Impact of Environmental Conditions and Dry Eyes

Environmental Factors Exacerbating Dry Eye: Air Pollution, Temperature, and More

Understanding air quality measurements

Air quality is assessed through the Air Quality Index (AQI), a scale that spans from 0 to 500. As the concentration of pollutants in the air intensifies, the corresponding AQI level rises. The following table delineates the ranges and recommendations associated with each AQI level.

An AQI below 50 is the target, representing a safe condition for everyone. However, once the AQI surpasses 50, vulnerable groups such as the elderly, pregnant individuals, children, and those with cardiovascular or respiratory conditions are the first to experience adverse effects. As the AQI exceeds 100, the risk extends to the general public.
Table 1 outlines AQI levels and guidelines.
Grading AQI Level Recommendations
Good 0 to 50 Little to no risk.
Moderate 51 to 100 Acceptable air quality but some sensitive individuals should avoid exposure due to the risk of respiratory symptoms.
Unhealthy for Sensitive Groups 101 to 150 The general public and sensitive individuals should avoid exposure due to the risk of irritation and respiratory symptoms.
Unhealthy 151 to 200 Health risk increased for the general public but greater risk for sensitive individuals. Avoid exposure.
Very Unhealthy 201 to 300 The risk of health effects is increased for everyone. Avoid exposure.
Hazardous 301 to 500 High risk of serious health effects for everyone. Avoid exposure.
In recent years, global apprehension regarding air quality has escalated. The World Health Organization (WHO) reported in 2019 that a staggering 99% of the world's population resided in areas with air quality below the recommended guidelines.
This concerning trend is particularly pronounced in major cities, where escalating urbanization, industrial activities, and heightened fossil fuel consumption have led to alarming levels of air pollution. Notably, cities like New Delhi, Dubai, and Beijing consistently experience Air Quality Index (AQI) readings surpassing 100.

Air Pollution and Modern Living:

Air pollution, a consequence of climate change, has a significant impact on dry eye disease. Exposure to particulate matter, chemicals, and gases in polluted air can irritate the eyes and hamper tear production, leading to symptoms like burning, itching, and a gritty sensation. Moreover, modern living habits such as prolonged computer use, air conditioning, and contact lens wear can also contribute to dry eye by drying out the eyes. 

Research exploring the correlation between diminished air quality and ocular surface diseases has revealed compelling evidence.

Saxena et al.'s study, conducted in heavily polluted regions of Delhi, uncovered that residents in these areas reported ocular discomfort, including redness and irritation, twice as frequently as the control group. Moreover, participants exhibited heightened indicators of ocular surface disease, as evidenced by the Schirmer test and tear breakup time.

In a separate Canadian study involving 77,439 individuals seeking emergency care for conjunctivitis, an investigation into the nexus between conjunctivitis and ambient air pollution levels revealed a robust connection. Notably, a pronounced association was observed between conjunctivitis and air pollution, particularly with elevated levels of nitrogen dioxide (NO2).

The impact of exposure to air pollutants, such as those emanating from vehicle emissions or forest fires, extends to the elevation of matrix metalloproteinases (MMPs), specifically MMP-9. This inflammatory marker has been linked to increased inflammation in patients with dry eye.

Notably, a study established that individuals exposed to higher Air Quality Index due to forest fires exhibited chronic dry eye and elevated MMP-9 levels. Interestingly, treatment with intense pulsed light (IPL) therapy showed improvements in MMP-9 levels for dry eye patients, although the efficacy diminished in individuals undergoing IPL treatment while exposed to poor air quality.

Temperature and Humidity:

Both extremely high and low temperatures can contribute to the development of dry eye disease. Maintaining suitable indoor temperatures and being mindful of temperature changes outdoors can help mitigate the risk of dry eye. Studies have shown that maintaining a cooler indoor environment within the range of 22.2 to 25.6 °C improves eye dryness symptoms. Similarly, maintaining an appropriate humidity level is crucial for preventing and managing dry eye disease. Low humidity can lead to ocular irritation and alter the tear film, while higher humidity levels have been associated with reduced dry eye symptoms.

