Color weakness / color blindness

With a color weakness (color vision disorder) people can only recognize certain colors to a limited extent. If red or green blindness is present, those affected have greatly reduced color vision and cannot distinguish many colors

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Color impairment / color blindness - briefly explained

The color visual impairment is a color vision disorder (anomaly), in which certain color tones can be seen more poorly due to a malfunction of the cones, such as green. Then there is talk of a green weakness. In the case of partially existing color blindness, a color cannot be seen at all because the cones have no function or are not created at all. In the case of complete color blindness, no colors are perceived at all, only light-dark contrasts, the person concerned sees his world in different shades of gray.

The cause of color vision disorders are mostly genetic predispositions (congenital form), more rarely they can be triggered by other diseases or medication (acquired form).

In order to diagnose a color vision disorder, the ophthalmological check-up is of great importance, since people with congenital color vision disorders often do not notice their impairment. With complete color blindness, those affected see very blurred and are clearly sensitive to glare, so that the diagnosis is usually made early in childhood.

A therapy for color vision weakness and color blindness is not possible. Animal studies at the Universities of Tübingen and Munich are very promising and there is hope that gene therapy will also be available for humans in a few years.

What are color vision disorders? What is color blindness?

Even if many people understand the same thing by the terms color impairment (color vision impairment, color blindness) and color blindness, there are nevertheless different underlying disorders.

  • Color vision disorder (color vision disorder)

A person who has a color impairment or weakness can only recognize some color tones to a limited extent. All of the sensory cells with which he sees in color (red, green and blue cones) are present in the retina. However, some of them function incorrectly - with a green weakness (deuteranomaly) the "green" cones are affected, with a red weakness (protanomaly) the "red" cones are affected. About eight percent of all men, but only 0.5 percent of women are affected by a color disorder.

  • Color blindness

Here the cones for a certain color have no function or are not created at all. One then speaks of a partially existing color blindness (partial color blindness). The person concerned then has, for example, green blindness (deuteranopia). On the other hand, one speaks of complete color blindness (achromatism) if no colors can be seen. The person concerned only sees his surroundings in different shades of gray. The reason for this is usually a complete absence of the cones on the retina, less often a disturbance in regions that are responsible for vision (for example diseases of the optic nerve or brain regions).

© W & B / Szczesny

Function of the rods and cones

In the retina of the eye there are two different sensory cells (photoreceptors) that are responsible for the ability to see: the cones and the rods. While the cones are responsible for colored vision during the day, the eye uses the rods to differentiate between light and dark, which is particularly important at dusk and at night.

There are three different types of cones: red, green and blue cones. Each of these three types is sensitive to its own color range - either red, green or blue. If the cones are stimulated by light of a certain wavelength, they convert this stimulus into electrical impulses. They get into the brain, where the actual color sensation takes place.

In the case of color vision impairment, the affected cones are restricted in their function. If there is partial (partial) color blindness, those affected only have two functional cone types, which significantly reduces color vision. In a green-blind person (deuteranopia) the green cones are missing or do not work, in a red-blind person (protanopia) the red cones accordingly.

It is very rare for people to be unable to perceive any color nuances - i.e. they only see black, white and shades of gray. In this case, there is total color blindness (achromatism).

Causes: How do color vision disorders / color blindness occur?

Color vision disorders can be congenital or acquired. Congenital color disorders are genetically inherited via the X chromosome. It is almost always a red-green disorder (see background information on inheritance below). In the congenital forms, both eyes are affected.

In the case of acquired color vision disorders, a blue-yellow sense disorder (tritanopia) is in the foreground. The triggers of an acquired color disorder include, for example, diseases of the retina such as age-related macular degeneration (AMD) or diseases of the optic nerve (optic nerve). But drug side effects can also lead to an acquired color disorder. A cataract can also weaken color vision, especially that of the color blue. Those affected only recognize this color when it is a clearly stronger blue. After the clouded lens has been replaced (cataract operation), the normal colors are noticed again in addition to the improvement in visual acuity.

In this article we mainly deal with the congenital color vision disorders, that is, especially restrictions in the red-green area. Acquired color impairment is often an impairment of the blue-yellow sense.

© W & B / Astrid Zacharias

Inheritance of red-green weakness

Red-green weakness is an x-linked recessive hereditary disease. This means that the disease is inherited via a gene on the X chromosome (sex chromosome) and only becomes manifest if it is not balanced by a healthy gene on an X chromosome.

A man has an X and a Y chromosome (XY).

A woman has two X chromosomes (XX).

If a woman has a defective and a healthy gene on the X chromosome (xX), then the healthy gene covers the diseased one and she has no color vision deficiency. But she can pass the defective gene on to her children via the affected chromosome, she is a so-called carrier (see our picture example above).

If a boy / man has a defective gene on the X chromosome (xY), this cannot be compensated for and the color weakness is therefore pronounced.

This also explains why color impairment occurs significantly more frequently in men than in women. A woman can only develop this if she receives a defective gene on the X chromosome from both parents (xx).

Symptoms: What symptoms do a color impairment / color blindness cause?

If a person sees certain colors faintly or not at all from birth, he is often not aware of this. After all, he has never seen what the colors normally look like. Only when relatives or acquaintances speak to the person concerned does he notice that he perceives colors differently or not at all. Therefore, early detection is of great importance.

