9He M, Zeng J, Liu Y, et al. Refractive error and visual impairment in urban children in southern China. Invest Ophthalmol Vis Sci, 2004,45(3) :793-799.
10Zhao J, Mao J, Luo R, et al. The progression of refractive error in school-age children: Shunyi district, China. Am J Ophthalmol, 2002, 134(5):735-743.
