The Advanced Glaucoma Intervention Study (AGIS): 5. Encapsulated bleb after initial trabeculectomy

PURPOSE: To compare the incidence of encapsulated bleb after trabeculectomy in eyes with and without previous argon laser trabeculoplasty and to asses s other risk factors for encapsulated bleb development. METHODS: After medical treatment failure, eyes enrolled in the Advanced Gla ucoma Intervention Study (AGIS) were randomly assigned to sequences of inte rventions starting with either argon laser trabeculoplasty or trabeculectom y. In the present study we compared the clinical course for 1 year after tr abeculectomy in 119 eyes with failed argon laser trabeculoplasty with that of 379 eyes without previous argon laser trabeculoplasty. Data on bleb enca psulation were collected at the time that the encapsulation was diagnosed, and 3 and 6 months later. RESULTS: Of multiple factors examined in the AGIS data for the risk of deve loping encapsulated bleb, only male gender and high school graduation witho ut further formal education were statistically significant. Encapsulation o ccurred in 18.5% of eyes with previous argon laser trabeculoplasty failure and 14.5% of eyes without previous argon laser trabeculoplasty (unadjusted relative risk, 1.27; 95% confidence limits = 0.81, 2.00; P = .23), After ad justing for age, gender, educational achievement, prescribed systemic beta- blockers, diabetes, visual held score, and years since glaucoma diagnosis, this difference remains statistically not significant. Four weeks after tra beculectomy, mean intraocular pressure. was 7.5 mm Hg higher in eyes with ( 22.5 mm Hg) than without (15.0 mm Hg) encapsulated bleb; at 1 year after tr abeculectomy and the resumption of medical therapy when needed, this excess was reduced to 1.4 mm Hg. CONCLUSIONS: This study, as did two previous studies, found male gender to be a risk factor for bleb encapsulation. Four studies, including the presen t study, have reported a higher rate of encapsulation in eyes with previous argon laser trabeculoplasty; in two of the studies, one of which was the p resent study, the rate was not. statistically significantly higher; in the other two studies the rate was significantly higher. The 4-week postoperati ve mean intraocular pressure was higher in eyes with than without encapsula ted bleb; with the resumption of medical treatment the two means converged after 1 year. (C) 1999 by Elsevier Science Inc. All rights reserved.