Metformin use linked to modest glaucoma risk reduction in diabetic patients

This systematic review and meta-analysis synthesized data from observational cohort studies involving over 1.2 million patients with diabetes to evaluate the association between metformin use and glaucoma incidence. The primary analysis of crude odds ratios showed no significant association (OR 0.96, 95% CI 0.87-1.06), suggesting that raw comparisons between metformin users and nonusers or users of other antidiabetic drugs did not indicate a clear effect. However, sensitivity analyses that excluded nonmetformin active comparators revealed a modest but statistically significant reduction in glaucoma risk (OR 0.92, 95% CI 0.87-0.98), hinting at a potential protective effect when more specific comparisons are made.

Time-to-event analyses provided further insight, with unadjusted hazard ratios showing a lower risk among metformin users (HR 0.86, 95% CI 0.79-0.93). After adjustment for confounders, the association remained significant but attenuated (aHR 0.88, 95% CI 0.80-0.96), indicating that metformin use may be independently associated with a reduced glaucoma risk in diabetic populations. These findings are consistent across different analytical approaches, though the magnitude of the effect is modest.

The certainty of evidence ranged from very low for comparator analyses to moderate for time-to-event analyses, reflecting limitations such as high heterogeneity (I² = 79.14% for crude OR analysis) and the observational nature of the studies. Safety data were not reported, and follow-up duration was unspecified, which constrains the ability to draw definitive causal inferences. Nonetheless, the practice relevance is notable, as identifying systemic medications that could modify glaucoma risk may inform prevention strategies for diabetic patients.

Key limitations include the reliance on observational data, which are prone to confounding and selection bias, and the high heterogeneity across studies. The authors caution against overinterpreting crude analyses, which showed no association, while sensitivity and time-to-event analyses suggested a possible protective effect. Funding and conflicts of interest were not reported, which may introduce additional bias.

In clinical practice, these results suggest that metformin use in diabetic patients might be associated with a modest reduction in glaucoma risk, but the evidence is not strong enough to recommend metformin specifically for glaucoma prevention. Further research, ideally through randomized controlled trials, is needed to confirm these associations and explore underlying mechanisms.

Overall, this meta-analysis highlights a potential link between metformin and reduced glaucoma incidence in diabetic patients, but the findings should be interpreted with caution due to the observational design and varying evidence certainty. Clinicians should consider these results as hypothesis-generating rather than definitive guidance for treatment decisions.