Effect of Providing Free Glasses on Children's Educational Outcomes in China: cluster randomized controlled Trial - Xiaochen Ma; Zhongqiang Zhou; Hongmei Yi; Pang, Xiaopeng; Yaojiang Shi; Qianyun Chen; Mirjam E. Meltzer; Saskia Le Cessie; Mingguang He; Scott Rozelle; Yizhi Liu; Nathan Congdon* (BMJ, 2014)