Information & Advice For students.
All there is to know about being
8% of the male population is colour blind.
4.5% of the UK population is colour blind. 2
What is Colour Blindness? Colour blindness also knows as colour vision deﬁciency, or CVD, affects approximately 1 in 12 men (8%) and 1 in 200 women in the world. There are different causes of colour blindness. For the vast majority of people with deﬁcient colour vision the condition is genetic and has been inherited from their mother, although some people become colour blind as a result of other diseases such as diabetes and multiple sclerosis or they acquire the condition over time die to the aging process, medication etc. Most colour blind people are able to see things clearly as other people but they are unable to fully ‘see’ red, green or blue light. There are different types of colour blindness all explained later in this booklet. The most common form of colour blindness is known as red/green colour blindness, and although known as red/green this does not mean sufferers mix up red and green, it means they mix up all colours which have some red or green as part of the whole colour. For example, a red/green colour blind person will confuse blue and a purple because they can’t ‘see’ the red element of the colour purple. Similar problems can arise across the whole colour spectrum affecting all reds, greens, oranges, browns, purples, pinks and greys. Even black can be confused as dark green or dark blue. The effects of colour vision deﬁciency can be mild, moderate or severe so, for example, approximately 40% of colour blind pupils currently leaving secondary school are unaware that they are colour blind, whilst 60% of sufferers experience many problems in everyday life.
Statistically speaking most people with a moderate form of red/green colour blindness will only be able to identify accurately 5 or so coloured pencils from a stand ard box of 24 pencil crayons. Depending upon which type of the condition a colour blind person is suffering from they could see the set of pencil crayons similarly to the following images.
The different types of Colour Blindness There are several types of inherited colour blindness and they fall into three following main groups.
ANAMALOUS TRICHROMACY - Protanomaly - Deutanomaly - Tritanomaly This type of colour blindness consists of three different conditions. They are protanomaly, which is reduced sensitivity to red light, deuteranomaly which is reduced sensitivity to green light and is the most common form of colour blindness and tritanomaly which is reduced sensitivity to blue light and is extremely rare.
In people with this condition all of their three cone types are used to perceive light colours but one type of cone perceives light slightly out of alignment. This cone is faulty.
People with deuteranomaly and protanomaly are known as red/green colour blind and they generally have difďŹ culty distinguishing between reds, greens, browns and oranges. They also confuse different types of blue and purple hues.
Most people with a moderate form of red/green colour blindness will only be able to identify accurately 5 or so coloured pencils from a standard box of 24 pencil crayons.
People with dichromatic colour vision have only two types of cones which are able to perceive colour i.e. they have a total absence of function of one cone type. A speciﬁc section of the light spectrum can’t be perceived and we call these sections ‘red’, ‘green’ or ‘blue’ areas. People suffering with from protanopia are unable to perceive any ‘red’ light, those
with deuteranopia are unable to perceive ‘green’ light and those with tritanopia are unable to perceive ‘blue’ light. People with both red and green deﬁciencies live in a world of murky greens where blues and yellows stand out. Browns, blues and purples, oranges, shades of red and green are easily confused.
DICHROMACY - Protanopia - Deuteranopia - Tritanopia
Rare People with monochromatic vision can see no colour at all and their world consists of different shades of grey ranging from black to white, rather like only seeing the world on an old black and white television set. This colour blindness is extremely rare and its symptoms can make life very difﬁcult.
MONOCHROMACY - Seeing no colour at all
1 in 33,000
The causes of Colour Blindness
Colour blindness is a usually a genetic condition (you are born with it). Red/green and blue colour blindness is usually passed down from your parents. The gene which is responsible for the condition is carried on the X chromosome. Red/green colour blindness is passed from mother to son on the 23rd chromosome which is known as the sex chromosome, as it also determines sex (gender). The 23rd chromosome is made up of two parts – either two X chromosomes if you are female or an X and a Y chromosome if you are male. The faulty gene for colour blindness is found only on the X chromosome. So, for a male to be colour blind the faulty colour blindness gene only has to appear on his X chromosome. for a female to be colour blind it must be present on both of her X chromosomes.
