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CP Lin, C Alt, S Schnell, C Framme, G Schuele, R Brinkmann; Selective Targeting of the Retinal Pigment Epithelium in vivo Using a Laser Scanner . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2533.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To develop a new laser scanning device that selectively targets the retinal pigment epithelium (RPE) without photocoagulating the neurosensory retina. Diseases that are thought to be caused by RPE dysfunction, including diabetic maculopathy, central serous retinopathy, and drusen, may benefit from this new treatment, which preserves the overlying photoreceptors and should be safe for use in the macula, close to the central vision. Methods: Previous work by Roider, Birngruber, and coworkers has shown that selective RPE targeting can be achieved with repetitive microsecond laser pulses at 514 or 527 nm. However, such pulses are difficult to produce in this wavelength range. Our new approach is to take a continuous wave (cw) laser, focus onto the retina, and rapidly scan the spot so that each RPE cell "sees" an effective microsecond pulse. Multiple pulse exposure is accomplished by repetitively scanning the laser beam in a predefined treatment pattern. Output from a diode-pumped cw Nd:YAG laser at 532 nm is delivered by a single mode optical fiber to a modified slitlamp that contains a two-dimensional acousto-optic deflector (AOD). The AOD scans the laser beam on the retina with speed and pattern that are software controlled. Experiments were performed in eight eyes of Dutch-belted pigmented rabbits. The laser spot size on the retina was 12.5 microns and the scanning speed was set to either 5 or 10 µsec per spot. The scan pattern consisted of six separated lines, each 300 microns wide, placed in a 300 micron square area. A total of 198 such lesions were created with varying laser power and number of pulses to determine the threshold and selectivity of the method. Results: Using laser power in the range of 50-150 mW at the retina, the treatment lesions were not visible ophthalmoscopically, indicating that the retina was not thermally coagulated. The lesions became visible with fluorescein angiography (hyperfluorescent) indicating selective damage to the RPE. With 5 µsec per spot scan speed, the angiographic ED50 thresholds were 87 and 66 mW for 10 and 100 scans at 100 Hz. With 10 µsec per spot, threshold values were 68 and 55 mW for 10 and 100 scans at 100 Hz. Conclusion: The cw laser scanner is effective in producing selective RPE lesions without thermal coagulation of the neuroretina and requires less than 100 mW of power. Thus the system can be made compact and inexpensive. The ability to produce arbitrary scan patterns at the retina is potentially useful for treatment of RPE disorders.
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