Factors and hazards

Yang Yiwei, a nearsighted 18-year-old high school student in Tianjin, got her first pair of spectacles five years ago.

"She was obsessed with all types of electronic devices, whether televisions, computers, or mobile phones," said Xie Hui, Yang's mother.

The family relocated to Tianjin in 2013 when Yang became a junior middle school student. As an introverted young woman, Yang didn't like making friends in the new environment.

"She chose to stay home all day during that period, watching TV and surfing the internet," Xie said, describing how her daughter started wearing glasses.

Li said nearsightedness is caused by a combination of genetic and environmental factors, but most people with a low level of nearsightedness usually develop the condition by focusing on close objects - whether it's a book or an electronic device - for too long.

This makes the muscles in the eyes too tense to change the shape of the lens, a convex structure in the eye. If that muscular tension is maintained, the diameter of the eyeball will grow irreversibly and people will gradually develop true myopia, he said.

"True myopia cannot be cured," Li said. "It can only be rectified. So, prevention is very important."

A 2015 Peking University report on visual health said China had a nearsighted population of 450 million in 2012. Without effective prevention or control, the report warned, the number would rise to 700 million by 2020.

A large nearsighted population would have an adverse effect on the country's development in some fields, such as the military, aviation and precision instrument manufacture, the report said.

In addition, myopia, as a type of vision defect, can lead to maculopathy (a pathological condition of the area at the center of the retina that is associated with sensitive, accurate vision), cataracts and retinal detachment. It could also add to the financial burden on individuals and the whole country, it added.