Immunohistochemical analysis of extracellular matrix bleb capsules of functioning and non‐functioning glaucoma drainage implants

Abstract

To detect by immunohistochemical means the changes in bleb capsules at the cellular level between functioning and non-functioning glaucoma drainage implants (GDIs). Three samples each of functioning (1 Baerveldt and 2 Molteno implants) and non-functioning filtration blebs (1 Molteno and 2 Ahmed implants) were studied. A non-functioning bleb was defined as an intra-ocular pressure (IOP) >21mmHg or a <20% reduction in IOP from baseline on three consecutive follow-up visits with maximal tolerated medication. The capsules were obtained between 6 and 108months after GDI insertion for medical reasons only. Primary antibodies were used to stain fibronectin, tenascin, laminin, collagen IV and smooth muscle actin (SMA). The samples were graded on the basis of the intensity and quantity of immunohistochemical staining into four categories as follows: no staining or a mild, moderate or marked staining. The non-functioning blebs expressed more fibronectin, tenascin and SMA through the whole capsule wall than the functioning blebs. In the functioning blebs, tenascin was found mainly in the inner layer of the capsule. More type IV collagen and laminin were also found in the non-functioning bleb capsules than in the functioning blebs. No difference was found between the bleb capsules irrespective of whether they had been perfused with aqueous humour immediately after surgery (Ahmed) or after a delay (Molteno, Baerveldt). Accumulation of extracellular matrix components and activated fibroblasts in the bleb capsules of non-functioning GDI indicates the presence of an active wound healing process, suggesting a possible reduction in filtration through the bleb wall.