Osmolarity Measurements
At the 19 clinical centers that had TearLab Osmolarity System (OcuSense Inc., San Diego, CA, USA), osmolarity measurement was taken at baseline and the six- and 12-month visits. At each center, both the clinician and technician completed a certification program that included review of the study protocol and instructional slides, and a written knowledge assessment of the tear film osmometer. Osmometer measurements were performed using an electrode to measure electrical impedance technology on 50 nL tear fluid samples in a TearLab Osmolarity System (OcuSense Inc.) operated according to the manufacturer's instructions. With the subject looking in primary gaze, the osmolarity test card tip was dipped into the tear film meniscus in the central portion of the temporal third of the lower eyelid. The osmometer was calibrated before each test using the control solution provided by TearLab. Patients were asked not to instill eye drops within two hours before any study visit examination. Before any diagnostic examination or instillation of any eye drops, tear osmolarity was measured once in each eye using disposable test cards provided by the manufacturer's osmometer system. Tear osmolarity was defined as normal if ≤308 mOsm/L and abnormal if >308 mOsm/L or if the measurement between the two eyes was >8 mOsm/L, based on the TFOS DEWS report.