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Ralf Brinkmann, Eric Seifert, Philipp Kleingarn, Svenja Sonntag, Dirk Theisen-Kunde, Yoko Miura; Origin of RPE damage and related thresholds for laser exposure in the µs time domain. Invest. Ophthalmol. Vis. Sci. 2019;60(9):3673.
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© ARVO (1962-2015); The Authors (2016-present)
The origin and extend of laser induced damage to the retinal pigment epithelium (RPE) and retina in the pulse range of microseconds (µs) is still not fully investigated, while it is currently actively addressed with different new laser systems. The range from few ns to 2 µs can clearly be attributed to thermomechanical damage owing to the disruption of RPE cells following vaporisation and microbubble formation around the intracellular melanosomes. Pulse durations exceeding 100 µs on the other hand predominately lead to thermal damage at least with energies close above damage threshold. This work focusses to explore these effects in the thermomechanical to thermal damage transition zone between 2 and 100 µs.
Irradiation was performed via a laser slitlamp with a laser wavelength of 514 nm and pulse durations which could freely be adjusted between 2 and 100 µs for single pulses or bursts. Porcine RPE-choroid-sclera explants and rabbit’s retina were irradiated with spot diameter fixed to 144 and 96 µm with a top hat beam profile, while cell damage was investigated by the vitality stain calcein-AM and fluorescein angiography, respectively. In order to explore the onset of microbubbles as prerequisite for thermomechanical damage, the increase of reflected light was recorded with a fast photodiode time-dependent relative to the laser pulse onset. Thus by integrating the pulse energy up to the onset time of microbubble provides precisely the energy until vaporization. Exemplary histology was performed to examine the damage range for selected pulse durations.
First experiments on explants show a logarithmic increase in threshold pulse energy for nucleation over the pulse duration. A threshold radiant exposure of 171 mJ/cm2 was found for 2.2 µs single pulses, which increases to 295, 521 and 777 mJ/cm2 for pulse durations of 5.2, 20 and 50µs, respectively. Statistically substantiated threshold data on explants and rabbits and exemplary histologies will be presented.
The achieved data provide a valid range of thresholds and are useful to classify new laser systems with respect to their predominant way of acting on the RPE and retina. The data are also useful to review and adjust ANSI standards and maximal permissible exposure (MPE) for laser pulse durations in the µs time range.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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