The eye is a delicate organ with a large and moist area exposed to the environment, making it more susceptible to air pollution than other body parts. However, the eyes' response to airborne pollutants ranges from no symptoms to severe irritation and chronic pain. Even when contact lenses are used, the eyes are still more sensitive to these effects.
Factors
The levels of hydrocarbons and nitric oxide in ambient air determine the severity of discomfort produced by air pollution.
The hydrocarbon chemicals particularly well-known for causing such irritation include C4 and C5 olefins. Hydrocarbons with branched chains have stronger effects on the eyes than straight chains, especially if the chain contains some double bonds away from the terminal carbon. The irritation caused by olefins is notably higher as compared to paraffin.
Among phenolic compounds, cyclohexene causes the most irritation as compared to benzene or cyclohexane.
Air pollution mainly occurs due to the irradiation of automobile exhaust. When exposed to such air pollution, a significant level of eye irritation occurs for up to four hours. This phenomenon has a half-life of 12 hours but bears no obvious relation with aerosol levels, ozone, peroxyacetyl nitrate, or aldehyde. The irritants in irradiated car exhaust also remain unchanged despite increases or decreases in relative humidity (between 30% and 80%) or temperature fluctuations (25 to 45 ºC).
The relationship between the particle size in automobile exhaust and the occurrence of eye irritation remains unclear; however, one researcher has indicated that below 0.2 microns, irritation is largely prevented. It is believed that the make and performance of the motor vehicle determine the emission of hydrocarbons and nitric oxide; however, individual hydrocarbon levels depend more upon the type of fuel used. Both these chemicals produce eye irritation equally.
Interactions of sulfur dioxide and trioxide at subthreshold concentrations with sodium chloride or carbon black particles precipitate inducing irritation.
Another study has shown some correlation between the levels of oxidants in the air and eye irritation at certain times of the year. The presence of aerosol is also suggested to be a critical factor. Oxidants can dissolve in the tear film and acidify it, further irritating the eye's mucous membrane.
Some of the air pollutants that are commonly found in metropolitan cities include:
- Carbon monoxide (CO)
- Nitrogen dioxide (NO)
- Sulfur dioxide (SO2)
- Arsenic, asbestos, benzene, lead, chlorofluorocarbons, particulate matter, and dioxin
The impact of climate change on the eye
Symptoms in the eye
Some of the symptoms that are frequently observed following ocular exposure to air pollution include:
- Burning and redness sensations
- Irritation
- Watering
- Discharge
- Allergy with severe itching, redness, discharge, swelling of the eyes, and difficulty in opening the eyes
- Increased risk of infections
- Itching
- Gritty sensation
- Visual difficulties, including refractive errors and impaired color vision
- Cataracts
- Cancers
Dry eye syndrome (DES) is the most frequent complaint among these symptoms, with the incidence of DES two times greater in women over 50. The eye's surface is inflamed and dry in DES, particularly when the patient wears a contact lens. As NO2 levels rise, conjunctivitis becomes a common feature.
Individuals at a particularly high risk of these effects of air pollution exposure include those who remain outside for a long time.
The Common eye ailment linked to pollution | Air Pollution | AMD | WION News
Management
The treatment of the eye symptoms of air pollutant exposure without the presence of an infection or allergy is to cool the eyes by washing them gently with clean water, followed by applying a cool compress.
Lubricating eye drops and the use of sunglasses are also helpful options. Contact lenses and eye makeup should be avoided until the eyes are healed completely.
References
Further Reading
US census data reveal socioeconomic drivers of air pollution-related cancer risks