Regular use of aspirin can more than double the risk of a leading cause of blindness in older people, research suggests.
Scientists found a significant link between taking aspirin on a regular basis and age-related macular degeneration (AMD).
The association could not be explained by a history of heart disease - the most common reason for regular aspirin use - or smoking.
AMD occurs when the middle of the retina becomes damaged, leading to the progressive blurring of central vision.
Wet, or neovascular, AMD, caused by the growth of abnormal blood vessels is the most serious form of the condition. Without treatment, wet AMD can result in a deterioration of vision within days.
The new research compared rates of wet AMD among more than 2,000 regular and non-regular users of aspirin over a period of 15 years.
Regular use was defined as taking aspirin once or more per week.
Among non-regular users, rates of wet AMD rose from 0.8% at five years to 1.6% at 10 years and 3.7% at 15 years. Corresponding rates for regular aspirin users were 1.9%, 7%, and 9.3%.
The study authors, led by Dr Gerald Liew from the University of Sydney in Australia, wrote in the journal JAMA Internal Medicine: "Currently, there is insufficient evidence to recommend changing clinical practice, except perhaps in patients with strong risk factors for neovascular AMD.. in whom it may be appropriate to raise the potentially small risk of incident neovascular AMD with long-term aspirin therapy."
Any decision on whether to stop aspirin treatment was "complex and needs to be individualised", said the researchers.
Commenting on the findings, US experts Dr Sanjay Kaul and Dr George Diamond, from Cedars-Sinai Medical Center in Los Angeles, wrote in the journal: "From a purely science-of-medicine perspective, the strength of the evidence is not sufficiently robust to be clinically directive."