RT Journal Article SR Electronic T1 Peripheral extent of the choroidal circulation by ultra-widefield indocyanine green angiography in healthy eyes JF British Journal of Ophthalmology JO Br J Ophthalmol FD BMJ Publishing Group Ltd. SP bjophthalmol-2020-316412 DO 10.1136/bjophthalmol-2020-316412 A1 Aditya Verma A1 Jyotsna Maram A1 Ahmed Roshdy Alagorie A1 Jano van Hemert A1 Darren J Bell A1 Michael Singer A1 Dana Keane A1 Jessica Carnevale A1 Muneeswar Nittala A1 SriniVas Sadda YR 2020 UL http://bjo.bmj.com/content/early/2020/08/22/bjophthalmol-2020-316412.abstract AB Aim To analyse the peripheral extent of choroidal circulation using ultra-widefield (UWF) indocyanine green angiography (ICGA) in healthy eyes.Methods UWF ICGA images of 55 eyes of 36 healthy subjects were captured using the Optos California (Optos, Dunfermline, United Kingdom) in this prospective observational study. Images were analysed to locate the peripheral extent of the visible choroidal circulation, and the boundary was marked in ImageJ (v1.52). Each pixel annotated as the border of the choroidal circulation was projected individually to its anatomically correct location on the three-dimensional model eye, and spherical trigonometry was applied (using the Optos software) to calculate its respective radial distance from the centre of the optic disc in metric units (corrected by stereographic projection) for each quadrant.Results The mean area of the peripheral extent was estimated to be 893.2 mm2 (95% CI: 844.2 to 942.3 mm2). The mean distance (range) of this boundary from optic nerve centre was 18.22 mm (95% CI: 14.0 to 23.14 mm). Multiple regression analysis with age, gender, axial length or ethnicity showed no relationship. There was excellent inter-grader reproducibility, with intraclass correlation coefficients of 0.95 (95% CI: 0.80 to 0.99, p<0.001) for distance and 0.99 (95% CI: 0.988 to 0.999, p<0.001) for area measurements.Conclusions The peripheral choroidal boundary may be defined using UWF ICGA. Knowledge of the normal extent and its variability is essential to understand the impact of disease on the choroidal vasculature.