title: Photoablative laser-grid trabeculectomy in glaucoma filtering surgery: histology and outflow facility measurements in porcine cadaver eyes.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Ophthalmology, University Eye Hospital Cologne, Germany. Philipp.Jacobi@uni-koeln.de
authors.forename: P C
authors.initials: PC
authors.lastname: Jacobi
authors.forename: T S
authors.initials: TS
authors.lastname: Dietlein
authors.forename: T
authors.initials: T
authors.lastname: Colling
authors.forename: G K
authors.initials: GK
authors.lastname: Krieglstein
mesh_terms: D000818:Animals; D000867:Anterior Chamber / Q000378:metabolism / Q000473:pathology; D001082:Aqueous Humor / Q000378:metabolism*; D002102:Cadaver; D003886:Descemet Membrane / Q000473:pathology; D005901:Glaucoma / Q000378:metabolism / Q000473:pathology / Q000601:surgery*; D066298:In Vitro Techniques; D007429:Intraocular Pressure; D017075:Laser Coagulation; D014130:Trabeculectomy / Q000379:methods*