Fighting Bleb Fibrosis After Glaucoma Surgery: Updated Focus on Key Players and Novel Targets for Therapy

Filtration bleb (FB) fibrosis represents the primary risk factor for glaucoma filtration surgery (GFS) failure. We reviewed the most recent literature on post-GFS fibrosis in humans, focusing on novel molecular pathways and antifibrotic treatments. Three main literature searches were conducted. First, we performed a narrative review of two models of extra-ocular fibrosis, idiopathic pulmonary fibrosis and skin fibrosis, to improve the comprehension of ocular fibrosis. Second, we conducted a systematic review of failed FB features in the PubMed, Embase, and Cochrane Library databases. Selected studies were screened based on the functional state and morphological features of FB. Third, we carried out a narrative review of novel potential antifibrotic molecules. In the systematic review, 11 studies met the criteria for analysis. Immunohistochemistry and genomics deemed SPARC and transglutaminases to be important for tissue remodeling and attributed pivotal roles to TGFβ and M2c macrophages in promoting FB fibrosis. Four major mechanisms were identified in the FB failure process: inflammation, fibroblast proliferation and myofibroblast conversion, vascularization, and tissue remodeling. On this basis, an updated model of FB fibrosis was described. Among the pharmacological options, particular attention was given to nintedanib, pirfenidone, and rapamycin, which are used in skin and pulmonary fibrosis, since their promising effects are demonstrated in experimental models of FB fibrosis. Based on the most recent literature, modern patho-physiological models of FB fibrosis should consider TGFβ and M2c macrophages as pivotal players and favorite targets for therapy, while research on antifibrotic strategies should clinically investigate medications utilized in the management of extra-ocular fibrosis.