XY - Female XX
- Female carrier
If a woman has only one colour blind gene she is known as a ‘carrier’ but won’t be affected.
She can however pass this X chromosome to her child. If it is her son then he will colourblind, but if he receives the ‘good’ X chromosome he won’t be colour blind. A colour blind boy can’t receive a colour blind gene from his father, even if his father is colour blind, because his father can only pass an X chromosome to his daughters. A colour blind daughter therefore must have a father who is colour blind and a mother who is a carrier (who has also passed the faulty gene to her daughter). If her father is not colour blind, a ‘carrier’ daughter won’t be colour blind. A daughter can become a carrier in one of two ways – she can acquire the gene from a carrier mother or from a colour blind father. An illustrated example of this can be seen on the back page of this booklet.
This is why red/green colour blindness is far more common in men than women. 7
The causes of Colour Blindness
Chronic Illnesses which can lead to colour blindness include Alzheimer’s disease, diabetes mellitus, glaucoma, leukaemia, liver disease, chronic alcoholism, macular degeneration, multiple sclerosis, Parkinson’s disease, sickle cell anaemia and retinitis pigmentosa.
Accidents or strokes that damage the retina or affect particular areas of the brain/eye can lead to colour blindness
Medications such as antibiotics, barbiturates, antituberculosis drugs, high blood pressure medications and several medications to treat nervous disorders may cause colour blindness.
Industrial/ environmental chemicals
Industrial or environmental chemicals such as carbon monoxide, carbon disulphide and some containing lead can also cause colour blindness.
Age – in people over 60 years of age physical changes can occur which might affect a person’s capacity to see colours.
If you have any eye test with an optometrist, they should test your colour vision as a matter of routine.
A recent study of 540 secondary school boys was undertaken on CVD. Only 20% of the boys had ever had a colour vision test at the opticians. 10
Diagnosis of Colour Blindness Colour blindness can be difﬁcult to detect, particularly in children with inherited colour vision deﬁciency as they may be unaware that they have any problems with their colour vision. A child with a severe condition such as deuteranopia may seemingly be able to accurately identify colours which they can’t see (e.g. red). This is because...
...they have been taught the colour of objects from an early age & will know that grass is green and strawberries are red.
It is important to request a colour vision test
from your opticians when on a regular eye test, as colour vision testing is not part of the standard NHS eye test. This means many opticians don’t bother to test for colour blindness.
Tests available for Colour Blindness There are many tests available to measure colour vision defects but the most common is the Ishihara Plate test. This can test for red/green colour blindness but not blue colour blindness. This is the test most likely to be used for routine colour vision screening in schools or medicals. This test is the most widely used for testing for red-green colour vision deﬁciency and contains 38 plates of circles created by irregular coloured dots in two or more colours. The plates will be put in front of you and you will be asked what number you can see on the plate. Some plates contain information which people with normal colour vision can see whilst others contain information that only people with colour blindness can see. If you make a certain amount of errors you will be diagnosed with colour blindness. Special Plate tests have been devised to diagnose young children who are not old enough to identify numbers. An example of Ishihara plates is shown in these extracts from Colorblind World. An example of these plates are available from the pack. You can test yourself and friends to determine whether you have any colour vision problems. It’s always good to be safe and check. If you struggle to identify any numbers, please double check with your teacher before diagnosing yourself. Once conﬁrmed, make sure to take a pocket size booklet home.
Living with Colour Blindness 12
Colour blind people face many difﬁculties in everyday life which normally sighted people are just not aware of. Problems can arise in even the most simple of activities including choosing and preparing food, gardening, sport, driving a car and selecting clothing.
Most red/green colour blind people won’t know if they have cooked a piece of meat rare or well done and they are unlikely to be able to tell the difference between green and ripe tomatoes or between ketchup and chocolate sauce. Colour blind people often try to eat unripe bananas because they can’t tell the difference between a green unripe banana and a yellow ripe banana – to them because both of the colours are the same shade they think they are the same colour. Some food can look repulsive if you are colour blind, and colour blind children can seem particularly fussy over green vegetables – spinach can look like cow pat and colour blind children probably mean it if they say their food looks like poo!
