Shades of Gray? The Facts of Color-blindness
Color-blindness is a common genetically inherited condition. For someone with color-blindness, a color television may not mean all that much. Red, white, and blue is an idea, and not necessarily something on the flag. They may understand that green means go, but their understanding probably doesn't extend much past that.
It is a condition that is difficult for those without color blindness to understand. "There is a remarkable amount of misunderstanding about this most common and natural disorder," says Jay Neitz, PhD, who teaches at the Medical College of Wisconsin in Milwaukee. He and his wife, Maureen Neitz, PhD, are considered among the leading researchers in this field in the country. "The lack of understanding is not just among the general public, but also among teachers and other professionals, even though color is used ever increasingly as a tool in education."
Color-blindness, in fact, is not blindness at all. Most people who are described as color blind can see colors, but not the same colors the rest of us do. "That's why, if I would call it anything, I would call it color deficiency," says Michael F. Marmor, MD, a professor of ophthalmology at the Stanford University School of Medicine in Palo Alto, California. "Color-blind people see differently, but they're not blind to colors."
More Than One Type of "Blindness"
The differences in the range and severity of color-blindness still surprises researchers. People who are not color-blind can distinguish between more than 100 hues (a hue is used to describe a particular grouping of colors, for example: pastel green and plain green, although different colors, are the same hue). Color-blind people, on the other hand, deal with an entirely different palette.
The most common type of color-blindness is red-green. Someone with severe red-green color-blindness can only see two colors. Dichromat vision (which means two colors) sees everything on the rainbow from red to green as yellow, and everything between blue and violet as blue. This means there are fewer difference in between colors like aqua or turquoises. A second less common type of color-blindness is blue-yellow which only affects 1 out of 100 colorblind people.
To try to understand what it may be like, imagine a pie chart in a textbook where each slice of pie is the same color, a red stop light that looks exactly like the light from a street lamp, or a mail order catalog where every pair of pants looks alike. You'll begin to get the idea.
"One might think that one could learn about the perceptual world of color blindness by interviewing a color-blind person, but this often leads to more misunderstanding than enlightenment," says Dr. Neitz. "It is impossible for them to imagine what they have never seen so they can't relate their world to that of the person with normal color vision."
Dichromats vs. Trichromats
Dichromats are about one-quarter of the estimated nine million color-blind people in the US, almost all of whom are men. The rest are categorized as anomalous trichromats, whose color vision is somewhere between normal and dichromatic.
This wide range extends from trichromats whose color vision is nearly identical with that of someone who sees all 100 hues to the most deficient dichromat who sees nearly everything is just two hues. A trichromat in the middle, however, can tell the difference between red and green, but gets stuck when asked to distinguish between olive green and brown.
Color-blindness: For Men Only?
Most color-blind people are men because the genetic deficiency is passed from mother to son in alternate generations. That means that if the mother's father was color-blind, there is a 50% chance her sons will also be color-blind.
Currently, there are no effective treatments or a single accurate test for color-blindness, and there is an active debate in the scientific community about whether either is needed. Dr. Marmor, for one, almost never tests for color-blindness, and the tone in his voice makes it clear what he thinks of treatments and cures. Things like pink-tinted contact lenses are "foolish and dangerous," he scoffs.
"It's just the way some people are," Dr. Marmor says. "I don't consider it a serious problem, and that's why I don't routinely test for it."
Dr. Neitz, on the other hand, points out that some sort of accurate measuring stick should be established, if only for those professions such as law enforcement, gemology, and people working with electricity, in which distinguishing between hues is necessary.
"When color is used to teach second graders," he says, "the color-blind student will be overwhelmed. An enlightened teacher might recognize that the student is color-blind, but an unenlightened teacher might conclude that the child has a learning disability or an attention deficit disorder."
That's why the Dr. Neitzes are developing a two-fold test, featuring genetic screening (since the color genes of the color-blind are different) and a simple pencil-and-paper process.
If you would like to learn more about the genetic component of color blindness or would like to try an informal color perception test, visit these internet sites below.
The American Academy of Ophthalmology
The Biology Project, University of Arizona
Color Perception Testing
Canadian Family Physician
Rosenthal O, Phillips R. Coping with color blindness . Avery Publishing Group; 1997.
Last reviewed January 2008 by ]]>Alexander J. Anetakis, MD]]>
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