Muted Rainbow – Color-blind Persons Can’t See the Full Range of Colours

When Paul Cprek was interviewing for jobs, he sometimes video chatted with his mother or sister beforehand for advice. He wasn’t concerned about what to say in interviews. He was worried about what to wear. Cprek is color-blind, and picking out a shirt and tie to match can be tricky. “[Job interviews are] all about first impressions, so I was curious, did I get it right?” says Cprek, 29, an investment consultant in New York City.

Color Uncoordinated

Color blindness describes various forms of an inherited trait that scientists call color vision deficiency, says Jay Neitz, PhD, professor of ophthalmology at the University of Washington in Seattle. Cprek has the most common type, red-green color deficiency, which affects about one in 12 men and one in 200 women of Northern European ancestry, according to the National Institutes of Health’s National Eye Institute in Bethesda, MD. Dark green and red look the same to him and are hard to distinguish from brown. He also has trouble distinguishing dark blue from purple.

Cprek was in elementary school when he first realized that he was color-blind like his paternal grandfather. “I was in art class and getting things wrong,” he recalls. Not seeing the range of colors that most people do still trips him up at times, but “it’s not a big obstacle for me in my daily life,” he says.

Color blindness is shorthand for a more complex process involving the eyes and brain, says Bart Leroy, MD, PhD, director of the ophthalmic genetics and retinal degeneration clinics at the Children’s Hospital of Philadelphia.

The retina uses two types of cells: rods, which are responsible for night vision, and cones, which are responsible for daytime vision, including color vision, he explains. The cones are divided into three types that absorb different wavelengths of light: red, green, and blue. Depending on what type of color vision deficiency a person has, cone cells are either missing or not sufficiently sensitive; the result is that only certain color information is being recognized and sent to the brain, says Dr. Leroy. A person with red-green deficiency doesn’t see those colors as most people do and may also have difficulty distinguishing between certain shades of blue and purple, which is comprised of red and blue.

A Genetic Link

While people with normal color vision can’t imagine not seeing all their favorite colors—think of a box of crayons with colors missing—people with color vision deficiency only know their environment as they perceive it. “People don’t know what they don’t see,” says Dr. Leroy.

Color vision deficiency is X-linked, meaning genetic mutations associated with the condition are passed along on the X chromosome, says Dr. Leroy. The condition is more likely to affect males, who have an X and a Y chromosome. Females have two X chromosomes, which allows any genetic mutations related to color blindness on one X chromosome to be overridden by normal genes on the other.

Children should be routinely tested for color vision, says Dr. Leroy. If they are color-blind, they and their parents and teachers can come up with strategies for dealing with activities where distinguishing color differences might be a problem.

Screening For The Condition

Karen Rae Levine learned her younger son was color-blind when his preschool teacher said he was having trouble with blue and purple patterns. She took him to an optometrist, who confirmed his color blindness and told her, “There’s nothing you can do, so don’t worry about it.”

Levine didn’t quite agree with that laid-back sentiment. She immersed herself in research and became an activist, pushing for color vision screening at her son’s school and elsewhere in the New York district where they lived at the time. “Color blindness often isn’t understood or even recognized, especially by the educational system,” says Levine, who now lives in Huntington, NY. “Teachers were shocked to learn that they probably had a color-blind child in every class.”

It’s important for teachers to know that color blindness is fairly common, says Levine. Otherwise, they may think a child isn’t following directions or doesn’t understand a lesson. In kindergarten, for example, everything is color-coded, she says. “The teacher says, ‘You sit at the red table. You sit on the orange square.’”

Her experiences as a mom with a color-blind son—including receiving a green Valentine’s Day card—led her to self-publish a children’s book, All About Color Blindness: A Guide to Color Vision Deficiency for Kids (and Grown-Ups Too), in 2013. She says kids may be reluctant to admit that they perceive colors differently than their friends, but she wants them to be confident in their abilities and speak up when they need to: “I am color-blind. Can you help me pick out a marker to make a rainbow?”

An Evolving Trait

The ability to see in three colors, or trichromatic vision, is a trait that evolved in higher-order primates, including humans, as they relied more on visual cues than on their sense of smell for survival, says James Lupski, MD, PhD, professor of molecular and human genetics at Baylor College of Medicine in Houston. Dr. Lupski has been involved in mapping the human genome and is interested in rearrangements of genetic coding that result in traits such as color blindness.

“Color blindness is a benign trait that doesn’t compromise your life too much,” he says. People can generally drive, for instance, because they know that red is at the top of a stoplight and green is at the bottom and can recognize when the light changes.

Before the 1980s, the “biological basis of color blindness was not understood at all,” says Dr. Neitz, who runs a research lab focused on color blindness with his wife, Maureen Neitz, PhD. The couple is developing gene therapy and genetic testing for color blindness.

Monkeying Around With Color

Dr. Neitz says he gets a lot of emails from people with color blindness. Men have confided, for example, that they can’t relate to their wife’s enthusiasm for a fall foliage tour or a sunset stroll. A friend with red-green color blindness told him he has trouble seeing when the key card to unlock a hotel room door signals the change from red to green. Other, more substantive concerns include not being able to pursue a color-dependent career such as airline pilot, police officer, or chemist, or getting in a car crash because a red light doesn’t register.

In a 2009 study published in Nature, the Neitzes’ team reported findings from a gene therapy study to address color vision deficiency in squirrel monkeys with red-green color blindness. The scientists injected a viral vector carrying a color pigment gene underneath the retina to replace the missing pigment. Dr. Neitz says there was some skepticism about whether it would work because the monkeys’ brains were already accustomed to processing a limited spectrum of colors. “Color vision is all about how the information that comes from the three different kinds of cones in the eye is processed by the brain,” he says.

But the monkey experiment suggests that the brain can adapt to new color information. Dr. Neitz says tests to evaluate the monkeys’ responses to color cues following gene therapy indicated that they could see a full range of colors. The goal is to test the approach in humans at some point, but color vision deficiency isn’t a high priority. “Obviously, there are far worse conditions we should be working on first,” Dr. Leroy says.

Basic Hues

Cprek works around his color blindness. If he plays a sports video game with a friend, he asks him to select team jerseys with the most contrast, usually white and a dark color. At work, he creates graphs and pie charts that provide contrast to his eyes. Highlighting in a document occasionally stumps him, but he asks his colleagues to double-check things if he isn’t certain.

Cprek says that while he asks for fashion advice for special events, he has learned that keeping things simple is the best way to go, especially off the job. “I try to stick with blue jeans and a white T-shirt instead of getting too creative with colors.”

Source: Brain & Life