What is colour vision deficiency?
Different colours are seen by special cells in the retina at the back of your eye. There are two types of cells, called rods and cones. Cones are concerned with colour vision. There are three types of cones: red cones, blue cones and green cones.
Each type of cone senses a different range of light. Therefore the combination of light sensed by the different cones allows you to know the colour you are looking at. For example, stimulation of green and red cones makes you see green. If all three types of cone are stimulated then you see white.
If you don’t have any of the three types of cone then you will only be able to see black, white and shades of grey. But this severe form of colour vision deficiency is very rare. In fact none of the eyecare team at Tauranga Eyecare team have seen this rare form – achromatopsia.
How common is colour vision deficiency?
Colour vision deficiency affects about 1 in 12 men and 1 in 200 women. It is much more common in men because the most common form (red-green colour vision deficiency) is passed on in a gene on the X chromosome carried by females.
Colour vision deficiency means you are unable to see certain colours. There are different types of colour vision deficiency. People with colour vision deficiency do not distinguish the same differences in colour that a person with normal colour vision does. They only see four colour bands (yellow-orange, grey,blue and violet and may fine distinguishing pastel colours very difficult.
What are the causes of colour vision deficiency?
For most people with colour vision deficiency the cause is inherited (genetic) and the special code inside each cell in your body (the gene) is passed on from your parents. The most common type – red-green colour vision deficiency – is caused by an abnormal gene on the X chromosome (female chromosome) and is much more common in males.
Much more rarely colour vision deficiency can develop later in life as a result of pathology or disease.
How is colour vision deficiency diagnosed?
Colour vision deficiency is usually first diagnosed using special coloured pictures called Ishihara plates. Ishihara plates are used to assess red-green colour vision. All males are routinely screened at a young age. Note that the Ishihara test is a screening test only and the number of errors made is not an indication of the severity of the defect. It also does not pick up blue-yellow defects. At Tauranga Eyecare we have a battery of colour vision tests and have a specialised lantern for the maritime industry.
What problems can colour vision deficiency cause?
Nearly all people with colour vision deficiency can see things as clearly as other people but they cannot see certain colours clearly. If you have red-green colour vision deficiency you will not be able to clearly see any colour which has some red or green as part of the whole colour. For example, you will confuse blue and purple (because red and blue make purple).
The effects of colour vision deficiency can be variable, ranging from mild to severe. Some people with colour vision deficiency are unaware that they’ve got it and in fact may be very surprised when diagnosed.
Colour vision deficiency does not prevent from driving. Traffic lights can be distinguished by the position of the light.
Colour vision deficiency may cause difficulty and frustration at school. Colour vision deficiency can also affect the choice of certain jobs and careers. The list of careers that may not be possible for a person with colour vision deficiency includes:
- Certain grades within the armed forces.
- Civil aviation: pilots, engineers, technical and maintenance staff, air traffic controllers.
- Customs and excise officers.
- Railways: drivers, engineers and maintenance staff.
- Fire service officers.
- Hospital laboratory technicians and pharmacists.
- Workers in paint, paper and textile manufacture, photography and fine art reproduction.
If you have any concerns over colour vision or are aware of a family history our optometry team can provide further testing and advice.