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.