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  • Title: [Selective RPE laser treatment with a scanned cw laser beam in rabbits].
    Author: Framme C, Alt C, Schnell S, Brinkmann R, Lin CP.
    Journal: Ophthalmologe; 2005 May; 102(5):491-6. PubMed ID: 15883846.
    Abstract:
    BACKGROUND: Selective RPE laser therapy with sparing of the neurosensory layer is possible by applying repetitive microsecond laser pulses. Macular diseases such as diabetic maculopathy, soft confluent drusen due to age-related macular degeneration or central serous chorioretinopathy were shown to be treated successfully-without concurrent laser scotoma-by this technique. It was the goal of this study to show, if selectivity could also be achieved using a conventional green cw-laser by scanning the beam across the retina during irradiation. MATERIAL AND METHODS: A cw-laser beam at 532 nm was coupled to a slitlamp via a single mode optical fiber. The spot (18 microm) was scanned across the retina of Dutch-belted rabbits through a contact lens using a two-dimensional acusto-optical deflector. The scan-field was 300 microm x 300 microm in size and consisted of six separate scan lines. The scanning speed was adjusted so as to produce 5 micros exposure at each absorber in the center of the scan line. The entire scan pattern was applied 100 times at each site at a frame rate of 100 Hz. Dose response curve was measured by variation of the laser power. ED(50)-thresholds for RPE damage were calculated by fluorescein angiographic leakage in irradiated areas after exposure to different laser intensities. The extent of selectivity was examined by light microscopy. RESULTS: Clinically the selective laser-induced RPE defect was demonstrated by fluorescein angiographic leakage and concurrent absence of ophthalmoscopic visibility. The angiographic ED(50)-damage threshold was 161 mJ/cm(2) (66 mW). Ophthalmoscopic visibility was not noticed even with the maximum available radiant exposure of 438 mJ/cm(2) (180 mW). Thus the safety range between angiographic and ophthalmoscopic thresholds had a factor of at least 2.7. First histological examinations revealed selective RPE destruction with intact photoreceptors for irradiation at laser power levels 2 times above angiographic threshold. CONCLUSION: Selective RPE targeting is feasible with a conventional green cw-laser when scanning the focused laser beam across the fundus with a speed such that every point in exposed RPE is irradiated for duration of 5 micros.
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