People who are color-blind can’t appreciate the rainbow of hues that so many of us take for granted. But not being able to see all colors properly goes beyond mere aesthetics. It can make simple everyday tasks a challenge — from traveling (say, differentiating the colors in a traffic light or reading a subway map) to eating (being able to tell if a banana you’re about to peel is ripe) to getting dressed (color-coordinating can be a nightmare).
Color blindness is often misunderstood. One common misconception is that people who are color-blind live in a world devoid of color. “In fact, the vast majority of people who have color blindness can see colors, but certain colors — red and green, in particular — appear washed out and muddy,” says ophthalmologist Jane Edmond, director of the Mitchel & Shannon Wong Eye Institute and a professor in the Department of Ophthalmology at Dell Medical School, at the University of Texas at Austin. “This can make distinguishing between certain colors a challenge.”
In fact, “color deficiency” is a more accurate way to describe the condition.
Color blindness can range from mild (some people only have trouble distinguishing colors in dim light, for example) to more severe, but the degree of severity doesn’t change and usually doesn’t affect the sharpness of vision. Trouble seeing the difference between red and green (or red-green color blindness) is the most common form of the condition. Both colors may take on a kind of brownish murky-greenish tone, which can make for some confusion. “One of my patients, who is red-green color deficient, would pick wild strawberries as a young child,” He would always come back with a basket of leaves, because he had a hard time distinguishing between red and green.”
An inability to distinguish between blue and yellow is much less common. Being completely color-blind (read: seeing things in black, white or shades of gray) is a severe form of the condition, called achromatopsia. It’s extremely rare and accompanied by bad overall vision.
The retina is covered with two types of light-sensitive photoreceptors, called rods and cones. Rods detect light and dark. Cones are responsible for color vision. There are three types of cones: One perceives longer (or red) wavelengths, another medium (green) wavelengths, and another short (or blue) wavelengths. Together, these cones allow us to see an entire spectrum of colors. If just one type of cone is faulty, the eye may have trouble seeing certain hues. Reasons for that include:
Genetics. In most cases, people are born color-blind — men far more frequently, because the X chromosome, passed on from mother to son, carries the genetic information for color vision. (According to the American Optometric Association, nearly 8 percent of males and 0.5 percent of females are born with color deficiency.) Males, who have an X chromosome and a Y chromosome (XY), only need an abnormal X chromosome to become color-blind. A color-blind woman has two abnormal X chromosomes (XX), one each from her mother and father.
Age. Color vision can also worsen with age. This is known as acquired color blindness. Cataracts, in particular, can throw things out of whack. “As we age, our lens can turn cloudy, which decreases the amount of light getting to the retina,” explains Edmond. “Over time, the aging lens can turn a yellow or brown color, which leads to altered color perception — sort of like looking through glasses with yellow- or brown-tinted lenses.”
Injury or disease. Damage to the optic nerve, or to parts of the brain that process color, or diseases such as diabetes, multiple sclerosis, Parkinson’s disease, Alzheimer’s and stroke can cause color blindness. Unlike congenital color blindness, these types of color vision problems affect men and women equally, and one eye may be affected more than the other.