Severity of Colorblindness Varies

Colorblindness is the inability to distinguish hues that are seen as different by people with normal color vision. There are several types of colorblindness and the severity of the condition varies from individual to individual. Sometimes known as color-vision deficiency, it affects one of every 12 men and one of every 230 women. It is more common in Caucasians than other ethnic groups.

The degree of color-vision deficiency varies from nearly normal to severely impaired color vision. The two most common varieties of colorblindness are red-green and blue-yellow. Red-green color-vision deficiencies are nearly 1000 times more common than blue-yellow ones.

People with normal color vision can distinguish more than 100 "hues." Colors may vary in brightness or saturation but still be of the same hue; pastel green and dark green are of the same hue, for example. On the other hand, people with the most severe forms of red-green colorblindness, called "dichromats," see only two hues. These hues may best be described by what people with normal color vision call blue and yellow.

A rainbow, seen by the normal eye, includes red, orange, yellow, green, blue, indigo and violet. But the dichromat sees red, orange, yellow and green as only one color -- yellow. He or she sees the other half of the rainbow as blue. For the dichromat, there are no intermediate hues such as blue-green, yellow-green, red-orange, violet, magenta, etc. In fact, the spectrum of colors between blue and green -- aqua, turquoise, etc. -- is devoid of color for the dichromat and is seen as gray or white. To dichromats, all colors appear as mixtures of black, white and gray with either blue or yellow.

Some dichromats have difficulty distinguishing between red and green and may confuse orange, yellow, brown and all the colors in the spectrum between red and green. Blue and violet may appear as the same color, while pink may appear white.

One of four colorblind people is a dichromat; the remainder are anomalous trichromats who have color vision that is better than dichromats but not as good as normal color vision. People with intermediate cases can't tell the difference between olive-green and brown, but they can see color in saturated magentas and blue-greens. However, they may have difficulty distinguishing light pink or pastel blue-green from white.

Cause and Effects

Color-vision deficiency is believed to occur when color-sensitive cells in the eyes, called "cones," do not recognize or send the proper color signals to the brain. Colorblindness is usually hereditary and is present at birth. Some colorblind individuals are missing an entire class of color-vision genes while others may simply have altered genes.

In addition, trauma to the eye or certain diseases of the eye, such as macular degeneration or optic neuritis, may affect color vision. Multiple sclerosis can also affect color vision. Some medications may disrupt normal color vision, as well. In addition, as the eye ages, its lens becomes more and more yellow, and this can change color perception.

Society has made few adjustments to aid colorblind individuals. In the US, the traffic "go" light is blue-green so that colorblind people can distinguish it from red more readily. Most colorblind people develop their own system to recognize colors or count on friends and family to help them. They learn to survive in a world where they are surrounded by people who see what they cannot. They may become very experienced at using brightness and saturation differences as cues and learn to call these differences "colors." The go-light, for example, may actually appear gray or white, to many dichromats.

Individuals with a family history of color-vision deficiency may wish to be tested for colorblindness, particularly if they are considering an occupation that requires distinguishing colors. Color-vision deficiency could be particularly challenging for occupations such as pilot, jeweler, graphic designer, photographer, electrician, ship's captain, law enforcement officer and train engineer. Employers often fail to realize how important normal color vision is to an occupation.

Parents may want to have their children tested for color-vision deficiency, especially for those children having difficulty in school. Many educational materials are color-coded. A simple pencil-and-paper test to identify color-vision deficiency in young children was developed at the Medical College of Wisconsin. A genetic test for colorblindness is also available, although there is no cure for colorblindness. Augmenting people's awareness of what it means to be colorblind and standardizing color-vision testing may go a long way toward helping people overcome what can be a sizable hurdle.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.