Joint Air Pollutant Exposure Linked to Eye Disease

A recent prospective cohort study conducted in Hong Kong revealed a substantial linkage between simultaneous exposure to multiple air pollutants and age-related eye disease incidence.

“Given that individuals are exposed to a complex mixture of air pollutants and that high collinearity exists among different pollutants, estimating the combined effect of multiple air pollutants on human health is essential,” wrote Yingan Li, department of ophthalmology and visual sciences, Chinese University of Hong Kong, and colleagues.1

The team collected information on more than 500,000 participants through the UK Biobank database; after excluding those with diagnoses prior to the study’s timeframe of 2006-2010, the total was narrowed down to 441,567 participants. These participants came from 22 different Biobank centers in England, Scotland, and Wales; 54.38% of participants were female and 45.62% were male. Of these, 55,104 were diagnosed with cataract, 11,940 with glaucoma, and 9060 with AMD over a follow-up period of 14.41 years.1

Air pollutants accounted for in the study included nitrogen dioxide (NO2), nitrogen oxides (NO), and particulate matter below 2.5 μm (PM2.5), between 2.5 and 10 μm (PM2.5-10), and at 10 μm or less (PM10). Mean annual pollutant concentrations were as follows:1

• PM2.5, 9.99 (1.06) μg/m3
• PM2.5-10, 6.43 (0.90) μg/m3
• PM10, 16.23 (1.90) μg/m3
• NO2, 26.64 (7.63) μg/m3
• NO, 17.35 (9.09) μg/m3

To measure potential joint exposure risk, the team created air pollution scores for each individual disease by totaling the concentrations of the pollutants and deriving the multivariable-adjusted risk estimates (β coefficients) from the final model.1

The hazard ratios (HRs) indicated that long-term exposure to any individual pollutant had a significant association with increased risk for cataract. Per interquartile range (IQR) increment, the HRs were 1.06 (95% CI, 1.05-1.07) for PM2.5, 1.01 (95% CI, 1.00-1.02) for PM10, 1.05 (95% CI, 1.04-1.07) for NO2, and 1.03 (95% CI, 1.02-1.04) for NO (all P <.05). Notably, there was no significant association between cataract incidence and PM2.5-10. Glaucoma and AMD exhibited significantly higher risk after exposure to PM2.5, NO2, and NO, while no significant connection was seen for PM2.5-10 or PM10.1

The team then utilized the weighted air pollution score of all 5 pollutants; results indicated that the risk of a given disease increased by 4-5% for each IQR increment in air pollution score. For cataract, HR 1.05 (95% CI, 1.04-1.06); glaucoma, 1.04 (95% CI, 1.02-1.06); AMD (95% CI, 1.04-1.07) (all P <.05). The highest quartile of air pollution score exhibited HRs of 1.13 (95% CI, 1.1-1.16) for cataract, 1.09 (95% CI, 1.03-1.15) for glaucoma, and 1.14 (95% CI, 1.07-1.22) for AMD (all P <.05) when compared to the lowest quartile. Li and colleagues suggest that these data present additive effects of exposure to potential mixtures.1

A nonlinear association was observed between air pollution score and both AMD and cataract; risk increased sharply at low pollutant concentrations, but began to slow as pollution levels rose, even declining in some instances. The team suspects this is the result of individuals seeking medical attention or altering lifestyles to avoid worsening air quality.1

One of the primary limitations of the study, as explicitly mentioned by Li and colleagues, is the limited data available on common pollutants. Carbon monoxide, sulfur dioxide, and other trace elements were not listed in the UK Biobank, which leaves the study with a smaller pool of contaminants to test. This limitation may result in similarly dangerous contaminants going unnoticed.1

Historically, data regarding combinations of air pollutants and the corresponding prevalence of eye disease have been lacking. There is no existing metric for measuring combinations of air pollutants.2 Li and colleagues enacted this study with the goal of highlighting the necessity for a set system of calculating air pollutants’ cumulative effects.

“Considering that many countries’ air quality standards are still well above the WHO Global Air Quality Guidelines in 2005, the findings suggest that stricter standards or regulations for air pollution control should be implemented in the future policy, making to alleviate the disease burden of cataract, glaucoma and AMD,” wrote Li and colleagues.1

References

1. Li Y, Zhang Y, Kam KW, et al. Associations of long-term joint exposure to multiple ambient air pollutants with the incidence of age-related eye diseases. Ecotoxicology and Environmental Safety. 2025;294:118052. doi:10.1016/j.ecoenv.2025.118052

2. Oakes M, Baxter L, Long TC. Evaluating the application of multipollutant exposure metrics in Air Pollution Health Studies. Environment International. 2014;69:90-99. doi:10.1016/j.envint.2014.03.030