We also learned from researchers, that only about 0.4% of alle women are colorblind. Why is this number not closer to 3 or even 4 percent? Does nature know, which X chromosome has to be used for the color receptors inside the eye?

Actually it is quite simple to understand and to tell you the truth, the low number of 0.4% is not really the whole story.

X-Inactivation

The biological process called X-inactivation, which takes place in a very early stage for each female embryo, is the source for this low number of women who suffer from color blindness. So let me show you what happens in that stage and afterwards, to understand it in more detail:

1. At first every cell of a woman has two X chromosomes.
   Let’s assume that one of them has some sort of red-green color blindness encoded in it.
2. In a very early stage of the embryo, X-inactivation takes place.
   Each cell inactivates one of its X chromosomes. This means about 50% will have the defective gene and the rest is not affected.
3. Every cell passes the inactivation on to its successors.
   Because of this, the ratio stays about the same during the whole life.

Now, what does this mean? — In the end we have actually three different possibilities concerning red-green color blindness in women:

1. Both X chromosomes are not affected: The woman has normal color vision.
2. Both X chromosomes are defective: The woman is red-green colorblind.
3. One X chromosome is affected: Due to X-inactivation this woman has about 50% of defective genes in her eye as well as 50% genes which are working perfectly right.

The last case of course is the most interesting one. Usually only one part of your family would be affected by red-green color blindness. In this case, as a woman, you are called a carrier of the defect, as only one X chromosomes is carrying this genetic irregularity. But if we have a closer look at it, you actually also have those defective color receptors inside the retina!

As we have several millions photoreceptors (cones) which are responsible for our color vision, the defective signals are in a way oversteered by the correctly working ones. So in “real life”, you as a carrier woman have normal color vision just with only about half of your for example green receptors working correctly.

Researchers could show in some cases that such women have slightly more problems in perceiving certain colors under special light conditions, for example dim light. But if I think about it, those women actually not only have three different types of receptors (red, green, and blue) but one more (red, green, defective-green, and blue)! Doesn’t this mean, that they might have an even better color vision then most of us? Might some of them have tetrachomatic vision?

If you want to learn more about X-inactivation in color blindness, read the article by by Shuai Chen from Stanford University on exactly this topic.

Some more recent news about a company specially built for genetic screenings for color blindness and a study on gene therapy for red-green color blindness also support the idea that there is hope for people suffering from color vision deficiency—or at least for our children, as a genetic treatment like this usually takes many many years to make its way to public availability.

Here is a short video on this topic and I hope we will soon get some more detailed information on it.

Gene therapy has proven to cure color blindness in squirrel monkeys— can the same process work for humans?

In last autumn researchers published The Cure of Color-Blind Monkeys. This was a first big step towards a possible treatment of red-green color blindness.

During the winter some further steps were taken to work towards this treatment. You can read more about this at Genetic Screenings for Color Blindness. And now there is a survey going on focusing again on this topic:

AlphaDetail, a healthcare marketing research company, is conducting an online survey with color blind individuals. Are you a color blind male who resides in the US and is interested in taking a survey to provide your opinions on potential color blind treatments?

If so, we would like to invite you, to take a 20 minute online survey. Please click on the following link if you are interested in participating and we will send you a unique survey URL within 48 hours: Color Blindness Survey. Please be advised that you will need to answer a few preliminary screening questions in order to determine your eligibility before participating in the survey. Upon your completion of the survey, you will receive an honorarium payment in the mail 2 to 4 weeks from the date of completion.

We look forward to hearing from you.
Sincerely,

AlphaDetail Member Services

It would be great if you could join this survey, as it might help all colorblind people to get a possible treatment of this disease in the near future. And please don’t forget to choose Colblindor as your referrer.

The short answer to this questions is simply: No. And the long answer: There is no cure for color blindness—yet. There are some scientific studies going on which had just recently quite a big breakthrough. This and some other interesting ideas about aids for colorblind people are the topic of this article of the Color Blind Essentials series.

First ideas

As with many other handicaps or diseases when some people learned that some others can’t really distinguish colors like themselves, laziness was the first thing which came to their mind. Because of that many colorblind people just started to learn color names more intensively—without any success.

