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Published on: May 2, 2020
Components responsible for the surface tension of human tears
1Nuffield Laboratory of Ophthalmology, University of Oxford, UK.
Current Eye Research
|July 23, 1999
Summary
Tear surface tension is primarily caused by a complex of tear lipocalin and specific polar lipids, not mucin. This lipid-protein complex, distinct from meibomian oil, is likely secreted by the lacrimal gland.
Area of Science:
- Ophthalmology
- Biochemistry
- Surface Science
Background:
- Previous assumptions attributed tear surface tension to mucin, but recent findings show minimal mucin presence.
- Commercial mucin, lysozyme, lactoferrin, and secretory IgA exhibit higher surface tensions than natural tears.
- The roles of tear lipocalin and lipids in tear surface tension remained uninvestigated.
Purpose of the Study:
- To investigate the influence of tear lipocalin and lipids on the surface tension of human tears.
- To identify the specific components responsible for maintaining normal tear surface tension.
Main Methods:
- Surface tension measurements using a micro-method on intact and delipidized human tears.
- Analysis of extracted lipids and their reintroduction to delipidized tear fluid.
- Identification of lipid components using Thin-Layer Chromatography (TLC) and Gas-Liquid Chromatography (GLC).
Main Results:
- Intact tears showed a surface tension of 42-46 mN/m, increasing to 53-55.5 mN/m after lipid extraction.
- Reintroduction of lipids restored surface tension, with phospholipids (phosphatidylcholine, sphingomyelin) showing significant effects.
- The lipid extract's chromatographic profile differed from meibomian oil, suggesting a unique tear lipid composition.
Conclusions:
- Tear surface tension is determined by a complex of tear lipocalin and a polar lipid fraction.
- This lipid fraction is extractable by lipid solvents and distinct from meibomian lipids.
- The lacrimal gland likely co-secretes lipocalin and this specific lipid fraction.
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