[1] Univ Ulster, Cathedral Eye Clin, Belfast, Antrim, North Ireland
[2] Univ Ulster, Biomed Sci Res Inst, Coleraine, Londonderry, North Ireland
[3] Royal Victoria Hosp, Dept Ophthalmol, Belfast, Antrim, North Ireland
[4] Univ Cambridge, Fac Biol, Cambridge CB2 1TN, Cambs, England