Colour blindness
eye; vision; blind; colour; color; Ishihara; blindness; retina;
Contents
About one in 12 boys is colour blind (8%), and 1 in every 400 girls (0.4%), so in each school class there are likely to be at least one or two people who are colour blind. Because they are colour blind from birth most people do not know that they are colour blind. They don't know that other people see things differently. Being colour blind can cause difficulties when it is important to be able to see lots of colours, such as on a computer screen or in art classes.
What is colour blindness?
The words 'colour blindness' are misleading. People who cannot see all colours are not 'blind' - they can see things as clearly as people who are not 'colour blind'.
- Colour blindness means that a person cannot 'see' some colours, or sees them differently to other people.
- Very few people who are colour blind are 'blind' to all colours. The usual colours which they see differently are greens, yellows, oranges and reds.
Colour blindness arises from the structure of the eye...
- In the retina at the back of the eye (the part of the eye that picks up light coming in), there are two types of light-sensitive cells called 'rod cells' and 'cone cells', and these react differently to light.
- Rod cells are very sensitive to light, and they can react to even very faint light such as light from a star in a hazy night sky, but they do not 'see' different colours. Rod cells allow us to see things around us at night, but only in shades of black, grey and white.
- Cone cells react to brighter light, and they help us to see the detail in objects. They also pick up colours.
- There are three types of cone cells; ones that pick up red light, others green and others blue.
- By combining the messages from each set of cone cells, we get the wide range of colours that we can normally see.
- Someone who is colour blind lacks one or more of these types of cone cells.
Who is colour blind?
- Red-green colour blindness is usually inherited. The genes that lead to red-green colour blindness are on the X chromosome (males have only one of these and females have two).
- If a mother 'carries' the gene for red-green colour blindness (one normal and one altered gene) she will not have a colour vision problem. About 50% of the sons of women who are carriers will be colour blind (although in any family it may not be 50% because the distribution of the genes is random).
- A daughter will not normally be red-green colour blind unless her mother is a carrier and her father is colour blind, but about 50% of daughters of women who are carriers will also carry the gene.
- Only 5% of people who are colour blind have blue colour blindness, and this is equal in males and females, because the genes for it are on a different chromosome (chromosome 7).
- Colour blindness can be due to a change in the chromosome during early development. It is not always inherited.
What problems can it cause?
- Many tasks that we do each day rely on us being able to separate things by their colour. If people are not able to see the difference in colour, they have to rely on other differences which may be harder to pick.
- For example, a person may only be able to tell red and green traffic lights apart by their position (red above green). In normal daylight this may be easy to do, but on a dark, wet night it may be much more difficult to know which is which. Similarly it may be difficult to notice a red brake light on a car.
- Because of this, there may be restrictions on driving permits.
- People with certain kinds of red-green colour blindness may be able to get a car driver's licence, but not a commercial driver's licence, or they may have restrictions preventing them from driving at night.
- In the classroom, some teaching tools may be colour-coded as well as being of different size. A child with colour vision problems may have to rely on size differences alone.
- On a computer screen, colour is often used for highlighting important words, and the only way some people may know that the words are important is because the shade is slightly lighter or darker.
- Some 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).
- Most everyday things can be done without colour vision being a problem, but some people with colour vision problems say they have some annoying difficulties, such as not being able to see whether fruit such as apricots are ripe.
What you can do
- Boys should have their colour vision tested when other people in the family are known to have colour vision problems. If people on both sides of the family are known to have colour vision problems, the girls should also be tested.
- Colour vision testing can be done by ophthalmologists (eye specialists) and optometrists (opticians) using specially designed charts (including ones called Ishihara Colour Plates). Some school health services and some doctors will also be able to test colour vision.
- After a colour vision problem is found, further testing might be needed to tell just exactly what the problem is, because this can affect whether the person will be able to do certain jobs, or be able to get certain types of driving licences.
- There are many sites on the Internet which have some colour vision checking charts (see the link below), but they cannot be relied on like special test charts printed on paper (which have very carefully shaded as well as coloured spots, lines or other objects). It is best to get checked face-to-face.
Helping people who are colour blind
- It usually helps people to know why they are having problems when others are able to do something easily. They may have begun to think that they are 'stupid', when their eyes just work differently to others.
- If teachers know that a student is colour blind, they may be able to choose ways of teaching and learning that do not need the student to pick colour differences.
Resources
The information on this site should not be used as an alternative to professional care. If you have a particular problem, see a doctor, or ring the Youth Healthline on 1300 13 17 19 (local call cost from anywhere in South Australia).