During World War II, the U.S. Army and Navy did not allow colorblind men to join because they were deemed unfit for combat. After visiting doctors in hopes of correcting their vision, some of these men were told that nothing could be done to remedy their color deficiency, while others were instructed to take vitamin A or to wear red and green glasses. Some doctors even suggested electrical muscle stimulation of the eye, according to a 1943 TIME magazine article.
Sixty-five years later, scientists have discovered a potential cure for colorblindness using gene therapy, according to a study recently published in the scientific journal Nature.
In the study, researchers from the University of Washington, University of Florida and the Medical College of Wisconsin used gene therapy to restore color vision in two colorblind adult squirrel monkeys, a species whose color deficiencies are almost identical to the deficiencies found in humans. The monkeys were prompted to identify different groups of colored dots among surrounding grey dots on a computer screen and were rewarded with grape juice if they guessed correctly. It was initially found that the colorblind monkeys could sometimes identify shades of blue and yellow, but always failed to identify the reds and greens.
The doctors then injected a harmless virus into the colorblind monkeys' eyes, inserting the red pigment that they lacked in their retinas. About 20 weeks after the pigment was added, they were able to better distinguish between reds and greens.
The eye has two types of receptors located in the retina: rods and cones. Rods focus on grey colors and allow the eye to see in low-light conditions, whereas cones allow the eye to perceive color, said Mohit Nanda, an ophthalmologist with Virginia Retina Consultants.
Normal color vision uses a mixture of the three primary colors - red, blue and yellow - to match any color of light. Color deficiencies occur when one of those primary colors is missing - usually red.
Color blindness is an X-linked recessive gene, which is why males are more likely than females to acquire the deficiency, Nanda said. Roughly 0.5 percent of the female population is colorblind, compared to 5 to 8 percent of the male population. Most people who are colorblind were born with the color deficiency, he noted.
Those who do have some type of color deficiency usually have trouble distinguishing shades of red and green, such as pastel pinks and pastel greens.
"The majority [of people affected by color deficiencies] have a mild disorder," he said.
A very small minority, about 0.01 percent of the total male and female population, lack the cones that allow them to identify blues and yellows, Nanda said.
Whatever their type of colorblindness, most people who have a color deficiency can lead normal lives. Sometimes, they may not even recognize that they have a color deficiency, Nanda said. It can, however, inhibit them from participating in activities and seeking careers that are color-dependent, such as interior design or military service.
Third-year College student Mandy Anderson said her cousin was not really affected by his color deficiency until he decided to take an art class.
"The teacher gave him a bad grade because he couldn't get the colors right," she said. "It was the first time he was made to think that it impacted him negatively."
Nanda said he has high hopes for the study's implications.
"Changing genes in monkeys is important - [this study] has a much greater impact for life-threatening diseases," he said. "If we can fix colorblindness, then in the long-term there is excitement about what we can do for more dangerous conditions"
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