In a sample survey of Rural Education Action Program jointly launched by the Chinese Academy of Sciences, Shaanxi Normal University and Stanford University, it's estimated only 10 percent of the 57 percent of China's rural middle school students who are nearsighted wore glasses in 2013.

Li Zhongliang was among the best of Shirman's first 47 students when he started teaching in Yunnan but fell behind over the semester because of nearsightedness.

"Imagine you're in a classroom and you can't see what's on the board for 12 hours a day," Shirman says.

"You get really bored, and you start misbehaving. It's like being in a prison because you can't leave either."

Li was later labeled as a "problem student" and dropped out at age 13.

"I felt extremely frustrated. I felt like I completely failed him," Shirman says.

"I knew what he needed. And I just didn't organize myself enough to get help for him in time."

Preventable problem

Vision issues can be easily diagnosed and corrected with glasses.

The main obstacles for students in remote areas to such basic services include awareness, accessibility and affordability.

Specialists who can give eye exams may be hours away.

"Spending a few hundred yuan on a pair of eyeglasses can be a major expense for the family," says Deng Zhaohua, a teacher from Hetou Middle School, which is located around 30 kilometers from Yunnan's Longling county.

"Even if students are aware they have vision problems, they still don't get timely correction because of financial reasons."

In 2012, Shirman worked with two other teachers to address the vision problems in his school. They invited a local optometrist to give eye exams. They found that a sixth of the 100 students needed glasses. But only six students had them.

Yang Fuxian was one of the students with vision problems. She was diagnosed with nearsightedness and received a pair of glasses from Education in Sight.

"The moment I put my glasses on, I knew I'm different from my peers, who don't have vision problems. I need to take better care of my eyes," the 21-year-old recalls.