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Colour blindness affects 1 in 12 males and 1 in 200 females. This means about 400,000 school children in the UK can't identify many different colours, not just reds and greens.
25% of colour blind people have a severe form, so around 100,000 school children are severely colour blind. The vast majority are boys.
Modern teaching uses colour to highlight, warn and explain. But what if the colours we describe are not the same for the children we're teaching?
Teachers, parents and carers need to know how to identify and support colour blind children.
Think about how children are taught in the early years:
If children are not ‘getting’ a percentage of what we are saying, they are not learning to full capacity. This can undermine their confidence at an impressionable age and give a poor foundation for future learning. Read more on colour blindness and education.
Colour blindness is usually inherited, caused by ‘faulty’ gene-sequencing in the DNA of the X-chromosome.
We have three types of cone cells in the retinas of our eyes. Each type detects either red (protan), green (deutan) or blue (tritan) light.
In Colour Vision Deficiency (CVD), the faulty sequencing means one type of cone cell can't recognise which wavelength of light it's receiving. The brain receives incorrect information, so someone with CVD is not able to distinguish between colours normally.
Women have two X-chromosomes and men have an X-chromosome and a Y-chromosome, so CVD is much more common in boys and men than in girls and women.
Blue blindness and total lack of colour vision (monochromacy) are rare, but red and green colour deficiencies are very common.
Colour blindness can sometimes happen because of other conditions such as diabetes and multiple sclerosis.
Children with other visual impairments, such as glaucoma and retinitis pigmentosa, are more likely to have colour vision defects. These may not present in the same way as genetic red / green colour blindness – different colours may be affected. Some medications such as chloroquine can also produce colour vision deficiencies.
Colour blind people can see clearly and in focus. To them, what they see is normal, so some colour blind people reach adulthood without realising they're colour blind.
People with CVD often have problems with reds, greens, browns, oranges and yellows because they see these colours as shades of ‘muddy’ green. They will be able to see blue and yellow, but may still confuse them, frequently mistaking blue for purple - purple contains red, which colour blind people don’t see, so purple appears as dark blue. Pastel colours generally all appear grey.
Green deficients can mistake green for greys or even pinks, whereas red deficients will sometimes confuse reds with black.
Colour vision screening is being phased out in schools, but opticians can test for the two main types of red / green CVD. Colour vision testing is not a statutory part of the NHS eye examination in the UK, so even if a child has had an eye test, only about 20% will have had colour vision tested too. Opticians can offer a free test, but parents and carers may have to ask for it.
The standard test is the Ishihara Plate test. Numbers formed from coloured dots are set within a circle formed from dots of a different colour. Depending on which numbers can be seen the optician can advise if someone is colour blind or not.
A special test is being developed for children who can't say which numbers they see, using eye gaze to determine which numbers are being seen. This will not be available for some time. A genetic screening test is available in the US, but is not yet licensed in the UK.
A guide for teachers and special educational needs co-ordinators
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Scope is a content partner of the Times Educational Supplement.
A row of different coloured pencils, as someone with full colour vision would see them
A row of different coloured pencils, as someone with colour blindness would see them
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