Ophthalmology

Color blindness

Synonyms in a broader sense

Medical: Achromatopsia, achromatism

English: achromatopsia, color blindness, acritochromacy

introduction

In the case of total color blindness, no colors, only contrasts (so light or dark) are perceived. Red-green blindness is often incorrectly referred to as color blindness, although this is color ametropia (Color anomaly) represents. A distinction is made between two forms: congenital color blindness and acquired color blindness.

Epidemiology

1 to 2 people per 100,000 are color blind. Total color blindness is therefore very rare. Women and men are affected roughly equally often. In Germany there are currently around 3,000 people living with this disease.

Causes of Color Blindness

In healthy people, the retina of the eye consists of light-dark receptors (rods) and color receptors (cones), of which there are three types:

Those that are red
the blue and
that absorb green light.

In our interplay, the three types of cones convey the different color impressions. If someone is color-blind, either all kinds of cones are missing or they are all inoperable, which is why the person concerned can no longer perceive colors, but sees the world in black, white and gray.

Color blindness can be congenital or acquired. More common is the congenital form, which is inherited as an autosomal recessive trait. Autosomal means that the disorder is not due to a gene in the sex chromosomes, which is why neither gender is preferentially affected. Recessive means that there must be two defective copies of the gene, i.e. mother and father have a "sick“Have to pass the gene on to your child in order for the disease (color blind) to break out. To date, four genes are known that are responsible for around 80% of color blindness.

There is also the acquired form of color blindness, in which the cause is not in the eye itself, but in the processing of the “color” signal to the brain. For example, it can result from a stroke, traumatic brain injury, and other brain injuries. This can be reversible, but often persists and is usually a bigger problem for those affected in everyday life than for those with congenital color blindness, as this means a major change.

Symptoms

The cones are not only important for color vision, but above all for sharp vision, since in the retina at the point of sharpest vision, the yellow spot, with which we usually fix points, there are only cones. The rods do not offer as good a resolution as the cones by far, but are more sensitive to light, which is why they are used in healthy people especially for twilight vision.

The four main symptoms of color blindness result from these characteristics: First, of course, the inability to perceive colors. For those affected, however, it is much more serious that their visual acuity (the VA) is significantly reduced. In addition, there are rapid, twitching eye movements (known as nystagmus), which can be traced back to the missing cones in the yellow spot: The body tries to find other fixation points than the yellow spot through the rapid movements and thus compensate for the reduced visual acuity.

The last symptom is the increased sensitivity to glare, which leads to photophobia (Photophobia) and is conditioned by the fact that only the highly light-sensitive rods absorb light stimuli. This means that the patients can hardly see anything in the light; For this reason, color blindness is sometimes referred to colloquially as "day blindness".

diagnosis

In the congenital form of color blindness, it is possible to use a blood analysis to examine the genes responsible for the disease and uncover mutations.

In addition, a so-called electroretinogram (ERG) can be carried out, in which the examined person is presented with light stimuli, the effect of which on the brain is then recorded with the help of electrodes. In the interpretation, the activities of cones and chopsticks can be assessed separately.

Color blindness therapy

There is currently no way to cure color blindness, although research is being carried out into gene therapy.

The "therapy for people who are color-blind" is therefore symptom-oriented: For example, glare from tinted glasses can be compensated for or visual acuity can be improved using magnifying aids.

What tests for color blindness are there?

Frequently used tests for the examination of color blindness are the Ishihara or Stilling-Velhagen color tables in which numbers or letter patterns are not recognized by patients with color vision disorders. The patterns have different color saturation, but the brightness value is identical to the background. This means that the recognition is independent of differences in contrast.

There is also the Farnsworth test in which 16 color discs are to be sorted according to color gradation. It starts with a dark shade of blue. Color-blind people tend to be confused within the series. Another possibility for determining color blindness is the anomaloscope, in which the color blind are supposed to create a certain yellow tone by superimposing red and green tones. People who are harder to recognize red shades mix in too much red, green-blind people mix too much green.

How do you test children?

In order to diagnose color blindness (achromatism) in children, tests can be used to examine them from around the age of three. However, the tests are not that different from those that are also used for adults. A typical test are the Ishihara color tables. It is checked whether the children recognize a pattern or picture, which is composed of different colored dots. While the color saturations differ, the brightness remains identical to the background. This means that the test is only dependent on color tones, but not on differences in contrast.

Instead of the usual patterns of numbers or letters for adults, animal motifs or other simple images can be used for children. Depending on their age and understanding of the task, even children can use an anomaloscope to mix a certain shade of yellow from green and red tones, or use the Farnsworth test to determine a color sequence

Can glasses help?

With color blindness, the sensory cells on our retina that are responsible for the perception of colors (the cones) are not functional. There are different cones for different color perceptions. In most cases of color blindness, only two of the three types of cones are intact. These disorders are mostly congenital, and they are inherited.

Unfortunately, glasses cannot compensate for such a change in the retina. However, people with color blindness usually develop their own strategies to compensate for this deficit. For example, at a traffic light they orientate themselves on whether the upper, middle or lower light is on and can thus get along without recognizing the color exactly.

Can you simulate color blindness?

It is entirely possible to simulate color blindness. If you look at the tests that are used to diagnose color blindness, you will see that they all require the patient's cooperation. So it is possible to take a test in such a way that it would indicate color blindness. For example, one could pretend that the patterns shown on the Ishihara tablets cannot be recognized.

However, there are boards that can expose such simulators. These are panels which, in addition to differences in color tones, also have differences in brightness. These boards should be recognized by healthy people and color-blind people alike. If someone is now simulating and claims to be unable to recognize these patterns, this is noticeable. However, most people try to simulate that they are not showing any color impairment and try to pass the test by memorizing the cards.

Relevance to the driver's license

In fact, a color disorder seldom leads to a restriction in driving. Color-blind people are allowed to get a driver's license and drive a car. Color blindness mainly includes red-green visual impairments. Only when the color sense fails completely (achromatopsia) are there restrictions. Here there is also a reduced visual acuity and an increased sensitivity to glare. People with green weakness usually have no problems. In the context of a red weakness it looks a little different. In this case, the retina only reacts to stronger red tones. Poor lighting conditions, storms, fog or dirty taillights of a car driving ahead pose dangers here.

Are cows or birds color blind?

Humans have sensory cells called cones. There are three types that can perceive red, green or blue colors, respectively. All other colors result from different compositions of these colors.

The cattle species lack the sensory cells for red light. You can therefore only perceive colors from the green-blue color spectrum. Birds even have four receptors instead of the three color receptors that humans do. You can also see ultraviolet light. In the twilight, however, their sense of color decreases much faster than we humans.

Summary

With color blindness, which is usually congenital, the complete failure of the cones results in an inability to perceive colors. However, this is usually the least problem for those affected, as they have only got to know the world in shades of gray from birth. The symptoms of reduced visual acuity and extremely increased sensitivity to glare are in the foreground.