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.