There were also some other techniques like warming one eye, electrical stimulation, injections of iodine or extracts of cobra venom, vitamins or flashing light. All this finally resulted in an official statement of different Academies and Medical Associations that no method had been found for the correction of color blindness, whether called ‘color weakness’, ‘color confusion’ or ‘color defectiveness’—which is still true as of today.

But there were also some good ideas around like color filters or spectacles with horizontally divided red and green sections.

Aids for colorblind people

If you have a closer look at the available tools for color deficient people, you have on one side the computer and all its possibilities and on the other side non-computer based aids.

On the non-computer side there is actually just one technique used: colored filters. These filters come in different forms:

• Lenses: Manufacturers of tinted lenses claim that their product can improve color vision for colorblind users. And people often read this as if they could almost cure your color blindness—which is wrong. Here are some facts about tinted lenses:
  • They have to be worn in only one eye, as otherwise fewer colors are seen.
  • It needs some time to get used to them and learn some new colors.
  • They can help you and enhance your color perception in certain situations.
  • You want be able to see more colors, but maybe other ones then you are used to.
  • Certain colors seem to vibrate or shimmer because of the usage in only one eye.
  • Worn while you are driving they can be a safety risk because of the worse perception at dim light situations.
• Glasses: It is almost the same for colored glasses as for lenses. The first products looked a bit strange as only one glass is tinted. Recent products have some coating which reduces this effect and makes glasses a true alternative for the lenses.
   
• Tools: There is a little tool called Seekey which is made of two tinted filters, one in green and the other in red. If you look through the filters on and off you can definitely distinguish more colors as a colorblind. This can be an advantage for some specific tasks in certain professions or in some everyday life situations. Such filters can also enhance certain diagnostic or medical instruments and help the colorblind operators to see what they otherwise wouldn’t spot that easy.

Many colored filters can help you to pass some color blindness tests, specially the famous Ishihara plates test. But this is not the correct purpose as those tests are usually there to assure, that your color vision isn’t a safety issue. Because of that in most cases tinted filters are not allowed to be used on such qualifying tests.

If we have a look at the computer based helpers for colorblind users, there are different tools available. Those tools make use of different techniques which can only be done digitally.

• Show the name of a color if you point to it.
• Shift the whole color spectrum around the color wheel.
• Highlight certain specific colors in a different color.
• Use a pattern to highlight certain tints.
• Some sophisticated algorithms which try to manipulate a picture to the effect that colorblind people perceive it still as normal but that certain shades can be distinguished better.

Such tools might really help you in some specific situations. But often they are not that easy to adapt for your personal purposes and sometimes just to cumbersome to handle. And don’t forget that all those tools can only be used while working on a computer, which is in everyday life often not such a big handicap for colorblind people.

Cure of color vision deficiency

As mentioned in the lead of this article there is to this day no cure for colorblind people available—but it looks like as if there is one for colorblind monkeys!

Monkey Performing Color Blindness Test

Jay Neitz, a well known vision scientist, and his team developed a gene therapy to enhance color vision. Colorblind monkeys were used as test animals. They received the gene injections directly into their eyes to build up the missing color receptor.

The monkeys had to perform a color blindness test and if they did well they received a reward. After a while they started to perform much better on a task they couldn’t accomplish before because of their vision handicap.

Due to this test result many colorblind people hope to be able to get rid of their color vision deficiency in the near future. Unfortunately this won’t come true that fast. And there are some difficulties which have to be overcome until this dream could get true:

• Gene therapy for red-green color blindness may not work for humans as well as it does for monkeys.
• Side effects of subretinal injections can include irritation or infection, in addition to the risks of permanent retinal detachment and blindness at the injection site.
• There could be adverse psychological effects associated with suddenly being able to see new colors and learning how to categorize them.

Also other institutions started to pick up this topic and are looking into the development of such a gene therapy to heal congenital color vision deficiency.

There is a possibility that a color vision handicap can disappear again. In some cases of acquired color blindness, specially for vision deficiencies which can occur after a hard hit on your head, it is reported that this handicap can disappear again after a certain time. Unfortunately this can’t be influenced and the process of healing can’t be used for all other colorblind people.

