Rheological Behavior Patterns in Artificial Tears.

SIGNIFICANCE

Rheological patterns were objectively calculated considering the first and last viscosity, besides the difference of viscosity with a specific shear rate. Shear thinning, shear thickening, thixotropic, and Newtonian behavior patterns were found.

PURPOSE

This study aimed to describe, in an objective way, the rheological behavior of several artificial tears.

METHODS

Seventy-eight artificial tears were included in this experimental analytical study. Its viscous behavior was measured using a cone-plate rheometer. An ascending and descending measurement range was defined for the shear rate from 1 to 1000 s-1 and vice versa. Hysteresis was calculated with the initial and final difference of viscosity. The rheological behavior pattern was calculated as the viscosity difference for the shear rate between 100 and 1000 s-1.

RESULTS

Four rheological patterns with different magnitudes were found: shear thinning, shear thickening, thixotropic, and Newtonian.

CONCLUSIONS

The viscosity of artificial tears always depends on the shear rate. It is possible to find two patterns simultaneously depending on the shear rate. These rheological patterns could serve to optimize the treatment with lubricants for different conditions of the ocular surface. In vivo studies are necessary to evaluate the clinical significance of these findings.