During controlled exposures to the airborne birch pollen allergen, Bet v 1, in an environmental exposure chamber (EEC), researchers assessed the non-inferiority of a topical mast cell stabilizer, N-acetyl aspartyl glutamic acid (4.9%, NAAGA), compared to fluorometholone (0.1%, FM). Furthermore, 24 patients with a history of birch pollen allergic conjunctivitis participated in the randomized, cross-over, investigator-blinded trial. Patients were randomly assigned to either 5 days of NAAGA followed by FM (n=12) or 5 days of FM followed by NAAGA (n=12). After each treatment, patients were exposed to a fixed airborne concentration of Bet v 1 in ALYATEC EEC. The primary outcome was the amount of allergen necessary to cause a conjunctival response (Abelson score of ≥5). For cross-over investigations, groups were compared using a linear model. When the lower bound of the risk ratio CI was more than 0.5, non-inferiority was accepted. The average time to conjunctival reaction at the screening was somewhere between 72.5 and 35.9 minutes. The reaction times for NAAGA and FM were increased to somewhere between 114.8 and 55.0 and somewhere between 116.651.5 minutes, respectively. Following NAAGA, the mean quantity of allergen required to elicit a conjunctival reaction was 1.165 ng, and after FM therapy, it was 1.193 ng. The conjunctival response risk ratio was 0.977 (95% CI: 0.812; 1.174), indicating non-inferiority. Compared with FM (58.3%), NAAGA had a lower rate of adverse events (29.2%). NAAGA was non-inferior to FM in exposures to airborne Bet v 1 in individuals with allergic conjunctivitis to birch pollen. The EEC was a useful model for imitating real-life allergen exposure and demonstrating the efficacy and safety of eye drops for allergic conjunctivitis treatment.