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Colour Vision Deficiency (CVD), also known as colour blindness

Colour vision deficiency (CVD) or colour blindness is when the eyes are unable to detect certain colours. People with colour vision deficiency find it difficult to tell differences between colours. How difficult this might be for someone depends on the severity of the colour vision deficiency.

This page contains a summary of our information on colour vision deficiency. To read our full information, download our factsheet:

What causes CVD?

CVD is caused when there is a problem with the cone cells. The visible spectrum is the range of colours and wavelengths that the eye can see. There are three types of cone cells which detect a range of different colours or wavelengths of light:

  • Red cone cells detect long wavelengths of light
  • Green cone cells detect medium wavelengths of light
  • Blue cone cells detect short wavelengths of light

CVD is most commonly genetic or inherited (meaning you are born with it). Inherited CVD does not improve or get worse with age. Most forms of inherited CVD do not affect the eye’s ability to see fine detail.

CVD can develop (be acquired) as the result of:

  • an underlying eye or health condition, such as optic neuritis from multiple sclerosis, or diabetes
  • a side effect of a medication
  • exposure to harmful chemicals
  • the ageing process

Red-green CVD

The most common forms of CVD are red-green deficiencies. These can be a form of dichromacy (where either the red or green cone cells are not working at all) or anomalous trichromacy (where either the red or green cells are not working fully).

If the green cone cells are affected, it can cause:

  • Deuteranopia – when the green cone cells are not working at all.
  • Deuteranomaly – when the green cone cells are not fully working.

If the red cone cells are affected, it can cause:

  • Protanopia – when the red cone cells are not working at all.
  • Protanomaly – when the red cone cells are not fully working.

How do red-green types of CVD affect colour vision?

Regardless of whether it is the red or green cone cells that are not working, the way that colour vision is affected is very similar. This is because there is overlap in the colours that the red and green cells can detect, so all colours containing red and green will be affected. This causes difficulty in telling the difference between:

  • reds, greens and browns
  • oranges and yellows
  • blues and purples
  • greys and pastel colours

People may see these colours as much duller than they would appear to someone with normal colour vision. People with red deficiencies may also confuse reds with black. The exact way that someone experiences colour with this type of CVD will be very individual as it will depend on the level of function of the cone cells.

What causes red-green CVD?

Red-green CVD is an inherited condition and therefore runs in families. You inherit genes from your parents. Your genes give the cells in your body the instructions they need to work well and stay healthy. If a gene has a mutation, there is a fault in their instructions and the cells using those instructions don’t work as they should.

The genetic fault that causes red-green CVD is passed on in what’s known as an X-linked inheritance pattern meaning the faulty gene lies on the sex chromosomes.

Each person has two sex chromosomes which determines their genetic sex at birth:

  • males have an X and Y chromosome and
  • females have two X chromosomes.

In the case of CVD, the colour deficiency gene is found on the X chromosome. A male has only one X chromosome that they inherit from their biological mother. If this has the faulty gene, then they will have CVD.

A female inherits two X chromosomes, one from the biological mother and one from the biological father. If they have a faulty gene on one X chromosome but a normal copy of the gene on the other, they are a carrier of the condition. This means they do not have CVD but can pass the faulty gene onto their children. For a female to be affected by CVD, she will need to inherit the faulty gene from both parents, which happens less commonly.

Red-green CVD is a lifelong condition, which doesn’t improve or get worse throughout life. Whilst CVD does not affect your visual acuity (ability to see detail), it may limit your eligibility to join some professionals or specialist jobs within certain professions. It can also have an impact on education, sport and elements of everyday life where ability to distinguish between colours is essential, for example, accessing information on websites, presentations or documents, shopping, reading maps, and cooking.

Red-green CVD can be easily picked up using traditional colour vision tests such as Ishihara plates, which have been designed to detect the presence of red-green CVD and provide a pass or fail. More specialised occupational tests can be used to check whether someone with a CVD would be able to meet the colour vision standards for certain occupations, for example, where the work requires the ability to accurately read colours of light for safety reasons.

