Color blindness is usually a genetic vision deficiency that limits the colors that an individual can detect. Color blindness resulting in black and white vision is extremely rare. Affected colors are generally limited to green and red, often appearing as shades of tan or brown. Less commonly, the blue color may also be affected.
The human eye detects color with photoreceptors located on the retina at the back of the eye. These photoreceptors come in two types, rods and cones. The rods fill the peripheral edges of the retina and are used in low-light conditions, such as night vision. The rods do not detect color well, but they do allow people to see in the dark.
Cones appear throughout the retina and contain pigments that respond to certain colors. The pigments communicate with the brain when they fire. This is how a person detects color. Cones require brighter light to work than rods, so we can't see colors well in the dark.
Color blindness is the result of certain cones misinterpreting the wavelengths that correspond to their respective colors. The colors red, green, and blue have corresponding wavelengths. Red wavelengths are longer, green colors make up medium wavelengths, and blue colors are made up of shorter wavelengths. If the green cones, for example, only respond to slightly longer wavelengths, the brain will interpret green as red.
There is no cure for color blindness, but it is generally not an inhibiting condition. Red and green traffic lights may look like similar shades of the same color, but those with color blindness use the position of the light as an indicator of when to stop or go. Color blindness becomes a problem if the job requires color separation. This could be the case with an artist or designer, for example, or an electrician who must see red, green, and yellow wiring diagrams.
Studies suggest that approximately eight percent of the world's male population is genetically colorblind, while less than one percent of the female population is affected. In addition to genetics, certain diseases or damage to the eyes can cause color blindness. Regular eye exams for color blindness in children and adults, and there are also many online color blindness tests. As people age, color sensitivity can decrease due to macular degeneration, cataracts, or other conditions.