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Colour blindness

Published by Bupa's health information team, March 2010.

This factsheet is for people who have colour blindness, or who would like information about it.

Colour blindness refers to a range of conditions that are characterised by an inability to see certain colours. About eight in 100 men and one in 100 women are affected by colour blindness.

• About colour blindness
• Types of colour blindness
• Symptoms of colour blindness
• Causes of colour blindness
• Diagnosis of colour blindness
• Treatment of colour blindness
• Living with colour blindness
• Questions and answers
• Related topics
• Further information
• Sources

About colour blindness

Colour vision

There are two types of light-sensitive cells in your eyes called rods and cones. They are both found in the retina, which is the layer at the back of your eye that processes images. Rods allow you to see in dim light or at night, whereas cones allow you to see in detail and distinguish colours.

There are three types of cone cells: red cones, green cones and blue cones. Each cone has a different level of sensitivity to light. When you look at an object, light enters your eyes and stimulates the cone cells. Your brain then interprets the cone cells allowing you to see the colour of the object. The red, green and blue cones all work together to allow you to see the whole spectrum of colours, for example when the red and green cones are stimulated to a certain level you will see the colour yellow.

Colour blindness

Colour blindness occurs when one or more of the cone types are faulty or missing. This means that you will have difficulty seeing the cone colour that is missing or faulty. For example, if the red cone is missing you won't be able to see colours containing red as clearly.

Most people with colour blindness can't distinguish certain shades of red and green.

Types of colour blindness

There are several different types of colour blindness.

Dichromatism

Dichromatism is when one of the cones is missing. There are three types of dichromatic colour blindness:

• protanopia - the red cones are missing
• deuteranopia - the green cones are missing
• tritanopia - the blue cones are missing

Anomalous trichomatsis

Anomalous trichomatsis is when you have all three cones but there is a fault in one of them making you less sensitive to certain colours. Again, depending on which cone is faulty, this will cause:

• protanomalous trichromatism - the red cones are less sensitive
• deuteranomalous trichromatism - the green cones are less sensitive
• tritanomalous trichromatism - the blue cones are less sensitive

Red cone and green cone defects are known as red-green colour blindness.

Monochromatism

Monochromatism is a rare type of colour blindness, where none of your cone cells function properly or only one type works as it should. This results in no colour vision - all you see is black, white and shades of grey.

Symptoms of colour blindness

The main symptom of colour blindness is a difficulty in distinguishing colours or making mistakes when identifying them. You may see only a slight difference in different shades of colour or if you have severe colour blindness, all colours look the same.

In particular situations this may be made worse, for example:

• in low-level lighting
• if the area of colour is small
• if you view a large area of colour at a distance
• if you try to distinguish pale colours or dark shades

Causes of colour blindness

Colour blindness is either inherited (you're born with it) or you acquire it as a result of an illness, ageing or exposure to chemicals.

Inherited colour blindness

Red-green and blue colour blindness is usually passed down from your parents. Red-green colour blindness, the most common form, is passed down on the X chromosome. Chromosomes are structures that contain genes - these contain the instructions for the development of cells, tissues and organs. If you're colour-blind, it means the instructions for the development of your cone cells are wrong and the cones are missing or less sensitive.

The X chromosome is a sex chromosome; males have an X and a Y chromosome whereas females have two X chromosomes. For a male to be affected, colour blindness only has to appear on his single X chromosome, whereas for a female to inherit colour blindness it must be on both X chromosomes. This is why red-green colour blindness is far more common in men than in women.

Blue colour blindness affects both men and women equally. This is because it's passed down on a non-sex chromosome.

If you have inherited colour blindness, it will stay the same throughout your life - it won't get any better or any worse.

Acquired colour blindness

You can become colour blind as a result of an illness, a side-effect of a medicine, and exposure to certain chemicals or a head injury for example.

Eye diseases like glaucoma, cataracts, age-related macular degeneration and optic nerve disease are all causes of acquired colour blindness. Other diseases, such as multiple sclerosis, liver disease and diabetes, can also cause colour blindness.

