Topic Overview

What is colour blindness?

Colour blindness means that you have trouble seeing red, green, or blue or a mix of these colours. It’s rare that a person sees no colour at all.

Colour blindness is also called a colour vision problem.

A colour vision problem can change your life. It may make it harder to learn and read, and you may not be able to have certain careers. But children and adults with colour vision problems can learn to make up for their problems seeing colour.

What causes colour blindness?

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.

See a picture of the eye that shows the retina and the macula.

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 red and green but can see blue and yellow.
• 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 gray.

How is colour blindness diagnosed?

Tests 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 well-child visits. Children with a family history of inherited eye problems should see an ophthalmologist by the age of three months.¹

How is it 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.

How can you help a child who has colour blindness?

Colour vision problems may make it harder for children to learn and read, which can lead to poor schoolwork and low self-esteem.

You can help your child these ways.

• Make sure your child is tested for colour vision problems during routine eye tests. The sooner you know there is a problem, the sooner you can help your child. Eye examinations should be done at all well-child visits.²
• Tell your child’s teachers and other school staff about the problem. This may be helpful. Suggest seating your child where there is no glare and using a colour of chalk that your child can see.

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