1 Department of Ophthalmology, National University Hospital, Singapore, Republic of Singapore; Department of Ophthalmology, National University of Singapore, Singapore, Republic of Singapore.
2 Moorfields Eye Hospital, London, UK.
3 Department of Ophthalmology, St. Thomas' Hospital, London, UK.
4 Moorfields Eye Hospital, London, UK; UCL Institute of Ophthalmology, London, UK. Electronic address: keith@keithbarton.co.uk.