Now that you have learned some fundamentals about color vision deficiencies like occurrences, causes, genetic inheritance patterns and more. It is now important to explain the different types of color vision deficiencies that people can suffer from. But before getting into that, it is key to learn how color vision actually works. This is essential due to the functionality of the eye being closely related to the three main types of color vision deficiencies.

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To see anything at all we need some tiny little helpers inside our eyes, called photoreceptors. There are two different types of them rods and cones. Both are sitting on the retina and pass information of light on to our brain. There are about 120 million rods which are very sensitive to light but not to color.

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The cones are the photoreceptors which are

responsible for our color vision. They are only

about 6 to 7 million of them, gathering together

very closely in the center of the retina, called

fovea centralis.

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Each of those cones is carrying one out of three

different photopigments and therefore reacts

differently on colored light sources. For each of 

these three types there exists a specific color

absorption curve with peaks at different points in

the color spectrum.

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           - S-cones: sensitive to short wavelength

             light with a peak at ca.420nm (blue).

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           - M-cones: sensitive to medium wavelength

             light, peak at ca.530nm (green).

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           - L-cones: sensitive to long wavelength light,

             peak at ca.560nm (red).

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Mixing together the information of those three different types of cones makes up our color vision. This is also the reason that only three main colors are needed if we want to mix together all visible colors, because we only have three sources of information for mixing our whole color spectrum.

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Based on the above knowledge about our visual system we can easily put together the list of different forms of color vision deficiencies. All of them have a direct relation to the available photoreceptors in the eye and are accordingly categorized.

 

           - Monochromatism: Either no cones available or just one type of them.

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           - Dichromatism: Only two different cone types, the third one is missing completely.

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           - Anomalous trichromatism: All three types bus with shifted peaks of sensitivity for one of them. This results in a smaller color 

             spectrum. 

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Dichromats and anomalous trichromats exist again in three different types according to the missing cone or in the latter case of its malfunctioning. 

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           - Tritanopia / Tritanomaly: Missing / malfunctioning S-cone (blue).

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           - Deuteranopia / Deuteranomaly: Missing / malfunctioning M-cone (green).

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           - Protanopia / Protanomaly: Missing / malfunctioning L-cone (red).

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For a more clear understanding, you can also call them blue-, green-, or red-weakness respectively -deficiencies. Unfortunately these terms did not really make their way and are not used very often. You could ask now, "What about red-green color vision deficiency or blue-yellow color vision deficiency? These are the ones I know but I cannot find on the list above.

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The problem with these terms is that they are not telling the truth! Many believe that if you suffer from blue-yellow color deficiency, this is the only colors you cannot distinguish. But this is completely wrong! Color vision deficiency does not relate to just two color hues you cannot distinguish, it is the whole color spectrum which is affected.

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Blue-yellow CVD relates to tritan defects and red-green CVD to all types of protan or deutan defects. 

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The above list displays the prevalence rates of each type of CVD. The ratios between the most frequently occurring types for men can simply be remembered as: 1 protanope to 1 protanomalous trichromat to 1 deuteranope to 5 deteranomalous trichromats. 

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It has already been discussed about what color vision deficiency is, that because of our genes more men than women are color vision deficient. Adding up all the numbers results in a total of 8% and 0.5% of women who are suffering from some type of CVD.

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Now that you know about the different types and categories of color vision deficiencies, you may now be wondering, "What does it really look like if you are color vision deficient? How do you see the world?"

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If you have normal color vision you may realize that

in the case of red-green color vision deficiency

(protanopia/deuteranopia) not only red and green

colors are affected but the whole color spectrum

is perceived differently. The same is of course true

for blue-yellow color deficiency (tritanopia). This is

based on the fact, that all colors are perceived as a

mixture of the three different cone types, and if one

of them is missing the whole color spectrum changes.

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The stimulations below shows how the color spectrum changes.

The lines are just meant as guides. Any line which ends in the

so-called copunctal point connects the colors of confusion for a 

certain type of color vision deficiency. A more severe color

deficiency simply results in thicker and longer confusion bands.

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                         Protan Lines                                                             Deutan Lines                                                             Tritan Lines 

 

Color deficient people see the world like people with normal color vision see it at dusk or dawn. At this time of day colors start to fade away which is comparable to a color vision deficiency.

 

EYE'S RESPONSE TO COLOR IN COLOR VISION DEFICIENCIES