At two years old, Andrew Nelson could recognize the letters of the alphabet. At three, he could count and memorize entire storybooks. “But when it came to the colors,” his mom, Jennifer, recalls, “he seemed to ask the same ones over and over.” One day, when Andrew was in the first grade, he mentioned that he'd left a book on the green chair in the living room. The chair was brown. A trip to the optometrist confirmed Jennifer's suspicions. Andrew is color deficient, a condition often incorrectly referred to as “color blind”.
Trichromacy
Normal color vision, or trichromacy, results when the three separate “populations” of cone photoreceptors in the retina are functioning correctly. Each population is identified by the colors to which it is most sensitive: red, green or blue. Color deficiency results when there is a defect in one of the cone photoreceptor populations. Lewis Reich, O.D. Ph.D., an associate professor in the College of Optometry at Nova Southeastern University in Fort Lauderdale, FL, explains that there are three broad types of color deficiency. Anomalous trichromacy usually occurs when there is a defect in the red or green receptors.
Dichromacy
Dichromacy, a more severe condition, results when one entire receptor population is missing. The third type of deficiency is known as monochromacy. Those affected are truly “color-blind”. Unable to see any colors, they usually have other visual problems as well. Thankfully, this condition is rare. The gene for color deficiency is carried on the female X chromosome. Since the gene is recessive, a female child will only inherit the condition if both her X chromosomes contain the defect. With only one defective gene, she'll be a carrier, able to pass the defective gene along to her children, but not color deficient herself.
A male child, on the other hand, stands a much higher chance of becoming color deficient. This will occur if his single X chromosome carries the defective gene. The result is that while only about 0.3 percent of girls are color deficient, the condition affects about 8 percent of boys. Of the three types of color deficiency, anomalous trichromacy is the most common, with “deutan” defects, which affect the child's ability to perceive the green tones in a color, occurring more frequently than “protan” defects, which affect his ability to perceive red tones. A blue deficiency is extremely rare but can be acquired as the result of injury or disease. The severity of the condition can vary widely.
Jennifer Nelson was alerted to the possibility of a problem with her son's vision when he misidentified the color of the chair. But, especially with a mild defect, there may be few clues. “People with a severe defect discover they have a defect,” says Dr. Gunilla Haegerstrom-Portnoy, professor of optometry and vision science at the School of Optometry, University of California, Berkeley. “Those with a mild defect may go for life without knowing they have one.” The only way to know for sure is to have your child tested by an optometrist or ophthalmologist.
One common test, easy for any school-aged child who knows his numbers, involves showing him pages of a book containing patterns of multi-colored dots. Some of those dots will be arranged in the shape of a number from 1 through 9. The figure is clearly visible to anyone with normal vision, but may be completely or partially invisible to a child with a red or a green defect. He may, for instance, read the number 8 as a 3, if he's unable to distinguish the dots that compose the left half of the figure from those in the surrounding field.
What Does the World Look Like to Someone with Color Blindness?
So how does the world look to the color deficient child? “Like an out-of-tune color TV,” says Jay Schlanger, O.D., a Los Angeles-based optometrist and a clinical instructor in optometry, “where the strength of the red isn't up to the strength of the other colors, or the strength of the green isn't up to the other colors.” Because all colors are made up of blue, green and red, any defect will affect a child's perception of the entire color spectrum. Depending on the severity of his condition, he'll distinguish far fewer shades and hues of color than his trichromatic peers.
Asking a color deficient child to sort the socks in his laundry could pose problems, especially if the jumble contains a mixture of indistinguishable greens and browns, blues and purples, pinks and grays. Pastels are even trickier. “The more washed out the colors are,” notes Dr. Haegerstom-Portnoy, “the harder the task is.” Andrew Nelson, who has a deutan defect, has no trouble identifying grass as green and tree-bark as brown. “It's the varieties and shades that he can't distinguish,” Jennifer says. “The olive green from a sierra brown, any tan or cream color from an off-greenish shade.” To a protan, red can appear dark and may even look black, making traffic lights and brake lights difficult to see. Dr. Haegerstom-Portnoy, who is herself red-deficient, explains that she can't see the red numbers on an LED clock unless she heightens the contrast by darkening the room.
When Should Children Be Tested for Color Blindness?
Experts agree it's important to test a child at around five years old, especially since teachers in the early grades tend to rely heavily on color-coded learning materials. “I would recommend alerting the teacher and providing them with specific examples of confused colors,” says Dr. Reich. “The teacher needs to be cognizant of the problem and in cases where the use of colors is important, they should be careful to name the colors for the students to prevent confusion.”
Color deficiency becomes more of a problem as a child grows and begins to explore his career options. “This is a biggie for us,” Jennifer Nelson admits. Andrew, now 19, had always dreamed of being a navy pilot, but was denied the opportunity to enter any of the elite military programs. All required he pass a color vision test. Also out was his second choice, a career in law enforcement. Other options closed to those with a color vision defect include careers in the fire department, coast guard and commercial aviation. Electricians and even camera operators in the movie industry also need normal color vision. Color deficiency can't be “cured”, nor can its effects be mitigated by early intervention. The sooner you find out though, the more you'll be able to help your child successfully navigate his world.