Wind Speed and Dew Point:

While wind speed has been linked to dry eye disease, further research is needed to establish a firm connection. However, dew point, which refers to the temperature at which air achieves maximum water saturation, has shown a positive correlation with tear break-up time, indicating that higher dew points may enhance tear film stability and alleviate dry eye symptoms.

High Altitude and Ultraviolet Radiation Exposure:

Living or visiting high altitude areas can pose challenges to eye health, as dry eye disease is prevalent in such conditions. Individuals engaging in outdoor activities at high altitudes are particularly susceptible to dry eye symptoms due to dryness, glare, and windy conditions. Proper eye protection, such as wraparound glacier goggles, can help shield the eyes from wind and ultraviolet radiation, which plays a crucial role in the development and progression of dry eye disease.

Allergens and Pollutants:

Understanding the impact of allergens and pollutants is crucial in diagnosing, treating, and preventing ocular allergies associated with dry eye disease. Grass and weed pollen, tree pollen, house dust mites, and pet dander are among the allergens that can exacerbate dry eye symptoms. Increased levels of ozone, NO2, and other air pollutants have also been associated with dry eye symptoms. It's important to recognize the potential role of other diseases associated with air pollution in worsening dry eye disease.

  • Grasses and Weed Pollen
  • Tree Pollen
    • Birch (Betulaceae family)
    • Hazel (Betulaceae family)
    • Alder (Betulaceae family)
    • Ash (Oleaceae family)
    • Japanese cedar (Cupressaceae family)
    • Horse chestnut (Sapindaceae family)
  • House dust mite
    • The house dust mite is typically considered the main causative allergen in perennial allergic conjunctivitis
  • Cat and dog dander

Other Pollutants: 

Urban Pollution: Gases and Particulate Matter

The release of gases and particulate matter from sources like motor vehicles, power stations, and factories significantly contributes to urban pollution. A study conducted in Korea focused on individuals living in urban and rural areas, examining the effects of outdoor pollution on the ocular surface. The results indicated that increased ozone levels and reduced humidity were associated with dry eye disease symptoms and diagnosis. Interestingly, nitrogen dioxide (NO2) specifically showed a link to dry eye disease, rather than particulate matter. Similarly, research in cities like Delhi and São Paulo demonstrated that higher air pollution levels were associated with more frequent ocular symptoms such as redness, irritation, and strain. Exposure to air pollutants also negatively affected tear production and stability, contributing to dry eye disease symptoms.

Volcanic Ash

While volcanic eruptions have been associated with ocular symptoms, including dry eye disease and conjunctivitis, there is no evidence of chronic or visually disabling effects caused by volcanic ash. However, chemicals present in volcanic ash, such as sulfur dioxide (SO2) and sulfate aerosols, can act as potential irritants, leading to eye irritation and respiratory symptoms.

Dust Exposure

Coal dust exposure, direct contact with coal mines, and specific occupational environments have been linked to impaired tear function and an increased risk of dry eye disease. A comparative study between coal miners and general workers found that coal miners exhibited lower tear production and shorter tear break-up time, indicating the potential impact of prolonged exposure to coal dust on tear function. Additionally, Asian dust particles, which contain various compounds, have been associated with higher conjunctivitis scores, suggesting a possible link between exposure to these particles and the development or exacerbation of dry eye symptoms. Similarly, occupational factors, such as increased dust and pollutant exposure in outdoor environments, were found to contribute to the higher prevalence of dry eye disease among certain occupations, as evidenced by a study comparing street sweepers to office cleaners in Nigeria.

Mercury Levels and Chromium Pollution

Environmental pollutants like mercury and chromium have also been implicated in the development and severity of dry eye disease. High blood mercury levels have been associated with an increased risk of dry eye symptoms, highlighting the potential impact of mercury pollution. Additionally, the presence of chromium in soil has shown a significant association with the incidence and prevalence of Sjögren syndrome, a condition that can lead to dry eye disease.

