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T.J. Millar, S.T. Tragoulias, P.J. Anderton; The effect of protein–meibomian lipid mixtures on "tear break–up time" using a rat model . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3866.
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Purpose: There is growing evidence that the interaction between tear proteins and meibomian lipids at the surface of the tear film is important for its stability. Therefore, we have investigated whether particular tear proteins mixed with meibomian lipids give greater stability to the tear film than others. Methods: Anaesthetised (ketamine/xylazine) Wistar rats were used in these experiments. Albumin (1mg/mL), lysozyme (3.2mg/mL) or lipocalin (1.2mg/mL) was dissolved in phosphate buffered saline (100% solution). Bovine meibomian lipids (1mg/mL in chloroform) were mixed 1:10 in phosphate buffered saline (100% solution). Individual protein or meibomian lipid solutions, or their mixtures were applied to a dry corneal surface. "Tear break up time" (BUT), the time for drying to appear at the corneal surface, was measured using specular reflection microscopy. For normal rat tears mixed 1:1 with phosphate buffered saline, BUT was 120s for complete dryness. Results: The proteins or meibomian lipids alone (mixed with saline) were very poor in maintaining a stable tear film with BUT beginning at <30s and complete dryness occurring at <60s. For albumin and lysozyme, a ratio of 60:40 with meibomian lipids gave the longest BUT which began at 60s and complete dryness was at 150s. Lipocalin mixed with meibum performed poorly at all ratios. A 40:60 ratio with meibomian lipids gave the best performance with BUT beginning at 30s and complete dryness occurring at 90s. Conclusions: Proteins, or meibomian lipids as single components (mixed with phosphate buffered saline) were less stable than normal tears on the rat ocular surface. Proteins interacting with meibomian lipids increased the stability of the tear film, but the ratio between the proteins and meibum was critical. Lipocalin, which is very lipophilic, was less able to maintain a stable tear film than the other proteins, either alone or as a mixture with meibomian lipids.
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