Air pollution has become a global menace in the 21st century.

Not only does it affect the environment but also harms your health and well-being.

Did you know that, in 2012, air pollution caused the deaths of around 7 million people worldwide? Quite alarming, isn’t it? While cardiorespiratory health is mostly known to be affected, regular contact with pollutants also harms your eyes.

Read more to find out about the damaging effects of pollutants on the human eye.

What is Air Pollution?

Air pollution is caused when high amounts of toxic gases, organic compounds, and particles accumulate in the air.

Both man-made activities and natural events can give rise to potential pollutants.

Some of these include gases, such as ozone, carbon monoxide, sulphur and nitrogen oxides, as well as organics like methane.

Fine particles generated by the burning of coal or during forest fires also act as pollutants.

Overview of Eye Disorders

Several diseases affect the eyes and cause weakened vision.

These diseases often develop due to age, injury, exposure to irritants, or even as symptoms of other diseases.

Dry eye syndrome affects the tear glands and is quite common in China. Strabismus prevents the eyes from aligning properly.

Allergic conjunctivitis and acute uveitis both cause severe inflammation in the eyes. Glaucoma is a common disorder wherein there is increased fluid pressure on the eyes.

How does Air Pollution Affect the Eyes?

This article explores the major eye disorders caused by regular exposure to air pollution.

Several investigative studies have recognized the relationship between exposure to the polluted air and the growing numbers of eye diseases.

High concentration of ozone in the air has been linked with dry eye syndrome, which particularly affects people in the metropolitan cities.

Contact with cigarette smoke during pregnancy increases the risk of developing strabismus in children. Exposure to nitrogen dioxide can increase the chance of allergic conjunctivitis in young children.

Cigarette smoke is also a risk factor for acute uveitis whereas glaucoma is caused by exposure to toxic metals.

Eye Problems Caused by Air Pollution

1. Air Pollution Causes Dry Eye Syndrome

Dry eye syndrome is a disorder affecting the tear film, which occurs due to a deficiency of the tears or an undue evaporation of the tears caused by environmental factors.

The tear film consists of three layers.

The protective outer layer of oil prevents evaporation, followed by a lubricating middle layer of water that moistens the eye, and an inner mucin layer that nourishes the cornea.

The tear film is maintained by the lacrimal (tear) glands, which are located on the upper corner of each eye.

Also referred to as keratoconjunctivitis sicca (KCS), dry eye syndrome is quite often characterized by reddening and inflammation of the surface of the eye and the lacrimal glands, which secrete the tears responsible for keeping the eye moist and healthy.

Dry eye disorder causes damage to the surface of the eye as the protective tear film is lost, leading to a variety of symptoms causing discomfort and pain. Around 1 out of every 7 elderly individuals aged between 65 to 84 years have often reported signs of dry eye.

While it is often caused due to age or environmental pollution, the disorder can also signal an underlying condition that might be life-threatening.

Patients with dry eye are also prone to developing possibly blinding infections like bacterial keratitis, which affect the cornea.

Furthermore, dry eye syndrome also increases the risk of developing complications after undergoing common procedures, such as laser eye surgery.

How does air pollution cause dry eye syndrome?

The association between air pollution and dry eye syndrome was initially explored by a study at the Malmö University Hospital in Sweden.

It was revealed that prolonged contact with air pollution caused an instability of the tears secreted by the lacrimal (tear) glands which led to dry eyes.

In a 2002 study by the All India Institute of Medical Sciences (AIIMS), New Delhi, it was revealed that high air pollution in the city had resulted in increased cases of dry eye syndrome.

The study had involved 400 healthy participants living within and outside the city. The results showed that almost 36% of the people living in the city developed abnormalities in their tear glands.

A more Korean recent study showed the link between poor quality air and the development of dry eye syndrome.

The researchers at the Gachon University Gil Medical Center proved that increased concentrations of ozone in the air affected the tear glands resulting in extremely dry eyes that caused pain and discomfort.

Summary
Dry eye syndrome is a very widespread problem that is experienced in the big cities. Air pollution is a major risk factor as pollutants, such as ozone, affect the tear glands which normally moisten the eyes.

