Introduction
Allergic conjunctivitis occurs in atopic individuals exposed to specific antigens and manifests as an early reaction, within minutes or hours of exposure to allergens, and may or not be associated with allergic rhinitis.1 IgE-mediated hypersensitivity inducing conjunctivitis is frequent, from 15-20% in general practice2, 3 to 40% in the US population when examined in an ophthalmological survey.4
In France, the prevalence of seasonal allergic rhinoconjunctivitis (SAR) was found to be 13% among 10-year-old children and approximately 20% among adults.5 Birch is one of the most frequent sources of allergens that induce rhinoconjunctivitis.6In the general French adult population, the prevalence of birch sensitization was 4.7%.7 A relationship between pollen counts and the occurrence of symptoms was shown recently.8 The frequency of the ocular response to natural exposure to birch pollen in sensitized patients was linear until birch daily average concentrations reached a plateau of 110 grains/m3, with a cutoff of ocular symptoms at 70 grains/m3 at the beginning of the season.9
In 1990, Abelson et al demonstrated a correlation between skin sensitization (grass pollen, ragweed pollen, and cat allergen) and positivity to conjunctival allergen challenge (CAC). This tool confirms allergen involvement in the diagnosis of allergic conjunctivitis, allowing precise selection of the patients in clinical studies. The CAC model is the only clinically validated method recognized by the Food and Drug Administration (FDA) for testing the efficacy of eye anti-allergic molecules.10 The practical aspects were described in a position paper of the European Academy of Allergy and Clinical Immunology (EAACI) Task Force.11
Environmental exposure chambers (EECs) have been in development since 1985 to study new therapeutics for allergic pathologies, including conjunctivitis.12, 13 EECs have the advantage of achieving reproducible and safe exposure with controlled levels of allergen for several hours in several subjects simultaneously by avoiding confounding factors during exposure.14, 15The ALYATEC EEC has been validated in mite and cat-induced asthma.16, 17 These studies demonstrated that the allergen exposures are standardized with an inter-test coefficient of variation of less than 30%.
To validate the ALYATEC EEC with birch pollen, we exposed patients affected by seasonal allergic conjunctivitis caused by birch pollen to airborne birch allergen. We investigated the amount of Bet v 1 and the time necessary to induce a conjunctival response in at least 50% of patients. We also evaluated the reproducibility of the exposures.