A Compositional Based Model For The Tear Film Lipid Layer英文电子书.pdf

A COMPOSITIONAL BASED MODEL FOR THE TEAR FILM LIPID LAYER* BY James P McCulley, MD, AND Ward Shine, PhD (BY INVITATION) ABSTRACT Background: The tear film lipid layer is formed from lipids secreted by meibomian glands of the eyelid. After initial analyses of these lipids we concluded that an understanding of the function of the various classes of lipids in a normal lipid layer could only be understood after detailed inves- tigations of both polar and nonpolar lipids of the meibomian gland. Methods: Meibomian gland secretions were obtained from normals. Lipids were separated by thin layer chromatography and high pressure liquid chromatography, and analyzed by UV absorbance, gas chromatogra- phy and mass spectroscopy. Results: Based on our analyses we concluded that the current under- standing of lipid layer composition and function were inadequate or mis- leading. We therefore propose that the more polar lipids function as a structure (with surfactant characteristics) upon which the functional sta- bility of the more nonpolar lipids are dependent. We further suggest that the interrelationships between lipid classes present, length of fatty acids and alcohols, their unsaturation, and hydroxylation are important for main- taining proper thixotropic characteristics of the lipid layer as well as opti- mal barrier properties. Conclusion: The tear film lipid layer is composed of 2 phases: (1) a thin polar phase adjacent to the aqueous-mucin phase and (2) a thick nonpolar phase associated with both the polar phase and the air interface. The structural characteristics of the polar phase and the barrier functions of the nonpolar phase are a direct result of specific compositional parame- ters. From the Department of Ophthalmology, The University of Texas Southwestern Medical Center at Dallas. Supported in part by an unrestricted gr