Clinical and histopathologic analysis of thin filtering bleb after trabeculectomy

Objective To analyze the clinical and histopathologic changes of thin filtering bleb and investigate the pathogenesis of hypotony and other related complications after trabeculectomy.Design Retrospective case series.Participants Thirty consecutive patients admitted to Zhongshan Ophthalmic Center for surgical revision of thin filtering bleb because of thin-bleb-related complications from January,1999 to September,2008.Methods The intraocular pressure and thin-bleb-related complications of the patients were recorded.The different mitomycin C(MMC)doses applied in trabeculectomy were analyzed.Marginal samples of the filtering bleb wall were taken for histopathologic examinations in seven patients with hypotony during surgical revision of the bleb.Main Outcome Measures lntraocular pressure,thin-bleb-related complications,MMC doses,histopathologic results of the filtering bleb.Results The time of surgical revision of bleb from trabeculectomy was 5 months to 9 years,average(49.0±33.3)months.The intraocular pressure before surgical bleb revision was 2.7-11.0mmHg,average(4.40±4.49)mmHg.The thin-bleb-related complications included:hypotony(21 cases, 70%),bleb leaking(18 cases,60%),shallow anterior chamber(2 cases,6.7%),hypotony-induced mac ular edema(7 cases,23.3%),huge thin bleb(5 cases,16.7%),overhanging filtering bleb(4 cases,13.3%),blebitis(5 cases,16.7%)and endophthalmitis(2 cases,6.7%).All patients had a history of MMC application in the trabeculectomy procedure,and 53.33%used high-dose MMC(≥0.286mg/ml).The histopathologic examinations disclosed degeneration,thinning,even local interruption of the bleb conjunctival epithelium.The subjacent connective tissue was fibroblastic and degenerated.Subconjunctival loose connective tissue containing clear spaces and conjunctival epithelium ingrow to form cyst-like structure were found.Conclusions The thin filtering bleb after trabeculectomy may cause many serious ocular complications.Local thinning and interruption of the conjunctival epithelium on the bleb due to MMC application(especially high-dose MMC)might be the main cause of hypotony.And disorganization of the subconjunctival connective tissue and epitheliam ingrowth might be also involved in the pathogenesis of hypotony.