colour blindness

The retina of the human eye has two types of receptors, rods and cones, the latter being responsible for capturing colors. There are three types of cones, each for one of the three primary colors that make up light: red, green, and blue, at their respective wavelengths of 575 nm, 535 nm, and 430 nm. Stimulating these receptors to a greater or lesser extent will allow the human eye to capture all the colors of the visible spectrum. If any of these types of cones does not work or is missing, the person will not perceive the corresponding color, a fact that is called color blindness or color blindness.

How is it produced?

Color blindness is suffered by 8% of men and between 0.5% and 1% of women. It is a genetic disorder. The genes that code for the pigments of the red and green cones are on the X chromosome, while those that code for the blue cones are on chromosome 7.

Color blindness for colors red (protanopia) and green (deuteranopia) It is the most frequent and is suffered in a greater proportion by men because it is a sex-related disease. If there is a mutation of these genes on an X chromosome, as the woman has a second X chromosome, she will not suffer from the disease, although she will be a carrier of it. For a woman to suffer from the disease, she should have both mutated X chromosomes, hence the prevalence of color blindness for red or green is very low in women. In contrast, the man with an altered X chromosome for these genes will suffer from color blindness, since he only has one X gene.

In the case of color blindness for the color blue (tritanopia)As it is linked to chromosome 7, men and women will suffer it in the same proportion, but in any case the incidence of this dyschromatopsia or alteration of color vision is much lower.

Symptoms

In the case of color blindness for the red or green color, when one of these types of cone is missing, the patient will not recognize one or the other color. The visual stimuli corresponding to the absent cones will be captured by the other cones, so that the patient will see both colors as one.

If he patient suffers from a blue blindness, he will be unable to recognize the color blue and will mistake it for yellow.

It may also happen that the patient has all three kinds of cones but some type of them (generally red or green) is abnormal, so that the one that the patient can recognize is more reduced, being able to see two shades as the same that, being similar, a person without said affectation would clearly recognize as two different tones. When this happens, we speak of abnormal trichromatisms or color weakness.

Much more infrequent are other more extreme alterations such as monochromaticism, in which two different types of cones are damaged, so that the patient sees all colors as shades of the same color, the one for which they have cones, or achromatism, in which the absence of the three types of cones makes the patient not distinguish the colors.

Diagnosis

The diagnosis will be based on the suspicion of relatives or friends of the patient, who will perceive this anomaly, since for the patient in his reality one or more colors have always been missing.

The most common method for diagnosis are the so-called Ishihara cards, a series of 38 cards in which there are numbers made up of colored dots on a background of dots of other primary colors that the colorblind person can confuse. While the non-colorblind person will easily distinguish the numbers, the color-blind patient will not see any of them based on their pathology.

The anomaloscope is a device that decomposes through a series of prisms and with it the patient must compare different colors and their tonality, luminescence and saturation. This device is very accurate to diagnose the different types of color blindness, since it uses spectral colors (of light) and not pigments, but its price is very high, so it is rarely used in diagnosis.

Treatment and prevention

There is no treatment for color blindness. There are a number of glasses and contact lenses that can help, but they are usually not very decisive.

And since it is a genetic abnormality, there are no preventive measures for color blindness.

• It is a genetic disorder suffered by more men than women.
• The most frequent is for the red and green colors, in which the patient does not recognize one or the other color.
• It cannot be prevented and, in terms of treatment, there are a series of glasses and contact lenses that can help, but they are not usually very decisive.