Declaration of interest
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.
Funding
The National Institute for Health Research and Biomedical Research Centre at Moorfields Eye Hospital and the UCL Institute of Ophthalmology (London, UK), Fight For Sight (London, UK), Moorfields Eye Hospital Special Trustees (London, UK), the Foundation Fighting Blindness, and Rosetrees Trust (Edgware, UK) provided funding for this study.