Genetic clues to the cause of short-sightedness have been uncovered that could lead to new treatments.
Scientists discovered 24 new genes that help trigger the currently incurable condition.
They include genes involved in brain and eye tissue signalling, eye structure, and eye development.
Carriers of the highest risk genes have a 10-fold increased likelihood of developing short-sightedness, or myopia.
An estimated 30% of Western populations and up to 80% of Asian people suffer from some degree of short-sightedness.
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The problem occurs when the eye grows too long and light is focused in the wrong place, in front of the retina's photoreceptors. This results in a blurred image.
The error can be corrected with glasses or contact lenses, but high levels of myopia are associated with an increased chance of retinal detachment, glaucoma and macular degeneration.
Although myopia is highly heritable, information about the genes responsible has been lacking.
To investigate the genetic causes of short-sightedness, scientists analysed data on more than 45,000 individuals.
They found 24 new genes for the trait, and confirmed the identity of two discovered previously.
Lead scientist Professor Chris Hammond, from the Department of Twin Research and Genetic Epidemiology at King's College London, said: "We already knew that myopia - or short-sightedness - tends to run in families, but until now we knew little about the genetic causes.
"This study reveals for the first time a group of new genes that are associated with myopia and that carriers of some of these genes have a 10-fold increased risk of developing the condition.
"Currently myopia is corrected with glasses or contact lenses, but now we understand more about the genetic triggers for the condition we can begin to explore other ways to correct it or prevent progression. It is an extremely exciting step forward which could potentially lead to better treatments or prevention in the future for millions around the world."
The research is reported today in the journal Nature Genetics.
Environmental factors such as reading, lack of outdoor exposure, and a higher level of education are also known to raise the risk of myopia.
The condition is more common among people living in urban areas. How these external influences might be affected by people's genetic make-up will be investigated next by Prof Hammond's team.
Currently one drug, atropine, is available that may reduce the progression of myopia. However, it dilates the pupils and causes problems with light sensitivity and reading. New options are badly needed, say the scientists.