Thermography is a non-invasive imaging technique, which uses infrared radiation reflected from an object to estimate the temperature of the object. This paper evaluates the use of thermography to assess allergic conjunctivitis objectively, by using an instrument called ocular surface thermographer (OST). Thirteen asymptomatic patients, with proven seasonal allergic conjunctivitis due to cedar pollen, were included in the study. A drop of 0.025% levocabastine ophthalmic suspension was instilled in one eye and artificial tears in the other eye in a masked fashion 10 minutes prior to a conjunctival allergen challenge (CAC). Then a drop of cedar pollen solution was instilled into each eye to induce the allergic reaction. The surface temperature of the inferior conjunctiva and conjunctival injection scores were measured before and 30 minutes after the CAC. After the CAC, the temperature increased by 0.67±0.10˚C in the artificial tear eyes but only 0.21±0.06˚C in the levacobastine eyes. The score for conjunctival injection was 1.38±0.24 and the chemosis score was 0.85±0.25 for the artificial tear eyes and 0.62±0.27 and 0.08±0.08 in the levacobastine eyes (P<0.01). There was a significant correlation between the conjunctival surface temperature and severity of conjunctival allergic reaction. They conclude that OST can be used objectively to evaluate topical anti-allergic agents.