Pollution's Impact: Cataracts And Eye Health

Air pollution is a mixture of gases and particles disbursed into the atmosphere due to human activities and natural sources. It is a major contributor to the global burden of disease, with 3.7 million deaths worldwide attributed to it in 2012, and 4.2 million in 2016. Outdoor air pollution is caused by vehicle emissions and fuel consumption, while indoor air pollution is associated with tobacco smoking, heating, cooking, and poor indoor ventilation.

Air pollution has been linked to several eye diseases, including conjunctivitis, glaucoma, cataracts, and age-related macular degeneration (AMD). Studies have shown that exposure to air pollution can cause irritation and inflammation of the conjunctiva, leading to conjunctivitis. Additionally, air pollutants such as PM2.5 have been associated with allergic conjunctivitis and glaucoma. Exposure to tobacco smoke is a well-known risk factor for cataracts, and age-related macular degeneration (AMD) has also been linked to traffic-related air pollutants.

While the impact of air pollution on the eye is evident, further research is needed to fully understand the underlying pathological mechanisms and the long-term effects of air pollutants on the eye.

Outdoor air pollution and its effects on the eye

Outdoor air pollution is a significant public health problem worldwide. It is a major environmental health hazard that was associated with 3.7 million deaths worldwide in 2012 and 4.2 million deaths in 2016. The increasing trend in attributable deaths from 1990 to 2015 was partially due to the increase in outdoor air pollution levels in low- and middle-income countries. In 2016, the International Agency for Research on Cancer (IARC) classified outdoor air pollution as a human carcinogen, according to adequate evidence, especially for lung cancer.

Composition of Outdoor Air Pollution

Outdoor air pollution is a complex mixture of gas-phase pollutants and particles at harmful levels that are disbursed into the atmosphere due to either natural or human activities. There are many pollutants in the atmosphere, such as sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon dioxide (CO2), nitrogen monoxide (NO), carbon monoxide (CO), nitrogen oxides (NOx), particulate matter 2.5 (PM2.5), and particulate matter 10 (PM10), mostly generated from burning fuels or industrial production. In addition to traffic and industry activities, daily life activities, including tobacco smoking, household decorating and cooking, also produce COx, NOx, and volatile organic compounds (VOCs).

Effects of Outdoor Air Pollution on the Eye

The cornea is the most sensitive structure in the human body due to numerous innervations in the ocular surface and thus is extremely sensitive to environmental agents. The eyes defend against potentially harmful external material with only a thin layer of precorneal tear film; as a result, human eyes are susceptible to the adverse effects of air pollution. The adverse effects of air pollutants such as CO, NOx, PM, and O3 on human eyes consist of mostly irritation and inflammation, with conjunctivitis being a frequent problem.

Numerous studies have tried to determine the impact of environmental toxins on the ocular surface. Saxena and colleagues found that persons who traveled to highly polluted areas where the PM level was five times higher than the WHO annual average limit of 60 µg/m3 suffered from extensive subclinical ocular surface changes. Versura and associates reported that the mixture of air pollutants led to cytological changes and inflammation in the ocular surface, contributing to eye discomfort. An increasing number of studies have indicated that air pollutants such as PM2.5 are associated with allergic conjunctivitis and glaucoma, and exposure to tobacco smoke can cause cataracts. Moreover, age-related macular degeneration (AMD) is related to exposure to traffic-related air pollutants.

Types of Age-Related Cataracts

There are several types of age-related cataracts. Their names refer to their location in your lens. To understand these types, it helps to learn a bit about the anatomy of your lens. The three most common types of age-related cataracts are:

• Nuclear sclerotic cataract, which forms in the nucleus.
• Cortical cataract, which forms in the cortex.
• Posterior subcapsular cataract, which forms in the posterior cortex. “Posterior” in this context means the “back” of your lens. This is the part that’s closest to your retina (which is behind your lens). “Subcapsular” means the cataract forms at the outer edge of the cortex, just beneath the lens capsule.

