Scientists have discovered strands of genetic code linked to short sight, the most common eye disorder in the world.

The findings shed light on what goes awry to make distant objects look blurred, and raises the prospect of developing drugs to prevent the condition.

Understanding the biological glitches behind short-sightedness could help researchers develop eye drops or tablets that could be given to children to stop their vision from failing as they get older.

Short-sightedness, or myopia, usually starts to manifest early on in life.

The extent to which genes are to blame varies, but for those with the worst vision, around 80% of the condition is caused by genetic factors.

Two separate studies, published in Nature Genetics journal, found variations in DNA that were more common in people with short sight. Chris Hammond, at King’s College, London, found one section of DNA on chromosome 15 was more common in people with myopia. Caroline Klaver, at Erasmus Medical Centre in Rotterdam, found another strand, also on chromosome 15, linked to short sight.

Myopia

The variations in DNA amount to misspellings in the genetic code. These alter the activity of three genes that control the growth of the eyeball and ensure light entering the eye is converted into electrical pulses inthe retina.

To find the gene, the first to be linked to short-sightedness, or myopia, the researchers compared the DNA of more than 4,000 British twins. Twins are often used in such studies because it is easier distinguish the different effects of nature and nurture.

They then confirmed their results by studying the genetics of another 13,000 British, Dutch and Australian individuals.

Some 45 per cent of Britons have the rogue gene and those who have two copies of it are almost twice as likely to be short-sighted as those who are free of it.

The gene, known as RASGRF1, is thought to play a key role in the development of the eye and the passing of visual signals to the brain for processing. When it is faulty, the eyeball may overgrow, making distant objects seem fuzzy or blurred.

Dr Chris Hammond, also of KCL, said: ‘Myopia, or shortsightedness, is the most common eye problem, affecting over a third of adults in the UK.

‘People who are extremely short-sighted carry significant risks of future vision loss. The retina can peel away from the back of the eye like wallpaper off a wall.

‘While we believe that environmental risk factors such as a lot of close work and lack of outdoor activity are implicated, we have not previously understood how people become short-sighted.

‘We hope that by understanding the mechanisms we can stop children from becoming shortsighted and stop short-sighted children from becoming more short-sighted.’

Myopia (Greek: ??????, mu?pia, “nearsightedness”), is a refractive defect of the eye in which collimated light produces image focus in front of the retina when accommodation is relaxed.

For those with myopia Visual perception, far away objects appear blurred and near objects appear clearly. With myopia, the eyeball is too long, or the cornea is too steep, so images are focused in the vitreous inside the eye rather than on the retina at the back of the eye. The opposite defect of myopia is hyperopia or “farsightedness” or “long-sightedness”—this is where the cornea is too flat or the eye is too small.

Eye care professionals most commonly correct myopia through the use of corrective lenses, such as glasses or contact lenses. It may also be corrected by refractive surgery, but this does have many risks and side effects. The corrective lenses have a negative optical power (i.e. are concave) which compensates for the excessive positive diopters of the myopic eye.

Alternative ideas and methods of treatment exist, most notably the claim that myopia is caused by excessive near sight work.