To see clearly, the light coming into your eye needs to be focused on the retina at the back of your eye. If your eye is too short, light focuses behind the retina and you are longsighted. People who are long-sighted have to focus more than they would do if they had perfect sight, particularly on things that are close up, but they are still able to see clearly. As children's eyes are smaller than adults' eyes, it is normal for children to be long-sighted, and this does not mean that they need glasses.

However, if a child is born very long-sighted, one eye may turn in as the child tries to focus on things. The child will need glasses to correct this and stop the turning eye becoming lazy (see later). Children who are long-sighted do not normally complain that they can't see things, but you may notice that they are having problems focusing or concentrating on things, particularly if they are close up.

If your eye is too long, light focuses in front of the retina and you are short-sighted. People who are short-sighted have difficulty seeing far away things such as the TV or board at school.

Children often become short-sighted when their eyes grow too much. Children with parents who are short-sighted are more at risk of developing the condition so we recommend that these children have their eyes examined regularly as children's eyes change as they grow.

Scientific studies have shown that children who spend time outdoors are less likely to be short-sighted, so encourage your child to spend time outdoors, but make sure you protect them from the sun.

If your eye is shaped more like a rugby ball than a football, light rays are focused on more than one place in the eye, so you don't have one clear image and things are distorted. Astigmatism often happens alongside either long- or short-sight and glasses are used to make the focus clear.

About 2-3% of all children have a lazy eye, clinically known as amblyopia. This may be because they have one eye that is much more short- or long-sighted than the other, or because they may have a squint (where the eyes are not looking in the same direction). If you notice your child appears to have a squint after they are six weeks old, you should have their eyes tested by an optometrist as soon as possible.

The sooner the child is treated, the more likely they are to have good vision. It is more difficult to treat a lazy eye if the eyesight has finished developing (usually around the age of seven). Don't expect your child to tell you if there is a problem.

The treatment will depend on what is causing the lazy eye:

• If it is simply because the child needs glasses, the optometrist will prescribe glasses to correct sight problems.
• If the child has a squint, this may be fully or partially corrected with glasses. However, some children may need an operation to straighten the eyes, which can take place as early as a few months of age.
• If the child has a lazy eye, eye drops or patching the other eye can help to encourage them to use the lazy eye to make it see better. Whether a child needs glasses or not depends on the shape and size of their eyes. Wearing glasses will not change their eye shape, and will not make your child's eyes worse. If your child has a lazy eye, wearing glasses may improve their sight permanently. Your optometrist will tell you how often and when your child should wear their glasses.

Around one in 12 men and one in 200 women has some sort of problem with their colour vision. If you suspect that your child has a colour-vision problem, or if there is a family history of colour-vision problems, ask your optometrist about it.

There is no cure, but you can tell your child's teachers, so that they are aware of the problem.

Colour Blindness Test