Air pollution constitutes one of the main threats to public health in Europe. Significant impacts on morbidity and mortality have been observed, even in cases of low exposure and when pollutant levels are within limits set by the European Union.2
Focusing on ocular surface diseases, patients commonly present with a type of conjunctivitis that is not strictly of allergic, infectious or dry-eye origin. Clinical studies and experience have shown a cause-and-effect relationship between these allergy-like symptoms and environmental factors, including outdoor air pollutants and poor indoor air quality.3
People with this ‘urban eye allergy syndrome’ experience ocular symptoms that are increased by chemical triggers and pollution in the atmosphere rather than by true allergens.
Proposed mechanisms for the syndrome include free-radical generation and oxidative stress; increased expression of pro-inflammatory cytokines; modification of key intracellular proteins or the innate immune response; stimulation of autonomic nervous system receptors; adjuvant effects on the immune system; and suppression of normal defence mechanisms.
It seems likely these all play roles at different stages of the developing syndrome. These individuals certainly appear not to be allergic to pollutants but rather to be experiencing an allergic-type response to pollutants stimulating the mucosal immune system.
In a recent large survey performed at a national level, focused specifically on ocular allergy, only 40% of subjects diagnosed as affected by allergic conjunctivitis had an associated allergic condition such as rhinitis, asthma or eczema.4 Therefore, it is quite common for patients with eye symptoms to request an ophthalmological evaluation before the allergy consultancy.
In this survey, pollens were indicated as the most frequent triggers; however, nonspecific environmental conditions, pollutants, cigarette smoke and particular weather conditions were also reported as common factors in inducing ocular symptoms.