Clinical applications of fundus autofluorescence in retinal disease

Abstract

Fundus autofluorescence (FAF) is a non-invasive retinal imaging modality used in clinical practice to provide a density map of lipofuscin, the predominant ocular fluorophore, in the retinal pigment epithelium. Multiple commercially available imaging systems, including the fundus camera, the confocal scanning laser ophthalmoscope, and the ultra-widefield imaging device, are available to the clinician. Each offers unique advantages for evaluating various retinal diseases. The clinical applications of FAF continue to expand. It is now an essential tool for evaluating age related macular degeneration, macular dystrophies, retinitis pigmentosa, white dot syndromes, retinal drug toxicities, and various other retinal disorders. FAF may detect abnormalities beyond those detected on funduscopic exam, fluorescein angiography, or optical coherence tomography, and can be used to elucidate disease pathogenesis, form genotype-phenotype correlations, diagnose and monitor disease, and evaluate novel therapies. Given its ease of use, non-invasive nature, and value in characterizing retinal disease, FAF enjoys increasing clinical relevance. This review summarizes common ocular fluorophores, imaging modalities, and FAF findings for a wide spectrum of retinal disorders.

Fluorescence lifetime imaging ophthalmoscopy

“…However, the emission is quite low and peaks at around 450 nm (Gallas and Eisner, 1987). On conventional fundus autofluorescence intensity images, melanin absorbs the short-wavelength excitation beam, decreasing the overall autofluorescence signal (Yung et al, 2016). FLIO measurement of pure melanin featured long values with decay times between 648 and 1600 ps (Dysli et al, 2016e).…”

“…The hallmark of dry late AMD is geographic atrophy which leads to irreversible central vision loss due to progressive degeneration of the RPE, the choriocapillary layer, and the outer retina (Bowes Rickman, Farsiu et al, 2013;Holz et al, 2014;Yung et al, 2016). RPE atrophy and consequent loss of intrinsic fluorophores results in an area with a low to extinguished fundus autofluorescence intensity signal with sharply demarcated borders.…”

“…AMD is classified in an early disease stage with presence of retinal drusen and thickening of the Bruch membrane, and late AMD. There are two forms of late AMD: neovascular AMD with accumulation of intra-or subretinal fluid, and dry AMD with geographic atrophy of the retina (Holz et al, 2014;Yung et al, 2016).…”

“…Therefore, melanin is likely to contribute to fluorescence lifetime measurements with FLIO (Gallas and Eisner, 1987;K€ onig, 2008) (Kayatz et al, 2001;Keilhauer and Delori, 2006;Han et al, 2009;Yung et al, 2016). However, given the major contribution of lipofuscin to the autofluorescence signal, it is difficult to identify weaker endogenous fluorophores using autofluorescence intensity measurement in the retina.…”

Interphotoreceptor Retinoid-Binding Protein Implications in Diabetic Retinopathy

“…A2E is known to be able to produce cytotoxicity by destabilizing membranes, generating reactive oxygen species and producing photo-oxidation [55][56][57][58]. Since A2E is a lipofuscin precursor, fundus autofluorescence can be clinically used to detect its presence [59,60]. However, hard exudates can decrease autofluorescence interfering with the evaluation of lipofuscin [61].…”