Air pollution has been linked to irreversible sight loss in new research.
Scientists from University College London (UCL) analysed more than 115,000 people over 15 years.
Results reveal the participants who were exposed to the highest levels of fine particulate matter (PM) were 8% more likely to develop age-related macular degeneration (AMD).
Released by vehicle emissions, PM floats unseen in the atmosphere. When smaller than 2.5μm (PM2.5), 400th of a millimetre, the particles can become lodged in the lungs.
AMD is the leading cause of sight loss in the UK, affecting more than 60,000 people.
Although unclear, air pollution may trigger a form of internal stress or inflammation that leads to the vision disorder.
“Here we have identified yet another health risk posed by air pollution, strengthening the evidence that improving the air we breathe should be a key public health priority,” said lead author Professor Paul Foster.
“Our findings suggest living in an area with polluted air, particularly fine particulate matter or combustion-related particles that come from road traffic, could contribute to eye disease.
“Even relatively low exposure to air pollution appears to impact the risk of AMD, suggesting air pollution is an important modifiable risk factor affecting risk of eye disease for a very large number of people.”
There are different forms of AMD. So-called dry AMD occurs when cells in the centre of the retina, the macula, slowly deteriorate.
Wet AMD is defined as abnormal blood cells growing into the macula, leading to a rapid loss of central vision.
Both conditions usually affect people in their 50s or 60s. Neither cause complete blindness, however, they can make day-to-day life challenging.
Dry AMD has no treatment, while drugs can help slow wet AMD’s progression. These must be administered quickly, however, before the macula becomes permanently scarred.
AMD of any form affects around 200 million people worldwide, which is expected to rise to nearly 300 million by 2040, the UCL scientists wrote in the British Journal of Ophthalmology.
With smoking a risk factor, the team felt it was “plausible” air pollution may also make people more susceptible to the vision disorder.
The scientists therefore analysed participants of the UK Biobank study, aged 40 to 69, who had no vision problems at the start of the research in 2006.
Over 15 years, the participants reported any AMD diagnosis.
More than 50,000 of the participants also had the thickness and number of their retina light receptors assessed between 2009 and 2012, with these measurements being AMD indictors.
Traffic and land use data gauged the participants’ average air pollution exposure.
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The results suggest exposure to the highest PM 2.5 levels was associated with an 8% increased risk of AMD, compared to the lowest exposure levels.
It is unclear how the risk varied according to different forms of AMD.
The findings remained true after the scientists accounted for other factors that may affect a person’s sight, like their underlying health and lifestyle.
Other pollutants were linked to changes to the eye’s retinal structure.
“Overall, our findings suggest ambient air pollution, especially fine [particulate matter] or those of combustion-related particles, may affect AMD risk,” wrote the scientists.
“It is possible the structural features observed may be unrelated to AMD, but associated with pollution-induced retinal toxicity.
“However, the direction of the relationships between air pollution and both AMD and associated retinal layer thicknesses indicate higher exposure to air pollution may make the cells more vulnerable and increase the risk of AMD.
“Our findings add to the growing evidence of the damaging effects of ambient air pollution, even in the setting of relative low exposure.
“If [the results] are replicated, this would support the view air pollution is an important modifiable risk factor for AMD.”
The UCL scientists and other experts have stressed the study was observational, and therefore does not prove cause and effect.
“Inevitably, there will be many differences between people who live in areas with different levels of air pollution, besides the pollution difference,” said Professor Kevin McConway from The Open University.
“One can never be certain everything relevant was dealt with and that’s why the results can’t establish air pollution causes an increased risk of AMD.
“A study that followed people up over time, rather than (as this one does) just looking at the pollution level outside homes and the condition of their eyes at one point in time, would help to clarify the position on cause and effect.”
Nevertheless, studies that confirm the UCL results could aid future treatments.
“We know from other research that a diet high in fruit and vegetables provides antioxidant nutrients that is protective against age-related macular degeneration, and further research is needed to see the impact of increasing fruit and vegetables in the diet on those in areas of high air pollution,” added Professor Anna Hansell from the University of Leicester.
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