Epidemiological aspects of allergic conjunctivitis.

The prevalence of ocular allergies has been increasing worldwide for the past several decades. The geographical distribution and hot spots of rhinoconjunctivitis have been documented in a global survey by the International Study of Asthma and Allergies in Childhood (ISAAC). ISAAC indicated that Africa, Latin America, and Japan were notable for their high prevalence of rhinoconjunctivitis. The outcomes of follow-up studies of regional differences and the characteristics of allergic conjunctivitis are summarized in this review. Currently, comorbid diseases and socioeconomic and environmental factors, including climate and air pollution, are proposed to contribute to the regional differences in the prevalence of allergic conjunctivitis. Of them, rhinitis has been shown repeatedly to be significantly associated with allergic conjunctivitis. Their mechanistic aspects on association with the prevalence of systemic allergic diseases have been reviewed by examining the birth cohort or in vitro analyses. A vision threatening form of ocular allergy, vernal keratoconjunctivitis, is prevalent in the African countries and Japan. Of the proposed associated factors, air pollution was shown to contribute not only to aggravating the symptoms but also to the increase in the incidence of its severe forms. Its mechanistic aspects are discussed in this review in the context of comorbid diseases.