People with colour vision deficiency are unable to see colours clearly and accurately. They may find it difficult to distinguish between different colours.
Colour vision deficiency is often referred to as colour blindness. However, true colour blindness, where no colour can be seen at all, is rare.
People with colour vision deficiency may have difficulty identifying pale colours or deep colours if the lighting is poor.
Colour vision deficiency can vary in severity. Some people are unaware they have a colour deficiency until they have a colour vision test. Others will experience a very slight difference in the way they appreciate different hues and shades of colour. In rare cases, a person may experience many colours that all appear to be the same.
Read more about the symptoms of colour vision deficiency.
Types of colour vision deficiency
There are two main types of colour vision deficiency:
- red-green deficiency – where people are unable to distinguish certain shades of red and green; it is the most commonly inherited type
- blue-yellow deficiency – this is a rare condition where it is difficult to distinguish between blue and green, and yellow may appear as a pale grey or purple
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 a result of a pre-existing health condition or as a side effect of a medicine.
Inherited colour vision deficiency occurs due to an abnormality in the retina (the film that lines the back of the eye). The retina is made of rod and cone cells. There are three main types of cone cells. In people with inherited colour deficiency, one type of cone cell is missing or does not function normally.
Read more about the causes of colour vision deficiency.
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 you may struggle to read a map or a document.
It is important to identify a colour vision problem early. If your child is diagnosed at an early age and teachers are made aware, their learning experience can be adapted.
Read more about diagnosing colour vision deficiency.
Treating colour vision deficiency
There is currently no cure for inherited colour vision deficiency because it is not possible to repair or replace the cone cells in the retina.
However, as colour vision deficiency does not cause any long-term health problems, treatment is not essential for you to be able to lead a normal, healthy life.
If you have colour vision deficiency as a result of a pre-existing health condition, or from taking a certain type of medication, it may be possible to improve your symptoms, either by treating the underlying condition or by using an alternative medication.
Most people with colour vision deficiency learn to adapt to their condition, and it is usually possible to find ways to compensate for your difficulty with colours. For example, it is possible to recognise the position of the lights on a traffic light, rather than the different colours.
Read more about treating colour vision deficiency.
In most cases, people with colour vision deficiency are unlikely to have 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 other medical conditions.
Having colour vision deficiency could also affect your career choice. This is because certain jobs, such as pilots 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 find it more difficult if their learning environment is not adapted to their specific needs.
Read more about the complications of colour vision deficiency.
If you have colour vision deficiency, you may have difficulty identifying pale colours or deep colours if lighting is poor.
Colour vision deficiency can vary in severity. Some people are unaware they have a colour deficiency until they take a colour vision test. Others will perceive hues and shades of colour differently. In rare cases a person may see many colours as the same.
Red-green deficiency is the most common form of colour vision deficiency. If you have red-green deficiency:
- you will have difficulty distinguishing between shades of red and green
- red, orange, yellow and green may all appear to be a similar colour
- red, orange, yellow and green may appear much duller than they would to someone with normal vision
- red, orange, yellow and green may only be distinguishable by their brightness and intensity
- shades of purple, such as lavender and violet, may also be difficult to distinguish
If you have a blue-yellow colour deficiency:
- you will find it difficult to distinguish between blue and green
- green will appear as a shade of blue
- yellow may only 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.
To see colour accurately, your eyes need to be able to distinguish between the three primary colours – red, green and blue.
How the eye detects colour
When light enters your eye, it passes through the lens at the front of your eye before reaching the colour-sensitive cells, called cones, of the retina (the layer of cells that lines the inside of the back of the eye).
There are three different types of cone cells – blue, green and red (also known as short, medium and long wavelength cones) – which detect different wavelengths of light.
The cones interpret which colour you are seeing and send a message to your brain through the optic nerve. If your cone cells function normally, you will be able to distinguish between hundreds of different colour combinations.
However, if you are missing one of the types of cone cells, or if the cones are not functioning normally, you may see colours differently.
Inherited colour vision deficiency
Most people with colour vision deficiency inherit the condition from their parents. An inherited colour vision deficiency usually affects the way you see green and red colours.