Colour blindness can be a side-effect of some medicines, such as anti-inflammatory treatments for rheumatoid arthritis, the contraceptive pill and some medicines for heart conditions. However, this is quite rare.

There is also some evidence to suggest that exposure to industrial chemicals, such as solvents, may cause colour blindness. Alcohol abuse and cigarettes have also been found to contribute.

The ageing process can be a factor. As you get older, you may experience subtle changes to your vision in general, including your colour vision.

Unlike inherited colour blindness, acquired colour blindness can vary over time. Symptoms may be mild and remain stable, or they can be severe and progress to more serious forms of colour blindness, such as monochromatism, very quickly. Often the cause of the colour blindness determines how severe your symptoms will be.

Diagnosis of colour blindness

Colour blindness can be difficult to detect, particularly in children with inherited colour blindness as they may be unaware that they have any problems with their colour vision.

If you have an eye test with an optometrist (a registered health professional who examines eyes, tests sight and dispenses glasses and contact lenses), your colour vision will be tested.

You can also see your GP if you have any problems with seeing colours. Your GP will ask about your symptoms and examine you. He or she may also ask you about your medical history.

To test your colour vision, your doctor or optician may use the Ishihara test, which is often used to diagnose red-green colour blindness. It's not suitable for testing blue colour blindness. Colour plates will be put in front of you and you will be asked what number you can see on the plate. Some of the plates contain information that people with normal colour vision can see, while others will contain information that only people with colour blindness can see. If you make a certain amount of errors, you can be diagnosed with colour blindness.

You may be referred to an ophthalmologist (a doctor who specialises in eye heath) for more tests to establish which type of colour blindness you have.

A new test being introduced to diagnose colour blindness is the 'Colour Assessment and Diagnosis' (CAD) test. This can be used for both red-green and blue colour blindness. In this test, you will be shown coloured blocks in a grey square that jump to new positions as you track them. The process will be repeated with different colours and shades. If you're colour-blind, you will eventually be unable to detect the blocks' movements. The CAD test can show how weak the colour was when it disappeared and therefore give you a measure of how severe your colour blindness is.

Treatment of colour blindness

There is currently no treatment for inherited colour blindness. Colour filters or tinted contact lenses can be used in some situations to enhance the brightness between some colours; these are occasionally used in the workplace.

For acquired colour blindness, once the cause has been established and treated, your vision may return to normal.

Living with colour blindness

Colour blindness can affect many everyday tasks; from re-wiring an electrical plug, to reading a map, to knowing when the traffic lights have changed colour. Being aware that you're colour blind will help prevent accidents and allow you to develop strategies to deal with any difficulties it causes.

Colour blindness may affect your career choices. For some professions, such as being a pilot or coastguard, good colour vision is essential and you may be tested if you apply for a position. If you're concerned about your colour vision, it's important to get a diagnosis and talk to your employer to ensure that your workplace remains safe.

Related topics

• Age-related macular degeneration
• Cataracts
• Glaucoma

Further information

• RNIB (Royal National Institute of Blind People)
  0845 766 9999
  www.rnib.org.uk

Sources

• Minimum colour vision requirements for professional flight crew: Recommendations for new colour vision standards. Civil Aviation Authority, April 2009, www.caa.co.uk
• Colour vision examination: A guide for occupational health providers. Health and Safety Executive. www.hse.gov.uk, accessed 11 December 2009
• Colour vision deficiency. Royal National Institute of Blind People (RNIB). www.rnib.org.uk, accessed 11 December 2009
• Colour vision examination: A guide for employers. Health and Safety Executive. www.hse.gov.uk, accessed 11 December 2009
• May SB. Review of environmental chemicals and neurotoxicity, 2007. Health and Safety Executive. www.hse.gov.uk, accessed 11 December 2009
• Alcohol and the eye. The Royal College of Ophthalmologists. www.rcophth.ac.uk, accessed 11 December 2009
• For medical practitioners: At a glance guide to the current medical standards of fitness to drive. Driver and Vehicle Licensing Agency.www.dvla.gov.uk, accessed 14 December 2009

This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.

Publication date: March 2010