2 Clinical Trials and Evaluation Unit, School of Clinical Sciences, University of Bristol, Bristol Royal Infirmary, Bristol, United Kingdom.
3 Belfast Reading Centre, Queens University Belfast, Royal Victoria Hospital, Belfast, United Kingdom.
4 Department of Ophthalmology, Queens University Belfast, Belfast, United Kingdom.
5 Department of Ophthalmology, Queens University Belfast, Belfast, United Kingdom; Centre for Public Health, Queen's University of Belfast, Belfast, United Kingdom.
6 Department of Eye and Vision Science, Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, United Kingdom. Electronic address: s.p.harding@liv.ac.uk.