Air Pollution and its Effects on the Ocular Surface
Depending on where your practice is located, air pollution may also need to be addressed as a cause of dry eye.
This article originally appeared in the October, 2018 issue of Optometry Times.
As eye care providers, we understand how a range of factors can impact vision and overall eye health. Oftentimes, patients come into our offices with dry eye complaints and we point to factors such as: age, dry air, increased digital device use or systemic medications. However, depending on where your practice is located, air pollution may also need to be addressed as a cause of dry eye.
As someone who practices in the New York City area, I absolutely consider air quality as a significant risk factor when it comes to dry eye. Over the course of any given year, I am in contact with several patients who travel to areas with better air quality for days, weeks or months at a time. Shortly after coming home, many of them report an increase in dry eye symptoms including: burning, stinging, tearing and fluctuations in vision. On the opposite end, I also see several patients who travel to places that are far more polluted than New York City and they come home with those same symptoms, sometimes even worse.
To give a brief overview of air pollution, it can be described as a complex mixture of pollutants including particulate matter, chemical substances and biological materials (1). Its adverse effects are difficult to avoid because unlike the food we eat or the water we drink, people generally cannot choose what type of air to inhale. This common sense statement can be bolstered by the most recent “State of Air” (2017) report released by the American Lung Association, which indicates at least 125 million Americans live in counties with an unhealthy quality of air.
The six common air pollutants acknowledged by the United States Environmental Protection Agency (EPA) include:
- Ground-level ozone
- Particulate matter
- Carbon monoxide
- Sulfur dioxide
- Nitrogen dioxide
Obviously, there are several health risks that come along with both chronic and acute exposure to air pollution such as: respiratory infections, cardiovascular problems and pulmonary disease. Those who assume the most risk from its dangers include: infants, pregnant women, those who work outdoors (especially in cities) and the elderly (1). Moreover, it can be supposed that the economic consequences of illnesses caused by air pollution are far reaching.
Some of the main overall health problems typically associated with air pollution include:
- Asthma attacks
- Wheezing, coughing and shortness of breath
- Cardiovascular disease
- Chronic obstructive pulmonary disease
- Lung cancer
- Premature death
Air Pollution and the Eyes:
As far as the eyes are concerned, a few international studies have attempted to detail the impact of air pollution on the ocular surface. One particular study suggests that high ozone levels and low humidity levels are associated with dry eye in the Korean population (2). Another study found evidence that outpatient visits for conjunctivitis increased significantly with higher levels of air pollution in Hangzhou, China (3). The results of these studies are interesting because not only is dry eye disease linked with air pollution, but also eye infections.
Additional research implies that particulate matter on the ocular surface is more harmful in dry eyes compared to normal eyes (4), which indicates that dry eye patients may be more vulnerable in places where air quality is low. Furthermore, increased levels of nitrogen dioxide (NO2) in the air is associated with nosebleeds, dry cough and eye irritation (5), which makes the case for a correlation between air pollution and dry eye disease even stronger.
From what we can tell, most of the main eye health problems associated with air pollution stem from increased levels of dry eye, which includes the following symptoms:
- Burning or stinging
- Increased hyperemia
- Fluctuations in vision
- Foreign body sensation
- Contact lens intolerance
Who’s at Risk?
In comparison, those of us who live in North America enjoy cleaner air than people in other growing regions of the world. For the most part, larger cities in the United States, Canada, Central America and most of the Caribbean barely make a dent on the global air pollution scale. However, this is not to suggest that we don’t have problems of our own and no current action is necessary to improve air quality.
The top ten cities in the United States with the highest levels of air pollution (ground-level ozone) are (6):
- Los Angeles-Long Beach, CA
- Bakersfield, CA
- Fresno-Madera, CA
- Visalia-Porterville-Hanford, CA
- Phoenix-Mesa-Scottsdale, AZ
- Modesto-Merced, CA
- San Diego-Carlsbad, CA
- Sacramento-Roseville, CA
- New York-Newark, NY-NJ-CT-PA
- Las Vegas-Henderson, NV
On the contrary, larger cities in several different parts of Asia (namely the Middle East, India and China) are developing at a faster rate than anywhere else in the world. This is also where the bulk of research on the topic of air pollution and eye health is being conducted. As of right now, there is some movement toward cleaner air in Asian cities, but nothing like the Clean Air Act is in place to restrict unhealthy levels of pollution (6). Suffice to say, people who live in these growing cities are more likely to deal with the consequences of air pollution on respiratory health and eye health and patients who travel to these places may experience more symptoms than usual.
