Babies born in summer are more likely to become short-sighted in late life, a study has shown.
As many as a quarter of all cases of short-sightedness are caused by too great an exposure to sunlight in the first weeks of life, say eye experts.
They are advising all parents to put sunglasses on their babies during the first weeks.
Scientists had already established that over-exposure to sunlight caused shortsightedness in animals.
Researchers who compared the months in which babies were born with whether they needed glasses later on say the principle also applies to humans.
A study of almost 300, 000 young adults-the largest of its kind-showed that those born in June and July had a 25 per cent greater chance of becoming severely short-sighted than those born in December or January.
Research leader Professor Michael Belkin, of Tel Aviv University, said it was because prolonged illumination(光照) causes the eyeball to lengthen-causing short-sightedness.
Hence the more light a newborn is exposed to, the more the eyeball lengthens and the worse the short-sightedness will be.
The mechanism which lengthens the eyeball is associated with levels of melatonin(褪黑激素), a pigment (色素) which protects the skin against harmful rays of the sun.
In young babies not enough melatonin is released as protection, meaning they are more vulnerable to sunburn and changes to eyeball shape.
Sight expert Professor Daniel O'Leary, of Anglia Ruskin University in Cambridge, said "At the moment we don't know the precise cause of why light exposure affects sight, but the evidence seems to prove that it is one of the reasons for people becoming shortsighted."
if parents don't know a proper way to protect their babies' eyes
