Synonyms in a broader sense
red-green blindness, red-green visual impairment, dyschromatopsia, color blindness (ugs), color vision deficiency, abnormal trichromasia, dichromasia
- Self test red-green weakness
- Online eye test
- Amsler grid test
Definition
The genetically caused red-green weakness is the most common color vision disorder and is often colloquially mistakenly called color blindness. The disease can be divided into a red-weakness (protanomaly) and a green-weakness (deuterine anomaly), whereby in both cases the colors red and green are difficult to distinguish. Furthermore, one differentiates between the rarer red blindness (protanopia) and deuteranopia (green blindness), in which the differentiation of the two colors is no longer possible.
Epidemiology
Red-green weakness is always congenital and affects about 9% of all men and 0.8% of women. It usually increases or improves over the course of life.
History
The red-green weakness was discovered by the English natural scientist and teacher John Dalton (*1766), who himself suffered from this disease. For this reason it is also known as Daltonism. Red-green weakness and blindness are X-chromosomal recessive hereditary diseases.
This means that the disease-causing gene is located on the X chromosome. Women need two defective gene copies in order to become ill, in men one is sufficient, since they only have one X chromosome. This explains why men are affected much more often than women.
There are three different color receptor types (cone types) in the retina of the human eye: red, green and blue cones. Each of them absorbs light in its specific color spectrum. In the case of red-green deficiency, there is now a mutation in the gene responsible for the red or green cones.
As a result, a changed visual pigment (opsin) is formed, which no longer permits correct color perception. In the case of red-green weakness, the gene is not only altered, but completely missing, which is why the corresponding color is then no longer recognized at all. People with red-green vision impairment perceive certain red and green tones only as gray tones, which means that they are unable to distinguish these two colors from each other, if at all.
However, most of those affected hardly feel this disorder as bad, since they have not known any other way of seeing since birth. Apart from the ability to distinguish between the red-green range, patients also develop the same color impression as those with normal vision, which leads to an impairment that can only be considered minor. There are, however, some professions that require very good vision, such as pilots, bus and cab drivers or police officers, which cannot be practiced with this limitation.
There are several ways to diagnose a red-green weakness. With the help of special color charts a red-green weakness can be determined and its characteristics determined. The Ishihara color charts (also called pseudoisochromatic color charts), named after their developer, are most commonly used for this purpose.
These tables (see: self-test red-green weakness) are circles filled with round color patches of different brightness levels. If color vision is perfect, a certain number, also composed of color patches, can always be seen in the center of the circle. This number is visible due to the ability to distinguish between red and green (or blue and yellow for the diagnosis of the much rarer green-blue weakness).
Patients with color vision impairment, however, cannot distinguish between the different colors, but only notice the contrasts that may be present, which means that, depending on the chart and the degree of their visual impairment, they may see no number at all or a different number than the person with normal vision. In the test, several tables must usually be viewed, whereby the number 12 should be visible on the first table for everyone. The Stilling-Velhagen tables are based on the same principle.
The Farnsworth test is a very accurate test. In this test, the examinee should place a certain number of color buttons in a color row that appears correct to him. For evaluation, the person performing the test has a piece of paper on which the correct sequence of color plates is arranged in a circle.
He then connects the color buttons on this piece of paper in the same way as the test person has arranged them, so that the healthy person should have created exactly this circle.The different types of ametropia provide characteristic patterns that deviate from this curve. The last possibility for diagnosis is offered by the Anomaloscope according to Nagel. Here the patient looks through an eyepiece at a round test field.
This is divided into two halves: The lower half is filled in as a “reference field” by a preset yellow (spectral yellow, sodium yellow). In the upper half, in the “mixing field”, the patient should mix spectral green and spectral red in such a way that the same color impression is created as by pure yellow and the circle finally appears monochrome. Someone with a weakness for green would have to add too much green in the mixing field to achieve the impression of sodium yellow, because he perceives green only weakly, a patient with a weakness for red would set too much red accordingly.
From the quantitative values for the green and red used, a quotient can be determined that allows an exact statement about the degree of color vision deficiency/red-green weakness. To date, there is no known therapy for red-green vision impairment and since the disease is inherited, there is no possibility for prophylaxis. The red-green weakness is a congenital, very common but not very serious disease that mainly affects men.
In everyday life, it is accompanied by only a very minor limitation, which many affected persons often do not notice at all or only very late, since they are not used to anything else. In order to determine the disorder or to describe it in more detail, there are various tests that are used, among other things, in recruitment examinations for pilots and police officers.
