Scientists believe they may be able to discover why children who spend much of their time indoors rather than playing outside are more likely to develop short-sightedness following a breakthrough study into the genetics of myopia.

More than two dozen genes have been linked to an increased risk of developing myopia, a finding that may finally allow researchers to understand why children today are more likely to become short-sighted than children in the past.

Myopia now affects about one in three people in the West and up to 80 per cent of people in Asia. In some countries in the Far East as many as 90 per cent of children are short-sighted, compared to less than 20 per cent a couple of decades ago.

Although short-sightedness tends to run in families and has a strong inherited component, the explosive increase in the condition over recent years has been linked with an increase in the time that children spend indoors either studying or playing computer games and watching TV, scientists believe.

A study of more than 45,000 people from Europe and Asia has identified 24 new genes that appear to be involved in triggering the onset of myopia. It has also confirmed the role of two further genes that were already suspected of being involved with short-sightedness, the scientists said.

“We already knew that myopia, or short-sightedness, tends to run in families, but until now we knew little about the genetic cause. This study reveals for the first time a group of new genes that are associated with myopia,” said Professor Chris Hammond of King’s College London, who led the study published in Nature Genetics.

“Carriers of some of these genes have a tenfold increased risk of developing the condition…It is an extremely exciting step forward which could potentially lead to better treatments or prevention in the future for millions around the world,” he said.

The human eye

Myopia is caused when the eyeball grows too long, causing light to be focussed just short of the light-sensitive retina at the back of the eye. Ambient light levels in childhood are thought to control the growth of the eyeball, with low light leading to myopia, Professor Hammond said.

Children who develop myopia when they are very young are more likely to suffer vision problems in later life compared to children who were not short-sighted. In extreme case, myopia can lead to serious vision problems after mid-life, such as glaucoma, detached retina and blindness caused by macular degeneration.

“The more serious problems are in middle age when there is a significant risk of visual loss. The main reason seems to be that the eyeball is longer and the retina is stretched over a wider area,” Professor Hammond said.

The discovery of 26 genes that each play a small but significant role in myopia opens the way to understanding the biochemical pathways that may lead to the overgrowth of the eyeball, and ways of preventing it, he said.

“Currently, possibilities to reduce progression of myopia are very limited. While one drug, called atropine, may reduce progression, it dilates the pupil and causes problems with light sensitivity and difficulty with reading,” Professor Hammond said.

“We’re finally trying to understand the mechanism involved that leads to short sight, which is something we do not see in other animals. The ‘stop signal’ that prevents the eye ball from continuing to grow is very powerful and we know to know how it works,” he said.

The interaction of the environment with genes is important in determining the risk of developing myopia, which has been linked with education, urbanisation and outdoor activity, Professor Hammond said.

“There is some data to suggest that short-sightedness is becoming more common in children in the UK. It’s very likely that sitting indoors on your computer games is not as good as being outdoors looking at the blue yonder,” he said.