  • Redness weakness / red blindness

If you have a weak sense of red, the color red is perceived more poorly and is also difficult to distinguish from green. Red is at the end of the visible spectrum. This means that a red-blind person has a shortened (smaller) visible spectrum and for him the red increasingly loses its brightness. A typical example is the supposedly "dark red" sweater that a person with a red-handedness bought. In reality, however, the sweater is light and pink.

Red blindness is of particular importance because people who do not perceive this color do not recognize a strong red either. For example, in foggy conditions, they do not see the red taillight of the car in front of them and therefore only recognize much later that a car is driving in front of them.

  • Greenness weakness / green blindness

People who perceive green more weakly only describe this color correctly if it is very strong, depending on how strong the weakness is.

If they are affected by green blindness, it is also difficult for them to distinguish between green and red.

  • Complete color blindness (achromatism)

Totally color-blind people, so-called achromats, have a visual acuity reduced to ten to 20 percent and see objects in daylight blurred and colorless. In addition, those affected often suffer from eye tremors (nystagmus) and are very sensitive to light. In low light conditions - for example at night - you can see almost as well as a person who recognizes colors normally.

People who do not recognize a certain color at all or only to a limited extent are only suitable to a limited extent for some professions.These may only be carried out after extensive tests have been passed. They also sometimes have problems in traffic. Correct color vision is essential for train drivers, pilots and also for the private boat license.

This is what the world looks like if you are green.

Ishihara test: A person with normal vision recognizes the number 74 in the picture, a person with weak green eyes an 11, because the weaker points cannot be seen.

© Your Photo Today / A1Pix

Diagnosis: How is color impairment / color blindness diagnosed?

  • Pseudochromatic test panels

So-called pseudoisochromatic tables (e.g. Ishihara tables, Vellhagen tables) help with the early detection of color vision disorders. These color tables are based on the fact that a person with impaired color vision also judges color tones on the basis of brightness and can therefore often name the correct color.

Therefore, the color tables used contain color circles of different sizes, which consist of different colors with different color contrasts but identical brightness. People whose sense of color is disturbed are deprived of their aid - the difference in brightness for recognizing the colors. On the boards there are letters or numbers that are composed of numerous colored dots. A person with normal eyesight can recognize a number or a letter from the dots. For small children there are boards on which no letters or numbers can be recognized, but animals or figures, for example. If there is a color vision disorder, the person concerned does not perceive the symbols shown or not perceive them correctly. These boards are well suited as a screening test (= preventive test). They can be used to determine whether color vision impairment or color blindness is present.

However, it is only possible to a limited extent to differentiate between the precise characteristics of the individual color vision disorders. If the patient has problems reading the boards correctly, an ophthalmologist can carry out an additional examination to classify the present color vision disorder more precisely using the so-called anomaloscope.

  • Anomaloscopic examination

The patient looks at two semicircles over a long tube. One semicircle consists of a pure yellow, the other a mixture of red and green. The patient is offered a certain yellow in the lower semicircle and he should match this yellow by mixing red and green in the upper semicircle. This test determines the red-green weakness. For example, if a person has a weakness in green, he mixes too much green with it. If he has a weakness in red, he adds too much red. The so-called anomaly quotient can be calculated from the color components and the extent of the color impairment can be determined. The examination is not that simple and cannot be carried out on young children. There are also anomaloscopes for diagnosing blue weakness, but these are only used very rarely.

The congenital total color blindness is diagnosed in infancy because of its pronounced symptoms.

Therapy: How is a color vision disorder / color blindness treated?

For congenital color impairment or color blindness, there is currently no therapy that can remedy the cause, as it is a genetic defect. However, gene therapy can be expected in a few years.

Time and again, special glasses or contact lenses are offered to correct a color vision disorder. However, experts point out that these glasses are of no use. They only change the color contrast and not the person's color vision. With the changed color contrast, the affected person may be able to read color tables correctly (for example Ishihara tables, see section Diagnosis). In return, he sees other colors completely wrong. These glasses are also not approved for aptitude tests - for example for a driver's license, sailing boat license or flight license.

For people who are completely color-blind, glasses with tinted lenses and appropriate strengths can alleviate the symptoms - especially the strong sensitivity to glare. It is not possible to improve visual acuity with glasses.

It is important that people are aware of any color vision impairment or that it is recognized early on. Because in many professions, employees must be able to recognize colors normally. This applies, for example, to bus drivers, locomotive drivers, pilots and also electronics technicians.

Our advisory expert:

Professor Dr. med. Thomas Berninger is a specialist in ophthalmology and has been a resident ophthalmologist near Munich since 1991. After two and a half years at the Max Planck Institute in Bad Nauheim, he began in 1984 at the Ludwig Maximilians University in Munich with Professor Dr. med. Otto-Erich Lund completed his specialist training. This was interrupted by an 18-month research stay at the Moorfields-Eye Hospital in London. The scientific focus there: the objective investigation of color vision.

In 1991 he completed his habilitation in ophthalmology at the LMU in Munich. For 30 years, Thomas Berninger has been organizing advanced training events for ophthalmologists at the Mathildenstrasse University Eye Clinic (Munich) with a focus on color vision, electrophysiology, and optic nerve and retinal diagnostics. His main areas of activity are the objective examination of visual function, the diagnosis and treatment of retinal diseases and children's ophthalmology.

Important note: This article contains general information only and should not be used for self-diagnosis or self-treatment. He can not substitute a visit at the doctor. Unfortunately, our experts cannot answer individual questions.