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S. Tragoulias, P.J. Anderton, G.R. Dennis, F. Miano, T.J. Millar; Evidence that Tear Proteins Are an Active Component of the Tear Film Surface . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2500.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Meibomian lipids form the surface of the normal tear film and are thought to be responsible for maintaining its low surface tension. It is now recognised that particular proteins in the tear film, such as lipocalin, are lipophilic and hence could also affect surface tension. Therefore, the surface activity of individual tear proteins was measured and compared with the surface activity of whole tears, and meibum. Methods: Meibum, albumin, ß-lactoglobulin, lipocalin, lysozyme, lactoferrin, or human tears were applied to an air/phosphate buffered saline interface in a Langmuir trough. The surface pressures were measured at 20°C or 37°C using a Wilhelmy balance as the film was compressed and expanded. Results:All proteins exhibited surface activity. The cyclic surface pressure – molecular area (П-A) profiles of albumin, ß-lactoglobulin, lipocalin, lysozyme and lactoferrin monolayers were sigmoidal and showed strong hysteresis between expansion and compression parts of the cycle. By contrast, the П-A profiles for meibum were more hyperbolic than sigmoidal and had little hysteresis between compression and expansion parts of the cycle. Whole human tears had a П-A profile similar to the protein profiles. When the tears were filtered through a 5kD molecular weight cut-off filter then the П-A profile was similar to meibum. Lysozyme alone appeared to show a difference if the temperature of the experiment was 37°C rather than the standard 21°C. Conclusions:By comparing the dynamic surface activity profile of tears with the individual components, there is strong evidence to suggest that not only are the proteins capable of surface activity, but they are also a major contributor to the surface activity of the tear film.
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