Colour Blindness is not an accurate term for the vast portion of the colour deficient population. The overwhelming majority of people that have trouble with accurate colour discrimination, can in fact see colour. It is just that the colour they see is different from someone that has normal colour vision.
True colour blindness is a very rare condition called ACHROMATOPSIA - it is estimated that approximately 1/33,000 people will exhibit this rare genetic defect.
If we can remember back to high school science we were taught that the eye was made up of rods and cones. The rod system at the back of the eye called the retina is mainly in the periphery and functions at its best in dim light. The cone system is found in the central part of the eye called the macula. There are cones also in the periphery of the eye but in far less concentration.
There are three different types of cones in the normal eye. They tend to respond in bright light and each cone is sensitive to different colour. All colours of the rainbow can be perceived as long as all three cones are function properly.
Colour deficiency is where things get interesting. The genetic variation which makes up the vast majority of colour perception problems is an X linked genetic problem. Without making this too complex, females have two X chromosomes and males have an X and a Y chromosome. Because colour deficiency is X linked it is very unlikely that a female will be colour deficient as both X chromosomes need to be affected. Colour deficiency though in males is very common as once they have an X chromosome that is deficient for colour they immediately exhibit the problem.
What is even more interesting is that even though the mother can pass the gene to both sons and daughters only the sons tend to have the problem. The daughters usually are carriers and they can pass it on to their sons! If you think this sounds complicated you are correct. In depth explanations of colour deficiency is explained in detail: CLICK HERE. If you venture to this link you have been warned, it will fry your brain!
The traffic lights on the left are normal colour perception, whereas the traffic lights on the right are those perceived by someone that has significant colour deficiency. The only clue they have between the red and the green is by intensity and the position on the traffic lights.
It is rarely an issue but if you have a severe red deficiency called protanopia in the state of NSW you are normally not allowed to hold a truck license.
Even though colour vision deficiency is not normally a big problem, as many as 10% of males are affected to some level. Females on the other hand are far less affected at around 0.5%.Males are 20 times more likely to be colour deficient.
It is very important that all children are screened for colour deficiency. A number of vocations have a colour vision test that must be passed, otherwise the candidate will be excluded. Many young boys want to be pilots. It is heart breaking to find out that you will not be accepted because of faulty colour vision. Having all children tested for colour vision will allow the child to be guided to another vocation without the emotional turmoil of being rejected later.
In a future post we will discuss the different types of colour vision tests. Stay tuned.