Bleb Encapsulation Research Articles

Restoring the function of the failed bleb

Failure of the filtering bleb after trabeculectomy with a gonioscopically patent drainage cleft is likely to be due to: encapsulation of the bleb; flattening of the bleb; or cystoid bleb. Encapsulated blebs and flattened blebs are usually associated with a high intraocular pressure (IOP) while cystoid blebs are not, but corneal ulceration due to the prominent cystoid bleb may make revision of the bleb necessary. If the IOP is raised it is best to proceed quickly to needling of the bleb using 5-fluorouracil. Sixteen patients underwent needling of the bleb, eight with encapsulated, six flattened and two cystoid blebs. Chronic open-angle glaucoma (10 cases) was the commonest glaucoma. Twelve patients obtained satisfactory control of IOP with mean pre-needling IOP for encapsulated blebs of 32 mmHg (4.27 kPa), flattened blebs 36 mmHg (4.8 kPa) and cystoid blebs 16 mmHg (2.13 kPa), while post-needling IOP for encapsulated blebs was 12 mmHg (1.6 kPa), flattened blebs 13 mmHg (1.73 kPa) and cystoid blebs 12 mmHg (1.6 kPa). Mean follow-up for encapsulated blebs was 15, flattened blebs 11 and for cystoid blebs nine months. Mean time between trabeculectomy and needling was: for encapsulated blebs 16 days; flattened blebs 24 days; and cystoid blebs 19 months.

Restoring the function of the failed bleb

AbstractFailure of the filtering bleb after trabeculectomy with a gonioscopically patent drainage cleft is likely to be due to: encapsulation of the bleb; flattening of the bleb; or cystoid bleb.Encapsulated blebs and flattened blebs are usually associated with a high intraocular pressure (IOP) while cystoid blebs are not, but corneal ulceration due to the prominent cystoid bleb may make revision of the bleb necessary. If the IOP is raised it is best to proceed quickly to needling of the bleb using 5‐fluorouracil. Sixteen patients underwent needling of the bleb, eight with encapsulated, six flattened and two cystoid blebs. Chronic open‐angle glaucoma (10 cases) was the commonest glaucoma. Twelve patients obtained satisfactory control of IOP with mean pre‐needling IOP for encapsulated blebs of 32 mmHg (4.27 kPa), flattened blebs 36 mmHg (4.8 kPa) and cystoid blebs 16mmHg (2.13 kPa), while post‐needling IOP for encapsulated blebs was 12 mmHg (1.6kPa), flattened blebs 13 mmHg (1.73 kPa) and cystoid blebs 12 mmHg (1.6 kPa). Mean follow‐up for encapsulated blebs was 15, flattened blebs 11 and for cystoid blebs nine months. Mean time between trabeculectomy and needling was: for encapsulated blebs 16 days; flattened blebs 24 days; and cystoid blebs 19 months.

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.

Management of Encapsulated Filtration Blebs

Increased intraocular pressure (IOP) in encapsulated filtration blebs was evaluated in 49 eyes of 49 patients followed for 6 to 48 months (mean ± standard deviation, 19.7 ± 12.6 months). Intraocular pressure increased from 10.2 ± 7.5 mmHg at 1 week postfiltration surgery to a peak of 26.1 ± 10.7 mmHg at 3 weeks postoperatively and then decreased to 16.2 ± 5.0 mmHg at 16 weeks and remained stable through the follow-up period. Thirty-nine eyes had a final IOP of 19 mmHg or less; 35 eyes required medical therapy alone (antiglaucoma drops, oral carbonic anhydrase inhibitors, and/or digital massage) with a final IOP of 14.1 ± 3.8 mmHg; and 14 eyes required surgical reintervention for medically uncontrolled IOP elevation, and five of these eyes required two or more surgical reoperative procedures. Vigorous medical therapy, including glaucoma medications, topical steroids, and digital massage, is particularly important for encapsulated blebs during the first 2 months after surgery. After this period, IOP decreases and often remains sufficiently reduced to avoid further surgical intervention.

The Development Encapsulated Filtering Blebs

The development of an encapsulated filtering bleb (Tenon's cyst) complicated 56 of 409 consecutive filtering operations (13.7%) performed during a 40-month period after January 1983. Fifteen eyes (27.8% of encapsulated blebs) required surgical revision. The recognition of bleb encapsulation occurred 20.4 ± 12.7 days (mean ± standard deviation) postoperatively. Prolonged duration of beta-adrenergic antagonist therapy was associated with an increased frequency of bleb encapsulation (180.6 ± 128.5 weeks without encapsulation, 229.0 ± 129.3 weeks with encapsulation, P < 0.009). Bleb encapsulation occurred in 42 of 272 eyes with previous argon laser trabeculoplasty, but in only 4 of 85 eyes without any previous anterior segment laser (P < 0.01). Encapsulated filtering blebs developed in 4 of 12 (33.3%) eyes with congenital glaucoma and 4 of 9 (44.4%) eyes with juvenile glaucoma (P < 0.0002). The intraocular pressures (IOPs) in the eyes with encapsulated filtering blebs were significantly elevated at 1, 2, and 3 postoperative weeks, and at final follow-up compared with eyes without bleb encapsulation.