Metformin and incidence of age-related macular degeneration in people with diabetes: a population-based 5-year...

Metformin has been identified as a potential treatment for age-related macular degeneration (AMD). Photographic screening for diabetic retinopathy provides an opportunity to conduct a case-control study with systematic AMD grading. We aimed to investigate associations between metformin use and incidence and progression of AMD at different grades.

We randomly sampled 2600 participants from 10 336 people aged ≥50 years with diabetes who attended retinopathy screening in 2011 (baseline) and were enrolled to the Individualised Screening for Diabetic Retinopathy study. 2545 of these participants had type 2 diabetes and gradable fundus photographs at baseline, which were graded using modified age related eye disease study grading. We used data including those on metformin prescription from general practitioner records. We used multivariate logistic regression to investigate associations between metformin and incidence or progression of early, intermediate and late AMD.

Of 2545 participants, 2089 attended and had gradable fundus images on year 5. Metformin was associated with reduced incidence of intermediate AMD by 5 years after adjusting for confounders (complete record OR 0.63, 95% CI 0.43 to 0.92, p=0.02). In univariate analysis, metformin was associated with reduced incidence of late AMD (OR 0.43, 95% CI 0.21 to 0.88, p=0.02) but this did not remain significant after adjusting for age and sex. The numbers progressing to late AMD were small. There was no association between metformin and the incidence of early AMD.

We have found a significant association between metformin use and reduction in incidence of intermediate AMD by 37% in people with diabetes over 5 years. Previous epidemiological studies of metformin and AMD have used secondary data on AMD. In this observational study, there were baseline differences between groups, although significant findings remained after adjusting for important confounders. Given metformin's anti-ageing therapeutic effects, the reduction in risk is plausible and warrants prospective clinical trials.