Previous surgery and resulting subconjunctival fibrosis
Aphakia
Inflammation
Previous filtering bleb failure
Long-term medical therapy
Neovascular glaucoma
Intraoperative complications (e.g. iris or ciliary process incarceration in the trabeculectomy fistula).
Early signs of a failing filtering bleb:
Gradual IOP elevation during the first 2-4 weeks
Excessive vascularization of the bleb
Flattening of the bleb with the disappearance of microcysts in the bleb
Retrospective studies have indicated that filtration surgery is more likely to be successful in older patients, patients without African heritage, and those without previous long-term medical therapy.
Management
Intra- or postoperative anti proliferative therapy (such as 5-fluorouracil or mitomycin-C) to decrease the likelihood of an aggressive postoperative fibroblast-mediated scarring process.
Sub-tenon's corticosteroid injections may be administered intra- or post-operatively.
Selective applications of digital pressure to the bleb should also be considered to promote aqueous flow into the subconjunctival space, thereby elevating the filtration bleb.