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R. Brinkmann, M. Rumohr, G. Hüttmann, N. Koop, G. Schüle; Mechanisms of RPE Damage for Laser Exposure in the µs to ms Time Range . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3939.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the mechanisms of Retinal Pigment Epithelial (RPE) cell damage for laser irradiation times from microseconds (µs) to milliseconds (ms). The range of suitable pulse durations to confine damage to the RPE shall be evaluated with regard to selective RPE treatment (SRT). Methods: A continuous wave (cw) Argon-ion laser beam (wavelength 514 nm) was externally modulated by an Acousto-Optic Modulator (AOM) in order to generate pulse durations of 5 µs, 50 µs, 500 µs and 3 ms. The light was coupled into a 50 µm core diameter fiber, its fiber tip was imaged with a slit lamp 1:1 onto freshly post mortem harvested porcine RPE samples. RPE viability was proved by the life/death marker calceinAM. In order to detect microbubble induced intracellular vaporization, acoustic transients were recorded with a hydrophone and changes in reflected light were detected with a photomultiplier. Temperature calculations and Raster-Electron-Microscopy (REM) served to support analyzing the observations. Results: At a laser pulse duration of 5 µs, short living intracellular microbubbles were detected optically and acoustically, slightly below the ED50 RPE damage threshold radiant exposure of 252 mJ/cm2. When damaged cells were observed, microbubbles were always present. At 50 µs pulse duration, the ED50 radiant exposure of 483 mJ/cm2 was slightly below, but close to the onset of microbubbles. At longer pulse durations, the ED50 cell damage thresholds were much lower than the radiant exposure needed for vaporization. Conclusions: Using a pulse duration of 5 µs, the RPE is most likely thermomechanically disrupted by microbubbles originating from vaporization around the individual melanosomes. With pulse durations of 500 µs and longer, a pure thermal cell damage has to be considered. Due to increasing heat flow from the RPE into the retina towards longer pulse durations, the risk of additional thermal damage of the photoreceptors grows.
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