COLOR VISION DEFICIENCY (CVD)
WHAT IS IT?
Color blindness is not 'color blindness'! There are still a plethora of people who still think that colorblind people cannot really see any colors. Therefore, this term is misleading. More than 99% of all colorblind people CAN see colors. Better terminology for this disorder is thus COLOR VISION DEFICIENCY, which describes this visual disorder much more precisely.
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Color vision deficiency affects about every 1 in 12 men, 8%, and 1 in 200 women,0.5%. With these numbers you can compute some very interesting probabilities in CVD:
- Approximately every 500th handshake is between two color vision deficient people.
- It is almost sure (probability: 94%) that at least one out of a football team is color deficient.
- If you pick 100 persons randomly, there is a tiny change (about 1.5%) that none of them are color vision deficient.
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Most individuals affected by this disorder are male, because the most common form called RED-GREEN COLOR VISION DEFICIENCY is encoded on the chromosome and therefore sex-linked. As red-green color vision deficiencies is inherited from a mother to her son, a father never passes this type of color deficiency on to his children.
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SO WHAT ACTUALLY IS COLOR VISION DEFICIENCY?
Simply put, if you are suffering from a color vision deficiency you are perceiving a narrower color spectrum compared to somebody with normal color vision.
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This short definition raises a few questions that will be answered throughout this site, that need to be answered in order to fully understand the term color vision deficient more clearly:
1. Why am I suffering from color vision deficiency at all?
2. What means narrower color spectrum compared to normal color vision?
3. Are there different types of color vision deficiencies?
4. How do I know if I am color deficient?
5. Is there some possibility to cure color vision deficiency?
6. Can I just live with it or do I have to be afraid of it?
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Color perception in the human eye is build up by three different types of cones. Each type is sensitive to a certain wavelength of light
(red, green, and blue) and every perceived color is therefore a mixture of stimuli of those three cone types.
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If one of those peaks of sensitivity is shifted towards another one
or if one is missing at all, you perceive a narrower color spectrum
— in other words you are color vision deficient. As a peak can be
shifted everything between a little bit and the whole way, any type
of severity is possible. The closer the peaks are the more severe
your color vision deficiency is: slightly, moderately, strongly, or
absolutely colorblind.
The type of affected cones also has a big impact on your color vision deficiency. As there are three different types of color receptors, there are also three different main forms: red (protanopia), green (deuteranopia), and blue (tritanopia) disorders. As red and green deficiencies result in quite comparable color vision problems, they are put together and known under the term RED-GREEN COLOR VISION DEFICIENCY.
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Much less common possibilities for color vision deficiencies are also glaucoma, aging, alcohol missuse, or a hard injury on your head. Those factors often cause some milder form of blue-yellow color blindness (tritanopia). Also, other facts like signal transmission can cause problems in color perception, but this is not fully understood yet. At allaboutvision.com you can find a short list of other possible causes of color vision deficiencies.
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Even though you know the cause of color vision deficiencies; how can we be color vision deficient at all in the first place?
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As you may remember, in most cases color vision deficiencies are a genetic disease which is inherited from the parents to their children. Meaning that if one or both of your parents is suffering from some type of color vision deficiency, there is a certain chance that you or your children will have the same vision disorder. The chance is strongly related to the type of color deficiency.
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Before we get into a sample inheritance pattern, we will have to have a closer look at our chromosomes. Sadly, it is not as simple as it could be because there are different chromosomes involved in color vision. On top of that, even on the same chromosome several different genetic code pieces are participating. The essence you should know is that, a red-green color blindness is a sex linked recessive trait and blue-yellow color vision deficiency is a autosomal dominant trait.
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- sex linked: encoded on the sex chromosome X; men only have one of them (XY) compared to women (XX).
- autosomal: encoded not on the se chromosome, equal for men and women.
- dominant: if it is encoded on one chromosome, you really suffer from it
- recessive: if you have another healthy chromosome, it won't show up.
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If you combine all of this together, we have more color deficient men than women — Why is this?
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CVD INHERITANCE PATTERN
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The above genetic codings lead directly to the inheritance
pattern. This also shows at a glance why there are more
men suffering from color vision deficiency than women.
The diagram to the right shows the inheritance pattern of
red-green color vision deficiency, which is by far the most
common type of color vision deficiency. As you can see,
this is a disorder which is passed on from a grandfather to
his grandson, whereas the mother is only a carrier of it.
A carrier is not affected because the trait is recessive. This
causes much more men to be red-green deficient, and
even more women to be carriers of this color vision
deficiency. The diagram can also show you that a woman
can only be a red-green deficiency if both of her parents
are at least carrying the disorder encoded in their genes.
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WHAT CAUSES CVD?
WHY AM I SUFFERING FROM CVD?
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