Colour blind people can get quite cross with electrical goods which have red and green LED displays to indicate either that a battery needs charging or the machine is on standby. An example might be a handheld games console with an indicator light which changes from red to green depending upon whether the unit is fully charged or needs recharging. This can be very frustrating, particularly for a child.
Trafﬁc Lights In Japan, for example, colour blind people are excluded from a number of careers and in many communist countries colour blind people are not permitted to drive because they are not always able to read coloured trafﬁc lights correctly. At night trafﬁc lights can be impossible to distinguish from street lights in certain conditions.
Careers with Colour Blindness Most colour blind people will have stories similar to the one below which tells about the difﬁculties that can affect them in the workplace. Many will have problems in fully accessing information from all kinds of everyday workplace sources including the internet, documents and presentations, photographs, maps, charts and diagrams.
Colour Blind Doctors Colour is important in medicine. Medical practitioners need to be able to see the redness of rashes, the yellowness of jaundice, and the blueness and purple when the patient is cyanosed, the pallor of anaemia and shock, and the colours of the healthy body. They need to be able see fresh blood in stools, vomit and sputum, the stains that differentiate cells in histology, and the colour codes used in hospitals and in specialised medical instruments.
Colour Blind Pilots Yes they do exist! Colour Vision Defective Pilots Association in Australia believe when it comes to flying colour blindness simply does not matter! The company now has over thousands of CVD affected pilots operating safely at the highest levels of industry including international airline captains.
“The problem with colour vision standards for pilots and air trafﬁc controllers is that there is very little information which shows the real, practical implications of colour vision defects on aviation safety" 13
Advice for Colour Blind Students If you think you might be colour blind DON’T WORRY! If you are then you aren’t on your own. There’s probably another child in your class who is colour blind too. There will deﬁnitely be quite a few colour blind kids in your school.
How can you tell if you are Colour Blind?
There are lots of different signs that someone might be colour blind but if you are, these are some of the things that might happen to you:-
– You probably try to ﬁnd ways to hide from friends, family and teachers that you aren’t sure about colours because you feel embarrassed.
- Your friends tease you if you make a mistake with colour, like if you are talking about cars and you get a colour wrong
– You might worry that you are stupid because everyone, even little children, seems to know their colours but you aren’t sure about them.
- You sometimes have trouble understanding what your teacher means because you can’t see the colours she’s talking about
– Sometimes you might not like to try new food because it looks horrible.
- You can’t always tell what colour of pencil to use for colouring in, or what colour paint to use or you might think you’ve used the right colour but someone tells you that you’ve got it wrong - You might get teased because people say your clothes don’t match and you can’t understand why they say that - You might have trouble telling the difference between 2 teams in a football match.
– You might not like to play sport if the team kits are confusing because you are worried about passing the ball to the other side. – You are probably often worried that the teacher might ask you to answer a question in front of the whole class that you might get wrong because of colours and you are frightened everyone will laugh at you because you can’t get colours right.
In school Don’t be afraid of telling you friends and teachers that you are colour bind – most people ﬁnd it interesting and will want to help you, but try not to get upset if they keep asking you what colour something is – if they do that just keep reminding them that ‘colour blind’ means you can’t always be sure of colours. If you can’t always work out what the teacher is trying to teach you because of problems with colours, make sure you ask the teacher – if you don’t the only person missing out will be YOU so it is up to you to speak up, even if you feel embarrassed. You can always ask the teacher quietly at the end of the lesson if you don’t want the whole class to hear.
How genetic Colour Blindness works: 1. A colour blind man and a non-colour blind woman Father Colour Blind XY
No Colour Blind Sons
Mother Not Colour Blind Not a Carrier
All Daughters 100% Chance Colour Blind Carriers
2. A non colour blind man and a colour blind carrier woman Father Not Colour Blind XY
50% Chance of Sons being Colour Blind
Mother Colour Blind Gene Carrier
50% Chance of Daughters being Colour Blind Carriers
3. A colour blind man and a colour blind carrier woman Father Colour Blind XY
50% Chance of Sons being Colour Blind
Mother Colour Blind Gene Carrier
50% Chance of Daughters being either Colour Blind or a Colour Blind Gene Carrier
Colour Blind Education Pack