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Soluble Mucin and the Physical Properties of Tears

1998; Springer Nature; Linguagem: Inglês

10.1007/978-1-4615-5359-5_33

2214-8019

John M. Tiffany, Jyotin C. Pandit, Anthony J. Bron,

Advanced Drug Delivery Systems

Human tears have a non-Newtonian viscosity,1 meaning that the coefficient of viscosity varies with the value of shear rate at which it is measured. Human tears display shear-thinning, so high-shear viscosity is low, approaching that of water at very high shear rates, but high at very low shear rates. This variation is advantageous in minimizing the drag during blinking but resisting gravitational drainage in the open eye. Tears also have a low surface tension with a mean value of 43–44 mN/m in normal subjects2 compared to about 72 mN/m for water. The standard belief for many years has been that both these properties depend upon the presence of goblet-cell (secreted) mucin dissolved in the aqueous tears, in equilibrium with the gel layer of mucus coating the conjunctival and corneal surfaces. We might suspect that unstimulated tears would contain a higher concentration of soluble mucin than stimulated tears, since they are in contact with the conjunctiva for longer than the more rapidly flowing stimulated tears. Model mucus solutions closely resembled human tears in their rheological3 and surfactant2,4 behavior. We have investigated these properties in relation to the macromolecular content of stimulated and unstimulated tears.