Abstract
Abstract: :
Purpose: To compare in vitro and in situ properties of a conventional Ahmed Glaucoma Valve with a newly designed valved glaucoma drainage implant (modified implant). Histological comparisons were also performed. Methods: Ahmed S3 implants and modified implants were bilaterally implanted in eight normotensive rabbits. The Ahmed implant served as control in one eye and the modified implant in the fellow eye. Tonopen® IOP readings were taken and slit–lamp exams were performed on post–op days 1, 3, and 7, then weekly afterwards for a total of 6 weeks. Pressure recordings were taken of each implant in situ at set flow rates to determine outflow facility. Eyes were enucleated for histological sectioning and staining. In vitro studies to study fluid flow were also performed to compare valve properties of both devices. Results: Three rabbits were excluded from study secondary to conjunctiva and tube extrusion of the modified implants. Of the 5 rabbits evaluated, there were no differences in IOP between the Ahmed implant (10.2 ± 3.2 mm Hg) and the modified implant (9.1 ± 1.8 mm Hg) at 6 weeks (p=0.36). At 2 ul/min flow rates, the steady state pressures were 16.1 ± 1.3 mm Hg and 28.5 ± 3.2 mm Hg (p=0.01) for the modified and Ahmed implant respectively. At 5 ul/min flow rates the corresponding pressures were 19.2 ± 1.1 mm Hg and 38.9 ± 5.1 mm Hg (p=0.04). Two modified implants failed to achieve steady state pressures, presumably due to tissue infiltration, and these eyes were excluded from flow rate analysis. Histologically, the capsule surrounding the Ahmed implant was avascular and showed dense layers of collagen while the tissue response to the modified implant showed collagen that was disorganized and loose in appearance with inflammatory cells and numerous microvessels present close to the implant surface. Conclusions: The modified implant had a greater outflow facility and correspondingly, a lower steady–state pressure than the unmodified Ahmed implant. The capsule was thinner and more vascular around the modified device. With additional refinement, this new implant may prove to be a viable alternative to conventional glaucoma drainage implants.