gms | German Medical Science

Background: Fundus autofluorescence imaging allows non-invasive mapping of naturally and pathologically occurring fluorophores of the ocular fundus. A further development, quantitative fundus autofluorescence (QAF), allows for the exact determination of retinal AF intensities. QAF has been shown to be decreased overall in age-related macular degeneration (AMD). The relationship between QAF and various AMD lesions – drusen, subretinal drusenoid deposits (SDD) – is still unclear, but would be relevant for pathophysiological understanding of AMD.

Methods: Multimodal imaging (OCT, QAF) was obtained in 28 eyes of 28 subjects with intermediate AMD. Using modified FIJI plugins, SD-OCT and QAF images were aligned, then AMD lesions (hard/soft drusen, SDD) were labelled in both individual SD-OCT scans and QAF. QAF images from all subjects were averaged to determine the average QAF value for each pixel in the central 30° of the retina (= standard AMD retina). QAF intensities in the lesion area were determined in FIJI, exported, and compared with QAF intensities of the standard AMD retina. The difference in QAF intensity was expressed as a z value (hypothetical parameter measuring the difference in QAF values in number of standard deviations).

Results: Lesions from 17 eyes of 17 patients (9 female; 71.6±7.6 years) with intermediate AMD were annotated to date. Overall, soft and hard drusen showed a very heterogeneous autofluorescence pattern with both increased and decreased autofluorescence. Soft drusen (n=13 patients) had on average decreased autofluorescence with a z-value of -0.091±0.0858. Similarly, hard drusen (n=3 patients) showed locally decreased autofluorescence in the area of the lesion (z-value: -0.003±0.001). SDD (n=3 patients) also had mostly reduced QAF in the area of the lesion (z value: -0.042±0.013).

Discussion: Interestingly, similar to the global QAF at the ocular fundus, the lesion-specific QAF was often reduced, making the AMD typical lesions important in the QAF analysis. While in SDD a reduced QAF could be due to “shadowing” of the RPE by the subretinal lesions, in soft and hard sub-RPE drusen the reduced QAF would be due to redistribution and loss of autofluorescent granules. Lesion-specific QAF values could thus be used in the future for detailed AMD classification, including to characterize AMD lesions more precisely. Autofluorescence of lesions may supplement OCT imaging with information on the health of the RPE and its intracellular composition in the future.