Evaluation of Bleb Characteristics after Trabeculectomy and Glaucoma Implant Surgery in the Rabbit

The characteristics of the conjunctival bleb are some of the most important factors for the surgical success of glaucoma filtering surgery. To improve surgical outcome, we investigated bleb histology after 3 different glaucoma surgeries. Surgery was performed in 21 white rabbits. Rabbits were randomized to trabeculectomy or implantation with EX-PRESS or a silicone tube (each n = 7). Bleb survival, intraocular pressure (IOP), and vascularity were evaluated. At 6 weeks, eyes were enucleated for histological analysis. Postoperative IOP at 2 weeks was significantly lower in the trabeculectomy and the EX-PRESS group than in the silicone tube group (p = 0.037) but not thereafter. Postoperative bleb survival (p = 0.542) and vascularity (p = 0.988) were similar among the 3 groups. Histologically, a capsule showing mild fibroblast proliferation associated with intercellular collagen was present around the surgical site. The thickness of the bleb was similar among all experimental groups, but it was significantly greater than in controls (p < 0.05). The inflammatory area did not differ between the EX-PRESS and the silicone tube group but was significantly greater in the trabeculectomy group than in the tube group (p = 0.031). A correlation between the thickness of the bleb wall and inflammation was found (r = 0.56, p < 0.01). EX-PRESS and silicone tube implants appear to be relatively inert, with little difference in biocompatibility and bleb survival. Since some degree of inflammation was still observed histologically in the bleb, more noninvasive surgical methods and more biocompatible materials may be desirable.