People with colour vision deficiency find it difficult to identify and distinguish between certain colours.
It's sometimes called being "colour blind", although total colour blindness (an inability to see any colour) is very rare.
Colour vision deficiency is usually passed on to a child by their parents (inherited) and is present from birth, although sometimes it can develop later in life.
Most people are able to adapt to colour vision deficiency and it's rarely a sign of anything serious.
Most people with colour vision deficiency have difficulty distinguishing between shades of red, yellow and green.
This is known as "red-green" colour vision deficiency. It's a common problem that affects around 1 in 12 men and 1 in 200 women.
Someone with this type of colour vision deficiency may:
In rare cases, some people have trouble with blues, greens and yellows instead. This is known as "blue-yellow" 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, particularly if it started suddenly or is getting worse.
Colour vision tests do not usually form part of the routine NHS eye test, but you can specifically ask for them.
Two of the main tests used to diagnose colour vision deficiency are:
There are a number of online tests using similar techniques that may help detect a possible problem, but it's best to have a proper test at an opticians if you have any concerns about your colour vision.
Colour vision deficiency is not usually anything to be concerned about.
Most people get used to it over time, it will not normally get any worse, and it's rarely a sign of anything serious.
But it can sometimes cause issues such as:
Overall, many people with a colour vision deficiency have few, if any, difficulties. They can do most normal activities, including driving.
There's currently no cure for inherited colour vision deficiency, although most people are able to adapt to it over time.
It may help to:
Visit Colour Blind Awareness for more information and advice about living with colour vision deficiency.
If your colour vision deficiency is caused by an underlying condition or a medication, your symptoms may improve by treating the cause or using a different medicine.
In the vast majority of cases, colour vision deficiency is caused by a genetic fault passed on to a child by their parents.
It occurs because some of the colour-sensitive cells in the eyes, called cones, are either missing or do not work properly.
Occasionally, colour vision deficiency may develop later in life as the result of:
Many people also find it more difficult to distinguish between colours as they get older. This is normally just a natural part of the ageing process.
The genetic fault that usually causes colour vision deficiency is passed on in what's known as an X-linked inheritance pattern.
Visit Colour Blind Awareness for more information about inherited colour vision deficiency, including diagrams illustrating how it can be passed on.