Comparison of time-resolved autofluorescence in the eye-ground of healthy subjects and patients suffering from age-related macular degeneration

摘要

Age-related macular degeneration (AMD) is the most frequent cause for blindness for person older than 65 years in western countries. Besides the subjective pain, it is also an economic problem in the ageing population. As the pathomechanism is unknown, no curative treatment is possible. International research for discovering of early age-related alterations at the fundus is directed on in vivo measurements of autofluorescence. One way is the measurement of fluorescence spectra. Unfortunately, any selective excitation of fluorophores is excluded by the absorption edge of the ocular media at 400 nm. Furthermore, the shape of fluorescence spectra is influenced by the spectral absorption of layers in front of the emitting fluorophore. Weakly emitting fluorophores are covered by intensive emitting substances. The most serious limitation in fluorescence measurements of the living human fundus is the maximal permissible exposure. For that reason, fluorescence spectra of the fundus can not be detected with a high spatial resolution. The detection of dynamic fluorescence provides substance-specific lifetimes Ti, amplitudes Ai, and information about the relative contribution Qi of components in fluorescence images. As these parameters are calculated for each image point, diagrams of Ti vs. Tj, Ai vs. Aj, and Qi vs. Qj can be drawn, in which specific clusters appear for healthy subjects or AMD - patients. The projection of lifetime - clusters onto corresponding axis represents histogram of the considered lifetime. The slope in the correlation between Ai and Aj can also be used as a discriminating mark. Considering image lines as intersection through characteristic anatomical structures (optic disc, macula) profiles of Ti, Ai, or Qi show changes of these parameters (e.g. depigmentation) as function of location, which might be specific for AMD.