Condition Basics

What is colour blindness?

Colour blindness is a vision problem that means you have trouble seeing shades of red, green, or blue or a mix of these colours. It happens when there's a problem with some of the cells found in the layer of nerves (retina) at the back of the eye.

Almost always, the problem runs in families and is something you are born with. It's found more often in males than in females. Colour blindness that you are born with can't be treated or corrected. But you can learn ways to adapt to being colour blind.

What causes it?

Most colour vision problems are inherited (genetic) and are present at birth.

People usually have three types of cone cells in the eye. Each type senses either red, green, or blue light. You see colour when your cone cells sense different amounts of these three basic colours. The highest concentration of cone cells are found in the macula, which is the central part of the retina.

Inherited colour blindness happens when you don't have one of these types of cone cells or they don't work right. You may not see one of these three basic colours, or you may see a different shade of that colour or a different colour. This type of colour vision problem doesn't change over time.

A colour vision problem isn't always inherited. In some cases, a person can have an acquired colour vision problem. This can be caused by:

• Aging.
• Eye problems, such as glaucoma, macular degeneration, cataracts, or diabetic retinopathy.
• Injury to the eye.
• Side effects of some medicines.

What are the symptoms?

The symptoms of colour vision problems vary.

• You may be able to see some colours but not others. For instance, you may not be able to tell the difference between some reds and greens but can see blue and yellow easily.
• You may see many colours, so you may not know that you see colour differently from others.
• You may only be able to see a few shades of colour, while most people can see thousands of colours.
• In rare cases, some people see only black, white, and grey.

How is it diagnosed?

Tests can measure how well you recognize different colours.

• In one type of test, you look at sets of coloured dots and try to find a pattern in them, such as a letter or number. The patterns you see help your doctor know which colours you have trouble with.
• In another type of test, you arrange coloured chips in order according to how similar the colours are. People with colour vision problems cannot arrange the coloured chips correctly.

Because a colour vision problem can have a big impact on a person's life, it is important to detect the problem as early as possible. In children, colour vision problems can affect learning abilities and reading development. And colour vision problems may limit career choices that require you to tell colours apart. The Canadian Paediatric Society recommends eye examinations at all newborn and routine checkups. Vision screening is recommended for all children at least once before entering school, preferably between the ages of 3 and 5. ^{footnote 1}

How is colour blindness treated?

Inherited colour vision problems cannot be treated or corrected.

For the most common type of colour blindness—red-green colour deficiency—no treatment is needed, because you function normally. You may not be aware that you do not see colours the way they are seen by others.

Some acquired colour vision problems can be treated, depending on the cause. For example, if a cataract is causing a problem with colour vision, surgery to remove the cataract may restore normal colour vision.

You can find ways to help make up for a colour vision problem, such as:

• Wearing coloured contact lenses. These may help you see differences between colours. But these lenses don't provide normal colour vision and can distort objects.
• Wearing glasses that block glare. People with severe colour vision problems can see differences between colours better when there is less glare and brightness.
• Learning to look for cues like brightness or location, rather than colours. For example, you can learn the order of the three coloured lights on a traffic signal.