Quantification of conjunctival vascular reaction by digital imaging

Background: No objective evaluation of the conjunctival provocation test (CPT) was possible until now. Objective: The aim of this study was to develop a tool that would enable us to monitor conjunctival allergic inflammation by objective measurements. Methods: Twenty-four patients allergic to grass pollen were challenged by a CPT with grass pollen and genuine grass pollen in the ''Vienna Challenge Chamber.'' Patients were randomized to treatment with placebo or topical application of an H1-receptor antagonist (azelastine). Vascular reaction of the conjunctiva was repeatedly monitored by special video equipment. The signal was sent to a digital frame grabber, and digital image analysis was done with the aid of the WCUE-3 program (Olympus Optical Co., Hamburg, Germany). Results: The CPT led to an immediate increase of the red density. This extension was linear within the first 15 minutes. During the long-term challenge, the increasing vascular effect lasted 2 hours. During active treatment a consistent reaction pattern was obvious; however, the corresponding levels were statistically lower (p = 0.022). Conclusion: The calculation of red density of the conjunctiva by digital analysis proved to be a sensitive tool for measuring the conjunctival allergic reaction. It is possible to overcome the insufficient subjective evaluation of the CPT by objective measurements of the vascular reaction.