Children living in heavily polluted cities could be at risk of going permanently blind, a study warns.
Researchers recruited 30,000 school children in China and had them undergo a series of vision tests to look for myopia, also known as nearsightedness.
Affecting nearly half of Americans, myopia causes distant objects to appear blurry while closer objects are clear.
While most cases can be treated with glasses or contact lenses, some forms can eventually lead to conditions like cataracts and glaucoma, which gradually cause irreversible blindness.
The team found that while cases of severe myopia were most strongly linked to genetic factors and younger age – when the eyes are more sensitive to pollutants – milder cases were tied to modifiable risk factors.
These included environmental contaminants emitted by cars, factories and powerplants, as well as access to green space outdoors.
It’s thought that air pollution triggers inflammation in the eye and disrupts tear film, a protective layer around the eye. Additionally, pollutants may damage the cornea, leading to scarring.
And reducing chemical contaminants by about 20 percent led to improvements in vision scores in children with mild myopia.
The researchers believe reducing pollution levels while children’s eyes are vulnerable and developing could improve vision levels before severe, lasting disease begins.
Researchers in China found environmental pollution contributed to myopia, or nearsightedness, in children (stock image)
Professor Zongbo Shi, co-supervisor of the study and professor of atmospheric biogeochemistry at the University of Birmingham in the UK, said: ‘While genetics and screen time are long recognized as contributors to childhood myopia, this study is among the first to isolate air pollution as a meaningful and modifiable risk factor.
‘Clean air isn’t just about respiratory health – it’s about visual health too. Our results show that improving air quality could be a valuable strategic intervention to protect children’s eyesight, especially during their most vulnerable developmental years.’
The study, published Tuesday in the journal PNAS Nexus, looked at 29,971 Chinese children in elementary, middle and high school, who were recruited between March 2021 and December 2023.
The majority (70 percent) were in elementary school, and 52 percent of participants were boys.
Nearly two-thirds also had at least one parent with myopia, as genetics are a know risk factor, and 85 percent lived in urban areas, which generally have more pollution that rural neighborhoods.
The team also measured levels of fine particulate matter (PM2.5), a group of microscopic particles that are emitted directly into the air from fossils fuels burned from factories and gasoline-powered stoves and cars, as well as burning wood in fireplaces.
These particles are so small that they are blind to the eye and the nose and lungs can’t filter them out, allowing them to travel to the bloodstream and induce widespread inflammation.
They also looked at nitrogen oxide (NO2), which is formed from fossil fuel combustion and released by vehicles, power plants and industrial processes.
Importantly, the researchers looked at China, which has a PM2.5 concentration six times greater than the World Health Organization’s safe limit. It’s also the world’s largest emitter of greenhouse gases, producing about 27 percent of global emissions.
The team measured levels of NO2 and PM2.5, which are emitted through fossil fuels burned from factories and power plants. Pictured above is a cloud of pollution over Denver, Colorado (stock image)
The above chart shows the improvement of children’s uncorrected visual acuity (UCVA) scores after researchers reduced pollution levels in a simulation. UCVA accounts of vision sharpness without corrective lenses
Overall, 53 percent of participants were diagnosed with myopia.
The team found younger age, parents having myopia and levels of NO2 and PM2.5 were the most significant drivers of myopia in children.
They found environmental pollution was more closely related to myopia, while children with more access to green space had clearer vision.
About 81 percent of cases of severe myopia were directly tied to non-modifiable risk factors like genetics and younger age, whereas environmental factors only contributed to 4.3 percent of severe cases.
However, environmental factors explained 12 percent of mild myopia cases, and behavioral factors like sleep and the amount of time spent outside in green space accounted for 13.6 percent of cases.
They also found PM2.5 pollution was linked to 44 percent more myopia cases in milder disease versus more severe forms of myopia.
The above map shows levels of PM2.5 in each US state as of 2020, the latest data available
The above map shows levels of PM2.5 in each US county as of 2020, the latest data available
The team also used machine learning to simulate ‘clean air’ scenarios and measure the impacts of lower concentrations of air pollution. They found reducing NO2 and PM2.5 levels by 20 percent improved children’s overall vision scores.
The researchers wrote: ‘Thus, roughly one-quarter of the risk in [mild] myopia was attributable to modifiable influences, nearly double the relative contribution seen in high myopia.’
The researchers wrote: ‘This pattern indicates that in children with school myopia, differences in pollution exposure have a stronger impact on vision, whereas in severe myopia cases, vision impairment is mainly driven by demographic factors, leaving environmental influences less influential.’
Study co-author Dr Yuquing Dai of the University of Birmingham said: ‘Myopia is on the rise globally, and it can lead to serious eye problems later in life. While we can’t change a child’s genes, we can improve their environment.
‘If we act early – before severe myopia sets in – we can make a real difference.’