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What is Color Blindness?
Color blindness is not ‘color blindness’! There are still a lot of people who think that if you are colorblind you really can’t see any colors. But the term is misleading, as more than 99% of all colorblind people can see colors.
A better wording would be color vision deficiency, which describes this visual disorder more precisely.
1.1 So what actually is color vision deficiency also known as color blindness? Simply put, if you are suffering from a color vision deficiency you perceive a narrower color spectrum compared to somebody with normal color vision.
This short definition raises a few more questions which need to be answered to understand the term color-blind more completely:
Why am I suffering from color blindness at all?
What means narrower color spectrum compared to normal color vision?
Are there different types of color vision deficiency?
How do I know if I’m colorblind?
Is there some possibility to cure color vision deficiency?
Can I just live with it or do I have to be afraid of it?
In the first chapter I will among other things answer the first two of those questions.
The others will be looked at in the following chapters of this eBook about COLOR BLIND ESSENTIALS. But first of all I would like to take you back to the 18th century…
1.2 History of color vision deficiency
The first scientific paper about color blindness was written by John Dalton in 1793 entitled “Extraordinary facts relating to the vision of colours“. Dalton himself was red-
green colorblind and as a scientist he took interest in this topic. He claimed that a colored liquid inside the eyeball is the source for a different color perception. This
was proved wrong only after his death, when his eyes were examined and no such liquid was found. After that Thomas Young and Hermann von Helmholtz were the first who described
the trichromatic color vision. And once a theory for human color vision was ready, the basics of color vision deficiency weren’t far away.
1.3 The cause of color blindness
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.
Now, if you 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 colorblind. 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 is your color vision deficiency: slightly, moderately, strongly, or absolutely colorblind. “What do you mean by «narrower color spectrum»?” Let’s say somebody with normal color vision can identify and distinguish 150 hues.
If you are colorblind this number starts to drop as you have fewer possibilities to create color mixtures from your color receptors. In case of absolute color blindness—missing one type of cone at all—you might be able to distinguish only as many as 20 different hues! 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 (protan), green (deutan), and blue (tritan) disorders. As red and green deficiency result in quite comparable color vision problems, they are often taken together and known as red-green color blindness.
You will find more information on the types of color blindness in the following two articles of this COLOR BLIND ESSENTIALS series. Much less common possibilities for color blindness are also glaucoma, aging, alcohol
misuse, or a hard injury on your head. Those factors often cause some milder form of blue-yellow color blindness (tritanomaly). Also other facts like signal transmission can cause problems in color perception, but this is not fully understood yet.
1.4 Why am I suffering from color blindness?
You know now the cause of color vision disorders, but we still have not evaluated why we can be colorblind at all. We learned that in most cases color blindness is a genetic disease which is inherited from the parents to their children.
This means, 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 handicap.
The chance is strongly related to the type of color blindness.
Before I get to show you a sample inheritance pattern, we will have a closer look at our chromosomes. Unfortunately it is not as simple as it could be, because there are different chromosomes involved in color vision.
And on top of that even on the same chromosome several different genetic code pieces are participating.
The essence you should know is, that red-green color blindness is a sex linked recessive trait and blue-yellow color blindness is an autosomal dominant trait.
sex linked: encoded on the sex chromosome X, whereas men only have one of
them (XY) compared to women (XX).
autosomal: encoded not on the sex chromosome, equal for men and women.
dominant: if it is encoded on one chromosome, you have really suffer from it.
recessive: if you have another healthy chromosome, it won’t show up.
If you combine this together, we have more colorblind men than women. — Why?
1.5 Color blindness inheritance pattern
The above genetic encodings lead us directly to the inheritance pattern. This will also show us on a glance, why there are more men suffering from color blindness than
women. The diagram on the right shows the inheritance pattern of red-green color blindness. 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 colorblind,
and even more women to be carriers of this color vision deficiency.
You can also learn from this diagram, that a woman can only be red-green colorblind if both of her parents are at least carrying the disease encoded in their genes.
1.6 Am I the only colorblind person?
No, definitely not. Color blindness is a very common disease which is found all over the world. Different scientific studies show, that roughly 8% of all men and 0.5% of all
women are colorblind. This numbers are supported by different studies and are about the same all around the world. The high difference between men and women is resulting
from the facts we just learned, that the most common form, red-green color blindness, is a recessive sex-linked trait. Knowing this numbers you can also compute some very interesting probabilities in
color vision deficiency:
Approximately every 500st handshake is between two colorblind people.
It is almost sure (probability: 94%) that at least one out of a football team is
colorblind.
If you pick out 100 persons, the chance is very low (< 1.5%) that none of them is
colorblind.
2 Types of Color Blindness
In the first part of COLOR BLIND ESSENTIALS we learned some fundamentals about color vision deficiency like the history, occurrences, causes, genetic inheritance patterns
and more. With this second chapter I want to explain you the different types color blind people can suffer from. But before we learn more about them we have to have a look at how color vision
actually works. We have to do so because the functionality of the eye is closely related to the three main types of color blindness.
2.1 How color vision works
To see anything at all we need some tiny little helpers inside our eyeballs, the so called photorecptors. There are two different types of them: rods and cones. Both of them
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.
The cones are the photoreceptors which are responsible for our color vision. They are only about 6 to 7 million of them but gathering together very closely in the center of the retina, the so called fovea centralis.
And here comes the clue: Each of those cones is carrying one out of three different photopigments and therefore reacts differently on colored light sources.
For each of this three types exists a specific color absorption curve with peaks at different points in the color spectrum.
S-cones: sensitive to short wavelength light with a peak at ca. 420nm (blue)
M-cones: sensitive to medium wavelength light, peak at ca. 530nm (green)
L-cones: sensitive to long wavelength light with a peak at ca. 560nm (red)
| Language | English |
| No. of Pages | 25 |
| PDF Size | 1 MB |
| Category | Education |
| Source/Credits | Drive.com |
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