Colour vision deficiency
People with colour vision deficiency are unable to see some colours clearly and accurately.
They may find it difficult to distinguish between different colours.
For example, reds, oranges, yellows, browns and greens may all appear to be a similar colour to someone with a red-green deficiency.
Other types of colour vision deficiency may make it difficult to identify pale or deep colours, particularly if the light is poor.
In many cases, completely different colours may appear to be the same – for example, people often confuse red with black.
Colour vision deficiency is often referred to as colour blindness. However, in true colour blindness, no colour can be seen at all. As this is very rare, colour vision deficiency is a more appropriate description.
Colour vision deficiency can vary in severity. Some people are unaware they have a colour deficiency until they have a colour vision test.
What causes colour vision deficiency?
In most cases, colour vision deficiency is an inherited condition (passed on from your parents). However, it can also sometimes develop as the result of a pre-existing health condition or as a side effect of a medicine.
Inherited colour vision deficiency occurs as the result of an abnormality in the retina (the light-sensitive layer of cells that line the back of the eye).
The retina is made of rod and cone cells, which respond to light and other neural cells that process the incoming signals.
There are three types of cone cells, and each type has a different sensitivity to light wavelengths.
One type of cone is most sensitive to light in the yellow-green part of the spectrum, one type is most sensitive to light in the green part of the spectrum, and one type is most sensitive to light in the violet part. They're known as long-wavelength (L), middle-wavelength (M) and short-wavelength (S) cones respectively.
As you look at an object, your brain compares the signals from the three cones, enabling you to see the colour of the object. If the L, M and S cones work together, you'll be able to see the full spectrum of colours. Normal colour perception is known as trichromacy.
If you have a colour vision deficiency, one or more cones will be missing or won't function normally, which means you'll be unable to see the full spectrum of colours.
Types of colour vision deficiency
The three main types of colour vision deficiency are often known as red-green colour deficiencies (two separate conditions) and blue-yellow colour deficiency (one condition).
Red-green colour deficiencies
Red-green colour deficiencies are the most common types of colour deficiency, affecting significantly more men than women (1 in 12 men have red-green colour vision deficiencies, but only 1 in 200 women).
The deficiencies arise from problems either with the L-cones or M-cones. People with these types of colour deficiencies confuse colours in the red-green spectrum.
A loss of M-cones is known as deuteranopia. If you're diagnosed with deuteranopia, it's likely you'll confuse colours in the red-yellow-green spectrum.
Deuteranomaly is a less severe form of red-green colour deficiency. If you're diagnosed with deuteranomaly, it's likely you'll have problems distinguishing different shades of the same colour in the red-yellow-green spectrum. It can vary in severity from mild to severe.
Protanopia is a loss of L-cones. Like deuteranopia, if you're diagnosed with protanopia it means you're likely to confuse colours in the red-yellow-green spectrum.
Protanomaly is a less severe form, where it's likely you'll have problems distinguishing different shades of the same colour in the red-yellow-green spectrum. It can vary in severity from mild to severe.
People with protanopia or protanomaly are likely to see red colours as darker than normal.
Blue-yellow colour deficiency
Blue-yellow colour deficiency is very rare, and usually associated with a deficit in the S-cones.
People with this type of colour deficiency have difficulty distinguishing between shades of blue and green. It's also known as tritanomaly or tritanopia.
Blue-yellow colour deficiency isn't linked to the sex chromosomes and occurs equally in men and women.
Recognising colour vision deficiency
Many people first become aware they have a colour vision deficiency when they have a problem identifying colours correctly. For example, a child may have difficulty naming colours or may struggle to read a coloured map or document.
It's important to identify a colour vision problem early. Your child's learning experience can be adapted if they are diagnosed at an early age and their teachers are made aware that they have the deficiency.
Colour vision testing isn't usually part of a standard eye test, so some people with a colour vision deficiency may not realise they have it.
Treating colour vision deficiency
There's currently no cure for inherited colour vision deficiency because it's not possible to repair or replace the cone cells in the retina.
However, studies being carried out in America may lead to a cure of some types of colour vision deficiency through gene therapy.
