Most ‘colour blind’ people can see things as clearly as other people, but they have difficulty distinguishing between some colours. This may have an impact upon a child’s experience at school and can also affect career options, for example joining the army or becoming a pilot. As most colour deficient people can see some colours, it is better to describe it as a colour vision deficiency (CVD) rather than colour blindness. There are some people who are unable to see any colour at all, but this is very rare.
In the normal eye there are three different types of cones. Some cones are best at capturing long wavelength (red) light. Others catch medium wavelength (green) light, while other cones respond best to short wavelength (blue) light. The signals from these cones are sent to the brain where they are perceived as colour. People with CVD are born with one or more cone types absent or different.
Most people with CVD are red/green deficient, which means they mix up all colours with some red or green in them. For example, a red/green CVD person will confuse blue and purple because they can’t ‘see’ the red element in purple. This is more severe in some forms of CVD than in others.
Colour vision may be affected by some eye diseases, but the most common cause of CVD is genetic. The gene for this is transmitted on the X chromosome (from your mother) and so it mainly affects men and boys, with around 8% of males and 0.5% of females having CVD. There are around 3 million people in the UK with some kind of CVD.
If someone has CVD, they may have difficulties distinguishing between different types of food – for example mistaking chocolate sauce for ketchup. It may also be very hard to get a child with CVD to try green vegetables as they will look unappetising. Older children may confuse colours on video games, maps or when studying chemistry.
If you have any concerns about your child’s vision, make an appointment for an eye examination with your optometrist. This will be paid for by the NHS. We recommend that children attend for their first eye test at any age if you have any concerns and if not, should attend for their first sight test at around 3-4 years. Your optometrist may not test for colour deficiency routinely so if you have a concern make sure you let them know.
Certain jobs require you to be able to recognise and differentiate between lights of certain colours. For example, seeing signals for aviation, railways or maritime. People wishing to apply for these jobs will be required to undertake a Lantern Test, which imitates actual signals. Those taking the test will be asked to name standardised coloured lights (principally red, green, yellow and white) of controlled brightness, colour and size. This is usually done in a dark room.
The Lantern Test is not usually carried out in community optometric practice. If you would like to take the test, contact the universities below:
There are other optometry departments across the UK who may be able to offer advanced colour vision testing and diagnosis:
There is currently no cure for genetic CVD. People with illnesses that have led to CVD, may find that their vision returns to normal when their illness has been treated.
Last updated: April 2025
