Abstract
Dysfunction of one or more components of the lacrimal functional unit results in an unstable tear film that can trigger eye irritation or cause ocular surface disease. There are distinct differences in the pattern of cornea and conjunctival disease and inflammation between aqueous deficient and aqueous sufficient tear dysfunction. There are accurate commercially available methods to measure tear volume. Diagnostic classification based on tear volume can guide therapy and identify patients with higher risk of developing disabling ocular surface disease or irritation.