[1] Univ Oxford, Nuffield Dept Clin Anaesthesia, Oxford, England
[2] Aneurin Bevan Univ Hlth Board, Dept Anaesthesia, Newport, Wales
[3] Univ Hosp Birmingham NHS Fdn Trust, Birmingham, England
[4] Univ Birmingham, Coll Med & Dent Sci, Birmingham, England
[5] UCL, Inst Ophthalmol, Fac Brain Sci, London, England
[6] Moorfields Eye Hosp NHS Fdn Trust, NIHR Biomed Res Ctr, London, England