Argon laser trabeculoplasty and pilocarpine effects on outflow facility in the cynomolgus monkey.

PURPOSE: We sought to determine whether and how prior argon laser trabeculoplasty (ALT) alters outflow facility, the pilocarpine-induced facility increase, and the morphology of the trabecular meshwork in cynomolgus monkeys. METHODS: Eleven cynomolgus monkeys underwent unilateral 360 degrees argon laser trabeculoplasty, eight in two 180 degrees sessions (seven 3 months apart, one 11 days apart) and three in a single session. Intraocular pressure (IOP, Golmann ap-planation tonometry), aqueous humor flow rate (AHFR, fluorophotometry), total outflow facility (two-level constant pressure perfusion) and response to intracameral pilocarpine, and morphology (light and scanning/transmission electron microscopy) were determined at various times. RESULTS: Resting total perfusion outflow facility 3 and 6 months after 360 degrees ALT was 30% higher in ALT-treated than in contralateral untreated eyes. There were no consistent or statistically significant differences between ALT-treated and contralateral untreated eyes in (a) IOP or AHFR before ALT, 5 weeks after initial 180 ALT, or 5 weeks after the second 180 ALT; (b) post-intracameral pilocarpine facility, or the dose-dependent facility response to pilocarpine 10 weeks after the initial 180 ALT or 3 and 6 months after the second 180 ALT; or (c) light or electron microscopic appearance of the trabecular meshwork or inner wall of Schlemm's canal 3-17 months after 360 ALT. CONCLUSIONS: This study indicates that (a) ALT alters the biomechanical properties of the monkey trabecular meshwork so as to modestly increase its hydraulic conductivity without affecting the facility response to pilocarpine-induced ciliary muscle contraction; and (b) young healthy monkey outflow tissues exhibit remarkable reparative and homeostatic capabilities.