What is a red-green deficiency?
Red-green deficiency is a genetically caused visual impairment in which affected individuals perceive the colors red or green less vividly than people with normal vision. This color vision deficiency causes difficulty in distinguishing between the two colors. In red-green deficiency, it can range from a mild color vision disorder to a complete lack of perception of the colors red and green.
Interesting facts about red-green deficiency:
- The term red-green deficiency encompasses two visual impairments: red deficiency (protanomaly) and green deficiency (deuteranomaly).
- Significantly more men than women are affected by red-green deficiency.
- A color vision deficiency is genetically determined and therefore always congenital. There is currently no therapy.
- Many affected individuals only realize in conversation with people with normal vision that their world is less colorful.
- The visual impairment always affects both eyes.
Red-green blindness: Am I affected?
Worldwide, 9% of all men and about 0.8% of women are affected by red-green deficiency. This type of color vision deficiency is therefore much more common than yellow-blue deficiency or complete color blindness. These occur with a probability of 1:100,000 each.
Those who perceive the colors red or green less vividly often do not notice this until advanced age. This is especially the case if the color vision deficiency is not pronounced. It may be that women notice that their men often misperceive colors. At this point, a test by an ophthalmologist or optician can provide certainty. For this purpose, the anomaloscope is used. The colorful Ishihara color test plates can also confirm an initial suspicion.
Test for red-green deficiency
The Ishihara images show colorful numbers or letters using round color spots in different shades and sizes that can only be recognized with normal color vision. The so-called pseudoisochromatic plates are placed at about 75 centimeters distance. If the patient does not recognize the respective figure within the first three seconds, this may indicate a red-green perception disorder.
In addition, color arrangement tests such as the Farnsworth D-15 test, where cones or chips of different colors must be sorted, can be helpful in diagnosis. A test by an ophthalmologist using an anomaloscope provides certainty to determine if a red-green deficiency is present. Here, the patient looks through a tube at a halved circle, with both halves appearing differently. Using rotating knobs, an attempt is made to adjust the color intensity.
How does a red-green deficiency manifest?
For those with red-green deficiency, the world is less colorful. While blue and yellow tones are perceived normally, the shades of red or green may appear simply colorless or may seem brownish-yellow or gray to the affected person. This mainly depends on the severity of the red-green deficiency. Only very few suffer from true color blindness.
Nowadays, children are examined for color vision deficiencies at the latest before starting school. The Color Vision Testing Made Easy test is suitable for them. It does not show complicated figures that young children cannot yet name, but simple symbols such as circles, stars, or dogs, for example.
Causes of a red-green perception disorder
A genetic defect causes an important substance essential for color perception not to develop normally. It is important to know the following: On the retina of our eye, there are two types of photoreceptors. They capture the light from our environment and convert it so that our brain can process it into a visual image. The so-called cones in the eye are responsible for color vision.
In red-green deficiency, the red or green cones are not fully functional. The cause lies in an amino acid sequence swap in the protein opsin responsible for color vision in the cones. If the gene for the corresponding opsin is missing and the cone for the affected color is not functional at all, this is called red-green blindness.
More details? Sensory cells and color vision
Color vision is an extremely complex process and essentially consists of three components: light, sensory cells, and brain. Light reflects in different wavelengths and encounters these sensory cells in the retina of our eyes:
- Blue cone cells for short-wavelength light
- Green cone cells for medium-wavelength light
- Red cone cells for long-wavelength light
The cone cells contain the pigment rhodopsin, which also consists of the protein opsin and the smaller molecule 11-cis-retinal. The structure of opsin differs among the three cones, making it differently sensitive to light.
Each cone cell covers a specific wavelength range, with overlaps possible. When light hits the opsin of the cones, the 11-cis-retinal changes its chemical structure and activates a series of processes within the cell and the neighboring nerve cell. This transmits the light impulse to the brain, where it is sorted and analyzed. For example, if there is a red deficiency, the sensitivity maximum in the R-cone shifts toward green. The red cones no longer cover the entire wavelength range of this color and react more strongly to green light.
Red-green deficiency glasses - We make the difference
Red-green deficiency is based on a genetically caused defect of the red or green cones in the eye. So far, there is no therapy. Glasses cannot correct color vision deficiency but can at least trick it. A so-called red-green glasses can be the gateway to a rainbow-colored world for patients. This type of glasses works basically like sunglasses. Both filter out a large part of the light spectrum entering our eye.
For people with red-green deficiency, the two colors can be intensified by special lenses that filter out part of the adjacent color spectrum. This makes it possible to distinguish the two colors again, and they appear individually in perception. To get the best and most colorful experience from the world, the visual aid should be used in bright daylight. Red-green glasses cannot compensate for color blindness.
That's unfair: Women see the world in all colors
It is a bit unfair: Why are mainly men affected by this phenomenon? The answer is relatively simple: The genes for opsins are located on the X chromosome. Since women have two of these, unlike men, and thus in most cases one without the mutation, this chromosome can compensate for the malfunction. If men have a mutation in the opsin gene, they cannot compensate for the defect. That is why significantly more men suffer from red-green deficiency.
Fortunately, those affected do not perceive this color vision deficiency as limiting. Red-green deficiency exists from birth and does not worsen significantly over life. For those with the deficiency, it is simply a normal state and does not disturb their aesthetic perception. However, it can make certain professions impossible. And then it really becomes unfair.
Which professions cannot be practiced with a red-green deficiency
To be clear - even with our glasses for colorblind people, many professions cannot be practiced. Unfortunately, this is not a complete substitute for natural color vision. Therefore, even if our glasses work perfectly, many professions do not accept them as a replacement.
Life with a congenital red-green deficiency is no less exciting. The brain can perceive around 200 hues including 26 saturation levels and 500 brightness levels. A mild color deficiency rarely reduces the quality of life of those affected. It only becomes difficult when an exact distinction between red or green is relevant for practicing the dream job.
Professions that generally cannot be practiced with red-green deficiency:
- Police officer
- Bus driver
- Truck driver
- Train driver
- Pilot
- Astronaut
Little boys often have adventurous great ideas for their future. Unfortunately, a red-green deficiency could stand in the way. Because, of course, police officers, bus drivers, and captains must be able to recognize all important signal lights, such as traffic lights, without problems. Electricians or painters also need full functionality of color vision.