Color blindness

Dr. rer. nat. Daniela Oesterle is a molecular biologist, human geneticist and trained medical editor. As a freelance journalist, she writes texts on health topics for experts and laypeople and edits specialist scientific articles by doctors in German and English. She is responsible for the publication of certified advanced training courses for medical professionals for a renowned publishing house.

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The term color blindness describes various forms of hereditary or acquired color ametropia. Depending on the type of color blindness, those affected either see no colors at all (achromatopsia) or they do not perceive certain colors (dichromasia). Find out everything you need to know about the causes, diagnosis and treatment of color blindness.

ICD codes for this disease: ICD codes are internationally recognized codes for medical diagnoses. They can be found, for example, in doctor's letters or on certificates of incapacity for work. H53

Color blindness: description

A person who can perceive all colors has three different types in the retina of his eyes from the sensory cells to color perception - the cone cells (for short: cones): The first cell type reacts specifically to red light, the second particularly to green, the third especially on blue light. Experts refer to color-savvy people, i.e. people in whom all three cones work properly, as trichromats (three = Greek "tri"; colors = Greek "chroma").

In the case of color blindness, either all three cone cells do not work or two of them do not work, or only one cell type does not work. Accordingly, a distinction is made between the following sub-forms of color blindness:

Achromatopsia or achromatism: There are no functioning cone cells at all.
Dichromasy: There are two types of cones that work.
Monochromatism: Only one of the three types of cone cells works.

With achromatism, those affected cannot perceive any colors, with di- and monochromatism only to a limited extent. The underlying defects can be genetic (congenital) or develop in the course of life. In the case of congenital color blindness, both eyes are always affected; in the case of acquired color blindness, this can only affect one eye.

Color blindness is one of the color vision disorders of the eye.

Color vision impairment (e.g. red-green visual impairment)

Color vision impairment is also one of the color vision disorders (color vision impairment). By this mant understands a visual impairment for a certain color - but that is not real color blindness! Because all three cone cell types work here, but one type does not work properly.

An example of such a color vision impairment is red-green visual impairment (red-green weakness). In some people affected, the green cone does not work properly (deuteranomaly), so that there are difficulties in seeing green and distinguishing it from red. If the red cone does not function correctly (protanomaly), those affected perceive red more poorly and can hardly distinguish it from green.

In the case of blue eyesight (tritanomaly), the blue cones work to a limited extent, so that the sensation for blue is reduced and this color hardly differs from yellow for those affected.

All of these forms of color blindness impair color vision, but less so than color blindness. They are called abnormal trichromatism by medical professionals.

Seeing - a highly complex process

The visual process is a very complex sensory performance of the human eye.It enables us humans to distinguish several million shades of color and to see them in the twilight. The starting point for this enormous achievement are two different light-sensitive cell types in the eye retina: the rod cells, which enable us to see in twilight, and cone cells for extensive color vision.

Most of the cone cells are found in the visual pit. This is a small depression in the retina at the fundus in the center of the "yellow spot" (macula) and the place for the sharpest vision. Depending on which color and thus which wavelength of light the cone cells can perceive, a distinction is made:

Blue cone cells (B cones or S cones for "short", i.e. short-wave light)
Green cone cells (G cones or M cones for "medium", i.e. medium-wave light)
Red cone cells (R cones or L cones for "long", i.e. long-wave light)

The optic nerve transmits the light stimuli perceived by the cone and rod cells to the brain. This sorts, compares and interprets the stimuli so that we can perceive the respective color.

Our brain can distinguish around 200 color tones, over 20 levels of saturation and around 500 brightness values. This results in several million color tones that humans can perceive.

Two color theories explain color vision

There are two plausible theories about color vision. These color theories try to explain how the brain manages to make the entire spectrum of colors perceptible from the three colors red, green and blue.

The Young-Helmholtz theory states that all colors can be mixed and produced from the three basic colors red, green and blue.

The so-called counter-color theory of Karl Ewald Konstantin Hering (1834–1918) relates to the phenomenon of colored afterimages: if someone looks long enough at a red circle and then at a white surface, a circle appears in the opposite color green. The colors and also black / white can be arranged in pairs: red – green, yellow – blue, black – white.