Your condition can vary from mild to severe but it will not get worse as you get older. Your colour deficiency will stay the same, provided you do not develop any other conditions or take medication that could affect your sight.
Other health conditions
Sometimes, colour vision deficiency can be caused by an illness or a pre-existing health condition. If you have colour deficiency as a result of a health condition, you will usually have problems seeing blue and yellow colours. Your colour vision may also be worse in one eye than the other.
Conditions which can cause colour vision deficiency include:
- diabetes – a long-term condition that is caused by too much glucose in the blood
- glaucoma – a group of eye conditions that affect vision
- optic neuritis – inflammation of the optic nerve (the nerve that transmits images to the brain) this 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 once you stop taking the medication.
Speak to your doctor if you find it difficult to distinguish colours after taking a medicine. They may be able to prescribe an alternative medication for you. However, do not stop taking prescribed medication unless your doctor specifically advises you to do so.
Medicines that can cause colour vision abnormalities include:
- ethambutol – a treatment for tuberculosis
- sildenafil (Viagra)
If you are exposed to chemicals as part of your job, you may be at risk of developing colour vision deficiency.
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 it is safe for you to continue working.
The Health and Safety Executive website provides more information and advice about health and safety at work.
Most people find their 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 doctor if you have symptoms that start suddenly or if you are experiencing severe colour vision deficiency.
Many people become aware they have a colour vision deficiency when they have problems identifying colours correctly.
Your child may have difficulty naming colours or you may struggle to read a coloured map or document. However, in mild cases, colour deficiencies may go undetected.
For example, someone with a colour vision deficiency may see a leaf as a different colour from someone with normal vision, but both will call the colour they see 'green'. However, the colour that the person with a colour vision deficiency sees may be what someone with normal vision would call 'yellow'.
It is important for colour vision deficiency to be identified early on as a child's learning experience relies heavily on the use of colour.
Colour vision tests
Your colour vision may be tested as part of an eye test carried out by an optometrist. An optometrist, also known as an ophthalmic optician, is a healthcare professional who examines eyes and is trained to recognise sight defects.
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 uses plates made up of multicoloured dots. Some of the dots will be a different colour and depict a number.
You will 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.
Different Ishihara plate tests can be used to detect different types of colour vision deficiency. The most common test is used to detect a red-green deficiency.
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 hues.
For example, you may be given coloured blocks of slightly different shades and be asked to arrange them from lightest to darkest. A particular pattern of mistakes could indicate you have a colour vision deficiency.
There is currently no cure for inherited colour vision deficiency because it is not possible to replace faulty light-sensitive cells in the retina responsible for accurately recognising colour.
If you have colour vision deficiency, it will not usually cause long-term health problems and treatment is not essential to lead a normal, healthy life.
Compensating and adapting
Most people with colour vision deficiency learn to adapt. You will usually find ways to compensate for your difficulty with colours. For example, it should be possible to:
- ask family members or friends to help you choose clothes and other coloured items – this is particularly important if you have severe colour vision deficiency
- ensure there is good quality lighting in your home and workplace – this may help you distinguish colours
- make teachers aware of colours your child has difficulty seeing – this will allow learning materials to be adapted accordingly
Tinted contact lenses
In some cases, you may be prescribed a tinted contact lens to wear in one eye to help you distinguish colours more easily. However, this only works for some people and it can affect your ability to judge distances and depth.
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.
It is therefore important you visit your doctor or optometrist (eye specialist) so they can determine what is 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, you should never stop taking prescribed medication unless specifically advised to do so by your doctor or another healthcare professional responsible for your care.
Colour vision deficiency will not usually affect your long-term health but it could affect your career choice.
Depending on the severity of your condition, you may be unable 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 involving paint, paper or textile manufacture
- train drivers and railway maintenance staff
If your child has colour vision deficiency, they may struggle at school unless the teacher is made aware of the problem.
As many learning materials are colour coded, your child may find it more difficult than most if their learning environment is not adapted to meet their specific needs.