Color Blindness - Description

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Photo by: The Sign

Normal color vision requires the use of special cells in the retina (the innermost lining) of the eye called cones. There are three types of cones—blue, green, and red—which allow an individual to recognize a large spectrum of colors. Cones sometimes do not function normally. When that happens, a person has trouble recognizing colors.

The three basic types of color blindness are as follows:

• Red/green color blindness. Red/green color blindness is the most common form of the disorder. It affects about 8 percent of all Caucasian (white) males and 0.5 percent of all Caucasian females. People with this disorder can distinguish red from green if the two colors are next to each other, but they cannot identify red or green by itself. For example, they can pick out red or green from a package of colored pencils, but if handed a red pencil, they could not identify that the pencil was red.
• Blue color blindness. Blue color blindness is rare. People with this disorder cannot distinguish blue or yellow. Both colors are seen as white or gray. The disorder occurs with equal frequency in men and women and usually accompanies certain other physical disorders, such as liver disease or diabetes (see diabetes mellitus entry).
• Total color blindness. Total color blindness is called achromatopsia (pronounced a-KRO-muh-tope-see-uh). This disorder is the rarest of all forms of color blindness. People with this disorder see everything as white, black, or some shade of gray. The disorder affects about 1 person in 33,000 in the United States. It is caused by hereditary factors. Achromatopsia is usually accompanied by other vision problems, such as extreme sensitivity to light.