Ask Doctor K: The science behind colorblindness

DEAR DOCTOR K: Why are some people colorblind?

DEAR READER: People who are colorblind are unable to see colors the way most people do. True colorblindness, in which everything appears black, gray or white, is rare. More often, “colorblind” people have trouble distinguishing colors from one another.

Light that enters our eyes is focused by the lens to fall on the back of the eye – the retina. Within the retina are 7 million cone cells. These specialized cells contain chemicals, called photopigments, that react to different wavelengths in light. The color of light is determined by its wavelength. Photopigments respond to blue, green or red light. Colorblindness occurs when the eye either lacks certain photopigments, or when these pigments do not work as they should.

Most people who are colorblind inherit the condition. Rarely, a condition that develops later in life causes colorblindness.

Symptoms of colorblindness depend on the type of cone cells affected:

RED-GREEN COLORBLINDNESS. In the most common type of colorblindness, people cannot distinguish green from red. That is, some people see red objects as being green, and other people see green objects as being red. It occurs when either the red or green cone cells are missing or are not working properly.

BLUE-YELLOW COLORBLINDNESS. This occurs when blue cone cells are missing or not working properly. People with this type of colorblindness see blue as green and may find it difficult to distinguish yellow or red from pink.

COMPLETE COLORBLINDNESS. True colorblindness occurs when none or only one type of cone cell works properly.

In the United States, about 7 percent of men and 0.4 percent of women have red-green color blindness. Inherited colorblindness cannot be “fixed.” But special corrective lenses can help people with red-green colorblindness to see color more accurately.