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C Framme, G Schuele, J Roider, R Birngruber, R Brinkmann; Threshold Determinations for Selective RPE Damage With Repetitively Pulsed Microsecond Laser Systems in Rabbits . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2530.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:As proven by preclinical and clinical studies selective RPE damage with sparing of photoreceptors is possible by applying repetitive short laser pulses of 1.7 µs in duration. It was our purpose to determine the ophthalmoscopic and angiographic damage thresholds for different pulse durations in the µs-time regime in order to evaluate the range of selective RPE treatment. Methods:Chinchilla Bastard rabbits were narcotized and placed in a special holder system. All animals were handled in accordance with ARVO guidelines for ethical treatment. Laser lesions were applied using a commercial laser slit lamp and irradiation with a Nd:YLF laser (wavelength: 527 nm, repetition rate: 500 Hz, number of pulses: 100, pulse duration: 5 µs, 1.7 µs, 200 ns) and for comparison with an argon ion laser (514 nm, 500 Hz, 100 pulses, 5 µs). In all eyes, spots (diameter 102 µm) with different energies were placed into the regio macularis. After treatment, fundus photography and fluorescein angiography were performed and radiant exposure for ophthalmoscopic and angiographic ED50 damage thresholds determined. Speckle measurements at the fiber tips were performed to determine intensity peaks in the beam profile. Results:Ophthalmoscopic ED50-threshold radiant exposures for the Nd:YLF were calculated to be 381 mJ/cm2 (5 µs), 479 mJ/cm2 (1.7 µs) and 450 mJ/cm2 (200 ns), the angiographic ones 201 mJ/cm2 (5 µs), 138 mJ/cm2 (1.7 µs) and 100 mJ/cm2 (200 ns). For the argon laser the angiographic ED50-threshold radiant exposure was 213 mJ/cm2 (5 µs) and the ophthalmoscopic one ≷365 mJ/cm2 (5 µs). A ratio of peak to average radiant exposure in the beam profile was 1.225 for the Nd:YLF and 3.180 for the argon laser (speckle factor). Conclusion:RPE damage thresholds for Nd:YLF and argon ion laser are similar if speckle factors are considered. Angiographic thresholds decreased with shorter pulse duration whereas ophthalmoscopic ones were relatively constant. The gap between angiographic and ophthalmoscopic threshold (therapeutical window) for the 200 ns regime (4.5 times above angiographic ED50) was wider than those for 1.7 µs regime (3.5 times) and for 5 µs regime (1.9 times). Thus selective RPE laser treatment might also be possible with 200 ns pulse duration, however the range of mechanical damage will probably increase.
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