Ka Wai Kam1,2, Srinivas K Rao3, Alvin L Young4,5. 1. Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong SAR, China. 2. Department of Ophthalmology and Visual Sciences, Prince of Wales Hospital, Hong Kong SAR, China. 3. Darshan Eye Care & Surgical Centre, Chennai, India. 4. Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong SAR, China. youngla@ha.org.hk. 5. Department of Ophthalmology and Visual Sciences, Prince of Wales Hospital, Hong Kong SAR, China. youngla@ha.org.hk.