This was the last part of the Color Blind Essentials series. If you would like to learn more details about color vision deficiency why don’t you browse my articles archive, try some of the color blindness tests or check out my tools including a color blindness simulator.

Discovery of red-green color blindness

Memoirs of the life and scientific
researches of John Dalton

Already John Dalton wrote about his color vision deficiency. Red, orange, yellow, and green all appeared to be the same color to him. The rest of the color spectrum seemed to be blue, gradually changing to purple. Dalton concluded already in the year 1798, that he can not see long wavelength red light—known as protanopia today.

Some recent genetic analysis of Dalton’s preserved eyes showed, that he was suffering from deuteranopia—another form of red-green color blindness. But anyway this is the first description of the red-green color vision deficiency.

In 1837 August Seebeck carried out some systematic color vision tests and found two different classes of red-green color blindness with differences in severity from weak to strong in both classes.

After that investigations started to gather more details and scientists learned a lot more about our color vision: The genetic source of color vision, its deficiencies and the precise knowledge about the mechanism of color vision in our eyes.

The facts

With the knowledge of the last two chapters on what color blindness really is and the different types of color blindness, we can put together the following list of facts about red-green color blindness:

Unfortunately many people don’t even know one of those seven basic facts on red-green color blindness. This often causes a lot of confusion and many misunderstandings related to this term.

Often confused colors

The following little story happened to me a few years back. I am suffering from a strong red-blindness, so this is really a true story:

I was standing on a balcony with a few friends on the fourth floor, looking into the grass fields down below us. After a while one of my friends asked, why the fire hydrant is standing in the middle of the field with no path close to it.

I looked down and asked: “Which fire hydrant?” — Silence — Laughter.

“Can’t you see that orange fire hydrant in the middle of the field? It stands out so obviously with its orange color!”

I couldn’t see it. Only after a while, scanning the field for a fire hydrant, I found it. But not because of its color but of its structure.

This story is very typical as orange and green are some of the big problem colors for red-green color blind people. But not only those colors are mixed up. Colors from the whole color spectrum can cause problems in terms of not being able to distinguish them if you are color blind.

The table on the left shows five example color pairs of confusion. As severity and type of color blindness can be very different, such color pairs are quite individual. I have chosen some colors in the color spectrum which I—as a strongly red-blind guy—can not distinguish.

As you can see, not only the base colors red and green cause problems. It is the mixture of the red part in the colors which makes colors indistinguishable for my eyes.

Remark: Moving in front of the computer screen or flipping the display fore- and backward can change the color perception a lot. Also if you print them out colors are perceived quite differently, specially from colorblind people.

On the other side not all reds and greens are indistinguishable colors for a red-green color blind person. Some greens and some reds can be seen and named even with a strong color vision deficiency.

Difference between red- and green-blindness

You know by now that red-green color blindness is actually just a generic term for any form of protan (red-blind) and deutan (green-blind) color vision deficiency. But what is the difference between those two or why are they often put together into the same pot?

Let us first have a look at the things those two different main types of color blindness have in common:

• The main axis of colors of confusion is the same and so both types have the same main problem colors: red, orange, yellow, green, brown.
• The genetic information is located at almost the same place on the X chromosome. Trichromatic vision developed much later in evolution while splitting the previous information of a single channel on red-yellow-green into those two different cone encodings.
• The peak of sensitivity for red and green cone types is very close to each other. Trichromatic anomalies result in the shift of one of those peaks towards the other one.

On the other hand there are also some differences which makes it possible to split red- and green-blind people into two separate groups while testing for color blindness:

• Red-blind people perceive the color red much darker. If you compare the results of Rayleigh matches—a color blindness test where you have to match yellow with a mixture of green and red—red-blind people use a much darker yellow to get a match.
• The colors of confusion in the blue-purple area of the color spectrum are quite different. Red-blind people will mix in much more red and still can get a match between blue and purple.

But if you compare those two types with blue-yellow color blindness the differences in between them are very small. Therefore you will most often just talk either about red-green or blue-yellow color vision deficiency and forget about the rest.

By the way, if you think about the term itself and combine it with all the facts gathered together by now, you should know that red-green color blindness actually doesn’t really exist at all ;-).

In the next part of Color Blind Essentials you will learn more about the different possibilities to test your color vision and how good these tests really are.