Red Green weakness

Red-green weakness: description

The red-green weakness (abnormal trichromatosis) is one of the color vision disorders of the eye. Those affected recognize the colors red or green in different intensities and can hardly distinguish them from each other. Colloquially, the term red-green-blindness is often used. However, this is not correct, because the vision for red and green is still present in varying degrees. In true red-green blindness, those affected are actually blind to the color.

The term red-green weakness summarizes two eyesight weaknesses: The Red-sightedness (protanomaly)in which the affected person can see the color red weaker and different from green. In the Green eyesight (deuteranomaly) People perceive the color green worse and can hardly distinguish them from red. Both visual impairments are genetic errors that affect the sensory cells for color vision.

Sensory cells and color vision

Color vision is an extremely complex process with essentially three important variables: light, sensory cells and the brain.

Everything we see in the day reflects light of different wavelengths. This light meets three different sensory cells in the retina of our eyes:

• Blue cone cells (B-pin or S-cone for “short”, ie short-wave light)
• Green pin cells (G-pin or M-pin for “medium”, ie medium wave light)
• Red cones (R-cones or L-cones for “long”, ie long-wave light)

They contain a pigment called rhodopsin, which consists of the protein opsin and the smaller molecule 11-cis-retinal. However, the structure of opsin differs within the three cones, so it is different light sensitive: Depending on the type of pin it reacts particularly intense on short-wave light (blue area), medium-wave light (green area) or long-wave light (red area).

Each cone cell thus covers a certain wavelength range, with the regions overlapping each other. The blue-pins are most sensitive at a wavelength around the 430 nm, the green-pins at 535 nm and the red-pins at 565 nm. This covers the entire color spectrum from red to orange, yellow, green, blue to violet back to red.

When light of the appropriate wavelength hits the opsin of the B, G, and R cones, the 11-cis retinal changes its chemical structure, activating a series of steps within the cell, and eventually adjacent neurons. These in turn relay the light pulses to the brain, where they are sorted, compared and interpreted. Since the brain is able to distinguish about 200 shades, about 26 saturation tones and about 500 levels of brightness, people can perceive several million shades – but not if a pin cell is not working properly as in the red-green weakness.

Red-green-weakness: Zapfenzellen weaken

In the red-green weakness, the opium of the green or the red cones are not fully functional because their structure has changed chemically:

If there is red-eye weakness, the opsin of the R-pegs is no longer most sensitive at 565 nanometers. The maximum sensitivity has shifted towards green. The red cones no longer cover the entire wavelength range for this color and react more strongly to green light. The more the sensitivity maximum is shifted in the direction of that of the green pegs, the less red color tones can be recognized and the worse red can be distinguished from green.

In the case of green visual impairment, it is the other way round: here the sensitivity maximum shifts from the opsin of the G-pin into the red wavelength range. So less greens are perceived and the color can be distinguished from red worse.

The red-green weakness is therefore not to be confused with the true red-green blindness, in which the function of the red or green cones is completely lost. Red-green-blind are completely blind to red or green.

Red-green-weakness: symptoms

Compared to the normal sighted, red-green-sighted individuals generally perceive far fewer colors: Although they are normal for a wide variety of blue and yellow shades, they see red and green weaker. The red-green weakness always affects both eyes.

The way in which the affected person still recognizes the colors depends on the severity of the red-green weakness: If the wavelength range of, for example, the R-cones is only slightly displaced in the G-cones, those concerned can see red and green relatively well, occasionally as good as a normal sighted person. However, the more the wavelength ranges of the G and R cones overlap, the less well they recognize the two colors: they are described in a variety of nuances – from brownish yellow to shades of gray.

Red-green-weakness: causes and risk factors

The red-green weakness is genetic and therefore always innate. The genetic defect lies on the gene for green pin Opsin (in green visual impairment) or on the red pin Opsin (in red-eye weakness). The defect occurs during the first cell division of the fertilized egg cell when paternal and maternal genetic material mix. In this process, also called “crossover”, the genes can be damaged in different ways. In all cases they lose gene sequences. The manifestation of the red-green weakness depends on which gene regions are lost, because some areas are more important for the function or the sensitivity maximum than others.

Red-green-weakness meets more men than women

Both opsin genes are localized on the X chromosome, which is why the red-green weakness occurs much more frequently in men than in women: the man has only one X chromosome, the woman two. In the case of a genetic defect of one of the opsin genes, the man has no alternative, but the woman can resort to the intact gene of the second chromosome. However, even if the second gene is faulty, the red-green-visual weakness also shows in the woman. Figures show that this event is rarer: about 1.1 percent of men and 0.03 percent of women have red-eye weakness. Green eyesight affects about five percent of men and 0.5 percent of women.

Red-green-weakness: examinations and diagnosis

To determine a red-green weakness, the ophthalmologist will first talk to you in detail. For example, he can ask the following questions:

• Do you know someone in your family with a red-green weakness?
• Do you only see blue and yellow as well as brown or gray tones?
• Have you ever seen red or green?
• Do you not see red and green with one eye or are both eyes affected?

Ishihara blackboard and anomaloscope

To detect a red-green weakness, the ophthalmologist asks the patient to look at so-called pseudoisochromatic panels, such as the Ishihara panels, which he sets up about 75 centimeters away. The panels consist of many small circles representing numbers or figures. The background colors and colors of the figures differ only in hue, but not in terms of brightness and saturation. Therefore, only a healthy normal sighted person can see the figures, a person with red-green weakness not. The patient is asked to view the panels with both eyes or only one eye. If he does not recognize the character within the first three seconds, the result is “false” or “uncertain”. From the number of wrong or uncertain answers, there is evidence of a red-green fault.

There are also color reading tests, such as the Farnsworth D15 test, where patients need to sort cones or chips of different colors.

For children from the age of three, the Color Vision Testing Made Easy test (CVTME test) is suitable. It does not show numbers or intricate figures, but simple symbols such as circles, stars, squares or dogs.

Whether a red-eye weakness or a green-Sehschwäche is present, determines the ophthalmologist with an anomaloscope. The patient must see through a tube on a halved circle. The halves of the circle are different colors. With the help of rotating wheels, an attempt should now be made to match the colors and their intensity. A healthy sight can match both hue and intensity; a sighted person only succeeds in adjusting the intensity. Also, a red-eye-watcher will mix in too much red, a green-eye-saver too much green.

Red-green-weakness: treatment

There is currently no therapy for the red-green weakness.

Red-green-weakness: Disease course and prognosis

The Red Green weakness does not change in the course of life – those affected can life or hard red and green difficult or not to distinguish from each other.