London, UK: People who live in areas with higher levels of air pollution are more likely to develop glaucoma and cataract, according to a large study presented today (Monday) at the 44th Congress of the European Society of Cataract and Refractive Surgeons (ESCRS). [1]
There is now strong evidence that being exposed to polluted air is harmful to the heart and lungs. Much less is known about the effects of air pollution on the eyes, even though they are directly exposed. Researchers say their findings add to the case for tighter air quality standards and pollution-reducing measures.
The research was presented by Dr Ahmed Alnabihi from King Khaled Eye Specialist Hospital and Research Center, Riyadh, Saudi Arabia. He said: "We've known for years that air pollution damages the lungs and heart, but its effects on the eyes have been much less studied and the existing evidence was scattered and inconclusive.
"Every day, we see patients losing vision to conditions like glaucoma and cataract. These diseases are labelled as 'age related' as though aging is the only culprit, but that always felt incomplete to me. If something environmental is accelerating these conditions, that changes our thinking and suggests we could take action to reduce the risks."
The study is a systematic review and meta-analysis, meaning the researchers gathered together all existing research in this area and pooled the data together. This included 41 separate observational studies, drawing on data from millions of people across East Asia and the UK and including some of the largest eye health databases in the world.
Researchers looked at levels of several types of air pollution: particulate matter (PM₂.₅ and PM₁₀), nitrogen dioxide, sulphur dioxide, ozone and carbon monoxide. They compared these with how many people were diagnosed with glaucoma, cataract or age-related macular degeneration.
This showed that the higher the levels of fine particulate matter (PM₂.₅), the greater the risks of glaucoma. People living in the most polluted areas had up to 70% higher odds of glaucoma compared to those in the least polluted areas. People living in more polluted areas also face a consistently higher risk of developing cataracts, and the more pollution, the greater the risk.
Dr Alnabihi said: "The clearest finding was for fine particulate matter — the tiny particles in smoke, vehicle exhaust and industrial pollution that are small enough to get deep into the body. For every meaningful step up in pollution exposure, the risk of glaucoma rose by around eight per cent and cataract by around four per cent. The evidence for age-related macular degeneration was less consistent, although some research supported a link. Other pollutants, including nitrogen dioxide and ozone, showed weaker or more mixed associations.
"Fine particles are thought to cause inflammation and oxidative stress in the body. Over years of exposure, these effects may damage the optic nerve, which is relevant to glaucoma, or the lens, which is relevant to cataract. Unlike most other organs, the eye is directly open to the environment. The ocular surface – the tear film, conjunctiva and cornea – has no barrier between it and outdoor air. That makes the biological plausibility here stronger than for some other organs.
"These findings add weight to the case for tighter air quality standards and pollution-reducing measures such as green spaces and traffic reduction in cities. Every major clean air policy has been justified primarily on the grounds of cardiovascular and lung health. Our paper adds a new organ system to that conversation. Policymakers who need to justify investment in emission controls now have one more evidence-based reason to do so, and it's one that affects our vision – a sense people are particularly afraid of losing."
The researchers say that more work is needed in this area, including studies of eye health in highly polluted regions.
Dr Filomena Ribeiro, ESCRS Immediate Past-President, who is Head of the Ophthalmology Department at Hospital da Luz, Lisbon, Portugal, and was not involved in the research, said: "Cataract, where the lens in the eye becomes cloudy, causes blurred vision and loss of sight. It is the leading cause of impaired vision worldwide affecting around 94 million people. In glaucoma, the main nerve that connects the eye to the brain becomes damaged, leading to vision loss if it's not diagnosed and treated early. Globally, glaucoma affects around 7.7 million people.
"Both conditions become more common as we get older, but this study indicates that people who are exposed to higher levels of air pollution are also facing a greater risk. This research adds eye health to the growing list of reasons to care about air quality."
