Daltonism: the symptoms

The symptoms of color blindness, or dyschromatopsia, are related to an abnormality of one or more categories of cones:

  • Abnormal trichromate: in this type of daltonism, the 3 categories of cones are present but the intensity is not the same.
    Symptoms: the colors are distorted.
  • Dichromate: one of the types of cones is deficient.
    Symptoms: the person does not see the colors like the others because a palette is absent.
  • Monochromate: very exceptionally only one type of cone is functional.
    Symptoms: the subject has a very limited vision of colors in a world plainly black and white for the achromate.

Color blindness is detected either in the family environment, at school by the teaching staff or during a medical visit.

John Dalton, an 18th-century physicist, is the one who has bequeathed his name to this peculiarity of color vision, but it was Dr. Ishihara who created the eponymous test to spot it. It consists of 38 boards formed by small circles inside larger circles lined with circles.

The colors used by the numbers are of a nuance different from those which form the frame. Where a normal trichromate will distinguish them without hesitation, a color-blind will see another number, depending on the type of daltonism.

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