Color-blind? Test determines type of color sense disorder

Color blindness (Achromasie) belongs to the color sense disturbances and designates in the narrow sense the complete inability to see colors. In a broader sense, the term is also used for color weaknesses such as red-green blindness. Whether a color blindness is present can be determined by tests, for example the Ishihara color chart.

Color blindness, also called Achromasie, refers to an innate or acquired disorder of color vision, ranging from a weakened perception of individual colors to complete blindness to colors due to missing or defective color sensory cells, the cones.

Depending on the extent of the disturbed perception of color, color vision disorders can be associated with serious limitations in everyday life and in professional terms. About eight percent of the male and about 0.5 percent of the female population suffer from a congenital or acquired disorder of normal color vision.

Red-green blindness is rare

Fortunately, color weaknesses are much more common than complete blindness to one or two colors . More than half of those affected (about five percent of the male and 0.4 percent of the female population) suffer from a green-ting , less than one-percent from a red weakness . A complete red-green blindness is observed much less frequently. Even more rare is the disturbance of blue-yellow vision and an anomalous three-color perception . The number of people affected is very small.

Symptoms of color blindness

Color blindness leads to the confusion of different colors. Which colors are exactly reversed, depends on the respective Farbsinnstörung.

There are several forms of color vision disorders. In dichromaticity there is a reduced sensitivity of the cones for either red or green. In red-eye-blindness , for example, the following confusion occurs during the visual process :

• Red with yellow and brown with green
• Violet with blue
• Dark red with black

The confusion colors at a green power are:

• Green with yellow
• Brown with gray

The blue kidney leads to the following confusions:

• Red with orange
• Blue with green
• Green yellow with gray
• Violet and pale yellow with white

In the case of red and green power, those affected do not recognize the colors red and green under unfavorable conditions, for example in traffic at high speed and poor visibility.

In trichromasia all colors are seen. However, one of the three components is weaker in color perception than the other two.

Gray instead of color: symptoms of complete color blindness

In the case of complete color blindness, only light / dark contrasts can be perceived during the day, meaning that those affected see a misty white / gray. Colorful appears as gray variants. That is why the disease is also called “day blindness” . Since the rod-shaped receptors are responsible for twilight vision and are also present in Achromasie unchanged, see color-blind people during the dusk normal. Furthermore, color-blind people react to bright light mostly hypersensitive (photophobia). Chopsticks are designed for lower light levels (twilight).

Since there are no functional pins, it is not possible to inhibit the rods in brightness, unlike people who are not color-blind. In addition, those affected have a 90 percent reduction in visual acuity (visual acuity) during the day, as the rods are located at a lower density in the central visual field. Because in the yellow spot (place of sharpest vision centrally in the retina) no functioning visual cells exist and the central visual acuity is consequently very bad, an ocular tremor (nystagmus) occurs. Quick eye movements are intended to compensate for the present defect. The eye-shaking is involuntary, the person concerned does not even perceive it.

Causes: Color blindness can also arise later in life

In the healthy eye, there are more than six to seven million color sensory cells in the area of ​​the macula (yellow spot) . These are three types of cones that can recognize the primary colors red, green and blue . From this all colors are put together. For seeing at dusk and at night, however, the sticks are responsible. They are particularly sensitive to light, since the amount of light during these times is correspondingly sparse. Chopsticks can only perceive shades of gray. There are people whose color perception is disturbed due to missing or defective pins.

Color blindness can be innate or acquired. For example, acquired disorders can be caused by illness or poisoning.

• Congenital color vision disorders usually affect both eyes. In the so-called dichromacy, the color sensation for one of the three primary colors, in particular red or green, is completely absent because the corresponding cone pigment is not present. It is colloquially falsely referred to as color blindness. However, those affected are not completely colorblind, since the color perception is based on the calculation of the excitement of different types of cones. If the spectrum at the long-wave end is shortened – the L-cones are missing – the affected person is red-blind (protanopia). On the other hand, if the M-cones are missing, then it is green-blind (deuteranopia). The vision process works via additive color mixing.
• The red-green Dichromasie there is also in attenuated form as red or green (protanomaly or Deuteranomalie). In most cases, there is a family predisposition here. Although the three types of cones work, the sensitivity of one type of cone (for red or green) is reduced because the corresponding color pigment system is weaker. As a result, colors like to be confused. The color weakness occurs more frequently than the complete absence of a color.
• A disturbance of the blue-yellow sense (tritanopia, tritanomaly), however, occurs much less frequently. Here are missing the so-called S-cones, so that the color blue can not be perceived. Furthermore, there is the variant that all pins are present, but a pin type has a wrong spectrum. This disturbed three-color vision is called anomalous trichromasia.
• The most serious, but fortunately very rare, is the so-called recessive-inherited achromatism . It is a total or almost total color blindness . The function of the color receptors in the retina (cones) has completely or almost completely failed in color vision disorders (color blindness, Achromasie) – either because they are almost or completely functionless due to lack of pigment or completely missing. Those who suffer from color blindness, therefore, basically only has rod receptors that allow the twilight vision in the normal sight.
• E rworbene color vision deficiencies may also be acquired later in life. The type of occurrence, often affects only one eye, is different from the congenital disorders. Acquired color sensory disturbances occur as a result of optic nerve or retinal center disease or due to symptoms of intoxication, such as medication. On one or both sides, the field of view for colors can be reduced. It can also come in the central area to color failures. In a cone dystrophy, the color vision is completely absent – this change the cones due to a genetic malformed pathology. As a result, waste products that arise during the process of vision can no longer be removed quickly enough and clog the cells, which then slowly perish.

Recognizing color blindness: the Ishihara test

Color blindness can be diagnosed using the Ishihara test . The Japanese ophthalmologist Shinobu Ishihara first described it in 1917. The Ishihara test uses color charts to reveal color vision problems such as red-green or blue-yellow vision problems.

The color charts consist of many individual pixels. While normal-normal numbers can be seen on the tablets, this is not or hardly possible for patients suffering from color weakness or color blindness. The test can be used from about the age of three . It should be done when, for example, children have difficulty painting with color or recognizing traffic lights. The degree of color vision weakness is not exactly analyzable, but estimable.