The zone theory of Johannes Adolf von Kries finally summarizes the two theories.

Color blind - what forms are there?

Color blindness can be broken down into a number of forms, depending on the number and type of non-functioning cone cells.

For example, people with dichromism are blind to a color because one of the three cone types does not work. Depending on which type of cone is defective, different forms of dichromatic vision can be distinguished:

Red blindness (protanopia): Sufferers are color blind to red because the red cones are defective.
Green blindness (deuteranopia): Affected people are color blind to green due to defective green cones.
Blue blindness (tritanopia): Sufferers are color blind to blue because the blue cones do not work.

With achromatopsia, you are usually completely color-blind - none of the three types of cones work. However, there is also an incomplete form that allows at least a remnant of color vision. In achromatic vision, however, only the rod cells for twilight vision work correctly, so that those affected can only differentiate between around 500 different levels of light and dark.

only the rod cells are active, this form of color blindness is also known as rod monochromatism.

Another form of color blindness is blue cone monochrome. Red and green cones are missing here. Those affected see their world like achromatic shades of light and dark, but still have a certain residual vision for the color blue.

Color blindness: symptoms

As described above, the symptoms of color blindness depend on which and how many of the three cone cell types are not working. It also plays a role whether color blindness is congenital or acquired.

Congenital and acquired color blindness

If color blindness is genetically determined, it already occurs after birth or in infancy. Affected people are always color-blind in both eyes. The impairment in vision does not improve or worsen in the further course.

In the case of acquired color blindness, on the other hand, possible visual disturbances such as reduced visual acuity or increased sensitivity to light can worsen over time.

Dichromasy: color blind with a defective cone

People with dichromacy (dichromates) either have a defective red, green or blue cone - so only two of the three cone cells function properly. This form of color blindness can only develop in the course of life. Then it is possible that the person concerned is color-blind in only one eye.

Red-blind: Red-blind people (protanopes) lack the cone for the long-wave light range, i.e. the one for red. Therefore, they are more difficult to distinguish between all colors in the red range and confuse red and green, red with yellow and brown with green. Attention: This form of color blindness and the red-green weakness are not the same!

Green-blind: Green-blind (deuteranopes) do not have a cone for the medium-wave light range, i.e. for green. Therefore they can hardly distinguish between green and red - the problems are thus similar to those of red blindness. Attention: Green blindness should also not be confused with red-green weakness.

Blue blind: Blue color blindness is less common than red and green color blindness. Those affected (called tritanopes) cannot see blue and also have difficulty seeing yellow. In addition, their visual acuity is usually greatly reduced, as there are far fewer blue cones on the retina than green or red cones.

Monochromatism: color blindness with two defective cones

Blue cone monochromatism is a rare form of color blindness. Those affected lack the red and green cones. They only see light and dark shades, although they still have a certain residual vision for the color blue. Other symptoms:

photosensitive eyes
overall poor eyesight
mostly nearsighted
involuntary eye tremors (nystagmus)

Achromasia: Color blind with three defective cones

People with complete achromatism cannot see any colors at all, but only perceive their environment in shades of light and dark. Aside from that:

extremely light-sensitive eyes
overall severely impaired vision
involuntary eye tremors (nystagmus)

There is another form of achromatism called partial achromatism. Those affected still perceive small remnants of color and see overall a little more sharply than people with complete achromatism.

Color blindness: causes and risk factors

Color blindness can either be congenital or appear in the course of life.

Congenital color blindness

Color disorders are usually hereditary, i.e. genetically determined. The disease occurs after birth and always affects both eyes.

About eight percent of all men have a congenital color disorder. In contrast, only about 0.4 percent of women are color-blind or color-vision impaired. The reason for this lies in the genes:

Most of the genes responsible for color blindness or color vision deficiency are found on chromosome X. Of this chromosome, men have only one, while women have two. This means that if a gene that can be responsible for a form of color blindness is defective on one of the X chromosomes in women, the second copy of the gene on the other X chromosome - if it is intact - can compensate for this. The affected woman can perceive all colors normally. Color blindness only occurs in women if the corresponding gene is defective on both X chromosomes.

