Colour vision deficiency

Page last reviewed: 13/07/2011

People with colour vision deficiency are unable to see colours the same way that most people do, and they may have difficulty distinguishing between two different colours.

Colour vision deficiency is often known as colour blindness. However, true colour blindness is where no colour can be seen at all, which is rare.

Colour vision deficiency occurs when the cells in the retina that interpret colour do not function normally. The retina is the thin layer of nerve cells that line the inside of the back of the eye. The cells are known as "cones" and they are able to process the three primary colours:

  • red
  • green
  • blue

Using the primary colours, the cone cells can interpret hundreds of different colours and shades. If someone has colour vision deficiency, the cone cells lack the right amount of chemicals to process colours accurately.

How common is colour vision deficiency?

Colour vision deficiency affects approximately one in 12 men, and one in 100 women. In most cases, the condition is inherited, although colour vision deficiency can develop as a result of a pre-existing health condition, or as a side effect of a medicine.

Types of colour vision deficiency

There are three main types of colour vision deficiency:

  • Red-green deficiency (deuteranopia). This is the most commonly diagnosed deficiency. People with this condition cannot distinguish certain shades of red and green.
  • Blue-yellow deficiency (tritanopia). This is a rare condition where it is difficult to distinguish between blue and green. Yellow can appear as a pale grey or purple.
  • Total colour blindness (achromatopsia). This is the rarest type of colour vision deficiency. It is where no colours can be detected and everything is seen in shades of black, white and grey. People with this condition have poor sight and are very sensitive to light.


There is no cure for colour vision deficiency, but it should not cause any other symptoms or health complications. It should also not affect other aspects of your vision, for example the ability to see distances or details.

In most cases, people are able to adapt to having colour vision deficiency. For example, by recognising the position of the lights on a traffic light, rather than the different colours, people with a colour vision deficiency are still able to drive.


The retina is the nerve tissue lining the back of the eye, which senses light and colour, and sends it to the brain as electrical impulses.

Page last reviewed: 13/07/2011

There are no obvious or physical symptoms of colour vision deficiency. Many people have the condition without being aware of it.

Problems identifying colours

If you have colour vision deficiency, you may have difficulty:

  • identifying pale colours
  • identifying deep colours if there is poor lighting, or if you are tired or stressed

Colour vision deficiency can vary in severity. Some people will only experience a very slight difference in the way that they appreciate different hues and shades of colour. For others, many colours will all appear to look the same.

Red-green deficiency (deuteranopia)

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, can also be difficult to distinguish.

Blue-yellow deficiency (tritanopia)

If you have a blue-yellow colour deficiency:

  • You will find it hard 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.

Symptoms in children

If your child has colour vision deficiency, you may notice that they have difficulty picking out colours or using colour-coded learning materials.

Page last reviewed: 13/07/2011

Your ability to see colour depends on your eyes being able to distinguish between the three main colours:

  • red
  • blue
  • green

How the eye detects colour

When light enters your eye, it passes through the lens (the transparent structure at the front of your eye) and reaches the colour-sensitive cells (cones) in your retina (the thin layer of nerve cells that line the inside of the back of the eye).

Chemicals in the cones interpret which colour you are seeing, and send an appropriate message to the brain through the optic nerve (the nerve that connects your eye to your brain). If your cone cells function normally, you will be able to distinguish between hundreds of different colour combinations.

However, if the cones in your retina lack some of the light-sensitive chemicals that they need to interpret colour accurately, you may only be able to see two of the three main colours (red, blue and green). The more chemicals that are missing in your cone cells, the more severe your colour deficiency will be.

Inherited colour vision deficiency

Most people inherit their colour vision deficiency from their parents. An inherited colour vision deficiency usually affects the way you see green and red colours.

Your condition may vary from mild to severe, but it will not get worse over your lifetime. Your colour deficiency will stay the same, provided you do not develop any other conditions, or take any 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 a health condition is causing your colour deficiency, you will usually have trouble 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 chronic (long-term) condition that is caused by too much glucose in the blood
  • glaucoma - a group of eye conditions that affect vision
  • macular degeneration - a painless eye condition that affects your ability to see what is directly in front of you
  • Alzheimer's disease - the most common form of dementia, which causes the loss of mental abilities such as memory and reasoning
  • Parkinson's disease - a chronic (long-term) condition that affects the way the brain coordinates body movements, such as walking and talking
  • alcoholism
  • leukaemia - cancer of the bone marrow and white blood cells
  • 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 worsens, your colour vision deficiency may become more severe.


Some medication can cause you to develop colour vision deficiency. If your deficiency is caused by medication, your sight usually corrects itself once you stop taking the medication.

Speak to your GP if you find it hard to distinguish colours after taking a medicine. They may be able to prescribe an alternative medication for you. However, never stop taking prescribed medication unless your GP specifically advises you to do so.

