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Peter Kayatz, Gabriele Thumann, Thomas T. Luther, Jens F. Jordan, Karl Ulrich Bartz–Schmidt, Peter J. Esser, Ulrich Schraermeyer; Oxidation Causes Melanin Fluorescence. Invest. Ophthalmol. Vis. Sci. 2001;42(1):241-246.
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purpose. The goal of this study is the characterization of the strong yellow
fluorescence of oxidized melanin in the retinal pigment epithelium
(RPE) and the choroid.
methods. Naturally occurring melanin in the human retina and choroid was
oxidized by exposing fixed and plastic-embedded sections of a human eye
to light and hydrogen peroxide. Synthetic melanin was also oxidized in
vitro by exposure to light and hydrogen peroxide. The fluorescence of
oxidized melanin was examined by absorption spectroscopy, fluorescence
spectroscopy, and fluorescence microscopy.
results. Naturally occurring melanin oxidized in situ exhibited a
lipofuscin-like yellow fluorescence. Oxidation of melanin in vitro
degraded the melanin polymer, resulting in a fluorescent solution.
Fluorescence spectroscopy gave an excitation maximum at approximately
470 nm and an emission maximum at approximately 540 nm for both natural
and synthetic melanin. Increasing the time of exposure to light or
hydrogen peroxide increased melanin fluorescence.
conclusions. The results indicate that the strong yellow fluorescence of melanin in
the RPE and choroid in situ is a property of oxidized melanin and is
not due to contamination of the melanin by proteinaceous or lipid
materials. The data presented allow a reinterpretation of the results
obtained from fluorescence investigations of melanin-containing tissue
and suggest a link between melanin degradation and lipofuscin
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