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Causes of short-sightedness

NHS Choices Medical Reference

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The exact cause of short-sightedness (myopia) is unknown, but it's thought to be the result of a combination of genetic and environmental factors that disrupt the

normal development of the eye.

How the eye works

Light passes through the cornea and into the lens, where it is focused onto the retina at the back of the eye to create an image. The image is converted into an electrical signal, which is transmitted to the brain via the optic nerve.

To produce a perfectly clear image, the cornea should be smooth and evenly curved, and the eye needs to be the right length. However, in most cases of short-sightedness the eye has grown too long. In a few people, the cornea may be more curved than normal.

These structural deformities mean that when you look at distant objects, the light is not focused directly onto your retina but a short distance in front of it. This results in the image that is sent to your brain being blurred.

Inheriting short sight

Short-sightedness is known to run in families. Children with one short-sighted parent have a greater risk of developing myopia of about a one in three chance. If both parents are short-sighted, the risk increases further to one in two.

Genetic research has identified 26 genes linked to short-sightedness. These are responsible for the eye's structure and development and signalling between the brain and the eye.

Close work

Environmental factors, such as reading, writing and using a computer, can increase your risk of developing short-sightedness.

One study found that children who read for 30 minutes or more each day were one-and-a-half times more likely to develop myopia than children who didn't read for this period of time.

Research has also shown that children who spend time doing outdoor activities, such as playing sports, are less likely to become short-sighted and existing short-sightedness may progress less quickly.

It is thought that this protective effect could be associated with the higher light levels outside than inside, and the fact that you are not constantly focusing on near objects.

An "everything in moderation" approach is recommended. Although children should be encouraged to read, they should also spend some time away from reading and computer games each day doing outdoor activities.

Future research

Research is currently underway to investigate how environmental factors affect the genes linked with short-sightedness. 

At the moment, glasses and contact lenses are the main treatments for short-sightedness. However, now more is understood about the role genetics plays in the condition, it may be possible to develop new treatments to correct the condition or prevent it getting worse.

Medical Review: November 28, 2013

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