Colour Blindness, What It Means and How to Help a Child Who Has It

Most people with colour blindness do not see the world in black and white. They see colour, but some colours look different from the way other people see them, and some pairs of colours are hard to tell apart. Because most forms do not blur vision, a child may have no other sign that anything is different. This guide explains what colour blindness is, why it runs in families, how it is tested and how a family can help a child who has it. The medical name is colour vision deficiency, and the facts come from the sight loss charity RNIB.

What colour blindness is

RNIB describes colour vision deficiency as a condition in which the eyes are unable to detect certain colours. People who have it find it hard to tell the difference between colours. How hard depends on how severe the deficiency is. The effect can be mild or strong.

For most people, colour blindness does not affect the ability to see fine detail, and it does not narrow the area they can see. It is a difference in how colour is sensed.

How the eye sees colour

The back of the eye contains cone cells, which detect colour. There are three kinds, and each reacts to a different range of light.

• Red cone cells detect long wavelengths of light.
• Green cone cells detect medium wavelengths.
• Blue cone cells detect short wavelengths.

Colour blindness happens when there is a problem with these cone cells. Most often the problem is genetic, which means a person is born with it. Inherited colour blindness does not get better or worse as the person gets older.

Red-green colour blindness

The most common forms are the red-green kinds. In one type, either the red or the green cone cells are not working at all. In another, they are working only partly. RNIB gives the medical names for these types.

• Deuteranopia, when the green cone cells are not working at all.
• Deuteranomaly, when the green cone cells are not fully working.
• Protanopia, when the red cone cells are not working at all.
• Protanomaly, when the red cone cells are not fully working.

Whichever cells are affected, the result is very similar, because the colours that the red and green cells detect overlap. Colours that contain red or green are all affected. This makes it hard to tell the following apart.

• Reds, greens and browns.
• Oranges and yellows.
• Blues and purples.
• Greys and pastel shades.

People may see these colours as much duller than they look to someone with normal colour vision. Those with a red deficiency may also confuse red with black. The exact experience is different for each person, because it depends on how well the cone cells still work.

Why it runs in families

Red-green colour blindness is inherited. The faulty gene sits on the X chromosome, which is why it is described as X-linked. This explains a pattern that many families notice.

A boy has one X chromosome, which he gets from his mother. If that chromosome carries the faulty gene, he will have colour blindness. A girl has two X chromosomes, one from each parent. If only one carries the fault, she is a carrier. She does not have colour blindness herself, but she can pass the gene on to her children. For a girl to be affected, she must inherit the faulty gene from both parents, and that happens less often.

RNIB adds that red-green colour blindness is lifelong. It does not improve and it does not get worse.

Blue-yellow colour blindness

Blue-yellow colour blindness is less common. It happens when the blue cone cells are affected. Tritanopia is the name when the blue cones do not work at all, and tritanomaly is the name when they do not work fully. It causes confusion between blues, greens, yellows, oranges and violets, and these colours may look paler or duller.

It can be inherited or caused by other eye or health conditions. It is not inherited in the same way as the red-green kind. Because it is not carried on the sex chromosomes, it affects males and females equally. It is rare, affecting less than one person in a hundred.

Complete colour vision loss

The rarest forms cause complete loss of colour vision. They are called monochromatism and achromatopsia, and both are inherited. Achromatopsia affects about 1 in 30,000 people. In another form, blue cone monochromatism, only the blue cone cells work, and it affects fewer than 1 in 100,000.

These conditions are different from ordinary colour blindness in an important way. The cone cells are responsible for both detail and colour. When they cannot work properly, a person has difficulty seeing any colour, and vision is also blurred. Other effects can include sensitivity to bright light, which makes daylight hard to cope with, and nystagmus, in which the eyes constantly move or wobble. Severity varies between people. RNIB stresses that achromatopsia does not cause total loss of sight, and that it is generally stable over time.

Achromatopsia is inherited in what is called an autosomal recessive pattern. To inherit it, a child must receive the faulty gene from both biological parents. A parent who carries only one copy does not have the condition. RNIB gives the chances when both parents are carriers. Each child has a 50% chance of being a carrier, a 25% chance of inheriting the condition and a 25% chance of inheriting two normal copies of the gene.

There is no cure at present, although research is looking at gene therapy. Some adjustments help.

• Glasses to correct short sight or long sight.
• Wraparound sunglasses to reduce light sensitivity and give protection from UV rays. Many people with achromatopsia find that red-tinted sunglasses help.
• Low vision aids and assistive technology for daily activities.

When colour vision changes later in life

Colour blindness is not always something a person is born with. RNIB explains that it can also develop later, as a result of one of these causes.

• An underlying eye or health condition, such as optic neuritis from multiple sclerosis, or diabetes.
• A side effect of a medicine.
• Exposure to harmful chemicals.
• The ageing process.

Because colour vision can change for these reasons, a change in how colours look is worth mentioning to a doctor. It is one more reason for a regular eye test to include a conversation about what you or your child are noticing.

How colour blindness is tested

Red-green colour blindness is easily picked up with traditional tests. The best known are the Ishihara plates, which are designed to detect red-green deficiency and give a pass or fail. For some careers, more specialised occupational tests check whether a person meets the colour standards needed, for example when the work involves reading coloured lights for safety.

RNIB points out one gap in the United Kingdom. School eye tests there do not include screening for colour vision deficiency. Its advice is to ask the optometrist at a child’s regular eye test whether the child’s colour vision has been tested. The same question is worth asking wherever a child’s eyes are tested.

Everyday life and school

Most forms of colour blindness do not affect the ability to see detail or the area of vision. Even so, RNIB says it can have an impact on education, playing sport and careers if it is not properly supported. It may also limit entry to some jobs where telling colours apart is part of the work.

It also touches daily life. RNIB gives these examples: reading information on websites, presentations or documents, shopping, reading maps and cooking. In a classroom, the same kinds of task can come up, for example reading a map or following information that depends on colour. The practical step is simple. Tell the child’s teacher about a diagnosis, so that the school can manage it. A guide on the signs a child cannot see the blackboard covers other clues that a vision problem is affecting schoolwork.

If a child has monochromatism or achromatopsia, the reduced level of vision may be greater, and RNIB notes that it is natural for parents to worry. Ask the eye specialist what support is available.

Questions to ask at an eye test

• Has my child’s colour vision ever been tested?
• Which test was used, and what did it show?
• Is this the inherited kind, or could something else be affecting colour?
• Should the school be told, and what should I say?
• Are there other eye problems that should be checked at the same time?

Other guides for families are gathered in the children’s vision section.

If you suspect it in your child

Ask for colour vision to be checked, and ask for the result in writing so the school can see it. For questions about a child’s colour vision, ask PEBS about colour vision testing. Those who would like to give can use the hospital’s published donation methods.

Colour blindness stays for life, and the first step in managing it is making sure that the people around a child know.

This article is general information and does not replace an examination by an eye doctor.