Effect of Novel Design Modifications on Fibrotic Encapsulation: An In Vivo Glaucoma Drainage Device Study in a Rabbit Model

PURPOSE: To quantify the effects of modified Ahmed glaucoma valves(®) (AGV) with anti-fibrotic plate coatings or a plate surface micro-pattern on outflow resistance and tissue response. METHODS: Twelve New Zealand rabbits were divided into four groups: commercially available AGV implants (n = 3), AGV with hydrophilic coating (n = 3), AGV with heparin coating (n = 3), and AGV with a plate surface micro-pattern (n = 3). After 6 weeks, the anterior chamber silicone tube was cannulated in situ and perfused with 2.5 μL/min of saline. The pressures were recorded with a perfusion system to measure outflow resistance. The rabbits were then euthanized followed by enucleation of all eyes for bleb histological analyses. RESULTS: Hydrostatic pressures were significantly lower in AGVs with the hydrophilic plate coating (mean difference −9.6 mm Hg; p < 0.001), heparin-coated plates (mean difference −4.4 mm Hg; p < 0.001), and micro-patterned plates (mean difference −18.6 mm Hg, p < 0.001), indicating lower outflow resistance compared to control AGV models. Fibrotic encapsulation was lower in hydrophilic plate coating (84.2 μm; mean difference −6.2 μm, p = 0.425), micro-patterned surface (63.7 μm; mean difference −26.7 μm, p = 0.003), and heparin plate coating (49.3 μm; mean difference −41.1 μm, p = 0.006) when compared to control AGV models. CONCLUSIONS: Modified AGVs with plate coatings and AGVs with micro-patterned plates both appear to reduce postoperative fibrotic encapsulation and aqueous outflow resistance by altering the tissue response to implanted materials. Further studies are needed to characterize the safety and role of plate surface modifications on glaucoma drainage devices.