Yang's spectacles enabled her to fully engage in classes.

"Otherwise, I'd feel agitated and be reluctant to pay attention to the teachers."

Most of her family's income is spent on Yang's and her two sisters' educations.

She's an accounting major at Yunnan University's Dianchi College.

"The timely eye care I received helped me become a university student," she says. "Without that, I might have become too bored and have had no desire to study."

Uncorrected refractive errors are the leading cause of visual impairment worldwide and cause a loss of educational opportunities for at least 13 million children ages 5 to 15.

Adults, too, experience exclusion from productive working lives because of their inability to see well, the World Health Organization says.

Columbia University graduate Sam Waldo also got involved in the program in 2012.

He believes uncorrected visual impairments affect not only students' grades but also their future employment. And their attitudes toward vision correction will also affect their children.

"People always talk about teaching someone how to fish versus giving them a fish," Waldo says. "What we're doing is more like giving someone a fish, but we also try to teach them how to fish. It's a really small cost to pay for a multifaceted, lasting, long-term impact."

Looking forward

Offering students eyeglasses is only a temporary solution to vision problems. The program must combine eye care with professional training and education to become more sustainable.

The team began working on the project full time from 2014. They started cooperating with a public hospital in Shangri-La a year later.

They've provided eye care for nearly 90,000 students in Yunnan's Longling and Shidian counties, which are officially recognized as impoverished according to the national standard.

"About 17 percent of students with vision problems were offered eye examinations and free eyeglasses with their parents' permission," Education in Sight's country director Yang Jin says. "We also work with teachers to educate students about vision problems."