OBJECTIVES: Dry eye disease (DED) is characterized by symptoms of ocular discomfort, visual disturbance and reduced tolerance to environmental stressors. DED has a significant negative impact on the quality of life (QOL) of persons affected, and imposes a massive burden on medical resources owing to its high prevalence and chronic nature. It is not known if available patient-reported outcome (PRO) instruments fully capture the scope of DED symptoms and their impact on QOL. The purpose of our ongoing research is to develop a PRO instrument that meets the needs of clinical studies investigating potential treatments for DED. METHODS: Patients with DED in five countries (United States, United Kingdom, Spain, Japan and Korea) were interviewed to identify their symptoms and the impact of the disease on QOL (n=120).  Based on these results, items were drafted that were tested in two web-based studies with mild-moderate DED subjects (n=106 and 156) and face-to-face interviews with severe DED subjects (n=22). RESULTS: Items enquiring about 8 additional symptom experiences (16 items grouped in doublets asking about frequency/intensity) were added to the original Ocular Comfort Index (OCI) using the same question format and response structure (fluctuating vision, light sensitivity, redness, foreign body sensation, excessive tearing, excessive blinking, ocular irritation and stickiness). Additionally, 2 items that enquired about the most bothersome symptom and the extent of bother, and 12 items that appraised how symptoms interfered with the ability to perform daily activities were included. CONCLUSIONS: Patient interviews suggest that available PRO instruments do not fully capture the scope of DED symptoms and their impact on QOL. The modified OCI (mOCI) will be used in clinical studies to facilitate its refinement and validation.