Dry eye is one of the growing concerns in ophthalmology today. Two definitions of dry eye have emerged, the first being the definition given at the 1995 National Eye Institute’s Dry Eye Conference – dry eye is a disorder of the tear film that causes damage to the ocular surface and eye discomfort due to a lack or excessive evaporation of tears. This definition has continued for more than a decade. The second definition was revised and added to the definition of dry eye at a working meeting held by the American Dry Eye Association in 2007, which synthesized a decade of research from around the world – dry eye is a multifactorial disorder of the tear film and ocular surface that causes ocular discomfort, interferes with visual function, and produces a state of tear film instability affecting the ocular surface with increased tear osmolarity and ocular surface inflammation. From these two definitions, the definitions weaken the concept of tear deficiency or excessive evaporation and emphasize the content of the role of tear osmolarity and ocular surface inflammation on dry eye and its impact on visual function, which reflects the current hot spots in clinical and basic research and trends in treatment.