Various tests exist to detect color blindness, a vision defect affecting color distinction, and affecting 8% of the male population against only 0,45% of women. The best known of these tests is that of Ishihara.

Color blindness (named after 18th century English physicist John Dalton) is a vision defect affecting the perception of colors. It is a genetic disease: it is due to an anomaly (absence or mutation) in the genes encoding the red and green pigments, both located on the X chromosome, or on the genes encoding blue, on chromosome 7 Color blindness is therefore hereditary, because one or both parents can pass on this genetic defect. It is more common in men because they carry two X chromosomes. More rarely, color blindness can be secondary to eye disease or a general illness (diabetes).

Depending on the genetic abnormality, there are different types of color blindness:

Monochromatism (or achromatism): the person does not distinguish any color and therefore perceives only in black, white and shades of gray. This anomaly is very rare.

La dichromie : one of the genes, and therefore one of the pigments, is absent.

• if it is the gene encoding red, the person is protanopic: he perceives only blue and green;
• if it is the gene encoding green, the person is deuteranopic: he perceives only blue and green;
• if it is the gene coding for blue, the person is tritanopic: he perceives only red and green.

La trichomatie anormale : one of the genes is mutated, the perception of color is therefore modified.

• if it is the gene encoding red, the person is protanormal: they have difficulty perceiving red;
• if it is the gene coding for green, the person is deuteranormal: they have difficulty perceiving green;
• if it is the gene coding for blue, the person is tritanormal: they have difficulty perceiving blue.

To detect these anomalies, various tests exist. Here are the main ones:

• le test the Ishihara, named after its Japanese creator Shinobu Ishihara (1879-1963), is the most frequently used. It allows detection of red and green perception deficiencies (protanopia, protanomaly, deuteranopia, deuteranomaly). It comes in the form of 38 so-called pseudo-isochromatic plates: in a circle there are dots of different sizes and colors, from which stands out, for the person who perceives normally (trichomate), a number. These plates are presented in a precise order to the patient, who must say the number he distinguishes or not.
• le test « color vision made it easy » is the children’s version of the pseudo-isochromatic test. Instead of figures, these are shapes that can be distinguished on the boards.
• les tests Panel D15 et Farnsworth-Munsell 100-hue, developed by Dean Farnsworth in 1943, come in the form of small colored dots to be put in the correct order.
• Le test d’Holmgren uses colored skeins of wool. Three of them serve as a reference: skein A for green, B for purple and C for red. The patient must choose among 40 other skeins 10 which are closest to color A, 5 to color B and then 5 to C. He must then classify them by color gradation. This test is mainly used to diagnose color blindness in sailors, railway workers and airmen, professions prohibited for color blind people due to the use of red and green signs.
• the Verriest test, created in 1981, is intended for children. it comes in the form of colored tokens to assemble, like a domino.
• le test the Pease and Allen (1988) is also intended for children. It comes in the form of 4 colored rectangles (white, red, green and blue) with a small square of a different color in one corner, at the top of the rectangle. The child must discern the colors.

These tests are carried out in the event of a suspicion of color blindness, in “families” of color blind people or when recruiting for certain professions (public transport jobs in particular).

There is no cure for color blindness, which neither worsens nor improves over the years. And people with color blindness usually get along very well with this little peculiarity.

There are, of course, glasses, and even special lenses, that have color filters to change the color spectrum, but they are generally little used.