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D. Schweitzer, F. Schweitzer, M. Hammer; Lifetime Measurements of Autofluorescence Might Discover Early Changes in Age–Related Macular Degeneration . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2165.
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© ARVO (1962-2015); The Authors (2016-present)
To find changes in dynamic autofluorescence as objective parameters for detection of early stages in age–related macular degeneration (AMD).
The time–resolved autofluorescence of the fundus was measured in 32 healthy subjects and in 11 AMD patients. For this study, the Jena Lifetime–Mapper was used in which the fundus was excited by laser pulses of about 100 ps full width at half maximum at 446 nm. The time–resolved autofluorescence was detected in time–correlated single photon counting. The measured signal of each pixel in the image was approximated by a tri–exponential model function. The parameters lifetime, amplitude, and relative contribution were considered in optical sections through the macula and through the optic disc in lifetime images.
In 40 deg. images, the lifetime tau 1 is most frequent at 185 ps in normals and 200–280 ps in AMD, tau 2 is most frequent at 1120 ps both in normals and in AMD, and the lifetime tau 3 is most frequent in normals at 5.04 ns but is widely distributed between 1.36 ns and 6ns in AMD. The dominating amplitude a1 of the lifetime tau 1 is 92% in normals and 87% in AMD. In contrast, the amplitude a2 of tau 2 is higher in AMD (12%) than in normals (6%). The amplitude a3 of tau 3 is low both in AMD (1%) and in normals (2%). In an optical section through the optic disc, the relative contribution Q1 of the first component is about 40% of the whole fluorescence outside the optic disc. In the optic disc, it goes down to 0%. The contribution of Q2 is constant (25%) along the optical section. The contribution Q3 is 35% and dominates in the optic disc (75%). Considering optical sections through the macula a loss in relative contribution of Q1 is detectable in AMD patients, in which a reduced static fluorescence intensity is already visible in the macula. In early stage of AMD, when no alteration of fluorescence intensity is visible, the contribution Q1 is constant, but a loss in the contribution Q2 and an increased Q3 are detectable in the macula.
Comparing the local distribution of Qi with the retinal anatomy, Q1 might originate from the retinal pigment epithelium, Q2 from neural retina, and Q3 from connective tissue. As the lifetime values in AMD and normals are comparable, probably the same fluorophores contribute to the autofluorescence and only the relative contribution changes. In early AMD, changes in macular autofluorescence are detectable by time resolved measurements, originating probably from the neural retina.
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