Colour vision deficiency

Also called Colour blindness

Affects around one boy in twelve, is usually undiagnosed at school, and is an education problem long before it is a medical one.

What it is

Difficulty distinguishing certain colours, most commonly reds and greens, from a difference in the light-sensitive cells in the retina.

It affects around 1 in 12 boys and 1 in 200 girls, because the commonest forms are inherited on the X chromosome. Complete absence of colour vision is very rare.

There is no treatment and it causes no other harm to the eyes. **Its importance is entirely educational and occupational**, and that is why it belongs here.

In England, routine school screening for colour vision was withdrawn, so most children are never tested. A child who cannot distinguish the colours on a chart, a diagram, a whiteboard marker or a coded reading scheme is at a real disadvantage, is frequently thought to be careless or slow, and often does not know anything is different because they have never seen otherwise.

Testing is quick and is available from any optometrist, and knowing changes how a child is taught.

Certain careers have colour vision requirements, including some roles in aviation, the emergency services, the armed forces, rail and electrical work. Finding out at 17 that a chosen career is closed is avoidable by testing early.

Acquired colour vision loss, particularly a new difficulty distinguishing reds, can indicate optic nerve disease and needs assessment.

Signs you might notice

Confusing colours, particularly reds, greens, browns and oranges.

Difficulty with colour-coded material: graphs, maps, wiring, colour-coded reading books, and coloured pens on a whiteboard.

Choosing unusual colours when drawing or dressing.

Saying colours look muddy or dull.

Often no complaint at all, because the person has nothing to compare with.

Get tested: any child with these difficulties, any family history, and any child before choosing career options.

Urgent, and different: a new change in colour perception in an adult, particularly reds looking washed out in one eye, which can indicate optic nerve inflammation or compression and needs assessment. See uveitis and giant cell arteritis.

How it can affect day-to-day life

The classroom is where it matters most. Coloured chalk or pen on a whiteboard, colour-coded worksheets, colour-banded reading schemes, science experiments with colour change indicators, and geography maps all disadvantage a child nobody has tested.

The fixes are cheap and effective: label colours in words, use symbols and patterns as well as colour, use high contrast, avoid red or green text on a whiteboard, and tell the child which colour something is when it matters.

Children are often teased, and being able to explain what it is helps.

For adults, everyday issues are traffic lights, judging ripeness of fruit and meat cooking, matching clothes, and reading colour-coded information. Apps that identify colours are genuinely useful.

Colour-correcting glasses are widely marketed. They can increase contrast between some colours for some people, and they do not restore normal colour vision, and they are not accepted for occupational colour vision tests.

Employers should be told where relevant, and reasonable adjustments apply.

Supporting someone well

Get children tested; an optometrist does it in minutes, and school screening no longer happens in most areas.

Test before career decisions are made, not after.

Tell the school, and ask for practical adjustments: label colours in words, use symbols as well as colour, avoid coloured pens on whiteboards, and use high contrast.

Do not use colour alone to convey information at home or at work.

Use colour-identifying apps for shopping, cooking and clothing.

Explain it to the child so they can explain it to others.

Be realistic about colour-correcting glasses; they help contrast for some and do not cure it.

Get any new change in colour vision in an adult assessed promptly.

Where to get help

A high street optometrist for testing, free for under-16s.

A GP practice or eye casualty for a new acquired change in colour vision.

The school SENCO for classroom adjustments.

RNIB for information on vision and education support.