Colour vision deficiency
Colour vision deficiency
Otherwise known as CVD or colour blindness
Colour blindness is the developed world's most common genetic condition.
Colour blindness is the developed world’s most common genetic condition. It affects one in 12 males (8%) and one in 200 females (0.5%). This means that about 450,000 children in the UK - that’s one child in every co-ed classroom - can’t identify many different colours, not just reds and greens.
Modern teaching uses colour to highlight, warn and explain. But what if the colours we describe are not the same for the children we are teaching?
Teachers, parents and carers need to know how to identify and support colour blind children to ensure they are able to fully access and understand information - especially where these children have complex needs and rely on technology such as Augmentative and Alternative Communication (AAC) to help them to communicate.
Why does colour blindness matter?
Colour is a fundamental tool in society and educators depend upon on the ability of pupils to be able to distinguish between primary colours from the earliest stages of their education. If we think about how children are taught in the early years even the most basic instructions often include colour (for example, pick up the red brick).
before reading, we encourage children to order things by forming colour patterns with beads
colour is used to describe almost everything, from the big brown dog to the green door for the loo; and
we ask young children to fill in colouring sheets in specific colours and sing songs about the colours of the rainbow
If children aren’t ‘getting’ a percentage of what we are saying, they can’t learn to full capacity. This can undermine their confidence at an impressionable age and give a poor foundation for future learning.
As children progress through school, ability to differentiate between colours becomes even more important. Without correct support they are often unable to understand information in textbooks, on the whiteboard, in websites and in software.
Until recently colour blindness was not considered to be either a Special Educational Need or a disability but the Department for Education now recognises that CVD can fall under both definitions.
What is colour blindness?
Colour blindness is usually an inherited condition (you’re born with it) and there is no cure. It’s caused by faulty gene sequencing in the DNA of the X-chromosome. Men have only one X-chromosome but women have two.
For a woman to be colour blind she must inherit the condition on both X-chromosomes and this explains why colour blindness is much more common in men.
We have three types of cone cells in the retinas of our eyes which allow us to see colour. Each type detects either red, green or blue light. In normal colour vision the red, green and blue cones work together letting us see the full spectrum of colours.
In colour vision deficiency, the faulty sequencing means one type of cone cell can’t recognise which wavelength of light it’s receiving. So the brain receives incorrect information, resulting in someone with CVD being unable to distinguish between colours normally.
Blue blindness and total lack of colour vision (monochromacy) are rare, but red and green colour vision deficiencies are very common.
Colour blindness can sometimes happen because of other medical conditions such as diabetes and multiple sclerosis and as a side-effect of some drugs and medications such as chloroquine.
Children with other visual impairments, such as glaucoma and retinitis pigmentosa, are more likely to have colour vision defects. Acquired CVD may not present in the same way as genetic red/green colour blindness – different colours may be affected, usually blues and yellows.
There is some recent scientific evidence which shows children with Autistic Spectrum Disorders have reduced ability to distinguish between colours than other children. Whilst not CVD in a strict sense, ability to absorb information in colour can affect learning so the simple techniques used to support people with CVD may also assist children with ASD.
What do colour blind people see?
Colour blind people can usually see clearly and in focus. To them, what they see is normal, so it’s not unusual for colour blind people to reach adulthood without realising they are colour blind. Often people only discover they are colour blind when they apply for certain jobs (such as the armed services) and the diagnosis can come as a shock.
It’s a common myth that people with colour blindness only confuse reds and greens. People with red and green types of CVD
actually experience problems with a wide range of colours. Greens, browns, oranges, easily mixed up because all these colours are seen as shades of ‘muddy’ green. There are many surprising combinations which often confuse colour blind people. For example, blues and purples/deep pinks are often mixed up. This is because pinks and purples are blue mixed with red. Red is a colour which colour blind people don’t see, so purple can appear as blue.
Pastel colours generally all appear grey.
Red/green colour blindness is a generic term for different types and severities of colour blindness, so people with CVD don’t all see colours in the same way as each other. For example green deficients can mistake greens for greys or even pinks, whereas red deficients will sometimes confuse reds with black.
Diagnosing colour blindness
Colour vision screening has been phased out
in schools, but opticians can test for the two main types of red/green CVD. Colour vision testing is not a statutory element of the NHS eye examination in England, so even if a child has had an eye test, you shouldn’t assume that their colour vision will have been tested too. Studies show that by Year 7 about 80% of pupils have never had a CVD test. It’s not uncommon for an
undiagnosed colour blind child to have been prescribed spectacles but not screened for CVD. Opticians can offer a free test, but, because it’s not part of the NHS eye test, 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 of dots of a different colour. Depending upon which numbers can be seen the optician can advise if someone is colour blind. There is no test for children who can’t say which numbers they can see, so children relying on eye gaze, for example, cannot be accurately tested for CVD at present.
For more information, tips and resources see www.colourblindawareness.org
Last updated by Kathryn Albany-Ward from Colour Blind Awareness: 9 January 2017
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