Indoor Risks Factors:

Sick building syndrome, characterized by acute health effects linked to indoor environments, can cause ocular discomfort, including dry eye disease. Air-conditioned buildings may negatively impact tear film stability compared to naturally ventilated buildings. Additionally, prolonged mask usage, as seen during the COVID-19 pandemic, can contribute to mask-associated dry eye, emphasizing the importance of proper mask fitting and regular breaks from mask usage.

Masks - COVID-19:

Prolonged mask usage during the COVID-19 pandemic can lead to mask-associated dry eye. Ensure proper mask fit and take regular breaks to minimize discomfort. Seek guidance from an eye care professional if needed.

Smoking and Other Substances:

Smoking:

Smoking directly impacts the ocular surface, causing tear film instability and damage. It alters the lipid layer, triggers inflammation, and affects meibomian gland function. Quitting smoking is essential for maintaining eye health.

Vaping:

Electronic cigarette vapor can harm the ocular surface, inducing corneal staining and inflammation. Nicotine and acrolein found in e-cigarette aerosols are potential culprits. Be cautious of the risks associated with vaping.

Substance Abuse - Crack Cocaine:

Crack cocaine use can lead to a condition known as Crack Eye Syndrome, characterized by microbial keratitis, corneal epithelial defects, and superficial punctate epithelial keratopathy.

How to Protect The Eyes

Wearing contact lenses in conditions of high air pollution is not advisable, as airborne particles can become trapped in the lenses, leading to increased eye irritation. In such situations, it is recommended that individuals, especially those engaged in occupations like firefighting or construction work, use goggles or face shields to protect their eyes from environmental pollutants.

For individuals exposed to poor air quality, such as firefighters or construction workers, it is advisable to opt for goggles or face shields instead of contact lenses. This is because particles present in the air can get trapped in the lenses, causing additional irritation to the eyes.

To create a protective barrier against environmental agents and alleviate eye discomfort, lubricants can be used. These tears not only dilute and wash away allergens from the ocular surface but also act as a barrier. Opting for preservative-free artificial tears is recommended, as the presence of preservatives may lead to irritation and dryness in some individuals.

In cases of significant ocular inflammation, the use of anti-inflammatory eye drops and therapies is warranted to effectively address the issue and promote eye health.

The Role of Eyelids in Eye Health

The eyelids play a vital role in protecting the eyes from external pollutants. They act as a physical barrier, shielding the eyes from dust, debris, and other harmful particles. However, pollutants can build up on the eyelids and lashes, causing a variety of eye problems.

Eyelid Cleansing

A simple way to remove pollutants from the eyelids and lashes is to wash them daily. This can be done in the morning and evening, as part of your regular eye care routine.

Here are the steps for eyelid cleansing:

  1. Wash your hands with soap and water.
  2. Apply a mild, non-irritating eyelid cleanser to your closed eyelids and lashes.
  3. Gently massage the cleanser into the eyelids for 1-2 minutes.
  4. Rinse the cleanser off with cool water.
  5. Pat your face dry with a clean towel.

Additional Tips for Eye Health

In addition to eyelid cleansing, there are other things you can do to protect your eye health:

  • Limit your exposure to pollution. If you live in a polluted area, try to stay indoors on days with poor air quality. You can also use an air purifier to improve indoor air quality.
  • Wear protective eyewear when outdoors. Sunglasses or goggles can help protect your eyes from airborne pollutants, dust, and UV radiation.
  • Stay hydrated. Drinking plenty of water helps maintain overall eye health and prevents dryness.

By following these tips, you can help keep your eyes healthy and looking their best.

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Source:

Alves, M., Asbell, P., Dogru, M., Giannaccare, G., Grau, A., Gregory, D., ... & Stapleton, F. (2023). TFOS Lifestyle Report: Impact of environmental conditions on the ocular surface. The Ocular Surface