Indoor air pollution and its effects on the eye

Indoor air pollution is a major health concern, especially in developing countries. The main sources of indoor air pollution are cooking and heating with solid fuels, tobacco smoke, and emissions from building materials and indoor facilities. Indoor air pollution is associated with several eye diseases, including conjunctivitis, dry eye, glaucoma, cataracts, and age-related macular degeneration.

The most common eye disease related to indoor air pollution is dry eye, which is characterised by symptoms such as dryness, discomfort, irritation, burning, itchiness, stinging, foreign body sensation, or light sensitivity. Dry eye can also be diagnosed based on signs such as decreased tear film stability, decreased tear production, and inflammation on the ocular surface.

The main pathological mechanisms underlying the development of eye diseases due to indoor air pollution include chronic inflammation, oxidative damage, and disruption of tight junctions.

The impact of air pollution on the development of cataracts

Air pollution is a mixture of gases and particles disbursed into the atmosphere due to human activities and natural sources. Outdoor air pollution is primarily caused by vehicle emissions and fuel consumption, while indoor air pollution is caused by tobacco smoking, heating, cooking, and poor indoor ventilation.

Outdoor Air Pollution

The main components of outdoor air pollution are ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), lead (Pb), carbon monoxide (CO), and particulate matter (PM). PM is further classified into coarse PM (PM10), fine PM (PM2.5), and ultrafine PM (PM1.0).

Outdoor air pollution has been linked to several eye diseases, including nonspecific conjunctivitis, allergic conjunctivitis, glaucoma, and age-related macular degeneration (AMD). Exposure to outdoor air pollution has also been associated with an increased risk of developing cataracts.

Indoor Air Pollution

Indoor air pollution is caused by tobacco smoking, the use of household decorating and cooking materials, and poor indoor ventilation. It has been linked to several eye diseases, including conjunctivitis, cataracts, and uveitis. Tobacco smoke, in particular, has been associated with atopic kerato-conjunctivitis, allergic conjunctivitis, and cataracts.

Impact of Air Pollution on the Development of Cataracts

Air pollution can cause oxidative stress, inflammation, and toxicity, which can lead to the development of cataracts. Oxidative damage to the lens increases with age, and air pollution can accelerate this process.

Several studies have found a positive association between exposure to air pollution and the development of cataracts. A study in Taiwan found that exposure

The impact of air pollution on other eye diseases

Air pollution has been linked to a number of eye diseases, including allergic conjunctivitis, dry eye disease, age-related macular degeneration, and cataracts.

Allergic Conjunctivitis

Particulate matter (PM) with a diameter of less than 2.5 μm (PM2.5) has been associated with allergic conjunctivitis in Japan. However, other pollutants such as nitrogen dioxide (NO2), carbon monoxide (CO), and oxidants (Ox) were not found to have any association.

Dry Eye Disease

Dry eye disease has been linked to increasing levels of NO2 and CO over ten years of exposure in Taiwan. In South Korea, dry eye disease was associated with the level of SO2, while exposure to NO2, CO, O3, and PM10 was not.

Age-Related Macular Degeneration

Traffic-related air pollutants have been found to increase the risk of age-related macular degeneration.

Cataracts

Cataracts are cloudy areas that form on the lens of the eye, and age-related cataracts are the most common type. Exposure to PM10, NO2, and SO2 was positively associated with cataract incidence, while O3 was negatively associated. However, the association between cataract and the quartile of PM2.5 measured during one year in 2015 was not clear.

Preventing cataracts and limiting exposure to air pollution

Cataracts are cloudy areas that form on the lens of the eye, causing vision impairment. Age-related cataracts are the most common type, but other types include paediatric, traumatic, and secondary cataracts.

The main cause of cataracts is the gradual breakdown of proteins in the eye's lens. However, certain risk factors can increase the likelihood of developing cataracts, or of developing them at a younger age. These risk factors can be environmental, medical, or genetic.

