Who's most at risk for color blindness

Zachary Lehr has trouble distinguishing some colors. The 6-year-old has a mild form of color blindness, a condition that affects 5 to 10 percent of the U.S. population, according to National Institutes of Health.

Color blindness has long been known to affect boys more than girls. Now, in the first major study on children and color blindness, researchers found that race and ethnicity also figure into one's risk for developing the disorder.

Research published in the journal Ophthalmology looked at 4,000 preschoolers aged 3 to 6 in California. The researchers found that almost 6 percent of Caucasian boys had color blindness, compared with 3 percent of Asian boys, almost 3 percent of Hispanic boys and less than 2 percent of African-Americans.

Girls were much less likely to have the condition. Across all racial and ethnic groups, no more than half of one percent of girls in the study were color blind.

Dr. Miesha Frempong, assistant professor of ophthalmology and pediatrics at the Icahn School of Medicine and pediatric ophthalmologist at Mount Sinai Hospital in New York City, says the condition is primarily genetic. "The problem in color vision deficiency is on the x-chromosome," Frempong told CBS News' Marlie Hall. "Girls have two x's, boys have one x. If a boy gets a bad x, he doesn't have another x, so he's going to be affected."

The condition occurs when specific gene mutations inhibit the ability of certain pigments in the optic nerve cells to sense color. These cells, called cones, are found in the retina. If only one of these pigments is missing a person may have trouble distinguishing between colors.

People who are color blind typically have trouble telling the difference between certain color categories such as red-green or blue-yellow. In rare cases, they may have a complete absence of color vision and see in only black and white. Red-green color vision deficiency is the most common type. There is no treatment or cure for the condition.

In Dr. Frempong's practice, she uses chips with different hues and color dot cards to diagnose patients. In order to see the numbers on the chips, a patient needs to be able to distinguish subtle nuances of different shades of red and green.

Early diagnosis for the disorder is key because studies have found color blindness can impact a child's performance and his ability to perform on tests. The researchers of the study at the University of Southern California School of Medicine and the USC Eye Institute, say screening for color blindness should therefore begin before age 4.

Thankfully, for Zachary, the disorder hasn't caused any notable learning problems. "It is a complete non-issue, and I don't expect it to be an issue going forward," his father, Sam Lehr, told CBS News.