A randomized, double-masked, placebo-controlled, multi-centre phase IIa proof-of-concept study to evaluate efficacy and safety of APD-209 Eye drops for treatment of acute phase adenovirus-induced EKC. The aims of the study are to investigate the therapeutic efficacy of APD-209 Eye drops as measured by adenoviral load, time to viral eradication, clinical resolution of EKC (objective and subjective assessments), presence of opacities, visual acuity and frequency of second eye infections, and to assess the safety and tolerability of APD-209 Eye drops in EKC infected eyes.