Understanding the role of lipids in tear-film stability
- Danielle Lurisa Leiske.
- Aug. 2011.
- Physical description
- online resource (xviii, 189 pages) : illustrations.
- Leiske, Danielle Lurisa.
- Frank, C. W. thesis advisor.
- Fuller, Gerald G. thesis advisor (primary).
- Swartz, James R. thesis advisor.
- Stanford University. Department of Chemical Engineering.
- Stanford University. Committee on Graduate Studies. degree grantor.
- Includes bibliographical references (p. 173-189). 129 refs.
- The tear film is the thin layer of fluid that covers the surface of the eye. While the functions of the tear film are numerous, the primary role is to protect the corneal surface. When an individual has dry eye disease the tear film breaks up and exposes the corneal epithelial cells, which leads to ocular irritation. The primary components of the outermost layer of the tear film are meibomian lipids, a mixture of long chain nonpolar lipids. Although this lipid layer is thought to play an important role in tear film stability, little is known about the structure and viscoelasticity of meibum, or how these properties relate to tear film stability in dry eye disease. The primary focus of this work was to understand how meibum behaves at an air-water interface to mimic the in vivo conditions of the tear film lipid layer. At room temperature meibum was found to form a predominantly elastic interfacial film, although the film became more fluid as it was heated to body temperature. Interfacial x-ray scattering at room temperature revealed ordered lattices and multilayers at high levels of compression that contributed to high elasticity. In bulk samples, small angle x-ray scattering identified two populations of lipid lamellar phases with unique melt behavior. Meibum collected from patients with meibomian gland dysfunction, a form of dry eye disease, contained the same crystalline phases; however, the prevalence of those phases was reduced indicating a quantifiable change in lipid composition. To ascertain whether meibum viscoelastic properties are relevant to tear film performance, the effects of surface elasticity on an advancing droplet were studied. While droplets covered with a Newtonian monolayer followed classical hydrodynamics, meibum and other insoluble surfactants with surface shear elasticity induced periodic stick-release of the contact line at low advancing velocities and non-ideal behavior at higher velocities. Finally, to explore how a water soluble surfactant may be used to repair a compromised lipid layer, the interactions between a poly(ethylene oxide)-poly(butylene oxide) block copolymer (EOBO) and a model phospholipid monolayer were studied. The lipids and EOBO remained phase separated at the interface, yet EOBO was able to restore the native lattice spacing and mechanical properties of the lipid monolayer, which could make it a valuable tool for a number of biological applications. Meibomian lipids are a complex natural extract with a number of remarkable properties. Although the lipids present in meibum are diverse, meibum can form an elastic interfacial film with ordered phases in bulk material or at an interface. We have shown a link between meibum structure and elasticity, which both depend on temperature. Major composition changes that occur with disease could alter meibum melt temperature and viscoelasticity, which will ultimately modulate the ability of meibum to stabilize the tear film.
- Publication date
- Submitted to the Department of Chemical Engineering and the Committee on Graduate Studies of Stanford University.
- Thesis (Ph.D.)--Stanford University, 2011.