Tip of the Month
Publishing date: November 2017
The Science behind the Tip
Bleb encapsulation may occur 2 to 6 weeks after trabeculectomy, when an elevated, tense, dome-shaped bleb develops with an associated rise in IOP. It is more commonly found after laser trabeculoplasty (incidence of 14.5% - 18.5%) (1).
While it is common practice to needle the bleb and inject 5-fluorouracil, a 2012 Cochrane review of the treatment of encapsulated blebs concluded that needling does not provide better results than conservative treatment (2). In a study using aqueous suppressants, all eyes responded successfully after a median period of 8 weeks (3). These results support an earlier study, where all patients treated conservatively achieved long-term IOP control, usually without topical treatment (4).
One possibility to explain this phenomenon is that by reducing the IOP medically, the bleb wall becomes less compressed and the microscopic collector channels in the bleb wall start to function, leading to a more porous bleb wall (4). Alternatively, it may simply be a consequence of change in the bleb morphology as part of the natural history of the post surgical period.
Contributor: John F Salmon MD - Oxford
1) Schwartz AL, Van Veldhuizen PC, Gaasterland DE et al. The Advanced Glaucoma Intervention Study (AGIS); 5. Encapsulated bleb after initial trabeculectomy. Am J Ophthalmol 1999; 127: 8-19
2) Feyi-Waboso A, Ejere HOD Needling for encapsulated trabeculectomy filtering blebs. Cochrane Database and Systemic Reviews 2012; 8. Art No: CD 003658. DOI: 10.1002/14651858
3) Costa VP, Correa MM, Kara-Jose N. Needling versus medical treatment in encapsulated blebs. Ophthalmology 1997; 104: 1215-20
4) Scott DR, Quigley HA. Medical management of a high bleb phase after trabeculectomies. Ophthalmology 1988; 1169-1173.
Tip Reviewer: Roger Hitchings
Tip Editor: John Salmon