Spectrally Resolved Fundus Autofluorescence in Healthy Eyes: Repeatability and Topographical Analysis of the Green-Emitting Fluorophores

The aim of this study was to report normal measurements of green-emitting fluorophores in the macula of healthy young individuals and to assess the repeatability of these quantitative metrics. To do so, healthy young volunteers were imaged twice (7 +/- 3 days apart) using a confocal blue-light fundus autofluorescence (FAF) device with a shorter excitation wavelength (peak at 450 nm) and the capability for separately detecting the red and green components of the emission spectrum. The main outcome measure was the percentage of area occupied by green-emitting fluorophores in the macula. In addition, this measure was performed in separate regions providing a topographical assessment in the foveal, parafoveal and perifoveal regions. Furthermore, the level of agreement between repeated measurements was evaluated. Thirty eyes from 30 healthy volunteers were included in this analysis. Mean age was 26.2 +/- 2.8 years (median: 25.0 years; range: 23.0-32.0 years). Median (interquartile range-IQR) area occupied by green-emitting fluorophores was 3.6% (1.9-4.7%) in the macular region. In the topographical analysis, this percentage was higher in the foveal area (median = 33.3%, IQR = 21.9-41.2%), as compared with both the parafoveal (median = 5.3%; IQR = 2.4-8.1%;p< 0.0001) and perifoveal (median = 0.5%, IQR = 0.2-0.8%;p< 0.0001) regions. The coefficient of variation (CV; ranging from 1.1% to 1.7% in the analyzed regions) and the intraclass correlation coefficient (ICC; ranging from 0.93 to 0.97) indicated high levels of repeatability. In conclusion, the assessment of green-emitting fluorophores is repeatable. The distribution of these fluorophores is highest in the foveal region. Assuming that flavin adenine dinucleotide (FAD) emits in the green autofluorescence spectrum, this variability could be secondary to an increased quantity of mitochondria in the foveal region.