Precise Measurement of Retinal Vascular Bed Area and Density on Ultra-wide Fluorescein Angiography in Normal Subjects

Abstract

To characterize and quantify the total retinal vascular bed area (RVBA) and vascular density (VD) in normal eyes using stereographically corrected ultra-wide-field (UWF) fluorescein angiography (FA). Cross-sectional study. Fifty-nine eyes of 31 normal subjects with no evidence of ocular disease underwent FA using the Optos 200Tx (Optos plc, Dunfermline, United Kingdom). Central and peripheral-steered FA images were montaged and stereographically projected. The early-phase FA was used to extract the retinal vasculature as a binary mask. Two independent, masked reading center-certified graders delineated the peripheral edge of the total retinal area (TRA) on a middle-phase frame. The RVBA and TRA were computed automatically in mm2 using software provided by the manufacturer. The VD was calculated by dividing RVBA by TRA. The mean RVBA was 42.3 ± 14.8mm2 for the entire retina, with no difference between male and female subjects (P= .439) or between right and left eyes (P= .407). The mean VD was 4.3% ± 1.4% for the entire retina, with no difference based on sex (P= .629) or laterality (P= .426). A negative correlation was observed between age and both RVBA and VD (RVBA: R=-0.6, P < .001; VD: R=-0.52, P < .001). Pairwise comparisons showed that subjects aged >65 years had smaller RVBA and VD than those younger than 50 years for the entire retina and in all quadrants. RVBA and VD can be extracted from UWF FA images using automated processing techniques and may provide a reliable alternative to measures such as nonperfusion area.