2. Air Pollution Increases the Risk of Strabismus

Popularly known as the ‘squint’, strabismus is a disorder wherein the eyes do not align properly to produce the right image.

It means that the eyes do not line up to look at the same thing. In this case, one of the eyes fixates on the object that the affected person wants to look at (fixing eye) while the other looks at something else (deviated eye).

Sometimes, if the person with strabismus covers their fixing eye, the abnormal, deviated eye will gradually move and fixate on what the person wants to look at.

The image produced by the deviated eyes will also be normal and not blurred like before. Such people often suffer from weakened awareness of depth.

In some cases, the vision in the deviated eye might get permanently weakened, even if the fixing eye is covered.

This condition is known as amblyopia, popularly referred to as the ‘lazy eye’. Amblyopia gradually develops in people who suffered from strabismus since childhood.

In such cases, the brain had continuously been suppressing the image formed by the abnormal eye.

Strabismus typically runs in families and is detected in early life. However, sometimes the condition develops later as an outcome of defective nerves or muscles, or due to some form of trauma.

It can also be caused by serious diseases that affect the nervous system or the eyes. Recently, air pollution has been proved to be a risk factor for developing the squint.

How does air pollution increase the risk of strabismus?

An early study by the Eye Institute in Philadelphia stated that air pollution increases the risk of several eye-related defects, particularly in people wearing contact lenses.

This would especially happen due to the presence of particulate matter (PM) in the air which easily enter the eyes making them vulnerable to diseases. Strabismus is also caused due to exposure to pollutants.

In line with the findings of this study, a population-based study was done by the John Hopkins University School of Medicine to inspect the relationship between exposure to cigarette smoke during pregnancy and the development of strabismus in children.

The results confirmed that infants borne of mothers exposed to the chemicals in cigarette smoke recorded increased cases of the squint.

Summary
Children are particularly harmed by air pollution. Exposure to particulate matter and cigarette smoke during pregnancy often leads to the birth of infants with a higher risk for strabismus.

3. Air Pollution Causes Allergic Conjunctivitis in Children

Allergic conjunctivitis (AC) is caused when individuals come in contact with allergens, such as dust, pollen, and fine particles.

These allergens interact with specific antibodies to bring about swelling, redness, and inflammation. When such inflammation occurs in the inner lining of the eyelids (conjunctiva), it is referred to as allergic conjunctivitis.

This disease is caused in certain people who are hypersensitive to otherwise normal particles.

There are several types of allergic conjunctivitis such as seasonal acute conjunctivitis (SAC), perennial Acute conjunctivitis (PAC), vernal keratoconjunctivitis (VKS), and atopic keratoconjunctivitis (AKC). They are caused by allergens present at a particular time.

SAC and PAC occur quite commonly as allergies of the eye due to the presence of environmental allergens, such as pollen or dust.

Antibodies against such allergens have been identified. VKC occurs particularly in warm weather and is, therefore, more common in the tropics. AKC often worsens during the months of winter.

Ocular (eye) allergy denotes one of the most widespread eye-related conditions observed in medical practice. While a single cause cannot be isolated, experts have defined a number of risk factors.

These include family history, pets, early childhood exposure, and air pollution.

How does air pollution cause allergic conjunctivitis?

A 2013 review by the Seoul National University College of Medicine showed that extreme air pollution in urban areas increases the risk of allergies.

These included diseases, such as asthma, allergic skin disorders, and even allergic conjunctivitis. Pollutants act as allergens and affect people who already have a family history of allergies.

In 2016, a more specific study by the Fudan University showed that outdoor air pollution did increase the risk of allergic conjunctivitis in children.

In fact, the collected data exposed that pollutants like nitrogen dioxide and ozone in the air caused irritation in the eyes of particularly sensitive children.

Summary
Ozone and nitrogen dioxide act as allergens which irritate the eyes and cause inflammation of the conjunctiva. Thus, air pollution acts as a major risk factor for the development of allergic conjunctivitis in children.