Colour vision deficiency doesn't cause any long-term health problems, so treatment isn't essential for you to be able to lead a normal, healthy life.
If your colour vision deficiency is caused by a pre-existing health condition or from taking a certain type of medication, it may be possible to improve your symptoms by treating the underlying condition or by using an alternative medication.
Most people with colour vision deficiency learn to adapt to the condition, and it's usually possible to find ways to compensate for your difficulty with colours. For example, it's possible to learn to recognise the position of the lights on a traffic light, rather than the different colours.
In most cases, having colour vision deficiency is unlikely to lead to long-term health problems.
However, if you have a red-green colour deficiency, it may be difficult for you to spot blood in body fluids, which can sometimes be an early sign of a medical condition.
Having colour vision deficiency could also affect your career choice. This is because certain jobs, such as pilots, train drivers, electricians and air traffic controllers, require accurate colour recognition.
If your child has colour vision deficiency, they may struggle at school unless the teacher is made aware of the problem. Many learning materials are colour coded and your child may have difficulty if their learning environment isn't adapted to their specific needs.
The different types of colour vision deficiency – top left: normal vision, top right: deuteranopia, bottom left: protanopia and bottom right: tritanopia
How common is colour vision deficiency?
Red-green colour deficiencies are the most common types of colour deficiency. They affect significantly more men than women (1 in 12 men compared with 1 in 200 women).
Blue-yellow colour vision deficiency is very rare. It occurs in less than 1 in 10,000 people worldwide and affects males and females equally.
Symptoms of colour vision deficiency
If you have colour vision deficiency, you may have problems doing everyday activities that most people take for granted.
Preparing food, driving, playing sport, understanding information and choosing clothes can all be problematic if you're unable to distinguish between different colours.
Being unable to recognise subtle changes in colour could also have potential health implications. For example, you might not be aware of a change in the colour of a person's skin if they suddenly became unwell.
Colour vision deficiency can vary in severity. Some people are unaware they have the condition until they take a colour vision test.
Pale or deep colours may be difficult to identify, particularly if the light is poor. A person with a colour vision deficiency will often see many different colours as the same.
Red-green colour deficiencies
Red-green colour deficiencies are the most common types. This means you'll have difficulty distinguishing between different shades of red, yellow and green, so that:
reds, oranges, yellows, browns and greens may all appear to be a similar colour
reds, oranges, yellows, browns and greens may appear much duller than they would to someone with normal vision
reds, oranges, yellows, browns and greens may only be distinguishable by their slightly different brightness and intensity
shades of purple, such as lavender and violet, may be difficult to distinguish and may both look blue because you can't see the red component in them
Some people also confuse reds with black.
Blue-yellow colour deficiency
If you have a blue-yellow colour deficiency:
you'll find it difficult to distinguish between blue and green
green may appear as a shade of blue
yellow may appear as a pale shade of grey or purple
If your child has colour vision deficiency, they may have difficulty picking out colours or using colour-coded learning materials.
If you have colour vision deficiency, you may find it difficult to distinguish between different colours
Causes of colour vision deficiency
Colour vision deficiency is usually inherited (passed on from your parents).
Sometimes it can be caused by a health condition or by certain types of medication.
Your condition can vary from mild to severe, but it won't get worse as you get older. Your colour deficiency will stay the same provided you don't develop any other conditions or take medication that affects your vision.
How the eye detects colour
When light enters your eye, it passes through the lens before reaching the colour-sensitive cells, called cones, of the retina. The retina is the light-sensitive layer of cells that line the inside of the back of the eye.
There are three different types of cone cells – blue, green and red, better known as short (S), medium (M) and long (L) wavelength cones – which are sensitive to different wavelengths of light.
When different wavelengths of light fall on the three types of cone cells, the cone cells send signals about wavelength to the brain. The cone signals are processed by the neural cells of the retina and transmitted to the brain, which produces our perception of shades of colour.
For example, if a colour changes from red to green, the M-cones will respond more, but the L-cones less. This relative change signals the change in colour.
If your cone cells function normally, you'll be able to distinguish between hundreds of different colour combinations.
However, if you're missing one type of cone cells, or if the cones aren't functioning normally, you may see colours differently or, in the most severe cases, not at all.
