Quantitative fundus autofluorescence in age-related macular degeneration

Fundus autofluorescence captures the fluorescence of the retina, specifically the retinal pigment epithelium (RPE). Within the RPE, fluorophores, including lipofuscin, melanolipofuscin, and melanosomes, fluoresce when excited by light of varying wavelengths. Quantitative fundus autofluorescence (QAF), which has been implemented using blue excitation light, enables mapping and quantifying lipofuscin and melanolipofuscin fluorescence. This is achieved by using a reference bar to standardize measurements. The technical functionality of QAF relies on repeatability and high image quality. Multicenter studies, however, indicate variability. Age-related lens opacities also affect QAF, necessitating individualized correction formulas for accuracy. Accordingly, this review focuses on the development and application of QAF, addressing technical considerations and its relevance to structural and cellular changes in age-related macular degeneration (AMD), and highlighting how QAF can provide clinically meaningful information for AMD diagnosis and therapy monitoring. In AMD, numerous independent studies have found reduced autofluorescence at the posterior pole and as AMD progresses autofluorescence further decreases. Typical AMD lesions, such as subretinal drusenoid deposits, have been associated with significant QAF reduction. On a cellular level, granule aggregation and degranulation are identified as histological correlates. Subcellularly, technologies like serial block-face scanning electron and structured illumination microscopy have revealed a reduced lipofuscin volumetric density and RPE dysmorphia associated with AMD's reduced autofluorescence. New software tools enhance QAF's potential for detailed lesion analysis. Future advancements in QAF include integrating new excitation wavelengths and combining quantified emission spectra and fluorescence lifetimes to improve early detection of AMD-related changes. Despite challenges, QAF continues to evolve, promising better insights into retinal health and disease.