Colour vision deficiency

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.

Outlook

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.