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A. Bindewald, F. Schutt, H. Specht, F.G. Holz; Preclinical Study for Intraocular Microablation of Choroidal Tissue Using a 308 nm UV Excimer Laser for RPE-Sheet Translocation . Invest. Ophthalmol. Vis. Sci. 2003;44(13):500.
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Purpose: Surgical excision of subfoveal choroidal neovascularization (CNV) in age-related macular degeneration (AMD) is usually associated with inadvertent removal of retinal pigment epithelium (RPE) and subsequent functional loss. Translocation of intact autologous RPE-sheets to cover this defect would be desirable as cell suspensions have not achieved satisfactory outcomes. To ablate choroidal tissue from autologous peripheral RPE/Bruch's membrane (BM)/choroid grafts we used a 308 nm UV Excimer laser attached to small probes for intraocular use. Methods: With a 308 nm UV Excimer laser (AIDA, TuiLaser AG, Munich) and laser probes of 200 micron in diameter choroidal tissue was ablated from excised grafts in human donor eyes. Energy of 1.2 mJ and 10 pulses per laser spot were applied. Distances of the tip to the tissue were varied from 0 to 200 micron in 20 micron steps. Specimen were evaluated morphologically with light and electron microscopy. Results: Histology showed an ablation rate of 6-7 micron per pulse at a energy of 38 mJ/mm². An increase of the distance of the tip to the tissue led to larger ablation areas with a non-linear decrease of the vertical ablation rate. Thermal effects were noted only in a lateral extent of 2-5 micron in the remaining choroidal tissue. All histological preparations had a natural ablation barrier in BM with these settings. Conclusions: Choroidal tissue of RPE/BM/choroid grafts can be efficiently ablated with a customized 308 nm UV Excimer laser. Less resistance for diffusion of metabolites and water would be expected compared to full-thickness grafts and, thus, better RPE and inner neurosensory retinal function. The small laser probes allow for entry via normal pars plana sclerotomies and, therefore, intraocular ablation. It is planned to translocate such grafts obtained after retinectomy from peripheral areas via an extramacular retinotomy under the fovea following CNV excision.
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