensory cells that convert quantums of light (photons) into the electrical signals for the nervous system. The photoreceptors in the retina of the human eye are called cones, rods and melanopsin-carrying ganglion cells.

The cones are responsible for color vision. They are at their greatest density in the center of the eye, know as the macula lutea or yellow spot. This is the area of the retina that provides the greatest spatial resolution.

The rods are responsible for light/dark vision and have a greater sensitivity than cones. They are therefore important for night vision. They are mainly found at the periphery of the field of view. The melanopsin-carrying ganglion cells are not considered to be visual cells as they do not transmit images to the central nervous system but merely provide brightness information for controlling the internal clock.