Inherited colour vision deficiency
Colour vision deficiency is a common inherited condition that's passed down from your parents.
Red/green colour vision deficiency is passed from a mother to her son on the 23rd chromosome, which is known as the sex chromosome because it also determines a baby's gender.
Chromosomes are structures that carry the genes you inherit from your parents. Genes are single units of genetic material that contain the instructions for the development of cells, tissues and organs.
If you have colour vision deficiency, the instructions for the development of the photopigments in one of the cone cells in the retina are usually faulty.
The cone cells may be missing altogether or, in the case of the L- and M-cones, may be missing the affected photopigment or they may be less sensitive to light. Alternatively, the pathway from your cone cells to your brain may not have developed correctly.
The 23rd chromosome is made up of two parts – either two X chromosomes if you're female, or an X and a Y chromosome if you're male.
The faulty gene for red-green colour vision deficiency is only found on the X chromosome, so for a male to have the condition the faulty gene only has to appear on his X chromosome. For a female to have colour vision deficiency, the gene must be present on both her X chromosomes.
A woman with only one colour vision deficiency gene is a carrier, but she won't have colour vision deficiency. When she has a baby she'll pass one of her X chromosomes to them. If she passes the X chromosome with the faulty gene to her son, he will have colour vision deficiency.
However, if he receives the "good" chromosome, he won't have the condition. If she passes it to her daughter, her daughter will also be a carrier.
A boy with colour vision deficiency can't receive a colour deficiency gene from his father, even if his father is colour deficient himself. The father can only pass an X chromosome to his daughters.
Therefore, a colour-deficient daughter must have a father who is colour deficient and a mother who is a carrier who has passed the faulty gene to her.
If her father isn't colour deficient, the daughter of a carrier mother won't be colour deficient. A daughter can become a carrier in one of two ways – she can either acquire the gene from a carrier mother or from a colour-deficient father.
This is why red-green colour vision deficiency is far more common in men than women (1 in 12 men have a red-green colour vision deficiency compared with only 1 in 200 women).
Blue-yellow colour vision deficiency affects both men and women equally because it's carried on a non-sex chromosome. It's much rarer than red-green colour vision deficiency.
Other health conditions
Colour vision deficiency can sometimes be caused by an illness or pre-existing health condition. If you have colour deficiency as the result of a health condition, you'll usually have problems seeing blue and yellow colours. Your colour vision may also be worse in one eye compared with the other.
Conditions that can cause colour vision deficiency include:
diabetes – a lifelong condition that causes your blood sugar level to become too high
glaucoma – a group of eye conditions that affect vision
optic neuritis – inflammation of the optic nerve; the condition is sometimes associated with multiple sclerosis
age-related macular degeneration – a painless eye condition that affects the retina
sickle cell anaemia – an inherited blood disorder where red blood cells develop abnormally
If your condition is treatable, it may also be possible to improve your colour vision deficiency. However, if your condition gets worse, your colour vision deficiency may become more severe.
Some medications can cause abnormalities in colour vision. If the abnormality is caused by medication, your sight will usually correct itself when you stop taking the medication.
Speak to your GP if you find it difficult to distinguish colours after taking a medicine. They may be able to prescribe an alternative medication.
However, you shouldn't stop taking prescribed medication unless your GP specifically advises you to do so.
Medicines that can cause colour vision abnormalities include:
ethambutol (a treatment for tuberculosis)
You may be at risk of developing colour vision deficiency if you're exposed to chemicals as part of your job. Chemicals known to cause problems with colour recognition include carbon disulfide and styrene.
Your health and safety should be protected in the workplace. If you develop a health condition such as colour vision deficiency, speak to your employer to ensure appropriate health and safety procedures are in place and that it's safe for you to continue working.
Most people's ability to distinguish colours deteriorates with age. This is a natural part of the ageing process and not something to be overly concerned about.
However, you should visit your GP if you have symptoms that start suddenly or if you're experiencing severe colour vision deficiency.
Diagnosing colour vision deficiency
Many people become aware they have colour vision deficiency when they're unable to identify colours correctly.
Your child may have difficulty naming colours or you may struggle to read a coloured map or document.
