Evidence on the neuroprotective properties of brimonidine in glaucoma

Background: glaucoma is the leading cause of irreversible blindness all over the world. The degree of visual field loss accounts for the severity of the disease and represents the main clinical outcome of treatment for patients affected by glaucoma. The alpha 2 agonists, like brimonidine, emerged in the 1960s as topical ophthalmologic treatment. Their neuroprotective mechanism in glaucoma is still debated, ranging from effect on extracellular glutamate, to ocular hypotension and blood flow.Objectives: this systematic review and meta-analysis aims at assessing the efficacy of brimonidine on visual field deterioration during glaucoma through the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) approach.Databases consulted: the literature search has been performed on PubMed, MEDLINE, ClinicalTrials.gov and Scopus up to June 10th, 2020.Study eligibility criteria, participants, and interventions: clinical trials assessing the effects of brimonidine on visual field in patients with glaucoma.Study appraisal: the eligibility of the studies has been assessed by two independent authors and the selection has followed the PRISMA flow diagram. The retrieved results have been subjected to risk of bias evaluation.Results: the search of literature has retrieved 418 papers, among which 5 are eligible for inclusion in the qualitative analysis. All the studies present high heterogeneity, therefore meta-analysis has not been possible. The results obtained suggest that brimonidine improves visual field, but the design of the clinical trials rises some concerns in terms of risk of bias.Conclusions: the evidence of neuroprotective effect of brimonidine is inconclusive and needs stronger support. Large double-blind randomized clinical trials are necessary to strengthen this evidence.