Air pollution in urban areas is linked to heightened risk of progressive and irreversible sight loss known as age-related macular degeneration (AMD), a major study of more than 52,000 people has found.
AMD is the leading cause of irreversible blindness among over 50s in Ireland and in high-income countries – with cases projected to reach 300 million globally by 2040.
After accounting for potentially influential factors including underlying health conditions and lifestyle, analysis of UK data show exposure to higher levels of tiny airborne pollutants known as particulate matter was associated with an 8 per cent increased risk of AMD.
It provides further evidence suggesting the PM2.5 form of particulate matter is causing a wide range of detrimental health impacts that in the past were under estimated.
“Our findings add to the growing evidence of the damaging effects of ambient air pollution, even in the setting of relative low exposure of ambient air pollution,” the UK researchers point out.
Known AMD risk factors include older age, smoking, a high-fat diet and genetic make-up, according to Prof David Keegan, a clinical ophthalmologist based at Dublin's Mater Hospital.
While the 8 per cent figure may seem low it is significant and, when combined with other known factors, could help find a pathway to better treatments, he said.
Participants had an average age of around 60 and the 8 per cent figure is likely to be compounded further over ensuing decades.
AMD is a painless condition gradually impairing central vision, and as a result both near and distance sight are affected with patients becoming unable to read, watch TV and recognise faces. Impaired vision increases risk of falls and injuries which significantly reduces quality of life.
Dry AMD is responsible for 90 per cent of cases whereas wet AMD is associated with significant loss of central vision if left untreated. However, if detected early, the latter is treatable in most cases with preserving or improving vision in 90 per cent of patients.
While progress had been made on wet AMD treatments, there was still a huge burden of untreatable disease, Prof Keegan said. He believed the PM2.5 findings were “particularly interesting” as they could help find “new routes to treatment” in preventing disease or arresting on-going deterioration.
Ambient air pollution could plausibly be associated with AMD through oxidative stress or inflammation, he confirmed. This meant PM2.5 was more likely to get into the bloodstream and cause damage to more active organs that consume high levels of oxygen, such as the eye.
The researchers, whose findings are published in the British Journal of Ophthalmology, also drew on data from 115,954 people participating in the long-term UK Biobank (UKBB) study by focussing on participants aged 40 to 69 with no eye problems at the start of this research in 2006. Using retinal imaging they identified changes in thickness of the retina indicative of AMD.
The study drew on estimates for pollutants including particulate matter, nitrogen dioxide and nitrogen oxides, which are most associated with traffic, to calculate average annual air pollution at people’s home addresses.
Dr Matthew Campbell, associate professor of genetics in Trinity College Dublin (TCD), noted it was an observational study so "correlation does not prove cause", but provided confidence the link made is real.
It added to public health indications showing the vulnerability of people of lower socio-economic status living in urban “hotspots” ie at higher health risk, which included having heart disease, breast cancer and Covid-19, he said.
Immunologist Dr Sarah Doyle, who is also based in TCD, said given smoking is such a high risk factor for AMD, it was plausible that increasing air pollution was also a factor. They may act in combination with a lot of other known factors including body mass index (BMI), she said.
The findings she added, support the view that air pollution is an important "modifiable risk factor" for AMD, but while a person could go to Switzerland where the air was cleaner, this was not "a therapeutic" option.
Prof Keegan believed Ireland would benefit hugely from a study on the scale of the long-term UKBB study, involving some 500,000 people and generating vast amounts of health data in a process greatly assisted by having electronic medical records with strong privacy protection.
A similar approach was deployed successfully in Ireland with retinal screening of diabetes patients, he confirmed.