Filtering bleb encapsulation increased by steroid injection.

In an attempt to enhance its pressure-lowering and fibroblast inhibiting effects, we administered 0.15 cc of 24 mg/ml dexamethasone, intra-Tenon's, directly over the fistula site following 16 consecutive filtering surgeries. The encapsulation rate in these eyes was 56% (9/15), as compared with 10% (2/20) in a retrospectively matched group of eyes that had undergone filtering surgery with dexamethasone given subconjunctivally 180 degrees away from the filter site. The effective concentration of dexamethasone achieved by the injections at the filter site apparently did not maintain the fibroblast inhibitory drug level and, in fact, supported fibroblastic growth, resulting in increased encapsulation. Because of the increased encapsulation rate and the lack of any demonstrable benefit associated with it, we do not recommend intralesional dexamethasone in filtering surgery. Commercial topical steroids with their lower concentrations also may act to promote rather than inhibit fibroblast growth. Prolonged steroid use after filtering surgery beyond the inflammatory phase of wound healing (about 2 weeks) may increase fibrosis in the area of the filter, resulting in a thick-walled bleb with few microcysts, one form of which is frank encapsulation. Thus, we recommend that topical steroids routinely be stopped by the third postoperative week if the level of inflammation permits.