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Seeing Color: Genetic and Acquired Color Vision Deficiencies
Jim Doane was humiliated when he passed the ball to a member of the opposing team with the red jerseys instead of to his own team with the green jerseys. His team lost. He said he had a short-lived career in high school as a fry cook because he couldn’t tell when the meat was cooked. He wanted to be a physician, but was told that career was closed to him, so he went into engineering instead. Now retired, Doane enjoys flying, but his license is limited to daylight hours because he can’t tell red from green.
Doane isn’t alone. Among the most common of genetic disorders, color vision deficiency (CVD), or colorblindness (so named although these people are not “blind” to color), is present in about eight percent of men and O.5 percent of women, frequently those of European descent. However, CVD is present in all races and nationalities, ranging in intensity from mild to severe.
A person who is mildly affected may assume he has typical color vision until he takes a test to detect the disorder. Many men who wanted to be fighter pilots during World War II were shocked not to pass the color vision test. This has also happened to people who apply for other jobs that require accurate color vision.
People who are moderately affected may notice problems in everyday activities, like matching socks or discriminating the colors of the rainbow. An office worker may be confused by a color-coded filing system. In addition, language is full of expressions that may have little meaning for those with CVD. Nancy Miller, one of the 0.5 percent of affected women, said, “You don’t realize how often people say things like, ‘Look at the pretty green sweater.’” She wanted to be an interior decorator but realized that goal was impossible because of her color vision. She went into drafting instead so she could work with black and white.
Like two percent of the male population (and a rare female), Jim Doane has a severe color vision deficiency. He has gotten into a wrong car and had to explain that to the police. “Then there are the speeding tickets in the Mustang due to the red speedometer needle on the green background,” he said. (He admitted he wasn’t completely innocent.)
CVD is commonly referred to as “red-green” colorblindness, because these colors are commonly confused. Often, they are also confused with other colors such as gray. Purple and blue typically appear the same because people with CVD don’t see the red in purple. Green is often confused with tan and brown.
CVD is a sex-linked recessive disorder. It is carried on the X chromosome. A male has an X and a Y chromosome and a female has two X chromosomes. When a male inherits an affected X, he will be affected because, unlike a female, he doesn’t have an unaffected X to dominate the affected X. Because a male always passes his Y chromosome to his sons, he does not pass CVD to his sons; he does, however, pass his X to his daughters, who are then “carriers.” Carriers typically don’t have symptoms. A woman has a 50 percent chance of passing her affected X on to each of her children. The females who inherit the X will, like their mothers, be carriers; the males who inherit the affected X will, like their maternal grandfathers, have CVD. A female must inherit an affected X from each parent in order to be affected herself.
Deficiencies in color vision can also be acquired. Aging can produce subtle changes in color vision. The most common color change results from the development of cataracts, or “foggy” lenses in the eye, which interfere with visual acuity and color vision, making some colors dull, especially blue and yellow. After having cataract surgery where a foggy lens is removed and replaced with an artificial lens, people commonly comment that everything appears more colorful.
Seniors are also more likely to take medications that may distort or reduce color vision. Blue-yellow color vision can be altered by certain medications used in seizure control and other medications used to treat heart ailments and arthritis. Aspirin and quinine can affect red-red color vision, as can some drugs used in the treatment of psychosis. Rarely, color vision may be adversely affected by trauma, such as a blow on the head.
Although acquired color vision deficiencies can sometimes be medically treated, there is nothing available to effectively treat inherited CVD. Colored lenses are available that may help colorize the world of some people with reduced color vision. The X-Chrom lens, a red contact lens worn in one eye, helps some people tell red from green, which is important in some jobs. Those who are interested in trying specialty lenses should check with their eye care professionals.
An avid bicyclist, Jim Doane is presently involved in re-doing his city’s bicycle map. It’s unreadable for him because of the colors used. That should keep him busy at night when he isn’t flying.
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