Diabetic retinopathy severity assessment using standard ETDRS fields and UWF color images: A comparative analysis

Abstract

Purpose: To assess the level of agreement between standard 7-field Early Treatment Diabetic Retinopathy Study (ETDRS) photography and ultra-widefield (UWF) color imaging in grading diabetic retinopathy (DR) severity. Methods: This retrospective study analyzed UWF color images of patients with diabetic retinopathy imaged at Tanta University Hospital between January 2024 and January 2025. UWF images were acquired using the Optos California system. A standardized ETDRS 7-field (7F) mask was applied to UWF images to simulate conventional 7F grading, followed by grading of the full unmasked UWF images. DR severity was graded independently by expert graders using ETDRS Diabetic Retinopathy Severity Scale (DRSS) levels. Graders were masked to corresponding grades between protocols. Agreement between 7F and UWF DRSS levels was assessed using weighted kappa (κw) statistics. Results: A total of 169 eyes from 94 subjects were included. Exact agreement between 7F-masked and UWF imaging was observed in 62 eyes (36.7%), while 139 eyes (82.2%) were within one DRSS step. Overall agreement between the two imaging protocols was moderate (weighted κw = 0.47). Additional peripheral retinal lesions were identified on unmasked UWF images in 123 eyes (72.8%). Among discrepant cases, 74.4% demonstrated lesions outside the 7F area, including predominantly peripheral lesions in 9.4% of eyes. Two eyes were reclassified from non-proliferative DR to proliferative DR due to peripheral neovascularization detected only on UWF imaging. Conclusions: UWF imaging demonstrates moderate agreement with standard 7-field ETDRS photography for DR severity grading but frequently identifies additional peripheral lesions that can increase disease severity. These findings highlight the diagnostic advantage of UWF imaging and caution against interchangeable use of imaging modalities in clinical practice and multicenter trials.