Grass is green, ripe tomatoes are red. For many people, these color names remain colorless concepts throughout their lives. Eight out of every 100 men, but only one out of 200 women only know some colors by hearsay. Even the English physicist John Dalton suffered from a color weakness - he perceived orange, yellow and green as yellows.
Why we can see colors
In order to see colors correctly, two steps are necessary: the colors must first be recognized correctly (identification), and they must be distinguished from one another (discrimination). The healthy eye has in its retina three types of color sensory cells, the cones. With these, it perceives the three primary colors red, green and blue and composes several million shades.
These six to seven million cones sit in the area of the macula (yellow spot), the site of greatest visual acuity in the eye, and are responsible for daytime vision. In the twilight and the night, the particularly light-sensitive rods, which can only perceive shades of gray, take over the visual function - that's why all cats are gray at night.
Color blindness and color weakness
People with a color vision deficiency, ie a disturbance of color perception, have cones that do not function at all or only to a limited extent. Therefore, they can not see any or certain colors.
- At rare total color blindness (Achroma [top] she) pins do not work at all. Therefore, only colorless images are perceived in shades of gray with different brightness values, comparable to the normal "rod view" in dim light. Partial color blindness lacks the color sensation for one (dichromaticity) or two (monochromatism) of the three primary colors.
- In a - usually familial - color weakness (abnormal trichromatosis), the color sensory cells work, but their sensitivity is reduced. Therefore, the colors of the affected cones (mostly red and green = protanomaly and deuteranomaly) are confused in certain situations: For example, if the red receptor is limited (as low as 10 percent), the red of a traffic light is perceived as green.
- At 60 percent of all color weaknesses, only one of the three basic sensitivities is disturbed. The red-green weakness (often misinterpreted as red-green blindness) is the most common form of color vision deficiency and occurs predominantly in boys.
Frequency and cause of color vision problems
Congenital disorders of color vision occur in 8 percent of men and 0.4 percent of women. 4.2 percent of the affected are deuteranomal, so have a green-black, 1.6 percent are protanomal, so show a red weakness. A green blindness has 1.5 percent (deuteranopia), 0.7 percent are protanop ("red-blind"). Disturbances in the blue area as well as total color blindness are very rare.
The color vision deficiency is usually due to heredity, but it can also be acquired. Restrictions on color vision occur in various diseases of the vein and retina. The complete loss of color sense is hereditary. The day blindness is caused by the failure of the pin apparatus of the retina.