The aim of this work was to evaluate conjunctival redness as an objective allergy symptom during the conjunctival provocation test (CPT). The CPT is an instillation of ophthalmic solution containing an allergen into the ocular mucosa. Allergic severity using the CPT was evaluated in the multicenter, randomized, controlled, double-blind, dose-finding study of 159 patients with birch pollen allergy where the mucosal sensitivity of the eye was assessed based on subjective and objective symptoms such as itching and redness, respectively. High-resolution digital photos were taken, arranged in image matrices, and analyzed by an external central observer to assess conjunctival redness. The photodocumentation method described here was successfully applied in a dose-finding study using the CPT. The evaluations of allergic severity carried out by an external observer agreed with the investigators' assessments.