M.S. Chemical Engineering, Oregon State University, 2004
B.S. Chemical Engineering, Oregon State University, 2003
Mechanical and structural analysis of Meibomian lipids
The tear film covers the surface of the eye and is responsible for protecting the cornea, lubricating the eyelid, and being optically clear. The structure and composition of this film are quite complex. In contact with the corneal surface is a 10 mm thick aqueous layer which consists of proteins and mucins. The superficial layer of the tear film that forms the interface between the aqueous layer and the air is a thin, 100 nm film composed primarily of lipids. The majority of the lipids that form this layer are extruded from the Meibomian glands, which are located on the inside of the upper and lower eyelids. These Meibomian lipids primarily consist of nonpolar species such as long-chain wax esters, cholesterol esters and fatty acids. As the outermost layer of the tear film, it is believed that the lipid layer is responsible for promoting tear film stability. Mechanical properties may influence the ability of the lipid layer to stabilize the tear film, which are a result of the local structure of the lipids, including crystallinity. Individuals with dry eye disease have inherently unstable tear films but the physical and chemical changes that cause instability are unknown.
We have used a variety of techniques to explore the basic mechanical and structural properties of Meibomian lipids. These include experiments of both lipid monolayers (used to model the lipid layer of the tear film) in a Langmuir trough and bulk samples. An interfacial stress rheometer is used to explore mechanical properties and a Brewster angle microscope to allows us to visualize the microstructure of monolayers. To measure structure on a molecular level we utilize small angle x-ray scattering. These experiments have been geared towards exploring changes with monolayer compression (surface pressure), compositional differences (by studying lipids from different animals), temperature dependence, and finally differences between lipids from normal and dry eye subjects. Ultimately we hope to fundamentally understand how lipid structure and fluidity influence stability so that dry eye treatments can be improved.
Leiske, D.L., Raju, S.R., Ketelson, H.A., Millar, T.J., & Fuller, GG. “The interfacial viscoelastic properties and structure of human and animal Meibomian lipids.” Experimental Eye Research, 90(5), 598-604, 2010.
Leiske, D.L., Kariumpour-Fard, A., Hume, P.S., Fairbanks, B.D., & Gill, R.T. “A comparison of alternative 60-mer probe designs in an in-situ synthesized oligonucleotide microarray.” BMC Genomics, 7(1), 72, 2006.