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.
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.