Otago Glaucoma Surgery Outcome Study: cytology and immunohistochemistry of trabeculectomy blebs

To describe findings of light microscopic examination of trabeculectomy blebs. Histologic and immunohistochemical features of blebs including cell types, and distribution of apoptotic cells and proapoptotic death messengers were examined in six eyes 6.0 to 25.9 years after trabeculectomy. All specimens showed a channel opening into a rectangular cleft in the middle layer of sclera. The channels showed degenerative changes with disintegration and loss of collagen fibers and few pyknotic cells. Changes were extensive on the upper surface of the cleft forming irregular channels extending through and around the edges of the superficial scleral flap into moderately cellular and vascular oedematous conjunctiva covered by intact epithelium. Immunohistochemical staining demonstrated migration of histiocytes from superficial blood vessels into the deeper layers where they apoptosed and disintegrated. Fas ligand+ proapoptotic death messengers were concentrated in the superficial conjunctival regions of blebs. These results indicated that the normal cell processes in functioning trabeculectomy blebs were similar to that of Molteno implant capsules. These processes involved migration of cells from superficial blood vessels into perivascular spaces and the deeper tissues where apoptosis occurred. Apoptosis was associated with breakdown of tissue matrix and release of proapoptotic death messengers that were transported by aqueous to the superficial layers where they suppressed collagen synthesis by inducing apoptosis in metabolically active cells.