LONG-TERM HISTOLOGIC-STUDIES OF THE BAERVELDT IMPLANT IN A RABBIT MODEL

Purpose: The Baerveldt glaucoma implant is an aqueous shunting device with large surface area that is installed through a single-quadrant co njunctival incision. A rabbit model of the Baerveldt implant was creat ed to obtain serial histology and clinical information over 1 year. Me thods: Modified versions of the Baerveldt implant (110 or 160 mm(2)) w ere implanted in 18 normal New ZeaIand white rabbit eyes. The rabbits were examined periodically and their intraocular pressures (IOPs) reco rded, They were killed at monthly intervals to obtain histology of the bleb capsules. Results: Thin capsules were present at 1 month, which consisted of lamellar collagen deposition surrounded by a granulomatou s reaction with multinucleate giant cells. Inflammatory cells (probabl y macrophages) were scattered on the inner bleb surface. The granuloma tous reaction resolved after 4 months. Subsequently, capsule thickness and cellularity remained relatively stable, although the collagen str oma became less compact over time. Sixteen rabbit eyes had initial IOP reductions of greater than or equal to 3 mm Hg compared with fellow e yes, which persisted up to 4 weeks postoperatively. Seven eyes (39%) e xhibited a hypertensive phase (IOP exceeded that of fellow eye by grea ter than or equal to 3 mm Hg) from 2 weeks to 3 months postoperatively . Conclusion: The Baerveldt explant is surrounded by a fibrous capsule that matures over time. The bleb histology in the rabbit model is sim ilar to that described with the Molteno implant in primates and humans , except for the eventual development of a fibroblastic inner lining i n the rabbit model, This contrasts with primate and human models, in w hich the inner lining remains an open mesh.