Dry eye disease is a common and major source of disability, whether occurring as a primary disorder or as a component of other diseases and its onset may be triggered or modified by exposure to systemic drugs, contact lens wear, ocular surgery and adverse environmental and work conditions. The development of a reliable, highly sensitive and specific test for the clinical diagnosis of dry eye is a major unmet clinical need, particularly to differentiate it from common conditions such as ocular allergy which exhibit similar presenting symptoms. Tear hyper-osmolarity is central to the dry eye disease process and the measurement of tear osmolarity could serve not only as a highly accurate diagnostic test but also as a measure of disease severity and a means to monitor treatment efficacy.