20. Zhan, M. Z., Saw, S. M., Hong, R. Z., Fu, Z. F., Yang, H., Shui, Y. B., Yap, M. K., and Chew, S. J. (2000) Refractive errors in Singapore and Xiamen, China--a comparative study in school children aged 6 to 7 years. Optom Vis Sci 77, 302-308

20. Zhan, M. Z., Saw, S. M., Hong, R. Z., Fu, Z. F., Yang, H., Shui, Y. B., Yap, M. K., and Chew, S. J. (2000) Refractive errors in Singapore and Xiamen, China--a comparative study in school children aged 6 to 7 years. Optom Vis Sci 77, 302-308