Marcus Ang1,2,3,4, Chelvin Ca Sng3,4,5. 1. Cornea and External Eye Diseases Department, Singapore National Eye Centre, Singapore. 2. Ophthalmology and Visual Sciences Department, Duke-NUS Medical School, Singapore. 3. Singapore Eye Research Institute, Singapore. 4. Moorfields Eye Hospital, London, UK. 5. National University Health System, Singapore.