[Comparison of parameters of time-resolved autofluorescence between healthy subjects and patients suffering from early AMD]

Abstract

Background: A fluorescence lifetime mapper (FLM) was tested for quantitative estimation of early alterations in age-related macular degeneration (AMD) which are assumed to be in cellular metabolism.

Method: In FLM time-resolved autofluorescence of the fundus is excited by picosecond (ps) laser impulses at 448 nm and detected in 2 spectral ranges (K1=490-560 nm and K2=560-700 nm) by time-correlated single photon counting. The time-dependent decrease in fluorescence intensity was approximated using 3 decay rates. The calculated lifetimes allow a comparison with endogenous fluorophores of cellular metabolism.

Results: Initially mean lifetimes were determined for 8 healthy subjects (K1: tau1=118 ps, tau2=584 ps, tau3=2826 ps, K2: tau1=104 ps, tau2=477 ps, tau3=1623 ps). In 15 AMD patients (AREDS categories I and II) the lifetimes were longer (K1: tau1=166 ps, tau2=986 ps, tau3=3309 ps, K2: tau1=137 ps, tau2=583 ps, tau3=1924 ps). The best separation between healthy subjects and patients with early AMD was possible by parameters 1 and 2 in the short-wave channel. Fluorophore-specific alterations in the macula could be demonstrated in isolated cases with advanced AMD.

Conclusion: Measurements in the 30 degrees fundus field demonstrated that specific alterations were already present even in early AMD and also outside the macula. These act in the neuronal retina, because parameter tau2 is related to this layer. Increases in the lifetime of parameter tau2 in the short wave channel could at least partially be determined by an increase of protein bound NADH, the content of which increases with reduced cellular respiration.