Air pollution’s impact on glaucoma
Dirty air is bad for us. It adds to the risk of many health conditions such as asthma, heart attack, stroke, dementia and glaucoma. This article was originally written by Liz Ball, Health Information Manager for Insight magazine.
Common sources of air pollution include cars, lorries, power stations, wood burners, gas hobs and forest fires. Worldwide, more than nine in ten people live with air pollution higher than recommended levels. In 2022, average UK levels of fine air pollution particles (known as PM2.5) were 1.66 times recommended limits.
Our eyes are open to air pollution. It’s possible that our eyes absorb pollutants directly from the air. Our tear film and the wall of our eyes give some protection, and it’s unclear how much pollution gets through. Alternatively, pollution can pass from our lungs into our blood, and blood carries pollutants around our bodies. Fine air pollution particles less than 2.5 micrometres in size (known as PM2.5) are particularly bad for our health because they’re so small they can get into our bloodstream and even cross from blood into our brain.
If you live somewhere with high levels of PM2.5, you’re more likely to have high eye pressure and primary open angle glaucoma (POAG). High eye pressure increases the risk of POAG. But the increased rates of POAG are greater than the increased rates of high eye pressure.
Glaucoma is damage to the nerve that takes information from your eye to your brain (your optic nerve). You can have glaucoma without high eye pressure; this is called normal tension glaucoma, and it’s a sub-type of POAG. PM2.5 levels are more strongly linked to normal tension glaucoma than to other POAG. In other words, air pollution appears to directly damage your optic nerve.
We do not know for sure how PM2.5 causes high eye pressure or glaucoma. It might cause inflammation (swelling) which damages your eye’s drainage system and your optic nerve. It might lead to build-up of protein plaques that damage nerves. It might affect the tiny blood vessels at the back of your eye, depriving nerve cells of oxygen. It might be a combination of all of these and more.
Living in an area with high air pollution for a long time increases your risk of angle closure. Angle closure is when the coloured part of your eye (your iris) blocks your eye’s drainage system. This block can lead to high eye pressure, which can lead to angle closure glaucoma.
Angle closure can happen slowly over months or years or suddenly. Going somewhere with high air pollution for a short time increases your risk of sudden (acute) angle closure in the few days afterwards. Sudden angle closure can lead to your eye pressure going very high very quickly. You might get eye pain, a headache, see coloured rings around lights and feel sick. If you get any signs of acute angle closure, you should get medical advice straight away. We don’t know why air pollution can cause angle closure.
But what difference does moving between areas with cleaner and dirtier air make? Does improving air quality in your home, for example by ditching your wood burner or gas hob, make any difference? We don’t yet know.
Other things, such as getting older and having a close relative with glaucoma, increase your risk of glaucoma more than air pollution does. But air pollution is interesting because it’s something that society can change. We don’t know if reducing air pollution would make any difference for people living with glaucoma now. But reducing air pollution would help reduce the number of people who develop glaucoma in the future. Plus, developing an understanding of how air pollution increases the risk of glaucoma might help develop new ways to prevent or treat glaucoma.