Cones (color sensitive receptors) containing single visual pigments selective for red, green, and blue light, are present in the normal human eye. Disturbances of color vision will occur if the amount of pigment per cone is reduced or if one or more of the three cone systems are absent.
Although defective color vision may be acquired as a result of another eye disorder, the vast majority of color blind cases are hereditary – present at birth. The gene for this is carried in the X chromosome. Since males have an X-Y pairing and females have X-X, color blindness can occur much more easily in males and is typically passed to them by their mothers.
Color blindness is rooted in the chromosomal differences between males and females. Females may be carriers of color blindness, but males are more commonly affected.
Color blindness is a malfunction of the retina, which converts light energy into electircal energy that is then transmitted to the brain. This conversion is accomplished by two types of photoreceptor cells in the retina: rods and cones.
The cones are responsible for encoding color. Each cone contains structures or visual pigments sensitive to one of three wavelengths of light: red, green, and blue. Normal persons are able to match all colors of the spectrum by mixtures of only three fundamental color sensitivities. Hence, the huge variety of colors we perceive stems from the cone cells’ response to different compositions of wavelengths of light.
Defects in color vision occur when one of the three cone cell color coding structures fails to function properly. One of the visual pigments may be present and functioning abnormally, or it may be absent altogether.
For practical purposes, all color-deficient individuals have varieties of red or green deficiency. Blue deficiencies are very rare. Color deficient patients are not completely red or green blind. Compared to persons with normal color vision, they have some trouble differentiating between certain colors, but the severity of the color deficiency is variable.
Color blindness is normally diagnosed through clinical testing. (See the Ishihara color test – the one most common test used) Although there is no treatment for color blindness, most color deficient persons compensate well for their defect and may even discover instances in which they can discern details and images that would escape normal-sighted persons. At one time the U.S. Army found that color blind persons can spot “camouflage” colors where those with normal color vision are fooled by it.
Some of the information in these pages was taken from:
An article by: Diana H. Heath, M.D., a member of the Morton Plant medical staff, specializing in ophthalmology. (formerly at http://www.zipmall.com/mpm-art-colorbl.htm)
A webpage written by Terrace L. Waggoner, O.D., Staff Naval Hospital, Pensacola (formerly at http://members.aol.com/nocolorvsn/color2.htm