Environmental risk factors

• Industrial chemicals
• Long-term exposure to UV light from the sun
• History of radiation therapy to the upper part of the body

Medical risk factors

• Diabetes or high blood sugar
• Glaucoma
• Use of corticosteroids to treat certain medical conditions
• Eye diseases such as retina pigmentosa or uveitis

Preventing cataracts

Although developing cataracts is a typical part of aging, there are steps you can take to protect your eye health and potentially slow the process:

• Don't smoke. Tobacco smoke raises your risk of cataracts.
• Protect your eyes from the sun by wearing sunglasses or eyeglasses with an anti-UV coating, or a hat with a brim.
• Get regular eye care and keep up with your appointments.

Limiting exposure to air pollution

Air pollution is a major contributor to the global burden of disease and has been linked to a number of negative health outcomes, including respiratory diseases and cancers. It is composed of a mixture of gases and particles, including particulate matter (PM), nitrogen oxides (NOx), and carbon dioxide (CO2), which are mainly generated from vehicle emissions and fuel consumption.

Outdoor air pollution

Outdoor air pollution is a significant public health problem worldwide and has been associated with a spectrum of health issues, including cardiovascular disorders, respiratory tract problems, ocular diseases, neurologic diseases, and cancer.

Ocular surface diseases

The cornea is the most sensitive structure in the human body, and the eyes are susceptible to the adverse effects of air pollution due to their thin layer of precorneal tear film. The adverse effects of air pollutants such as CO, NOx, PM, and O3 on human eyes consist mostly of irritation and inflammation, with conjunctivitis being a frequent problem.

Preventing ocular surface diseases

• Wear sunglasses or eyeglasses with an anti-UV coating, or a hat with a brim, to protect your eyes from the sun.
• Avoid outdoor activities when air pollution levels are high.
• Use eye drops to keep your eyes lubricated and reduce irritation.

Glaucoma

Glaucoma is positively related to national levels of PM2.5. PM2.5 has been shown to induce the production of NO and interleukin 8, causing increased oxidative stress. It can also increase oxidative stress and induce NLRP3 inflammasome-mediated pyroptosis in trabecular meshwork cells, leading to the development of ocular hypertension and glaucoma.

Preventing glaucoma

• Limit exposure to outdoor air pollution, especially PM2.5.
• Use eye drops to reduce intraocular pressure.
• See an ophthalmologist for regular eye exams and glaucoma screenings.

Retinopathy and maculopathy

Air pollution can induce oxidative stress, activate inflammatory pathways, and increase coagulation. The retina is susceptible to oxidative stress due to its high consumption of oxygen and high proportion of polyunsaturated fatty acids.

Preventing retinopathy and maculopathy

• Limit exposure to outdoor air pollution, especially PM2.5 and NOx.
• Maintain a healthy weight and manage blood sugar levels to reduce the risk of diabetic retinopathy.
• Eat a healthy, balanced diet rich in antioxidants to reduce oxidative stress.

Indoor air pollution

Indoor air pollution is associated with indoor tobacco smoking, dissipation of compounds used in building materials and decorations, cooking with oil and high heat, burning coal or biomass for cooking or heating, and using pesticides. It can lead to health problems such as asthma, autism, and childhood cancer.

Ocular surface disease

Tobacco smoking affects the ocular surface, resulting in symptoms such as itchiness, redness, and irritation of the eyes. It can also cause disorders such as atopic kerato-conjunctivitis and allergic conjunctivitis.

Preventing ocular surface disease

• Avoid indoor tobacco smoking and secondhand smoke exposure.
• Use air purifiers or filters to reduce indoor air pollution.
• If you smoke, consider quitting. Resources are available to help you quit.

Cataracts

Cataracts have long been linked to cigarette smoking. Smoke causes oxidative stress and consumes antioxidants that offer protection against cataract formation. Epidemiological research has shown that indoor cooking using biomass fuel is also related to cataracts and blindness.

Preventing cataracts

• Avoid indoor tobacco smoking and secondhand smoke exposure.
• Use air purifiers or filters to reduce indoor air pollution.
• If you smoke, consider quitting. Resources are available to help you quit.
• Eat a healthy, balanced diet rich in antioxidants to reduce oxidative stress.

Frequently asked questions