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Proceedings Paper

Selective RPE photodestruction: mechanism of cell damage by pulsed-laser irradiance in the ns to um time regime
Author(s): Ralf Brinkmann; Jan Roegener; Charles P. Lin; Johann Roider; Reginald Birngruber; Gereon Huettmann
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Paper Abstract

The subject of this study was to investigate the threshold radiant exposures for bubble formation at single porcine melanosomes in suspension and for porcine RPE cell damage when using pulse durations in the ns to microsecond(s) time regime. A frequency doubled Nd:YLF laser ((lambda) equals 527 nm) with adjustable pulse duration between 250 ns and 3 microsecond(s) and a Q- switched Nd:YAG laser ((lambda) equals 532 nm, (tau) equals 8 ns) were used for the single pulse irradiation. Fast flash photography was applied to probe vaporization around individual melanosomes while a fluorescence viability assay was used to probe cell vitality. Applying single ns laser pulses to RPE cells, an ED50 threshold radiant exposure of 84 mJ/cm2 was determined, which is close to the vaporization threshold around single melanosomes. When irradiating with pulse durations of 3 microsecond(s) , a threshold of about 223 mJ/cm2 was measured, which is only 40% lower of the vaporization threshold around the single melanosome at that pulse width. This can be explained with heat contribution from adjacent melanosomes, which increases towards longer pulse durations. Calculations are in good agreement with the experimental results when assuming a surface temperature at the melanosome of 140 degrees Celsius and an absorption coefficient of 8000 cm-1 to initiate vaporization. It can be concluded that the origin of RPE cell damage for single pulse irradiation with a duration of 8 ns results from transient microbubbles around the melanosomes, which lead to a transiently increased cell volume and subsequently a rupture of the cell structure. It is also likely that the same effect plays the major role when using pulse durations up to 3 microsecond(s) .

Paper Details

Date Published: 14 June 1999
PDF: 7 pages
Proc. SPIE 3601, Laser-Tissue Interaction X: Photochemical, Photothermal, and Photomechanical, (14 June 1999); doi: 10.1117/12.350041
Show Author Affiliations
Ralf Brinkmann, Medizinisches Laserzentrum Luebeck GmbH (Germany)
Jan Roegener, Medizinisches Laserzentrum Luebeck GmbH (Germany)
Charles P. Lin, Wellman Labs. of Photomedicine, Massachusetts General Hospital, and Harvard Medical School (United States)
Johann Roider, Univ. of Regensburg Eye Clinic (Germany)
Reginald Birngruber, Medizinisches Laserzentrum Luebeck GmbH (Germany)
Gereon Huettmann, Medizinisches Laserzentrum Luebeck GmbH (Germany)

Published in SPIE Proceedings Vol. 3601:
Laser-Tissue Interaction X: Photochemical, Photothermal, and Photomechanical
Steven L. Jacques; David H. Sliney; Gerhard J. Mueller; Gerhard J. Mueller; Andre Roggan; Andre Roggan; David H. Sliney, Editor(s)

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