4. Air Pollution Causes Acute Uveitis

Uveitis is made up of a number of diseases, which often lead to the development of complete blindness.

Based upon the part of the eye affected, it can be categorized as anterior, intermediate, posterior, and panuveitis.

Uveitis is an inflammatory disorder which causes swelling, pain, and discomfort.

Anterior (front part) uveitis is the most common for inflammation in the eye. Its incidence varies across the general population of various countries around the globe.

This disorder typically causes inflammation of the coloured part of the eye (the iris). It might also affect the front part of the ciliary body, which is involved in changing the shape of the lens.

Anterior uveitis usually weakens the eyesight in the acute stage. However, the consequence of this disease is far more alarming and can leave a lasting impact on the vision.

The disease normally involves acute, chronic, or repetitive attacks that affect the quality of life. Patients often suffer from severe pain, redness, blurred vision, and watering of the eye.

The disease was described to be infectious, such as viral or bacterial. Sometimes, it is also caused as a result of a more threatening underlying condition.

Other times, the immune cells simply target the iris resulting in an autoimmune disorder. The disease can also be caused by wearing a contaminated lens or due to some drugs. Recently, air pollution has also been proved as a risk factor.

How does air pollution cause acute uveitis?

In 2015, a study by the University of California, San Francisco showed that pollutants released in cigarette smoke increase the chance of developing anterior uveitis.

It is because the fine particles that make up the smoke irritate the eyes, particularly the iris.

Prolonged exposure to this form of pollution causes inflammation, swelling, and redness in the eyes, which affect vision. Fine particulates released by motor vehicles also affect the eyes and cause blurred vision.

Summary
Cigarette smoking often releases particles into the air that irritate the eyes. Long-term contact with the iris can lead to anterior uveitis, which affects eyesight.

5. Air Pollution Causes Open-Angle Glaucoma

Glaucoma is one of the leading causes of blindness due to damage to the optic nerve.

The major risk factors are an increase in fluid pressure on the eyes, family history, African-American ancestry, high blood pressure, and diabetes. The most common type is open-angle glaucoma.

Open-angle glaucoma occurs slowly over time and has no symptoms. Side gaze or peripheral vision begins to be affected and can lead to permanent loss of eyesight unless treated.

The reason behind blindness in open-angle glaucoma is optic nerve damage.

There are three things that usually happen in this disease.

The drainage canal in the eye gets clogged which does not allow fluid to leave the eye. This builds up pressure which slowly damages the optic nerve. As a result, peripheral vision is weakened.

How does air pollution cause open-angle glaucoma?

A 2016 population-based study by the Yonsei University examined the effects of air pollutants on the eyes.

The results showed that heavy metals, such as cadmium, play a major role in causing open-angle glaucoma, particularly in young men working in the industries.

It was concluded that excessive contact with air pollutants like heavy metals increased their concentrations in the blood.

High levels of cadmium in the blood increase fluid pressure on the eye and are responsible for optic nerve damage, which is one the main reasons behind open-angle glaucoma.

Summary
Open-angle glaucoma is one of the most common forms of glaucomas. It is often caused by heavy metal air pollutants like cadmium, which affect the optic nerve.

Conclusion

To summarize, it can be said that air pollution contributes to a wide range of eye disorders. Dry eyes are the most common nuisance in big cities.

Children are particularly susceptible to pollutants as they can develop strabismus as well as allergic conjunctivitis. Fine particles can also acute uveitis while exposure to industrial pollutants can lead to glaucoma.

Hence, it can be seen that the eyes are the most vulnerable to damage caused by air pollution.

In fact, children and the elderly are more prone to developing diseases as their eyes are quite sensitive to any kind of particles.

Also, if you have a history of allergies, it is always advisable to protect your eyes, particularly during the daytime.

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Team AirHealth.in
Author

This article is written by AirHealth's team which consists of writers with degrees in medicine, biotechnology, pharmacy, nutrition, engineering, etc. The work is peer-reviewed by the core team or by our Advisors before it is published. Check out more about us in "Our Team" section.

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