Precise montaging and metric quantification of retinal surface area from ultra-widefield fundus photography and fluorescein angiography

BACKGROUND AND OBJECTIVE: Accurate quantification of retinal surface area from ultra-widefield (UWF) images is challenging due to warping produced when the retina is projected onto a twodimensional plane for analysis. By accounting for this, the authors sought to precisely montage and accurately quantify retinal surface area in square millimeters. PATIENTS AND METHODS: Montages were created using Optos 200Tx (Optos, Dunfermline, U.K.) images taken at different gaze angles. A transformation projected the images to their correct location on a three-dimensional model. Area was quantified with spherical trigonometry. Warping, precision, and accuracy were assessed. RESULTS: Uncorrected, posterior pixels represented up to 79% greater surface area than peripheral pixels. Assessing precision, a standard region was quantified across 10 montages of the same eye (RSD: 0.7%; mean: 408.97 mm²; range: 405.34-413.87 mm ²). Assessing accuracy, 50 patients' disc areas were quantified (mean: 2.21 mm²; SE: 0.06 mm²), and the results fell within the normative range. CONCLUSION: By accounting for warping inherent in UWF images, precise montaging and accurate quantification of retinal surface area in square millimeters were achieved.