New Concepts for Glaucoma Implants - Controlled Aqueous Humor Drainage, Encapsulation Prevention and Local Drug Delivery

Glaucoma is a common cause of blindness in industrialized countries and is the most frequent cause of irreversible blindness worldwide. Since raised intraocular pressure (IOP) has been implicated as the major risk factor, the main goal of all glaucoma treatment is to reduce IOP sufficiently to prevent continuous irreversible retinal ganglion cell damage and progression of visual field loss. Pharmacological reduction of IOP is first-line therapy, followed by laser treatment of the trabecular meshwork and filtering glaucoma surgery, and cyclophotocoagulation of the ciliary body or allogenic implants. The most important glaucoma implants are presented (MOLTENO, AHMED, BAERVELDT, KRUPIN) together with more recent developments (Ex-Press, Eyepass, iStent, Gold micro shunt). Drainage into the suprachoroidal space is a promising option, but is also limited by scarring of the new created outflow route due to proliferation and adhesion of fibroblasts. A deeper understanding of fibroblasts in the related eye compartments is required. Characterization of scleral, choroidal, and, as a reference, Tenon fibroblast subtypes, is possible based on gene expression patterns. Alongside mitomycin C and 5-fluorouracil, newer drugs to prevent fibrosis have been proposed, offering effects that are more specific and more physiological. Effectors involved in wound healing phases and signaling pathways are potential targets for pharmaceutical intervention. Downregulation of growth factors like TGF-ß and their downstream effectors may suppress proliferation and differentiation of fibroblasts, extracellular matrix deposition, wound contraction, and neovascularization. Furthermore, current approaches to local drug delivery in glaucoma implant technology are briefly summarized.