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D. Schweitzer, M. Klemm, S. Quick, F. Schweitzer, M. Hammer, S. Jentsch; New Method for Combination of Functional and Geometric Information Based on Time-Resolved Autofluorescence Measurements. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1398.
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To find a relation between metabolic function, determined by fluorescence of endogenous fluorophores, and anatomical structures of the eye.
The time-resolved auto-fluorescence signal I(t), determined from the eye, consists of fluorescence contributions of several anatomical structures, which are excited by the same pulse but at different times. This time shift can be determined, when a free parameter tci is included in the model function for exponential approximation of normalized decay of fluorescence.In this way, it can be determined which decay time τi originates from which layer i. Furthermore, the degree of fluorescence decay (mono- or double-exponential) of single layers will be calculated. The geometrical distance between layers is the product of the time difference tci, multiplied by the velocity of light, and divided by 2 times the refractive index.
The time-resolved auto-fluorescence was excited by an excitation pulse of 100 ps full width at half maximum at 448 nm, applying the fluorescence lifetime mapper . The fluorescence was detected by time-correlated single photon counting between 490 nm and 560 nm with a time resolution of 12.5 ps. The time-resolved fluorescence of the eye was approximated by the extended model function. The calculated time distance tci between lens and fundus fluorescence was 173.3 ps. Using the refractive index of the vitreous n = 1.3668, the distance between lens and fundus was calculated as 19.01 mm, which is in good accordance with the distance given in Gullstrand's eye (18.8 mm).
The proposed model function for the fit of time resolved fluorescence of a layered structure results in functional metabolic information by auto-fluorescence and geometric information by the same measurement. If a time resolution of less than 30 fs can be reached, the fluorescence in a layered structure can be evaluated with a geometric resolution comparable to the OCT technique. Thus, functional and structural diagnostic information are available simultaneously. Schweitzer D et al. Towards Metabolic Mapping of the Human Retina. MICROSCOPY RESEARCH AND TECHNIQUE 70:410-419(2007)
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