1. Zhejiang Provincial Center for Disease Control and Prevention, Hangzhou, P. R. China
2. Northwestern University School of Medicine, Chicago, Illinois, USA
3. Department of Ophthalmology, The Central Hospital of Jinyun County, Jinyun, Zhejiang Province, P. R. China
4. Department of Ophthalmology, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, P. R. China
5. Center for Preventive Ophthalmology and Biostatistics, Department of Ophthalmology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA