Blue-light versus green-light autofluorescence: lesion size of areas of geographic atrophy

Blue-light fundus autofluorescence (FAF) imaging is currently widely used for assessing dry age-related macular degeneration (ARMD). However, at this wavelength, the fovea appears as circular zone of marked hypofluorescence, due to the absorption of macular pigment (MP). This dark spot could be misinterpreted as an atrophic area and could lead to difficulties in identifying small, central changes. The purpose of the study was to analyze differences in image quality, FAF patterns, and lesion size, when using conventional blue-light (Λ(1) = 488 nm) and green-light (Λ(2) = 514 nm) FAF. Patients older than 50 years with central areas of geographic atrophy (GA) secondary to ARMD were enrolled. Images were recorded with a modified confocal scanning laser ophthalmoscope (cSLO). Image quality and patterns were analyzed. The quantification of the GA was performed with customized image-analysis software. In total, 95 eyes were included. The borders of the central atrophic patches and the boundaries of the preserved foveal island were better identified in 514-nm images. In both excitation wavelengths the signal-to-noise ratio was sufficient for the identification of the FAF pattern. Significant differences were observed in the size of the GA areas detected in the 488- and 514-nm wavelength images (4.29 ± 3.76 mm(2) vs. 3.80 ± 3.68 mm(2); P < 0.001). The green-light FAF images (514 nm) are superior for the accurate analysis of small, central, pathologic changes, and for the determination of the central GA lesion size. Using only blue-light FAF could lead to an overinterpretation of the size of atrophic patches and the center involvement, because it suggests the presence of atrophy in the fovea.