Rheological behavior of commercial artificial tear solutions.

PURPOSE: To measure the rheological behavior of artificial tears to gain insight into the potential role of rheology in predicting the efficacy of artificial tear solutions for the treatment of dry-eye disease (DED).

SETTING

Research laboratories of I-MED Pharma, Canada, Rohn and Associates, Inc., New Jersey, and Hydan Technologies, New Jersey.

DESIGN

Laboratory investigation.

METHODS

Twenty commercially available artificial tear drops were purchased in Canada and the United Kingdom. Rheological measurements of viscosity and normal stress as a function of shear rate were performed at 25°C.

RESULTS

For comparison of the rheological behavior, the various artificial tears were sorted into 3 groups: group A, which exhibit significant non-Newtonian shear-thinning behavior; group B, which exhibit moderate non-Newtonian shear-thinning behavior; and group C, which exhibit Newtonian behavior throughout the shear rate range. Results of normal stress difference, N1, as a function of shear rate were concordant with the rheological testing, indicated the viscoelastic nature of the samples in groups A and B, whereas members of group C did not exhibit any elasticity.

CONCLUSIONS

The various artificial tear solutions were sorted into groups based on their Newtonian or non-Newtonian behaviors. The results suggest that non-Newtonian solutions should provide better comfort and longer-lasting symptomatic relief for DED. It remains to be confirmed clinically if there is a direct correlation between the rheological behavior of artificial tears and their ability to provide prolonged relief in DED, or if other factors are more important.