For example, reds, oranges, yellows, browns and greens may all appear to be a similar colour to someone with colour vision deficiency.
Sometimes mild colour vision deficiencies may go undetected. For example, a child who has inherited the condition may be unaware that they have a problem distinguishing between different colours.
It's very important to identify colour vision deficiency early because a child's learning experience relies heavily on the use of colour.
Colour vision tests
It's important to be aware that colour vision tests don't form part of the standard eye test. Many opticians don't carry them out unless they're specifically asked to do so.
You could therefore have colour vision deficiency but be unaware that you're having problems perceiving colour.
This can lead to problems – for example, a school leaver may suddenly find that they can't pursue a certain career because they have colour vision deficiency.
You may need to ask your optician to carry out a colour vision test for you.
There are several different tests for checking colour vision. Two of the tests you may have are described below.
The Ishihara test is the most commonly used test for checking colour vision. It can only screen for red/green deficiencies. Specialist tests are needed to diagnose blue/yellow colour vision deficiency.
The Ishihara test uses plates made up of multicoloured dots. Some of the dots will be a different colour and depict a number.
You'll be asked to look at the plate and say if you see a number. A note will be taken of numbers you have difficulty identifying or you identify incorrectly.
You may have a colour vision deficiency if you have problems completing the Ishihara plate test.
The arrangement test is where you arrange coloured objects in order of their different shades of colour.
For example, you may be given coloured blocks of slightly differing shades and be asked to arrange them from one shade to another.
A particular pattern of mistakes could indicate that you have a colour vision deficiency.
Treating colour vision deficiency
There's currently no cure for inherited colour vision deficiency.
This is because it isn't yet possible to replace the faulty light-sensitive cells or missing photopigments in the retina that are responsible for accurately recognising colour. The retina is the light-sensitive layer of cells that lines the inside of the back of the eye.
Colour vision deficiency won't usually cause any long-term health problems and treatment isn't essential to lead a normal, healthy life.
Compensating and adapting
Most people with colour vision deficiency learn to adapt and find ways of compensating for the problems they have identifying or distinguishing colours.
For example, you may be able to:
ask friends or family members to help you choose clothes and other coloured items – this is particularly important if you have severe colour vision deficiency
install good quality lighting in your home and workplace to help you distinguish colours
make teachers aware that your child has difficulty identifying and distinguishing between different colours so that learning materials can be adapted accordingly
Tinted contact lenses
Tinted contact lenses that you wear in one eye are available on prescription to help you distinguish colours more easily.
However, they only work for some people and they can affect your ability to judge distances and depth. They also often reduce the intensity of lights you can see.
Other eye conditions
Most cases of colour vision deficiency are inherited, but your ability to perceive colours may be affected by an underlying eye condition.
If you have problems distinguishing colours, it's important that you visit your GP or optometrist (eye specialist) so they can determine what's causing your colour vision deficiency.
If an underlying eye condition is the cause, your colour vision deficiency may be improved if the condition can be treated.
Some types of medication may also make it difficult for you to distinguish between colours. If this is the case, you might be prescribed an alternative medicine.
However, never stop taking prescribed medication unless you're specifically advised to do so by your GP or another healthcare professional responsible for your care.
How colour vision deficiency can affect your life
Colour vision deficiency won't usually affect your long-term health, but it could affect your choice of career.
Depending on how severe your condition is, you may be not able to do certain jobs that require accurate colour recognition.
For example, jobs you may be excluded from include:
some positions in the armed forces
customs and excise officers
fire service officers
hospital laboratory technicians
certain flying-related roles, such as pilots and air traffic controllers
jobs that involve the manufacture of paint, paper or textiles
train drivers and railway maintenance staff
There are many other jobs you may not be excluded from but may find more difficult than someone who has normal colour vision – for example, marketing, web design and medicine.
It's very important that a child with colour vision deficiency is identified early so their teacher can be made aware of the problem.
Colour vision deficiency isn't currently recognised as a special educational need (SEN) and teachers aren't routinely trained to recognise or work with colour vision deficiency.
As many learning materials are colour coded, your child may have difficulties if their learning environment isn't adapted for their needs.
Colour vision deficiency