Frequency of different forms of color blindness

Achromatism, i.e. complete color blindness, and blue cone monochromatism are very rare: about one in 30,000 people suffer from achromatism, and one in 100,000 from blue cone monochromatism.

The incidence of blue blindness is given as 1: 13,000 to 1: 65,000. Green blindness occurs in about 1.0 to 1.3 percent of men and about 0.01 to 0.02 percent of women. About 1.0 percent of men and 0.02 to 0.03 percent of women are affected by red blindness.

Acquired color blindness

In contrast to congenital color blindness, acquired color blindness can either appear in both or only one eye. It affects men and women equally. Possible triggers are, for example:

Diseases of the retina (such as macular degeneration, diabetic retinopathy = a secondary disease of diabetes mellitus)
Diseases of the visual tract (such as optic nerve inflammation, optic nerve atrophy)
Eye disorders (such as cataracts or glaucoma)
stroke

Poisoning with medication (e.g. sleeping pills) or environmental toxins can also cause color blindness.

Color blindness: examinations and diagnosis

If you suspect you may be color blind, you should see your ophthalmologist. First, he will ask you about your state of health, possible (pre-) illnesses and your color vision in order to collect your medical history (anamnesis). Possible questions are, for example:

Is a Family Member Color Blind?
Do you think the stem of a tomato is the same color as the tomato itself?
Since when have you had the feeling that you cannot distinguish red from green (or blue from yellow)?
Has your eyesight decreased significantly in the last few months or years?
Do you still see all the colors in one of the two eyes or are both eyes color-blind?

Test with color charts as well as color test tests

To determine color blindness, the ophthalmologist uses so-called pseudoisochromatic tables. The most common one in the world is the Ishihara tablet. It is named after its Japanese inventor and is suitable for uncovering red-green disorders (red-green weakness, red blindness, green blindness):

The Ishihara color tablets show small circles with a number inside each. All circles and the numbers they contain are shown as colored spots, in such a way that the background and figure differ from one another only in terms of color, but not in terms of brightness and saturation. Therefore, only a healthy color seer can see the numbers, not someone who has problems distinguishing between red and green. With around 38 such color tables, the doctor checks both eyes or just one eye of the patient from a distance of around 75 centimeters. If the patient does not recognize a number within the first three seconds, the result is "wrong" or "unsure". The number of incorrect or uncertain answers then gives rise to indications of a red-green disorder.

Ishihara tablets, however, do not help in recognizing blue-yellow disturbances. For this, the doctor either uses so-called Velhagen-Stilling tables or carries out certain tests (standard pseudoisochromatic plates test, Richmond HRR test, Cambridge color test).

The Color-Vision-Testing-Made-Easy-Test (CVTME-Test) is suitable for children from the age of three. The only difference to the tables mentioned is that simple symbols such as circles, stars, squares or dogs are shown as figures instead of numbers.

There are also color tests such as the Farnsworth D15 test, in which those affected have to sort cones or chips of different colors.

Color blind: Other test methods

The anomaloscope is an ophthalmological examination device used to determine color blindness. The patient must look through a tube at a halved circle. The halves of the circle are different colors. The patient can use the rotating wheels to try to match the colors and their intensity to one another. A visually healthy person can match both hue and intensity; a color blind person can only adjust the intensity.

With the help of electroretinography (ERG), ophthalmologists can determine the function of the retina. To do this, the electrical activity of the rod and cone cells is measured.

Genetic tests are used to determine congenital color blindness with complete certainty. In this way, mutated genes responsible for the disease can be detected.

Color blindness: treatment

So far there is no therapy against color blindness. As for the innate form, scientists are now increasingly hoping for gene therapy. However, this is still in the clinical trial phase.

Color blindness: disease course and prognosis

Congenital color blindness does not change in the course of life. On the other hand, with acquired color blindness, a deterioration in visual acuity is possible over time.

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