Sunday, July 8, 2012

Colour Blindness

Colour blindness means that a person cannot 'see' some colours, or sees them differently from other people. Very few people who are colour blind are 'blind' to all colours. The usual colours that they see differently are greens, yellows, oranges and reds. It is important to diagnose colour blindness in children as a child who is colour blind can have difficulty at school, especially in the early years when many activities use colours, such as drawing and sorting blocks. Using a computer can be a problem too for someone who is colour blind.
When do children begin to recognize colours?
All of the cells and nerve pathways in the eye and the brain are present from birth.
Very young children can see the difference between colours if they are not colour blind. They do not see colours very well at first but soon begin to like colours, especially bright colours.
Many children are able to recognise and name colours by the time they are 4.
What is colour blindness?
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 cells, '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. Using rod cells we can 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.
Red-green colour blindness is usually inherited, and occurs in about 8% of males and only about 0.4% of females. Only 5% of people who are colour-blind have blue colour blindness, and this is equal in males and females. Colour blindness can be due to a change in the chromosome during development. It is not always inherited.
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.
In the classroom, blocks or other teaching tools may be colour coded as well as being of different size. A child with colour vision problems may have to rely only on size differences alone.
On a computer screen, colour is often used for highlighting important words and the only way some children may know that the words are important is because the shade is slightly lighter or darker.
Some workplaces 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 mangoes are ripe.
What can be done?
All boys should have their colour vision tested when other people in the family are known to have colour vision problems. This testing can be done most easily when a child starts to know numbers (around the time that he starts school) or when he is older. If people on both side of the family are known to have colour vision problems, all the girls should also be tested.
In any group of about 20 boys, it is likely that one or two will have a colour vision problem. If, at school, a lot of tasks are colour coded, these boys may have learning difficulties, so it is worth knowing if a child has a colour vision problem, so that ways for him to learn can be found that do not rely on colour.
Colour vision testing is done using specially designed charts (including ones called Ishihara colour plates).
This column has been written by medical specialists at Apollo Hospitals India. This is a health awareness initiative of AsiaMed Connect in partnership with Apollo Hospitals India and with the cooperation of The Independent in Bangladesh. For free online medical consultation readers may send emails to .


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