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Previous studies of laser-induced multiple-pulse damage measurements of the retina determined inconsistent thresholds in the thermo-mechanical damage regime. This inconsistency might be due to biological variability, measurement techniques as well as methodological challenges which occur during the use of explants. For better comparability with state-of-the-art measurements, we use a top hat irradiance profile to produce a uniform energy density and monitor the beam profile at the retinal pigment epithelium layer. This approach is applied in order to determine damage thresholds in the lower nanosecond regime for pulse sequences. The irradiation experiments were performed using a Q-switched, frequency-doubled Nd:YAG laser (532 nm wavelength, 1.8 ns pulse, 25 Hz, 319 μm-diameter, squared top hat). Freshly isolated porcine eyes were used as models for measurements of laserinduced thermo-mechanical damage. After removal of the sensory retina the retinal pigment epithelium layer attached to the sclera was irradiated. Four pulse trains (N = 1, 10, 100 and 1 000) were examined and evaluated concerning damage threshold via fluorescence microscopy. The ED50, expressed as energy per pulse, decreases from 33.9 J for N = 1 to 20.3 J for N = 1 000. The multiple-pulse threshold trend which was measured can neither be described by current methods such as the probability-summation-model nor by the N−0,25- approach which is also partly used within the laser safety standard. Therefore we discuss possible pulse interactions which could explain the multiple-pulse behavior in the thermo-mechanical damage regime. Their implications might present the build-up of a new, more accurate theory to describe the reduction factors of thermo-mechanical damage-inducing doses with increasing pulse numbers.
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