AbstractObjectiveIrritable bowel syndrome (IBS) is a chronic disorder associated with an abnormal gastrointestinal microbiome. Microbiome–host interactions are known to influence organ function including in the central nervous system; thus, we sought to identify whether IBS may be a risk factor for the development of glaucoma.DesignTwo prospective cohort studies.SubjectsThe 1958 United Kingdom Birth Cohort (UKBC; 9091 individuals) and the Danish National Registry of Patients (DNRP; 62,541 individuals with IBS and 625,410 matched general population cohort members).MethodsIn the UKBC, participants were surveyed throughout life (including at ages 42 and 50). The DNRP contains records of hospital‐based contacts and prescription data from the national prescription database.Main Outcome MeasureThe main outcome measure was incidence of glaucoma. In the UKBC, incident glaucoma at age 50 (n = 48) was determined through comparison of survey responses at ages 42 and 50 years. In the DNRP, glaucoma was assessed by hospital diagnosis (n = 1510), glaucoma surgery (n = 582) and initiation of glaucoma medications (n = 1674).ResultsIn the UKBC, the odds ratio (OR) of developing glaucoma between ages 42 and 50 in persons with a chronic IBS diagnosis was increased [OR: 5.84, 95% confidence interval (CI): 2.26–15.13]. People with an IBS diagnosis in the DNRP had a hazard ratio (HR) of 1.35 for developing physician‐diagnosed glaucoma (95% CI: 1.16–1.56), an HR of 1.35 for undergoing glaucoma surgery (95% CI: 1.06–1.70) and an HR of 1.19 for initiating glaucoma medication (95% CI: 1.03–1.38).ConclusionsIn two large European cohort studies, IBS is a risk factor for glaucoma.