What can we do?
At the very least, we are not going to know more until additional large-scale studies are put into place. However, from the data that already exists, it may be useful to start educating patients about the risks of elevated air pollution levels on the ocular surface, whether in the form of dry eye or acute conjunctivitis. In my opinion, it would also be wise to inform travelers going to more heavily polluted areas about the reality of what their eyes may be facing when they get there. If nothing else, patients can start by consulting one of several air quality index maps to track air pollution in real time across the globe (airnow.gov or waqi.com).
From an eye care standpoint, the best way to alleviate the effects of air pollution on the eyes is to take an avoidance stance, but this is obviously not always possible. A reasonable approach would be to keep the eyes lubricated with preservative-free artificial tears and be mindful of cleaning eyelids and lashes after a lengthy amount of time outdoors when pollution levels are highest. Patients could also invest in a pair of wraparound sunglasses to wear outdoors in heavily polluted areas. If severe exacerbations occur, patients may need a short course of topical corticosteroids to reduce inflammation and provide relief for both the signs and symptoms of dry eye.
If chronic dry eye disease develops seemingly as a result of air pollution, we would currently treat the situation like any other dry eye patient using the appropriate available medications such as Restasis or Xiidra. Since the air quality is comparatively good in the United States and the rest of North America, the signs and symptoms of dry eye and/or conjunctivitis may be more apparent in patients travelling to more heavily polluted area such as the Middle East, India or China. Furthermore, dealing with a patient who travels to areas of high pollution may be a good indicator of how to treat the situation locally, if it does become a problem.
In today’s eye health climate where dry eye disease is at the forefront of the conversation for doctors and patients alike, the more information we have at our disposal, the better the likely outcome. Moreover, if your practice is located in a region with higher levels of air pollution, it may benefit you to consider this information. If nothing else, communication about this subject matter between doctor and patient is a positive step in preventing flare-ups on the already fragile ocular surface.
Dr. Maria Pribis is a 2009 graduate of the Pennsylvania College of Optometry at Salus University. She is currently in private practice in Stamford, CT where she specializes in anterior segment disease with a focus on the ocular surface. She is also an instructor for KMK Educational Services and the founder of OcularPrime, an eye health website focused on patient education. In 2015, she was named Connecticut’s Young OD of the Year.
- Effects of health on air pollution: a narrative review by Mannucci, PM, Harari, S, Martinelli, I, Franchini, M. Internal Emerg Med 2015 Sept;10(6)657-62)
- Potential Importance of Ozone in the Association Between Outdoor Air Pollution and Dry Eye Disease in South Korea, Hwang, SH, Choi, YH, Paik, HJ, Wee, WR, Kim, MK, Kim, DH. JAMA Ophthalmology 2016 March 10
- Air pollution and outpatient visits for conjunctivitis: A case-crossover study in Hangzhou, China. Fu, Q, Mo, Z, Lyu, D, Zhang, L, Qin, Z, Tang, Q, Yin, H, Xu, P, Wu, L, Lou, X, Chen, Z, Yao, K. Environ Pollut 2017 Dec 23: 1344-1350
- Comparing the Effects of Particulate Matter on the Ocular Surfaces of Normal Eyes and a Dry Eye Rat Model, Han, JY, Kang, B, Eom, Y, Kim, HM, Song, JS, Cornea: 2017
- Acute air pollution-related symptoms among residents in Chiang Mai, Thailand, Wiwatanadate, P Journal of Environmental Health, 2014 Jan-Feb;76(6):76-84
- State of the Air 2017. www.lung.org/assets/documents/healthy-air/state-of-the-air/state-of-the-air-2017.pdf.