(56e) Rheology of the Tear Film Lipid Layer in Health and Disease

The Tear Film Lipid Layer (TFLL) is a 50-200 nm layer of lipid that covers the exposed surface of the eye. The composition of the TFLL is approximately 60-70% nonpolar lipids (wax esters, cholesterol and cholesterol esters), and about 15% phospholipids and glycolipids, forming a duplex layer.

The functions of the TFLL include lowering of the tear surface tension to minimize dewetting of the tear film, and the homeostasis of tears through the retardation of evaporation. Both of those functions require the formation of a stable, continuous lipid layer that resist the compression and expansion cycles due to blinking.

In previous studies, we have found significant differences in the evaporation rate of fluids covered with Meibomian lipids between patients diagnosed with various Meibomian gland pathologies vs. healthy patients. In this work, we measured the surface rheology of Meibomian lipid layers by the method of oscillation of a pending drop, and compared the surface rheology of the TFLL of the cases and the controls.