Air pollution, as defined by the Oxford English Dictionary, is “the presence in or introduction into the air of a substance which has harmful or poisonous effects.” Air pollution may derive from both human-made and naturally occurring substances and conditions.

In 2021, Tainio and colleagues reported that air pollution may deleteriously impact overall quality of life by decreasing physical activity levels during episodes of elevated air pollution or in chronically polluted environments. More recently, Mandell and colleagues (2020) reported that both air pollution and weather adversely impact dry eye, but in different ways.

Because the eye is continually exposed to atmosphere, and its primary protection from undesirable atmospheric elements is the multilayer tear film, the quality and health of tears is vital to maintaining a healthy ocular surface. In a 2018 Taiwan-based study, Zhong and colleagues used the database of the more than 1 million members of the National Health Insurance of Taiwan and identified 25,818 dry-eye subjects who met the study criteria. They evaluated patient records and environmental data, specifically air pollutants, temperature, and relative humidity, over a nine-year period, from 2004 to 2013.

Using this data, they also evaluated factors associated with early occurrences of dry eye disease (DED), specifically age, gender, and season. They noted that subjects most likely to experience early onset were the elderly (53.6%) and females (68.9%) and that onset was typically during spring. Multivariate analysis of the data also showed a positive association between atmospheric levels of carbon monoxide, nitrogen dioxide, and increased temperature. Interestingly, there was a negative association between DED and relative humidity.

In a 2020 study conducted at the Miami Veterans Affairs Healthcare eye clinic, Huang and colleagues evaluated the association between the symptoms and signs of dry eye and indoor environment, including temperature, humidity, and air pollutants. The authors identified a study sample of 97 veterans who had varying severity of DED. They evaluated objective signs using standard examination and subjective severity of symptoms using the Ocular Surface Disease Index (OSDI).

It is interesting to note that increased humidity levels were associated with worse signs and symptoms. Air pollution as defined by atmospheric particulate matter of 2.5μm or less in size was also associated with dry eye. The authors concluded that particulate matter increased the risk for dry eye.

The Environmental Protection Agency (EPA) has identified several populations that are at risk from exposure to air pollution. These groups include children, pregnant women, older adults, and individuals who had preexisting heart and lung disease (EPA, 2022). As health care providers, we should be aware of the potential ocular complications of air pollutant levels and, especially during periods of elevated atmospheric particular particles, inquire regarding signs and symptoms of dry eye. CLS

REFERENCES

1. Tainio M, Jovanovic Andersen Z, Nieuwenhuijsen MJ, et al. Air pollution, physical activity and health: A mapping review of the evidence. Environ Int. 2021 Feb;147:105954.
2. Mandell JT, Idarraga M, Kumar N, Galor A. Impact of Air Pollution and Weather on Dry Eye. J Clin Med. 2020 Nov 20;9:3740.
3. Zhong JY, Lee YC, Hsieh CJ, Tseng CC, Yiin LM. Association between Dry Eye Disease, Air Pollution and Weather Changes in Taiwan. Int J Environ Res Public Health. 2018 Oct; 15:2269.
4. Huang A, Janecki J, Galor A, et al. Association of the Indoor Environment With Dry Eye Metrics. JAMA Ophthalmol. 2020 Aug 1;138:867-874.
5. EPA. Research on Health Effects from Air Pollution. 2022 Feb 16. Available at epa.gov/air-research/research-health-effects-air-pollution . Accessed Aug. 24, 2022.