The 3 types of color blindness (and how to detect them)

Color blindness or color blindness consists of an alteration in the perception of colors, which is transmitted, for the most part, in a hereditary way. The difficulty to see one or more colors will depend on the number of cones that do not work, since they are the receptors of color vision. In this way, we will talk about achromatopsia when it can only be seen in white, black and gray; of dyschromatopsia if one of the cones is affected or abnormal trichromatopsia that has the three types of cones but with diffusions in these, generating an alteration in the tonality of the colors. If you want to know more about how humans perceive color and what types of color blindness exist, read on.

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    How is the perception of color produced in humans?

    Vision, which is one of the five senses of the human being, is possible thanks to the function of two types of receptors that we have in the retina called rods and cones. In reference to the rods, which are only found on the periphery of the retina, they allow us to see in black and white, they are activated in low intensity lighting, this means that they will work better in the dark and there are twice as many of these receptors than cones. As we have said, they are more sensitive to darkness, although they take longer to adapt to it and respond better to light of short wavelengths, that is, to darker lights, in this way they will be the receivers that work more at night.

    On the other hand, the other types of visual receptors, the cones, are found both in the periphery of the retina and in its central part, called the fovea, they are the ones that allow us to see in color. In this way they will be activated in light of high or medium intensity, acting mainly during the day. They are less sensitive to darkness, although they adapt faster to it than canes, they also present a higher acuity than these, allowing a better view of details.

    As we have already mentioned, cones are the receptors of sight in charge of perceiving colors. This receptor is made up of three different pigments called opsins that are the basis for color and detail vision. In this way, each one of the opsins is encoded by a different gene depending on whether they allow to perceive longer or shorter wavelengths, this refers to whether there is more or less distance between the beginning and the end of a complete wave.

    So we have three opsins, one of them will be the one that allows us to see the colors with the longest wavelength, with the greatest distance between points, which belongs to red; another will let us see the colors of medium wavelength that refers to green and finally, the third, will provide us with the perception of colors with low wavelength that refers to blue.

    Eye anatomy

    The Trichromatic Theory and the Theory of the opponent processes

    There are different theories that try to explain the perception of color, the two main and best known are the trichromatic theory and the theory of opposing processes. We will see that both are equally valid to respond to how color is perceived, as they are complementary to each other. The first, trichromatic, will better explain how the process occurs at the receptor level and the second, that of opposing processes, will do so in reference to higher processes, such as the functions of ganglion cells or the thalamus.

    Regarding the trichromatic theory, it is also called by Young-Helmholtz by its creators, it proposes that the perception of color will be the result of three receptor mechanisms with different spectral sensitivities, that is, the action of the three opsins. In this way, a light with a certain wavelength will activate each opsin in a different way, to a different degree, and the type of color that we perceive at the end will depend on this distinction in activation.

    Regarding the other theory, that of the opposing processes, it was proposed by Ewald Hering, this one says that in the receivers there are three biochemical mechanisms that will act in the opposite way at different wavelengths. So we have the black / white mechanism that responds positively to white light, longer in length and negatively in the dark, when there is no light and the wavelength is shorter; the red / green mechanism responds positively to red or longer length light and negatively to green or shorter length; and finally the blue / yellow mechanism that will also respond positively to the longest wavelength, which in this case is yellow, and negatively to the shortest wavelength, which would be blue.

    The author will say that the different positive responses are due to the integration of a chemical substance in the retina and, on the contrary, the negative responses will be given by the breakdown of said substances. This theory would be supported by different observations or effects.

    In the first place, in the afterimage effect it is shown that if we look at a color for a time close to thirty seconds, when we move our sight and fix it on a white background we see that the perceived color will be the opposite of that belonging to the initial image , that is, the opponent's color will appear that is a match to the initial one according to Hering.

    The second effect would be that of simultaneous contrast, this refers to the fact that if we have a gray color on top of a red background, the gray will acquire a similar tone to green. The same will happen with blue, which will make the gray appear more yellowish. Finally, another observed effect is that of color blindness that always occurs by opposing pairs, in other words, that subjects who cannot see red will also have green affected and with blue and yellow the exact same thing happens.

    Trichromatic theory

    What kinds of color blindness are there?

    Color blindness, also known as color blindness, is a genetic disorder that is transmitted in a hereditary way and that affects the correct perception of colors. Thus, if we keep in mind what we have explained above, we can deduce that the affectation will be in the cone receptors, those that allow color vision, specifically in one or more of the three genes responsible for generating the cone pigments.

    There are different types of color blindness depending on the degree of alteration presented, that is, we will talk about different types of color blindness depending on whether one or more of a pigment gene malfunctions. In this way we will have anomalous trichromatic, monochromatic or dichromatic color blindness.

    1. Trichromatic color blindness

    In anomalous trichromatic vision, the subject presents the three types of cones, this means that they have the ability to see different wavelengths and different colors, although their operation is not entirely normal, thus leading to confusion of one color with another.

    In this way, it is linked to the less serious alteration and is the type of color blindness with the highest prevalence of affected people. The problems of these individuals will be similar to those of dichromatic color blindness, which we will see below, but with a less degree of alteration, what is altered is the color tone, not the impossibility of perceiving the color.

    Trichromatic color blindness

    2. Monochromatic color blindness

    Monochromatic color blindness or achromatopsia is the name it receives the type of visual blindness that is most affectedSince in this case no gene for the pigments of the cones works and it can only be seen with the rods, this means that it will only be seen in white, black and shades of gray. This problem may be caused by the lack of cones, that is, as we mentioned before, be a genetic alteration or it may be due to a trauma that the subject has suffered and has affected color vision, this condition is known as achromatism cerebral.

    Monochrome color blindness

    3. Dichromatic color blindness

    Finally, the best-known type of color blindness is dichromatic, which consists of an impossibility to see some colors, this means that the subject will be partially blind according to what color. There are three different classes of dyschromatopsia, all of them hereditary and linked to sex, this refers to the fact that one of the two sexes will be more affected. In this case, it will be men who will present the greatest number of affected people.

    One of the types of dichromatic color blindness is protanopia, which consists of not having the gene that creates the long wavelength pigments, in this way the subject will not be able to perceive the red color, a second class is deuteranopia which in this case the affected individuals will not be able to perceive the medium wavelengths, thus losing the possibility of perceiving the color green. These first two kinds of color blindness are the most common. Finally, the third type is tritanopia, which is the least frequent and refers to blindness to blue and yellow, thus perceiving only green, red and gray.

    One of the most used techniques to detect, diagnose and be able to classify what type of dichromatic color blindness the subject presents is the Ishihara test, it consists of letters with different numbers of different colors, surrounded by dots of different colors and sizes. In this way, depending on the color combination that occurs, it will be impossible to differentiate the number if you have one type of color blindness or another.

    isihara test
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