Table 2.

Correlation among pollutants and effects on the ocular surface

Air pollutants	Emission source	Effects on ocular surface	Key references
Particulate matter (PM2.5/PM10)	Vehicle emissions, industrial processes, wildfires	Increased tear film instability, oxidative stress, inflammation, dry eye symptoms	[2, 56, 73, 74, 76, 78, 104, 105]
Ozone (O3)	Vehicle emissions, industrial processes	Oxidative stress, inflammation, exacerbation of dry eye symptoms	[2, 73, 74, 79, 80]
Nitrogen dioxide (NO2)	Vehicle emissions, industrial processes	Inflammation, oxidative stress, reduced tear production	[2, 73, 74, 79, 80]
Sulfur dioxide (SO2)	Fossil fuel combustion, industrial processes	Conjunctival irritation, dry eye symptoms, increased inflammation	[2, 56, 106, 107]
Carbon monoxide (CO)	Vehicle emissions, industrial processes	Increased oxidative stress, irritation of ocular surface	[2, 73]
Volatile organic compounds (VOCs)	Industrial processes, paints, cleaning agents	Tear film instability, irritation, exacerbation of inflammation	[2, 56, 73]
Tobacco smoke	Active and passive exposure	Tear film instability, increased evaporation, oxidative stress, mucin alteration, goblet cell loss, inflammation	[2, 94, 95, 97–100, 108]
Other toxic gases	Vehicle emissions, industrial processes	Corneal damage, inflammation, irritation of the ocular surface	[2, 56]

Note: Because duration of exposure (acute vs. chronic) is not uniformly reported in all studies, pollutants were not further categorized by exposure type in order to avoid overinterpretation