TOPIC: Glaucoma is the leading cause of irreversible blindness despite having good prognosis with early treatment. We evaluated the global extent of undetected glaucoma and the factors associated with it in this systematic review and meta-analysis of population-based epidemiological studies. CLINICAL RELEVANCE: Undetected glaucoma increases the risk of vision impairment, which leads to detrimental effects on the quality-of-life and socio-economic well-being of those affected. Detailed information on the extent and factors associated with undetected glaucoma aid in the development of public health interventions. METHODS: We conducted a systematic review and meta-analysis of population-based studies published between January 1, 1990 to June 1, 2020. Article search was conducted in online databases (PubMED, Web-of-Science), grey literatures (opengrey) and non-government organization (NGOs) reports. Our outcome measure was the proportion of glaucoma cases that were undetected previously. Manifest glaucoma included any form of glaucoma reported in the respective study and may include primary-open-angle-glaucoma (POAG), primary-angle-closure-glaucoma (PACG), and/or secondary glaucoma. Undetected glaucoma was defined as glaucoma cases that were undetected prior to diagnosis in the respective study. Random-effect meta-analysis was used to estimate the pooled proportion and factors associated with undetected glaucoma. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines in our study. RESULTS: We identified 61 articles from 55 population-based studies (N= 189,359 participants; N= 6,949 manifest glaucoma; N= 5,558 undetected glaucoma). Globally, more than half of all glaucoma cases were previously undetected in each geographical region. Regionally, Africa (OR 12.70, 95% CI 4.91, 32.86) and Asia (OR 3.41, 95% CI 1.63, 7.16) had higher odds of undetected glaucoma as compared to Europe. Countries with low human development index (HDI, <0.55) had higher proportion of undetected manifest glaucoma as compared to countries of medium to very high HDI (≥0.55, all P <0.001). In 2020, 43.78 million POAG cases were undetected, of which 76.7% reside in Africa and Asia. CONCLUSION: Undetected glaucoma is highly prevalent across diverse communities worldwide, and more common in Africa and Asia. Strategies to improve detection are needed to prevent excess visual disability and blindness due to glaucoma.