In the UK, school eye tests don’t include screening for CVD. It’s a good idea to ask the optometrist (optician) at your child’s regular eye test about whether your child has had their colour vision tested.

Blue-yellow CVD

Blue-yellow CVD is less common than red-green CVD and occurs when the blue cone cells are affected.

  • Tritanopia is where the blue cones are not working at all.
  • Tritanomaly is where the blue cones are not working fully.

Blue-yellow CVD affects the ability to see light in the short wavelength (blue) part of the spectrum. This causes confusion between blues, greens, yellows, oranges and violets. The appearance of these colours may also be duller or paler.

Blue-yellow CVD can either be inherited or caused by other underlying eye or health conditions.

It is not inherited in the same pattern as red-green CVD and is not inherited on one of the sex chromosomes. This means that is affects males and females equally. However, it is still quite rare, affecting less than one percent of people.

Monochromatism and achromatopsia

Monochromatism and achromatopsia are both inherited eye conditions that cause complete colour vision loss.


Achromatopsia is a rare inherited condition affecting 1 in 30,000 people. Faults in several genes have been identified to cause achromatopsia. These faults mean that the cone cells cannot work properly.

Cone cells are responsible for seeing detail and colour and therefore people with this condition have difficulty seeing any colour and will also have blurred vision. It can also cause sensitivity to bright light (photophobia), so seeing in daylight can be difficult. It can also cause nystagmus, where the eyes move or ‘wobble’ constantly, and this can also affect vision. How severe these symptoms are can vary between different people, but achromatopsia doesn’t cause total loss of vision and is generally stable over time.

Complete achromatopsia is when the cone cells don’t work at all causing colour blindness. Incomplete achromatopsia is where the cone cells still work to some extent so some colour vision may be present.

Rarely achromatopsia can develop later in life. For example, cerebral achromatopsia can develop due to brain damage caused by a stroke.

Achromatopsia is inherited in an autosomal recessive pattern. This means that to inherit this condition, both your biological parents would have to carry the faulty gene for the condition. If you inherit the faulty gene from one parent but not the other, then you are a carrier – this means you don’t have the condition but could pass on the faulty gene to your children. If two people carry the gene then their children have a 50% chance of being a carrier, 25% chance of inheriting the condition, and 25% chance of inheriting two completely normal copies of the gene.

Blue Cone monochromatism

Blue cone monochromatism is a rare inherited condition where only the blue cone cells are working. It affects less than 1 in 100,000 people.

It causes severely impaired colour vision, blurred vision, light sensitivity and nystagmus from birth. People with this condition are also short sighted (myopic).

It is caused by genetic changes on the X chromosome. This means that it affects males more frequently than females.

Is there any treatment for achromatopsia and cone monochromatism?

There is no cure for these conditions at present. Research is looking into potential gene therapy treatment to replace the faulty gene with a healthy copy.

Some adjustments can be made to help manage with these conditions including prescription glasses to correct any short or long sightedness. People may also benefit from wraparound sunglasses to reduce the light sensitivity and provide UV protection. Many people with achromatopsia find that red tinted sunglasses help with light sensitivity.

Low vision aids and assistive technology can help with daily activities. Assessment at a low vision clinic will also be beneficial. For more information call our Helpline on 0303 123 9999 or visit our low vision services.

Further help and support

Most forms of CVD do not affect your visual acuity (ability to see detail) or your visual field (the whole area of vision you have). Therefore, someone with CVD cannot be registered as sight impaired (partially sighted) or severely sight impaired (blind).

However, CVD can impact upon education, playing sport and careers if not properly supported. It’s important to let your child’s schoolteacher know about a diagnosis of CVD so that this can be managed. The Colour Blind Awareness organisation provides further advice and support for children and families.

If your child is diagnosed with monochromatism or achromatopsia they will have a reduced level of vision which means they may meet the criteria to be registered as sight impaired or severely sight impaired. It’s completely natural to be concerned and normal to find yourself worrying about what it means now and in the future. We’re here to support you every step of the way, and to answer any questions you may have – just get in touch with our Sight Loss Advice Service.

Page last reviewed: Aug. 9, 2023

Next review due: Aug. 9, 2024