Medicines that are used to treat the following health conditions may cause colour vision deficiency:

  • heart problems
  • high blood pressure (hypertension)
  • infections
  • nervous disorders
  • psychological problems


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
  • fertilisers
  • styrene

Your health and safety should be protected in the workplace. If you develop a health condition such as colour vision deficiency as a result of your job, speak to your employer to ensure that your health is being adequately cared for and that it is safe for you to continue working.


Most people find that their ability to distinguish colours deteriorates with age. This is a natural part of the ageing process and is not something to be overly concerned about. However, if your symptoms start very suddenly or you are experiencing severe colour vision deficiency, contact your GP.

The transparent structure at the front of your eye.

The retina is the nerve tissue lining the back of the eye, which senses light and colour, and sends it to the brain as electrical impulses.

Optic nerve
The nerve that connects your eye to your brain.


Page last reviewed: 13/07/2011

Many people become aware of their colour vision deficiency through social situations. For example, your child may have difficulty naming colours, or you may struggle to read a map or document.
However, in cases where people see an alternative colour, colour deficiencies can often go undetected. For example, someone with a colour vision deficiency may see leaves as a different colour from someone with normal vision, but both people will call this colour "green". However, the colour that the person with a colour vision deficiency sees may be what someone with normal vision sees as yellow.  

It is important to try to get colour vision deficiency diagnosed early in life. If your child is diagnosed at an early age, it will help with their learning at school.

Colour vision tests

You may have your colour vision tested as part of an eye examination by your optometrist. An optometrist (also known as an ophthalmic optician) examines eyes and tests sight, and is trained to recognise sight defects.

Your optometrist may be able to check your colour vision by asking you to read numbers that are printed in different colours, or to name the colours of different lights. Some further tests are described below.

Arrangement test

The arrangement test is where you arrange coloured objects in order of their different hues. For example, you may be given sheets of paper all of slightly different shades and be asked to arrange them so that they get darker. A particular pattern of mistakes could indicate that you have a colour vision deficiency.

Pseudoisochromatic plates

Colour vision deficiency is often assessed using pseudoisochromatic plates. These are pictures that are made up of multicoloured dots. Some of the dots will be a different colour and will make up a number.

You will be asked to cover one eye as you look at the plate and say if you see a number on the plate. A note will be taken of any of the numbers that you have difficulty identifying, or you identify incorrectly. You will then have to repeat the test while covering the other eye.

There are different pseudoisochromatic plate tests to detect different types of colour vision deficiency. The Ishihara plate test is the most common test, and is used to detect a red-green deficiency.

If you have difficulty in completing the pseudoisochromatic plate test, you may have a colour vision deficiency.

Page last reviewed: 13/07/2011

There is currently no cure for inherited colour vision deficiency because it is not possible to repair or replace the faulty cells in the retina (the thin layer of nerve cells that line the inside of the back of the eye).

However, having colour vision deficiency will not cause you any long-term health problems. Therefore, treatment is not essential in order for you to lead a normal, healthy life.

Compensating and adapting

Most people with colour vision deficiency learn to adapt to their condition. You will usually find a way of compensating for your difficulty with colours, particularly with the help of your family and friends. For example:

  • You should be able to drive safely once you know the different positions of traffic light signals (rather than relying on the colours of the lights).
  • You or your child may need help in picking out clothing and other coloured items, particularly if you have severe colour vision deficiency.
  • Ensuring that there is good quality lighting in your home and workplace may help you to distinguish different colours. 
  • Teachers can be made aware of colours that your child has difficulty seeing, and their learning materials can 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 often affects your ability to judge distances and depth, and only works for some people.

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 to visit your GP or optometrist (an eye specialist) so that they can determine the cause of your colour vision deficiency.

If you have an underlying eye condition, 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 may be prescribed an alternative medicine, which should restore your colour vision. However, you should never stop taking prescribed medication unless specifically advised to do so.

The retina is the nerve tissue lining the back of the eye, which senses light and colour, and sends it to the brain as electrical impulses.

Page last reviewed: 13/07/2011

Having colour vision deficiency will not affect your long-term health. However, it could affect your career or job choice.

This is because you may be excluded from certain types of jobs that require accurate colour recognition in order to be carried out effectively. These jobs may include:

  • some positions in the armed forces
  • customs and excise officers
  • fire service officers
  • hospital laboratory technicians
  • pharmacists
  • electricians
  • those involving aviation, such as pilots and air traffic controllers
  • those involving paint, paper or textile manufacture
  • railway drivers and maintenance staff

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 harder than most if their learning environment is not adapted to their specific needs.

Page last reviewed: 13/07/2011

There are no procedures or medicines that can prevent inherited (genetic) colour vision deficiencies.

However, if you developed colour vision deficiency as a result of a pre-existing health condition, or by taking a certain type of medication, the condition may be prevented either by treating your condition or by using an alternative medication.


Genetic is a term that refers to genes the characteristics inherited from a family member.

Content provided by NHS Choices and adapted for Ireland by the Health A-Z.

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