Association of metformin use among diabetics and the incidence of primary open-angle glaucoma – The Chennai Eye Disease Incidence Study

PURPOSE: Studies have reported the usage of metformin being associated with the reduced risk of progression of glaucoma. The current study aims to determine the association of metformin usage among subjects with diabetes mellitus and the six-year incidence of primary open-angle glaucoma (POAG). METHODS: In this prospective cohort study, subjects who did not have glaucoma at the baseline and had a follow-up after a six-year interval were included. Details such as medical and drug history, applanation tonometry, gonioscopy, pachymetry, optic disc evaluation, and automated perimetry were collected. Incident POAG was defined as subjects who do not have glaucoma at baseline and developed glaucoma as classified International Society of Geographical and Epidemiological Ophthalmology Classification at the follow-up. The association between the subjects who were on metformin for treatment of diabetes mellitus and development of incident POAG was assessed. RESULTS: Among the 4302 eligible participants, 128 (3%) had incident POAG. There were 905 (21.0%) subjects who had diabetes mellitus of which 142 (15.7%) were using metformin. Of the subjects with POAG, 92 (71.9%) were nondiabetics and 36 were diabetics (28.1%). Among the diabetics, the incidence of POAG among those on metformin was 5.6% (8 participants) and those not on metformin was 3.6% (28 participants). There was no difference in the incidence of POAG in subjects with diabetes mellitus, with and without metformin use (P = 0.25). Logistic regression showed no association of metformin use with the incidence of POAG (OR: 1.33, 95 CI: 0.58–3.04, P = 0.49) after adjusting for age, gender, and place of residence. CONCLUSION: The current study did not find any association between the effects of metformin on the incidence of POAG.