“We know that time outdoors is protective, and so kids should spend probably up to two hours a day outside,” Hammond said.
Myopia can be corrected with glasses, laser surgery or contact lenses. Later in life, however, sufferers are more likely to develop sight-robbing conditions such as cataracts or glaucoma, the researchers said.
Experts predict that by 2050, nearly 5 billion people worldwide will have myopia. That compares to about 2 billion in 2010.
Genes have been linked to a person’s risk for the condition, but even if it has a genetic component, that doesn’t account for the dramatic increase, Hammond said.
For the study, his team collected data on nearly 2,000 twins born in the United Kingdom between 1994 and 1996.
The researchers reviewed results of eye tests, as well as social, economic, educational and behavioral data on the twins between the ages of 2 and 16. They also had questionnaires completed by parents and teachers.