McCulley J P, Shine W
Department of Ophthalmology, University of Texas Southwestern Medical Center at Dallas, USA.
Trans Am Ophthalmol Soc. 1997;95:79-88; discussion 88-93.
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 investigations of both polar and nonpolar lipids of the meibomian gland.
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 chromatography and mass spectroscopy.
Based on our analyses we concluded that the current understanding of lipid layer composition and function were inadequate or misleading. We therefore propose that the more polar lipids function as a structure (with surfactant characteristics) upon which the functional stability 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 maintaining proper thixotropic characteristics of the lipid layer as well as optimal barrier properties.
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 parameters.
泪膜脂质层由眼睑睑板腺分泌的脂质形成。在对这些脂质进行初步分析后，我们得出结论，只有在对睑板腺的极性和非极性脂质进行详细研究之后，才能理解正常脂质层中各类脂质的功能。
从正常人获取睑板腺分泌物。脂质通过薄层色谱法和高压液相色谱法分离，并通过紫外吸收、气相色谱和质谱进行分析。
基于我们的分析，我们得出结论，目前对脂质层组成和功能的理解是不充分的或具有误导性的。因此，我们提出极性更强的脂质起到一种结构（具有表面活性剂特性）的作用，极性较弱的脂质的功能稳定性依赖于此结构。我们进一步表明，现存脂质类别之间的相互关系、脂肪酸和醇的长度、它们的不饱和程度以及羟基化对于维持脂质层适当的触变特性以及最佳屏障特性很重要。
泪膜脂质层由两个相组成：（1）与水 - 粘蛋白相邻的薄极性相，以及（2）与极性相和空气界面相关的厚非极性相。极性相的结构特征和非极性相的屏障功能是特定组成参数的直接结果。
