Department of Ophthalmology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China; Key Laboratory of Ocular Fundus Diseases, Chinese Academy of Medical Sciences, Beijing, China. Department of Ophthalmology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China; Key Laboratory of Ocular Fundus Diseases, Chinese Academy of Medical Sciences, Beijing, China. Electronic address: chenyx@pumch.cn.