Implants to Treat Glaucoma: Promising or Not?

Glaucoma is one of the leading causes of blindness and its prevalence increases with age. The most common form, primary open-angle glaucoma, is a chronic, slowly progressive optic neuropathy characterised by the loss of retinal ganglion cells and their axons, leading to irreversible visual field loss. Elevated intraocular pressure (IOP) is the only modifiable risk factor for glaucoma. Reducing IOP to a level that is safe for the patient's eye has been shown to slow disease progression. Lowering IOP in open-angle glaucoma is achieved by eye drops, selective laser trabeculoplasty (SLT) and/or surgery. Many patients are treated with IOP-lowering eye drops, which require lifelong continuous instillation. However, as with other chronic, asymptomatic diseases, adherence to glaucoma treatment is poor for various reasons and is associated with faster disease progression. The purpose of this review is to discuss several sustained-release systems that have been investigated to reduce IOP over time, to address barriers to adherence and improve quality of life. Among these, non-invasive drug-eluting delivery systems such as contact lenses, punctal plugs, and conjunctival ocular inserts have not reached the market. Currently, only two intracameral implants have been approved by the Food and Drug Administration for single use due to corneal safety issues. The biodegradable bimatoprost implant releases the drug continuously for 4-6 months, and its effect on IOP may extend for up to 2 years in 25% of patients. The non-biodegradable intracameral implant releases travoprost for 36 months, when it needs to be removed. However, additional data are needed to assess safety following repeated administration, as well as in broader patient populations and in combination with other treatment approaches such as SLT. Several other biodegradable intracameral implants that release prostaglandin analogues are undergoing clinical trials. In the future, intraocular implants containing genetically modified cells that secrete neurotrophic factors may potentially offer an IOP-independent neuroprotective strategy, complementing existing IOP-lowering implants in glaucoma management.