Colour Blindness
Colour Blindness
Seeing colours
Did you see the bird’s head in the picture? What colour was the beak?
When you and a friend look at the same picture, how do you know that you are seeing the same colours?
What is colour blindness?
If you are ‘Colour blind’, you see colours differently from most other people. But you do see colours and you are not blind.
What are my chances of having some form of colour blindness?
If you are a boy its a one in every twelve chance that you are seeing the picture differently, and if you are a girl its much less common, only a one in 200 chance.
If I am seeing it differently from my friends, how do I know?
Some people live their whole lives and never realise that they are seeing the world differently from most other people. If you suspect you are colour blind, get checked by an optician or a doctor.
What would make you suspect that you or a friend has colour blindness?
Mixing up red and green in crayons, matching outfits,
Colouring a picture with the wrong colour (e.g., purple for brown),
Difficulty in seeing shades of colour, maybe whilst choosing outfits to wear.
Mixing up red, green, purple and brown.
Difficulty in reading words if red on green background
Difficulty reading street signs
How do I check if I am colour blind?
See a doctor or an optician for a proper test. They will use charts designed by Ishihara, a Japanese surgeon, a hundred years ago. It involves seeing numbers written in dots in different combinations of colours for the numbers and the backgrounds.
There are many sites on the internet which claim to diagnose colour blindness. Be careful, most of these sites are trying to get you to spend money with them.
What is happening in the eye that causes colour blindness?
At the back of the eye the light hits the retina, and this is where colour is detected using cone cells (photoreceptors). There are three types of cone cells: one for red light, one for green light and one for blue light. Signals from these cones go to the brain via the optic nerve. The brain then converts the nerve signals into ‘seeing’ colours. In normal vision this can be a whole range of shades and hues.
In colour blindness, one or more of the cone types don’t work properly. As a result the brain doesn’t receive the right signals and the brain then interprets the signals to ‘see’ different colours. These are then not the same as most other people ‘see’. For instance they may see brown for purple.
Can colour blindness be cured?
No but once you understand your eyes are different, so much is explained. If a child is shown to be colour blind, parents and teachers can use books and sheets in the appropriate colours to help the child. An older person can be aware when interpreting road signs.
Can colour blindness be inherited?
Yes.
The gene, inheritance factor, for colour blindness is carried by a mutation on the X chromosome. Males have XY and females XX chromosomes. If a female has a problem with one X, the other compensates so there is no problem. If a male has a problem with his X chromosome, he has a problem. This is why colour blindness is more common in males than females. One in twelve boys and one in 200 girls have some form of colour blindness.
With advances in knowledge about the human genome and chromosomes, mutations have been found on 19 different chromosomes which can lead to colour blindness.
Is it possible that someone cannot see any colour?
It is very rare, but some people cannot see any colour at all and they see things in shades of grey, like looking at a ‘black and white’ photo or an old ‘black and white’ film.
Does colour blindness affect the ability to draw and paint?
No, in fact some of the famous painters were thought to be colour blind.
SBM Aug 2018
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