OBJECTIVES: : To develop a new patient-reported outcomes (PRO) measure assessing the comfort of topical ocular drop applications - the Eye Drop Comfort Scale (EDCS) in an adult population who have an ophthalmologic condition. METHODS: In alignment with FDA PRO Guidance, development occurred across three ocular categories (inflamed, non-inflamed, and post-surgical) and included literature review, and the conduct of two sets of interviews with topical ocular drop users: focus groups interviews to elicit concepts for a draft measure, and cognitive debriefing interviews to refine items and further establish content validity. RESULTS: Results from the nine focus groups (n=61 eye drop users; 3 groups per category) provided concepts that were appropriate, comprehensive, and relevant to patient experiences with topical ocular drop application comfort in each of the categories. Qualitative analysis demonstrated that saturation was achieved for these concepts, resulting in a fifteen item measure assessing sensations or symptoms experienced after instillation of a topical eye drop. Patient input from the cognitive debriefing interviews documented patient understanding of the items, response scale and recall period as well as confirmation of concept relevance. The interview results supported content validity of the tool. The EDCS is designed to be self-administered and may be completed in hard copy or on an ePRO tablet. CONCLUSIONS:  The EDCS is a brief, comprehensively developed measure designed to assess the comfort or discomfort experienced after the instillation of eye drops in patients with inflamed, non-inflamed or post-surgical conditions. Results of the qualitative research provided evidence to support the content validity of the EDCS. The next phase of development of the EDCS is psychometric evaluation. Future uses of the measure in clinical studies may facilitate identification of improved treatment modalities in development as well as allow comparison of topical ocular drop comfort and safety between products to inform patients, and prescribers.