Air pollution and Eye Diseases

There is an often overlooked association of air pollution and eye Diseases. The bad quality of environmental air can result in premature break-up of the preocular tear film and corneal epithelial damage causing significant irritation and discomfort…..
By Dr Vikas Veerwal

Air pollution is a serious health issue that impacts quality of life, as long term exposure is associated with respiratory and cardiovascular problems, as well as increased hospital admissions and healthcare spending. These phenomena have been observed in the west as well as in Asia, and with urbanization, such problems are expected to worsen with time.

In severe cases, pollution can even increase mortality but by improving environmental conditions, it has been shown that health indicators can respond favourably. According to the World Health Organization, air pollution consists of different particulate including particulate matter (PM), ozone, carbon monoxide (CO), nitrogen dioxide (NO2) and sulphur dioxide (SO2). The number after PM refers to the aerodynamic diameter of the particles; i.e. PM10 refers to particles <10 μm, and PM2.5 refers to particles less than 2.5 μm. PM10 is generated from construction and road dust, whilst smaller particles (PM 2.5) are derived from combustion sources such as wood and biomass fuels. Regardless of the type of pollutant, pollution is a widespread issue as it can affect occupations both outdoors and indoors.

Eye structures are continuously and directly exposed to the environmental air pollutants. Due to the constant contact of the preocular tear film, cornea and conjunctiva with the surrounding air, toxins can damage or alter the physiology of these ocular structures. The quality of environmental air can result in premature break-up of the preocular tear film and corneal epithelial damage causing significant irritation and discomfort.

Air pollution can affect the eye, causing complaints of eye redness, irritation, watering, foreign body sensation, and blurring of vision; however the link to the environment is sometimes overlooked by eye professionals. Conditions associated with air pollution are primarily: different forms of conjunctivitis, allergies, red eye syndrome, dry eye syndrome and meibomian gland dysfunction.

High concentration of toxic pollutants in the air may also cause a narrowing of the retinal vessels, which leads to disorders in its microcirculation. The connection between air pollution and cataract has also been suggested. Since the ocular surface can be easily examined, it can also serve as an indicator of the impact of pollution on health. Despite the importance of the effects of pollution on the eye, research in this area has remained limited in regards to direct associations of the types of pollution with different ophthalmological abnormalities.

Pollution causing the epidemic of Dry Eye Syndrome (DES)
Our tear film is composed of three components: aquatic, lipid and mucous. Disorders in production, vaporization or composition of tear film are thought to be a cause of dryness of the eyes. Dry eye syndrome (DES) is the most common ophthalmic condition, its frequency varying between 11–58%. Many factors can have an influence on the occurrence of DES’s symptoms: smoking cigarettes, drinking alcohol, low humidity, air pollution, sunlight exposure, wearing contact lenses, socio demographic factors, ophthalmic surgeries in the past. Schirmer’s test and break-up time (BUT) test are often used in diagnosing DES.

In people living in the big cities disorders of tear film were observed more often. In inhabitants of polluted metropolis results of Schirmer’s test and BUT test were significantly lower than in those living outside of the city (13.4 mm vs. 16 mm; 13 s vs. 19.2 s). In one study conducted at All India Institute of Medical Sciences, Delhi it was observed that environmental conditions have a very significant effect on ocular surface health and incidence of subclinical ocular surface changes was high among persons travelling in highly polluted area.

Inhabitants of strongly polluted areas of Delhi in India complained about reddening and irritation of the eyes two times more often than the control group. A study conducted on 55 inhabitants of Brazil showed the association between exposure to a high concentration of NO2 and disorders of the tear film and a feeling of eye discomfort.

It is more of a concern for wearers of contact lenses, because in this group the influence of air pollution is more visible. Another study held in Southern Korea on 16,824 people showed the connection between high levels of ozone and NO2 in the air and low humidity and occurrence of DES. High level of PM10 and NO2 in big cities was associated with shortening of break-up time, indicating increased dryness.

Use of Face Masks and dry eye disorders
With the current Covid-19 pandemic, use of face masks has certainly become essential. Widespread use of face masks, while helps the prevention of novel corona virus transmission, it has shown to increase ocular dryness and irritation. Patients wearing masks for extended periods may be more likely to experience these symptoms. With use of face masks air blows upward from the mask into the eyes. This increased airflow likely accelerates the evaporation of the tear film which, when continuous for hours or days, may result in ocular surface irritation or inflammation.

What can be done to protect your eyes better
There are many steps you can take to help minimize the effects of air pollution on your eyes.

1. Avoiding exposure: The golden rule, of course, would be to avoid exposure to harmful pollutants. On days when the pollution levels are noted to be high or there is a public health warning, stay indoors. You can easily check current air quality index on your phone using different apps that are readily available. In case you cannot avoid exposure to the environment and have to step out, make sure you wear protective eyeglasses which will minimize your exposure to the pollution causing agents.

2. Hand hygiene: Wash your hands often and try not to touch your eyes

3. Increase water intake: Stay hydrated as it helps in adequate tear formation. It becomes imperative when external factors such as smog increase your chances of dry eyes and eye irritation.

4. Eat Healthy: Have a healthy diet rich in Omega 3 fatty acid including lots of green leafy vegetables, carrots, spinach, almonds, walnuts, berries and fish which are extremely good for the eyes.

5. Wear sunglasses when outdoors.

6. Avoid eye rubbing: In case of significant irritation, avoid rubbing your eyes repeatedly as it predisposes to risk of infections. Cold compresses of the eye may help in reducing itching and irritation sensations.

7. Lubricating eye drops: While many over-the-counter lubricating drops are available in the market, it is essential to get your eyes examined by your Ophthalmologist before using any eye drops.

8. Reduce screen time: While the COVID pandemic has significantly increased our screen time, we need to understand that long hours of exposure to different devices exacerbates dry eye symptoms. Avoid the excessive use of screen devices, including mobile phones and laptops. If essential, ensure adequate and frequent periods of rest to avoid eye fatigue, dry eyes, and computer vision syndrome.

9.In case of persistent irritation, redness or itching, you must visit your Ophthalmologist for an evaluation. Appropriate and timely intervention can prevent long term damage to your eye and improve your symptoms.

Conclusion
The dramatic rise of air pollution in the big cities all over the world in recent years caused growing concern about its adverse effect on human health. Eyes remain particularly vulnerable to air pollution. Both chronic, long-lasting and short-term exposure is harmful with exposure to a high dose of toxic air pollutant resulting in symptoms of conjunctivitis or dryness even on the same day. Tear film, cornea, and conjunctiva have constant contact with ambient air, so toxins that it contains can directly affect them and interfere with its functions.
Limiting exposure to high levels of air pollutants, using protective eye gear, lubricating drops when advised, and timely visiting an Ophthalmologist to get yourself evaluated are some of the measures that can help us through this environmental crisis. However, the most important issue is to urgently introduce systemic solutions to reduce the levels of air pollution before significant and permanent damage to our health takes place. Individuals, society, organisations and government need to work at every level to tackle this significant health problem.

Figure: Images showing allergic reaction of the conjunctiva and dry eye causing poor ocular surface resulting in discomfort, photophobia and irritation to the patient.

(The author is Associate Consultant – Cornea, Cataract and Refractive Services, Centre for Sight, New Delhi)