Grass is green, ripe tomatoes are red. For many people, these color designations remain colorless terms throughout their lives. Eight out of 100 men, but only one out of 200 women know some colors only by hearsay. Color vision deficiency – colloquially often simplified as color blindness – can have many manifestations. Red-green deficiency is one of the most common forms of color vision deficiency. Learn more about the causes and treatment of color vision deficiencies here.
Function of cones and rods
To see colors correctly, two steps are necessary: Colors must be correctly recognized in the first place (identification), and they must be distinguished from one another (discrimination). For this purpose, the healthy eye has three types of color sensory cells in its retina, the cones. With these, it perceives the three primary colors red, green and blue and composes several million color tones from them. These six to seven million cones are located in the area of the macula (yellow spot), the area of greatest visual acuity in the eye, and are responsible for daytime vision. At dusk and at night, the particularly light-sensitive rods, which can only perceive shades of gray, take over the visual function – which is why all cats are gray at night.
Forms of color blindness and color deficiency.
People with color vision deficiency, a disorder of color perception, have cones that do not function at all or only to a limited extent. Therefore, they cannot see any or certain colors.
- In the rare total color blindness (achondroplasia or achromatopsia), the cones do not function at all. Therefore, only colorless images in shades of gray with different brightness values are perceived, comparable to normal “rod vision” in twilight.
- In partial color blindness, color perception is absent for one (dichromasia) or two (monochromasia) of the three primary colors.
- In a – usually familial – color deficiency (anomalous trichromasia), the color sensory cells function, 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 impaired (already from 10 percent), the red of a traffic light is perceived as green.
- In 60 percent of all color deficiencies, only one of the three basic sensitivities is disturbed. Red-green deficiency (often mistakenly equated with red-green blindness) is the most common form of color vision deficiency and occurs predominantly in boys.
- Blue blindness (tritanopia) is comparatively less common and results in affected individuals having difficulty seeing the color blue or identifying yellow.
Frequency of forms of color vision deficiency
Congenital disorders of color vision occur in 8 percent of men and 0.4 percent of women. 4.2 percent of those affected are deuteranomalous, meaning they have green deficiency, and 1.6 percent are protanomalous, meaning they show red deficiency. 1.5 percent have green-blindness (deuteranopia), 0.7 percent are protanopic (“red-blind”). Disorders in the blue range are very rare, as is total color blindness.
Cause of color vision deficiency
Color vision deficiency is mostly due to heredity (genetic), it then neither gets better nor worse with time. However, color vision deficiency can also be acquired, in which case changes in its course are also possible. Limitations for color vision occur in various diseases of the choroid and retina. Complete loss of color vision is hereditary. Day blindness results from failure of the cone apparatus of the retina.
Diagnosis: How color vision deficiency is diagnosed
Color vision is tested primarily by means of special boards with different colored dots (Ishihara boards); the test can be performed from about age 3. Color blindness: picture test for red-green deficiency and co. The first signs are that the affected child has difficulty painting with colors or recognizing traffic lights. However, those affected usually quickly succeed in compensating for these symptoms: They then simply memorize the arrangement (top = red, bottom = green) or the colors of objects they know.People with color vision deficiency do not see gray, but simply perceive many shades of color differently – as if they had fewer initial colors available in a paint box for mixing than a person with normal vision. This has not only disadvantages – some things are perceived better or with more contrast. Affected individuals with total color blindness often suffer from severe glare sensitivity and impaired vision.
Treatment: what can be done about color vision deficiency?
There is no therapy for congenital color vision deficiency; surgery or similar forms of treatment are not possible. However, in some cases, correction is conditionally possible:
- People with total color blindness often wear dark sunglasses. Depending on the light conditions, these glasses use special edge filters that filter out certain colors from the sunlight. Magnifiers or small binoculars allow people to read small print or see into the distance.
- For people with red-green deficiency, there are glasses with special lenses that filter out certain color spectra differently; however, this changes the perception of other colors.
- There are devices that can detect colors. They send a small beam of light to the object and measure how much light comes back. This allows the device to report what color an object is. However, the practical use is controversial.
- Research is underway into the possibilities of gene therapy to correct total color blindness.
Depending on the severity of the color vision deficiency, it can limit career choices – for example, people with color vision deficiency may not become pilots, train drivers or captains.
