More than 20 million Americans experience some form of color blindness, which is the inability to distinguish certain colors. The majority of these people inherit this color vision deficiency, though there are eye disorders that also can cause the problem.

Color blindness affects about 8 percent of men, and approximately 0.5 percent of women. The gene for color blindness expresses itself only when there is no corresponding "normal" color vision gene. Since men only have one X chromosome, the chances of color blindness showing up in men are much higher than in women, who have two X chromosomes. Women may be carriers of the color deficient gene, but not experience color defective vision.

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Seeing Objects in Color
When light enters the eye, it passes through several structures before striking the light sensitive receptors in the retina at the back of the eye. These receptors are called rods and the cones. Rods are responsible for night vision, and cones are responsible for color vision, functioning best under daylight conditions.

Each of the three types of cones, red cones, blue cones and green cones, has a different range of light sensitivity. In an individual with normal color vision, the cone population consists of 74 percent red cones, 10 percent green cones and 16 percent blue cones. The stimulation of cones in various combinations accounts for the perception of colors. For example, the perception of yellow results from a combination of inputs from green and red cones, and relatively little input from blue cones. If all three cones are stimulated, white is perceived as the color.

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 functioning abnormally, or it may be absent altogether.

Most color-deficient individuals have varieties of red or green deficiency. Blue deficiencies are very rare. Color-deficient people are not completely red or green blind. Compared to people with normal color vision, they have some trouble differentiating between certain colors, but the severity of the color deficiency is variable.

Many people think anyone labeled as "color-blind" sees only black and white--like watching a black and white movie. This is a big misconception and is not true. It is extremely rare to be totally color-blind. (The complete absence of any color sensation is called monochromasy.) Less than 1 in 1,000 of those affected by color blindness see only black and white, or shades of gray, and live in a monochromatic world.

Color blindness is normally diagnosed through clinical testing. Although there is no treatment for this affliction, most color deficient people compensate well for their defect and may even find they're able to discern details and images that escape normal-sighted people.

For Parents and Teachers
What Teachers, School Nurses, and Parents, Should Know About Being Color-Blind

Recently tinted prescription glasses have become available to people who have trouble distinguishing shades of red and green from other colors. In this system, the new lenses are coated with a color filter, usually magenta or orange, that, when worn by a color-blind person, can turn a muddy-brown Christmas tree green. This is the result of a combination of the tint and the lens itself, resulting in a different result for the eye, beyond just the simple lens coatings that have been available for years.

A recent U.S. government report points out that there is no known cure for color blindness and that sufferers should not to be misled by claims of a cure. ColorMax officials simply state that their glasses will improve the color perception of many people.

There are even computer glasses with sophisticated progressive lenses that enable the wearer to easily switch from reading a book to reading a computer screen. This has potential to help reduce the impact of computer vision syndrome (CVS).

In any event, these online tests should not replace a thorough examination by a doctor. It should however, give you some insight regarding your color vision acuity.