Interventions
This was an open, single-center study designed to determine the
concentration of airborne Bet v 1 inducing an allergic conjunctivitis
response in patients allergic to birch pollen during allergen exposures
to birch pollen extracts in the EEC. During the first screening visit,
the patient gave informed written consent and underwent the following
procedures and assessments: medical history review, skin prick testing
to birch pollen allergen (ALK-Abello® ), and a blood draw for
specific IgE to birch
(Betula verrucose, Phadia ImmunoCap, Thermofisher®). The second
screening visit was for an individual conjunctival allergen challenge
(CAC) to birch allergen. All responders in the CAC were included in the
present study.
The CAC was performed according to the updated EAACI
guidelines.1, 11 This procedure consisted of the
instillation of 20 µl of diluted birch allergen extract (100 IR
lyophilized extract, Stallergenes Greer®) in the inferior-external
quadrant of the bulbar conjunctiva in incremented dilutions at 10-min
intervals: 3, 6, 12, 25, 50, and 100 IR/ml.11 The
clinical response was assessed by the Total Ocular Symptom Score (TOSS)
with the same cumulated positivity criteria for the CAC and EEC
exposure. If the TOSS was <5 at 10 minutes after each
instillation, the test was considered negative. The next concentrated
dose was then instilled until a positive response was reached.
Step 1 of the study consisted of two consecutive EEC exposures to the
same birch pollen extract (Expo 1
and Expo 2). The primary endpoint of the study was met when 50% of the
patients were positive. The main judgment criteria were the amount of
Bet v 1 inducing a positive conjunctival response after EEC exposure. In
addition, we compared the intensity of the clinical response induced in
patients exposed to birch pollens using the TOSS and the mean time to
reach a positive ocular response (i.e., TOSS ≥ 5). In step 2, we studied
the reproducibility of the allergen exposure. Patients who responded to
Expo 1 and Expo 2 were enrolled in step 2 and exposed two additional
times on 2 consecutive days (from Expo 3 to Expo 6). Each double EEC
exposure test was separated by 7 days.