Thursday, August 26, 2010

Cones (retina)

Cones, or cone cells, are photoreceptor cells in the retina of the eye that function best in relatively bright light. The cones gradually become sparser towards the periphery of the retina. There are between 6 to 7 million cones in the retina, concentrated in the central yellow spot known as the macula. They provide the eye's color sensitivity.

Cones are also able to perceive finer detail and more rapid changes in images, because their response times to stimuli are faster than those of rods. There are three kind of color-sensitive cones in the retina of the human eye, corresponding roughly to red, green, and blue sensitive detectors.

Because humans usually have three kinds of cones with different photopsins, which have different response curves and thus respond to variation in color in different ways, they have trichromatic vision. Being color blind can change this, and there have been reports of people with four or more types of cones, giving them tetrachromatic vision.