People who are colour blind usually have difficulty with the colours green, yellow, orange and red. Colour blindness is inherited and is caused by a lack of specific colour-sensitive cells in the eye. More boys than girls are affected by colour blindness.
People who are colour blind 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.
The term ‘colour blindness’ is misleading. A more precise term is colour vision deficiency (CVD). People who can’t see all colours can still see things (other than colour) as clearly as people who are not colour blind.
Very few people who are colour blind are blind to all colours. The usual colours that people have difficulty with are greens, yellows, oranges and reds.
Eye cells 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, there are two types of cells:
- 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 colour blind 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.
Inheritance of colour blindness
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 colour blind 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 aircraft, demand that their workers have normal colour vision. Other occupational groups will not allow a worker who is colour blind 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 while in the early years of school.
Colour vision testing can be done by ophthalmologists (eye specialists) and 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.
Treatment for colour blindness
There is generally no treatment to cure colour blindness. However, certain types of tinted filters and contact lenses may help a person to distinguish different colours better.
Optometrists can supply a singular red-tint contact lens to wear on the dominant eye. This may enable the wearer to pass some colour blindness tests, but they have little practical use.
Where to get help
- Your doctor
Things to remember
- People who are colour blind 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.
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Joanna Briggs Institute
Fact sheet currently being reviewed.
Last reviewed: February 2012
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