Researchers say the critical period for developing myopia is during elementary and middle school. They suggest that when children are in school, they should also spend at least 2 hours a day outside.
An analysis of data from around 14,000 people finds that those carrying a variant of a gene called APLP2, were five times more likely to have myopia (nearsightedness) if they had spent an hour or more reading each day when they were children.
However, people who carried the gene variant but did not spend so much time reading when they were children had no additional risk of developing myopia.
The study, led by vision researchers at Columbia University Medical Center in New York, NY, is published in the journal PLOS Genetics.
Myopia is an eye condition where people can only see sharp images when they look at near objects, with objects in the far distance appearing blurred. This is usually caused by the eye being elongated, so that when looking at distant objects, the focal point of the projected image inside the eye is in front of the retina and not on it.
The researchers note that myopia is the most common vision disorder worldwide and is reaching epidemic proportions in some regions. For instance, in the US, prevalence of myopia has climbed from 25% to 44% of the adult population in the last 30 years. In some parts of Asia, as many as 80% of young adults are affected.
Research shows myopia is a major risk factor for potentially blinding eye disorders such as cataracts, glaucoma and retinal detachment. The risk of developing these disorders is comparable to that of high blood pressure for stroke and heart attack, the authors note.
'First evidence of gene and environment interaction in myopia'
Lead author Dr. Andrei Tkatchenko, Assistant Professor of Ophthalmic Sciences, says that for several decades we have suspected, but lacked hard proof, that a mix of genes and environmental factors - such as doing lots of close work like reading - leads to myopia. However, he notes their findings are "the first known evidence of gene-environment interaction in myopia."
He and his colleagues point out that while they do not how the APLP2 variant leads to myopia, they suspect it has something to do with increased production of APLP2 protein, which may cause the eye to elongate.
They found mice with hardly any APLP2 protein in their eyes that spent time in environments that mimic reading were less likely to develop myopia.
"By reducing the level of APLP2 in the eye, you can reduce susceptibility to environmentally induced myopia," Dr. Tkatchenko says. "This gives us an opportunity to develop a therapy to prevent myopia in everyone, regardless of the APLP2 variant they carry."
Such a prospect is still a long way off, however, as researchers are yet to discover how to reduce APLP2 in humans. Such treatment would also only work in young children whose eyes had not yet started to elongate.
Meanwhile, Dr. Tkatchenko urges parents to ensure their children spend time outdoors to reduce their risk of developing myopia.
"We pretty much know all the environmental risk factors: time spent reading increases the risk, while time spent outdoors reduces it," he notes, and concludes:
"The critical period for myopia development is during elementary and middle school, so when kids are in school, make sure they also spend at least two hours outdoors each day."
In the following sequence of three videos, Dr. Tkatchenko summarizes the study, advises parents on what they can do to help prevent nearsightedness in their children, and explains how myopia develops.
Meanwhile, from another study published earlier this year, Medical News Today learned that cataracts may be treatable with eye drops instead of surgery. Using eye drops containing a steroid that dissolves the protein clumps that cause the lens of the eye to go cloudy, researchers successfully treated cataracts in dogs.