School of Medicine, University of Western Sydney, Locked Bag 1797, Penrith, NSW 2751, Australia.
Exp Eye Res. 2013 Nov;116:79-85. doi: 10.1016/j.exer.2013.08.012. Epub 2013 Aug 22.
Tear film stability decreases with age however the cause(s) of the instability are speculative. Perhaps the more saturated meibum from infants may contribute to tear film stability. The meibum lipid phase transition temperature and lipid hydrocarbon chain order at physiological temperature (33 °C) decrease with increasing age. It is reasonable that stronger lipid-lipid interactions could stabilize the tear film since these interactions must be broken for tear break up to occur. In this study, meibum from a pool of adult donors was saturated catalytically. The influence of saturation on meibum hydrocarbon chain order was determined by infrared spectroscopy. Meibum is in an anhydrous state in the meibomian glands and on the surface of the eyelid. The influence of saturation on the surface properties of meibum was determined using Langmuir trough technology. Saturation of native human meibum did not change the minimum or maximum values of hydrocarbon chain order so at temperatures far above or below the phase transition of human meibum, saturation does not play a role in ordering or disordering the lipid hydrocarbon chains. Saturation did increase the phase transition temperature in human meibum by over 20 °C, a relatively high amount. Surface pressure-area studies showing the late take off and higher maximum surface pressure of saturated meibum compared to native meibum suggest that the saturated meibum film is quite molecularly ordered (stiff molecular arrangement) and elastic (molecules are able to rearrange during compression and expansion) compared with native meibum films which are more fluid agreeing with the infrared spectroscopic results of this study. In saturated meibum, the formation of compacted ordered islands of lipids above the surfactant layer would be expected to decrease the rate of evaporation compared to fluid and more loosely packed native meibum. Higher surface pressure observed with films of saturated meibum compared to native meibum suggests greater film stability especially under the high shear stress of a blink.
泪膜稳定性随年龄增长而降低，但不稳定的原因尚不清楚。或许婴儿的泪膜脂质更饱和，有助于泪膜稳定。在生理温度（33°C）下，泪膜脂质相转变温度和脂质碳氢链有序性随年龄增长而降低。更强的脂质-脂质相互作用可以稳定泪膜，因为只有打破这些相互作用，泪膜才会破裂，这是合理的。在这项研究中，通过催化使来自成人供体的泪膜饱和。红外光谱法测定了饱和度对泪膜脂质碳氢链有序性的影响。在睑板腺和眼睑表面，泪膜处于无水状态。使用 Langmuir 槽技术测定了饱和度对泪膜表面性质的影响。天然人泪膜的饱和度并未改变碳氢链有序性的最小值或最大值，因此在远高于或低于人泪膜相转变温度的温度下，饱和度不会影响脂质碳氢链的有序或无序。饱和度使人类泪膜的相转变温度升高超过 20°C，这是一个相对较高的数值。表面压力-面积研究表明，与天然泪膜相比，饱和泪膜的后期起飞和更高的最大表面压力表明，与天然泪膜相比，饱和泪膜的分子排列更有序（分子排列刚性），弹性更高（分子在压缩和膨胀过程中能够重新排列），这与本研究的红外光谱结果一致。在饱和泪膜中，在表面活性剂层上方形成紧凑的有序脂质岛，预计会降低与天然泪膜相比的蒸发速率，因为天然泪膜更具流动性，排列更松散。与天然泪膜相比，饱和泪膜的膜具有更高的表面压力，这表明其具有更高的膜稳定性，尤其是在眨眼时受到高剪切应力的情况下。
