The incidence of nearsightedness among students will be taken into account when assessing a school's quality of education, the Ministry of Education has said.

The new criterion was passed by the ministry earlier this month, and made public on Sunday. Education departments across the country must carry out physical education programs in primary and secondary schools to help prevent myopia, the ministry said.

"Schools must enhance physical education, guarantee students have enough rest time, reduce homework and improve classroom lighting," the circular published on the ministry's website said.

In 2002, a study found 27 percent of primary students and 63 percent of high school students were nearsighted, more than double that of three decades ago.

The ministry publishes such reports every 10 years.

Too much schoolwork and not enough outdoor activities were to blame for the increase in myopia.

Zhao Huan, 16, a Beijing high school student, said more than two-thirds of his classmates are nearsighted.

"I began to wear glasses three years ago and my eyesight has progressively got worse," Zhao said.

"People say myopia is mainly caused by genetic factors but my parents both have perfect eyesight."

The ministry said primary and high schools must guarantee at least one hour of sports a day for students.

Genetically, Asian people tend to suffer more from nearsightedness than Western people, medical experts said.

Reading at close range, watching TV and playing computer games for prolonged periods of time, while doing little or no exercise, are the major causes of myopia, the experts said.

Improper lighting and poor quality blackboards were also causes. "Sufficient sleep and a good diet can help prevent myopia," Li Lite, a professor with the China University of Agriculture, said.