Photoablative Laser-Grid Trabeculectomy in Glaucoma Filtering Surgery: Histology and Outflow Facility Measurements in Porcine Cadaver Eyes

Abstract

Mid-infrared laser technology opens new perspectives in experimental glaucoma surgery. The aim of the study was to determine the efficacy of grid-laser trabeculectomy to reduce aqueous outflow resistance sufficiently in perfused porcine cadaver eyes. Twenty-five freshly enucleated porcine cadaver eyes were randomly assigned to either laser-grid trabeculectomy (LGT), conventional trabeculectomy (CT), or control. In all surgical cases a scleral flap was prepared in a standardized manner. In order to penetrate into the anterior chamber a 1 x 2 mm sclerectomy was performed in CT, and 10 transscleral ablation craters were created in LGT. An erbium:YAG laser (2.96 microm) was used for transscleral photoablation. Radiation was delivered in a single 6 mJ-pulse of 200 micros duration by means of an articulated zirconium fluoride optical fiber and a 200 microm quartz fiber-tip. Outflow facility was measured at a constant perfusion pressure. Laser-grid trabeculectomy (LGT) yielded reproducible ablation areas varying between 210-300 microm in diameter, with 90% being full-thickness penetrations. Collateral thermal damage was less than 30 microm. Outflow facility measurements revealed a statistically significant increase (mean +/- SD) from 0.255 +/- 0.096 microL/min/mm Hg in control eyes (n = 9) to 0.772 +/- 0.157 microL/min/mm Hg in the LGT group (n = 9), and 2.957 +/- 0.602 microL/min/mm in the CT group (n = 7). Flattening of the anterior chamber, folding of Descemet's membrane, and iris prolapse were only observed in the CT eyes but not in the GLT group. Application of the laser-grid trabeculectomy produces patent transscleral perforation with minimal collateral tissue damage and effects a significant reduction (67%) in outflow resistance without any postoperative hypotony-related complications.