*4.3.2 Tear osmolarity*

Tear osmolarity is the most accurate method to diagnose DED. Tear hyperosmolarity is considered as pathogenic factor causing ocular surface inflammation, symptoms, and tissue damage which can lead to DED. This condition can occur in many situations including insufficient tear production, meibomian gland dysfunction, and exposure. There is a commercially available objective point of care test (TearLab Osmolarity System; TearLab, San Diego, California) that can measure the osmolarity of a 50-nL tear sample and is easier to use [30, 58, 59]. A reading of 308 mOsms/L or greater indicates tear osmolarity disruption. This test must be completed quickly to avoid any evaporation of tear sample. Although reproducible, this test is difficult to perform in clinic setting.
