Progressively Increased Variation in Tear Osmolarity Mirrors Dry Eye Severity—Reply

In Reply Our study does not invalidate the utility of tear osmolarity as a biomarker of ocular surface disease, but rather raises questions about the clinical utility of measuring osmolarity using the TearLab system owing to the high variability of measurements at a single session and across sessions in both patients with dry eye and controls.¹ We agree that there is substantial evidence regarding tear instability and hyperosmolarity in the pathophysiology of dry eye disease; however, much of the previously published research used different methods of measurement rather than electrical impedance as used in the TearLab system.