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Martin Hammer, Lukas Kreilkamp, Lydia Sauer, Thomas Ach, Theodore Smith, Christine Curcio; Fundus autofluorescence from drusen is spectrally different from that of lipofuscin. Invest. Ophthalmol. Vis. Sci. 2017;58(8):48.
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© ARVO (1962-2015); The Authors (2016-present)
Histology studies have shown a distinct difference in the autofluorescence spectral and temporal characteristics of drusen and lipofuscin of retinal pigment epithelium (RPE)1-3. We determined if spectral differences between lipofuscin and drusen autofluorescence could be detected in vivo.
50 eyes in 43 patients (mean age: 73.5±8.3 years), suffering from non-exudative age related macular degeneration (AMD), were investigated by fluorescence lifetime ophthalmoscopy (FLIO, Heidelberg Engineering). Fluorescence was excited at 473 nm and recorded in two spectral channels: 498-560 nm and 560-720 nm. The intensity ratio of the short and the long wavelength emission (spectral ratio), giving a relative measure of spectral fluorescence emission, was determined. Drusen were segmented from autofluorescence intensity images and color fundus photographs and spectral ratios were averaged over drusen and non-drusen areas. In order to include data from the posterior pole only, measurements were restricted to the area of the ETDRS-grid, centered at the macula. In a subgroup analysis, hard and soft were distinguished.
Spectral ratios of all drusen were significantly higher than that of non-drusen areas (0.64±0.13 vs. 0.56±0.08, p<0.0005) indicating a green-shift of the drusen fluorescence compared to that of lipofuscin (fig.1). The green-shift was higher in the soft drusen than in the hard drusen (spectral ratio 0.65±0.14 vs. 0.57±0.05, p=0.012).
Although our method does not record full spectra, it clearly shows a hypsochromic shift of drusen fluorescence compared to that of lipofuscin. This is in agreement with recent ex vivo hyperspectral histology data demonstrating a green autofluorescence spectrum specific to drusen 1, 3, 4. The shift is expected to be even greater for drusen in isolation since our in vivo measurement at the druse records a mixture of druse emission and that of the overlying RPE. These data show that drusen contain other fluorophores than those in RPE lipofuscin. Possibly, there is also a different fluorophore composition in hard and soft drusen.References:1. Marmorstein et al. IOVS 2002;43:2435-2441.2. Schweitzer et al. IOVS2012;53:3376-3386.3. Tong et al. Retina 2016, doi 10.1097/IAE.00000000000013254. Ben Ami et al TVST 2016;5:5.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Fig. 1: Fluorescence intensity (left) and spectral ratio (right, blue color of drusen indicate shorter emission wavelengths).
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