(444d) Influence of Meibomian Lipids in Health and Disease on Tear Film Evaporation

The Tear Film Lipid Layer (TFLL) is a thin layer of lipid produced mainly by the Meibomian glands, which are located inside the lids. The TFLL has an approximate composition of 60-70% nonpolar lipids (wax esters, cholesterol and cholesterol esters), and 15% polar lipids (phospholipids and glycolipids). The thickness of the TFLL varies depending on the eye aperture, and values between 32-200 nm have been reported. The functions attributed to the TFLL include maintaining the lid margin in a hydrophobic state to avoid tear overflow, the lowering of the tear surface tension, and the retardation of evaporation. There has been a number of experimental studies trying to measure the specific influence of the TFLL on evaporation, but the results have been unimpressive and equivocal. In this work, we propose two different systems to quantify the influence of the TFLL on the evaporation of the tear film. The first system consist on the measurement of the volume of pendant drops, and the second systems relies on the evaporation induced by non-axisymmetric contact points. For the determination of the evaporation we used Meibomian lipids obtained from healthy controls and from patients suffering from varios Meibomian gland pathologies, and found that the evaporation of fluids covered with Meibomial lipid films can be as low as 50% of pure water.