Colorblindness is the inability or diminished ability to see or discriminate between colors in normal lighting. Usually, the condition is due to faulty retinal cones in the eye. It also tends to be sex linked, which means that it resides on the X chromosome. Women have two such chromosomes; to see normally, they need only one with undamaged genes that make photo-pigments. Men, on the other hand, have but one X chromosome. As a result, they are much more commonly diagnosed with colorblindness.
In 1798, the English chemist John Dalton realized he was colorblind and published a paper about the condition. Colorblindness is often seen as a disability, yet studies have shown that it can help people penetrate color camouflage. Although it is often inherited, it can also be caused by physical or chemical damage.
Individuals who have the rarest type of colorblindness, monochromacy, see the world as though they were watching black-and-white television. People with dichromacy may see red as dark (protanopia), have trouble telling the difference between red and green (deuteranopia), or lack blue color receptors (tritanopia). Less severe is anomalous trichomacy, which may manifest itself as either protanomaly (poor red-green discrimination), which occurs in 1 percent of men, or deuteranomaly (mildly diminished red-green discrimination), which is found in 5 percent of men.
Essentially, colorblindness can be divided into two broad categories: total and partial, the latter of which makes it hard for people to tell red from green or blue from yellow. Roughly 8 percent of men of Northern European heritage have some degree of red-green deficiency. In contrast, only 0.5 percent of women of similar background have the condition.
When colorblindness is inherited, it may be apparent from birth. Alternatively, it can begin in childhood or adulthood. Its severity may remain constant or increase with time. Some forms of it can even lead to legal blindness. Non-inherited colorblindness may be caused by trauma, retinal exposure to ultraviolet light, vitamin A deficiency, diabetes, or macular degeneration. The Ishihara color test and the Farnsworth Lantern Test have both been used to diagnose colorblindness. The latter has found particular favor in the U.S. Army and Navy.
There is no cure for colorblindness. Tinted spectacle or contact lenses can increase a person’s discriminative ability in some areas of the color spectrum, but they usually lower discrimination in other areas. The eyeborg, invented in 2003, allows colorblind people to hear sounds that represent certain colors in their environment. Some colorblind artists have used this device to help them create their artwork. Another landmark discovery occurred in 2009, when scientists used gene therapy to produce trichromacy in monkeys who previously experienced dichromacy.
In the U.S., approximately 7 percent of men (and 0.4 percent of women) have some degree of trouble telling red and green apart. Most colorblindness takes the form of anomalous trichomacy, which causes only some difficulty in red-green discrimination. Individuals who do experience dichromacy often use texture and shape clues to aid in color discrimination.