Babies born in the summer months have a greater chance of being nearsighted and requiring glasses than those born in the winter, a new study has found.

"It is probably a long-term effect of early-life exposure to natural light that increases the chances of a child becoming short-sighted," study co-author Michael Belkin of Tel Aviv University's Goldschleger Eye Research Institute said in a release.

Scientists suggest that early-life exposure to natural light could be one cause of severe nearsightedness.
(CBC)

For the study, scientists at Tel Aviv University's Goldschleger Eye Research Institute examined the files of 276,911 adolescents between 2000 and 2004.

They classified nearsightedness into three categories: mild (between –0.75 and –2.99 diopters), moderate (between –3 and –5.99) and severe (–6 or worse). The amount of daylight per day was also broken into four "photoperiods" of 90 to 91 days each.

Those born in June or July have a 24 per cent greater chance of becoming severely myopic, or nearsighted, than those born in December or January, according to the study, published in the August issue of the clinical eye journal Ophthalmology.

In terms of prevalence, 9.2 per cent of severe myopia and 2.6 per cent of moderate myopia cases occurred in June and July, while 8.4 per cent of severe and two per cent of moderate cases occurred in December and January.

The study notes that severe and moderate myopia were significantly more prevalent in people born in months with longer photoperiods than in those born in shorter ones. As well, it found that the longer the photoperiods, the greater the person's chance of being nearsighted.

"Such findings might suggest that the amount of light exposure generates a biological signal that can influence the emmetropization process [the stage of life when the length of the eye and its focal ability are balanced out]," Belkin said.

The authors stress that myopia can be caused by other factors — such as genetics —and that only 2.2 per cent to 5.6 per cent of severe myopia can be attributed to the season of birth or perinatal light.