Of an extracellular matrix in human pre-corneal tear film

A theory relating viscosity to fluid flow rates in human tear film was developed and from that theory arises a relationship between viscosity, tear-film thickness and vertical drainage rates at the air-tear interface. Human tears were collected in capillary tubes at rates, on average, of less than 1 microliter min-1. Protein concentration was slightly higher than values reported in the literature and electrophoretic distributions of tear-film proteins were normal. Viscosity of the tear films were measured at 35 degrees C (physiological temperature). Vertical flow rates of tear film were measured in the inter-blink period either by observing the movement of lipid plaques at the air-tear interface or by observing naturally occurring contaminant specs (size around 1 micron). Tear film vertical flow rates were at least an order of magnitude lower than those predicted from collected tear-fluid viscosity measurements. It was concluded that collected tears are not representative of the whole pre-corneal tear film and that the tear film includes a fluid flow-inhibiting matrix whose structural components have a longer time-constant of exchange than the soluble proteins of the collected tear fluid.