Alastair K Denniston1, H Nida Sen2. 1. University Hospitals Birmingham NHS Foundation Trust, Birmingham B15 2GW, UK; Academic Unit of Ophthalmology, Institute of Inflammation and Ageing, University of Birmingham, UK. Electronic address: a.denniston@bham.ac.uk. 2. National Eye Institute, National Institutes of Health, Bethesda, Maryland, USA.