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D. Schweitzer, M. Hammer, E.R. Gaillard; Comparison of Autofluorescence Lifetimes: In vivo Measurements at the Fundus versus Co-enzymes and Metabolic By-products . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3615.
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Purpose: To find a substance-specific interpretation of most frequent lifetimes of autofluorescence, detected at the living fundus. Methods: Lifetime images were detected by a modified laser scanner ophthalmoscope, adapted with a pulse laser and an unite for time-correlated single photon counting. Lifetimes were calculated in bi-exponential fits. The presentation of the frequency of lifetimes in certain regions of interest results in characteristic maxima. Results: Lifetimes of fundus fluorophores are influenced by properties of the embedding matrix, resulting in an increased standard deviation of the calculated lifetime and in overlapping of lifetimes of several fluorophores. Influences of single fluorophores can be separated by provocation tests. Breathing of 100% oxygen reduces the contribution of the reduced form in the redox pair NAD-NADH. On the other hand, in dark adaption the metabolism increases (Cringle et al.), resulting in a relative lack of oxygen and, thus, the NADH fluorescence is increased. The frequency maximum of lifetime at 400 ps decreases during breathing 100% oxygen, but increases in dark adaption in a region temporal the optic disc. These changes point to reduce nicotinamid-adenindinucleotide (NADH). Measurements of pure free NADH confirm this assumption. A narrow maximum at 700 ps corresponds well with the lifetime of synthesised A2E, measured with the same apparatus as used for in vivo measurements. Surprisingly, no contribution of free FAD was found in dynamic autofluorescence measurements at the fundus until now. Conclusions: The detection of changes in metabolism at cellular level might be possible by measurements of dynamic autofluorescence of endogenous fluorophores. Ref.: Cringle et al. (2002) Invest Ophthalmol Vis Sci 43, 6, 1922-1927 Supported by German TMWFK Grant A 309-00015
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