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January 2010

Ask the Doctor

Why can't I see certain colors?

Catherine Cukras, M.D.
Catherine Cukras, M.D. Staff Clinician
National Eye Institute

If you've headed off to work wearing one red sock and one green one, you may have gotten dressed in the dark--or you may have a color vision defect.

Approximately 1 in every 76 Americans has a color vision defect, according to the National Center for Health Statistics. This problem, aside from impacting a person's sense of fashion, affects cells in the back of the eye called cones, says NEI staff clinician Dr. Catherine Cukras.

Color vision defects are usually hereditary, and are more common in males.

Cones allow us to identify differences between colors. Each of the three types of cones is most sensitive to a particular wavelength of light: red, green or blue. If any of the cone types are damaged or missing, a person won't be able to distinguish between certain colors.

Most people who have color vision defects have trouble seeing differences among colors in the red-green range, Dr. Cukras says. Problems with colors in the blue-yellow range are less common. Even more rare is total color blindness, in which the eye can only recognize white, black and shades of gray, she explains.

The impact of color vision defects can vary from person to person. "For some, the differences among colors are just not as obvious as for people who have normal color vision," Dr. Cukras says. "For others, different colors can actually look exactly the same."

Color vision defects are usually hereditary, and are more common in males. Though color vision defects might be inconvenient for people whose careers depend on color vision, such as decorators, most people can adapt relatively easily.

"It just means that a lot of men have women pick out their ties," Dr. Cukras says.

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Department of Health and Human Services NIH, the National Institutes of Health