Abstract

SA.09.01

Steps for metabolic mapping at the fundus

Schweitzer D.¹, Hammer M.¹, Schenke S.¹, Jetsch S.², Schweitzer F.^1
1Experimentelle Ophthalmologie, FSU Jena; ²Fachbereich Sci-Tec/Augenoptik, Fachhochschule Jena

Objective: To determine parameters characterizing the cellular metabolic state at the fundus.
Methods: Measurement of fluorescence of endogenous fluorophores e.g. of redox pairs NADH-NAD, FADH2-FAD are suited for evaluation of cellular metabolism. The strong fluorescence of lipofuscin covers the weak fluorescence of coenzymes. A discrimination of fluorophores with good spatial resolution at the fundus can be reached by fluorescence lifetime. Based on Heidelberg HRA, a fluorescence lifetime ophthalmoscope was developed and clinically tested. For interpretation of in vivo measurements, it was to determine whether fluorophores of the redox pairs (NADH-NAD, FADH2-FAD) are spectrally detectable in isolated structures of porcine eyes. The discrimination of fluorescence contribution of ocular structures was also to investigate based on emission spectra or lifetime.
Results: All ocular structures (cornea, aquous humour, lens, vitreous, neuronal retina, retinal pigment epithelium, choroid, sclera) exhibit autofluorescence. The emission spectrum of NADH is detectable in lens and neural retina by 350 nm excitation. Excitation at 446 nm results in the emission spectrum of FAD, detectable in sclera, cornea, neural retina, and choriod. In the weak fluorescence of RPE of young porcine eyes, the spectrum of lipofuscin is not detectable. A discrimination of ocular structures is heavy when based on fluorescence spectra, but is possible by fluorescence lifetime.
Conclusions: Measurement of fluorescence lifetime is a first step for characterization of cellular metabolism. The combination of specific excitation, emission, and lifetime is optimally used for discrimination of fluorophores in the new lifetime ophthalmoscope. The knowledge of the fluorescence properties of ocular structures is helpful for interpretation of fluorescence lifetime measurements of the human fundus.

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