Abstract
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.
Highlights
Fundus autofluorescence (FAF) is a non-invasive imaging modality which is used to record the retinal and retinal pigment epithelial (RPE) autofluorescence [1,2,3]
When the retina is excited with a blue light, other minor fluorophores in addition to lipofuscin contribute to the detected fluorescence of the posterior eye
The area occupied by green-emitting fluorophores was investigated by importing the color-coded fundus autofluorescence (FAF) image in the software called “FAF Color Segmentation Tool” and developed by CenterVue
Summary
Fundus autofluorescence (FAF) is a non-invasive imaging modality which is used to record the retinal and retinal pigment epithelial (RPE) autofluorescence [1,2,3]. When the retina is excited with a blue light, other minor fluorophores in addition to lipofuscin contribute to the detected fluorescence of the posterior eye. These minor fluorophores emit in the short-wavelength emission range (510–560 nm, green spectrum) [4]. The excitation and emission spectra of these green-emitting fluorophores have been extensively characterized.4 They are known to emit a very weak fluorescence intensity and a strategy to increase the activation of these green-emitting fluorophores is to employ a lower wavelength (~450 nm) to excite the retina [4,6,7,8] The excitation and emission spectra of these green-emitting fluorophores have been extensively characterized. Importantly, they are known to emit a very weak fluorescence intensity and a strategy to increase the activation of these green-emitting fluorophores is to employ a lower wavelength (~450 nm) to excite the retina [4,6,7,8]
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