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Colour Blindness or Colour Deficiency?

People who are colourblind can’t see some colours or see them differently from other people. Colour blindness is inherited, and affects more boys than girls. Out of 20 boys, it is likely that one or two will have a colour vision problem – about 8% of the male population, compared to less than 0.5% of the female population.

The term colour blindness is misleading. A more precise term is colour vision deficiency (CVD). That is because 99% of all colorblind people are not really color blind but color deficient. Often people who are colour deficient, are not even aware that they are so, because they can’t easily compare what they see to what others are seeing.

It is also very rare to be blind to all colours. The usual colours that people see differently are yellows, greens, oranges and reds.

Eye anatomy and vision

All the cells and nerve pathways in the eye and brain are present from birth. In the retina, at the back of the eye, the two types of cells are:

  • Rod cells – these are sensitive to light, but they do not see different colours. We use rod cells to see things around us at night, but only in shades of black, grey and white.
  • Cone cells – these react to brighter light and help us to see detail in objects. They also pick up colours. There are three types of cone cell, which pick up red, green and blue light respectively. By combining the messages from each set of cone cells, we get the wide range of colours that we normally see. Someone who is colourblind lacks one or more of these types of cone cells.

Symptoms of colour blindness in children

The signs that your child may be colour blind include:

  • difficulties recognising and identifying different colours beyond the age of around four years
  • the inability to separate things by their colour

The symptoms are often so mild that some children do not know they are colour blind or deficient. Parents may find signs of colour blindness when children are learning their colours.

Inheritance of colour deficiencies

Colour blindness is most commonly a genetic condition. Some colour blindness is genetically inherited, while other colour blindness arises as a result of a genetic change (mutation) during development.

Colour blindness can also arise as a result of trauma that causes brain or retinal damage, degenerative eye disease and other causes.

Red–green colour blindness
Red–green colour blindness is usually inherited. It occurs in about eight per cent of males and only about 0.4 per cent of females. This is because the genes that lead to red–green colour blindness are on the X chromosome (sex-linked).

Males have only one X chromosome and females have two. In females, a functional gene on only one of the two X chromosomes is sufficient to produce normal colour vision.

Blue–yellow colour blindness

Only five per cent of people who are colourblind have blue-yellow colour blindness. This is equal in males and females, because the genes for it are located on a non-sex chromosome (Chromosome 7).

Non-inherited genetic colour blindness

Colour blindness is not always inherited. It can also be due to a chromosomal change (mutation) during development.

Challenges of colour blindness

Many tasks that we do each day rely on us being able to separate things by their colour. There are varying degrees of colour vision deficiency, and the degree of intensity of the light and the nearness of the object can also affect colour vision ability.

If people are not able to see the difference in colour, they have to rely on detecting other differences. For example, a person may only be able to tell red and green traffic lights apart by their position (red above green). On a dark, wet night this may be difficult to do.

Driving and colour blindness

Many people with red–green colour blindness will be able to get a car driver’s licence, but may not qualify for a commercial driver’s licence or may have restrictions that mean they cannot drive at night.

Most people who are colour blind can identify the difference between the red and green lights used in modern traffic lights. Those who cannot may check the position of the lights that are lit – red/stop is always at the top.

Occupations and colour blindness

Certain occupations, such as piloting an aircraft, demand that their workers have normal colour vision. Other occupational groups will not allow a worker who is colourblind to do certain work – for example, where wiring or warning lights are colour coded.

Diagnosis of colour blindness

If a lot of tasks at school are colour coded, children with colour vision problems may develop learning difficulties. It is often recommended that all children, especially boys, have a routine colour vision check with your optometrist while in the early years of school.

Colour vision testing can be done by optometrists, using specially designed charts. Some school health services will also be able to test children’s colour vision.

If a colour vision deficiency is found, further testing might be needed to tell exactly what the nature of the deficiency is, as this will affect whether the person will be able to do certain jobs or be able to get certain types of driving licences.

Any child who is found to be colour blind should be told that colour blindness is not a disease.

Things to remember

People who are colourblind usually have difficulty with the colours green, yellow, orange and red.
Colour blindness is usually inherited and affects more boys than girls.
Colour blindness is caused by a lack of particular colour-sensitive cells in the back of the eye.

If you have any further questions relating to colour deficiency or would like to be tested for it, please call or email us to make an appointment.

This text has been adapted from better health.gov.vic.au

Click here for 50 Facts about colour vision


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