1. Laura Cushley is a PhD Candidate at the Centre for Public Health, Institute of Clinical Sciences A, Grosvenor Road, Belfast, BT12 6BA; Neil Galway is a Lecturer in the School of Natural and Built Environment, Stranmillis Road, Belfast, BT9 5AG; Tunde Peto is a Professor of Clinical Ophthalmology in the Centre for Public Health, Institute of Clinical Sciences A, Grosvenor Road, Belfast BT12 6BA; all at Queen’s University Belfast;.