Do you have difficulty telling if colours are blue and yellow, or red and green? Do other people sometimes inform you that the colour you think you are seeing is wrong? If so, these are primary signs that you have a colour vision deficiency.
Don’t worry if this is the case, as you’re not alone. Colour blindness affects 300 million people worldwide, and occurs due to an abnormality of the retina, the layer of cells at the back of the eye that are sensitive to light.
Most people who are considered "colour blind" can see colours, but some might appear washed out and are easily confused with other colours.
Think of your eye as a camera. The front of the eye contains a lens that focuses images on the inside of the back of the eye. This (the retina) is covered with special nerve cells that react to light.
These retinal nerve cells include the rods and cones. The rods and cones react to light because they contain pigments that change when light strikes them.
The cones are responsible for colour vision. There are several kinds of pigments present in three types of cone cells. Some cones react to short-wavelength light, others react to medium wavelengths and others react to longer wavelengths.
For people with normal vision, the brain compares the signals from all three cones enabling a person to see the colour of an object. This is called 'trichromacy'.
But for people who are colour blind, one or more cones will be missing or won't function normally, which means they will be unable to see the full spectrum of colours. This is called 'dichromacy'.
Figures from Colour Blindness Awareness suggest that approximately 40% of colour blind pupils leaving secondary school are unaware they are colour blind, while 60% of sufferers experience many problems in everyday life.
In most cases, colour blindness is inherited, but it can also develop as the result of a pre-existing health condition, or as a side effect of certain medicines.
How to test for colour vision deficiency
Ask for a colour vision test at an opticians if you think you or your child may have a colour vision deficiency. Two of the main tests used to diagnose colour vision deficiency are:
- the Ishihara test – where you're asked to identify numbers contained within images made up of different coloured dots.
- Colour arrangement test– where you're asked to arrange coloured objects in order of their different shades.
The Ishihara test
How to treat colour blindness
There's currently no cure for inherited colour vision deficiency, although most people are able to adapt to it over time. However it may help to:
- Tell your child's school if they have problems with their colour vision, so learning materials can be adapted accordingly.
- Make use of technology – computers and other electronic devices often have settings you can change to make them easier to use, and there are a number of mobile phone apps available that can help identify colours for you.
- Try special tinted lenses – these are worn in one or both eyes to help you distinguish between certain colours, although they don't work for everyone.