A recent study published in BMJ Open Ophthalmology has found that people with type 2 diabetes who use metformin may have lower odds of developing intermediate age-related macular degeneration (AMD). The research analyzed retinal images from more than 2,000 patients over a five-year period.
The study was based on data from the Individualised Screening for Diabetic Retinopathy (ISDR) project in Liverpool, United Kingdom. Researchers conducted a retrospective analysis using prospectively collected screening data to examine whether metformin prescription is linked to AMD incidence. After excluding participants with ungradable images or type 1 diabetes, the final sample included 2,089 individuals aged 50 and older with clinically validated type 2 diabetes.
Participants underwent retinal fundus photography at the start of the study in 2011 and again after five years in 2016. Images were graded according to a modified Age-Related Eye Disease Study (AREDS) classification system. Disease severity was categorized as no AMD, early, intermediate, or late AMD.
Researchers used multivariable logistic regression models to evaluate the association between metformin use and new cases of AMD. These models adjusted for several factors such as age, sex, glycated haemoglobin (HbA1c), duration of diabetes, presence of diabetic retinopathy, and other variables. However, information about smoking habits, diet, and supplement use was limited.
The results showed that metformin users had approximately 37% lower odds of developing intermediate-stage AMD compared to non-users over the five-year period (p = 0.01). Adjusted odds ratios ranged from 0.63 to 0.66 (p = 0.01–0.02). The findings reflect relative rather than absolute risk reduction.
In unadjusted analyses, there appeared to be an association between metformin use and reduced incidence of late-stage AMD; however, this lost statistical significance after adjusting for age and sex due to small numbers of late-stage cases.
No significant link was observed between metformin use and early-stage AMD development. The researchers noted that those not prescribed metformin tended to be older and had a higher baseline prevalence of AMD but stated that the association with intermediate disease persisted even after adjustment for these differences.
The authors caution that causality cannot be established based on this observational study alone: "This study provides observational, image-based evidence suggesting an association between metformin use and a lower incidence of intermediate AMD, but does not provide definitive proof of a protective effect." They also highlighted limitations such as incomplete lifestyle data collection and lack of detailed information on medication dose or adherence.
Metformin is widely used as an inexpensive treatment for type 2 diabetes with a well-established safety record. Previous studies have suggested it may have anti-inflammatory properties beyond its role in controlling blood sugar levels.
Because effective treatments for early stages of AMD are lacking—current therapies mainly target advanced wet-stage disease—the findings support further investigation into repurposing existing drugs like metformin for preventive purposes among people at risk for vision loss due to macular degeneration.
Clinical trials are needed before any recommendations can be made about using metformin specifically for preventing progression toward sight-threatening forms of macular degeneration.
