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WP Jackson, R Secker, C Amos; Assessing The Variable Viscosity Of Lens Comfort Drops And Demonstrating Their Non-newtonian Behavior . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3143.
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Purpose: To determine the non-newtonian viscosity character of eight lens comfort drops and compare these results to similar data already established for natural tears. Method: Seven commercially available lens comfort drop solutions and one investigational formulation served as the test articles in these studies. The viscosity measurements were completed using the Rheometric Scientific FRSII rheometer with couette geometry, which ensured more accurate viscosity measurements at low shear rates. An internal circulation bath maintained the temperature at 252°C throughout the determinations and each of the solutions was tested for its viscosity at the following constant shear rates: 1, 2, 3, 4, 5, 8, 13, 20 s-1. Triplicate measurements were made of each test solution. The resulting data points for each solution were fit to a power regression curve and compared to previously published results on normal human tears Results: A solution exhibiting non-newtonian behavior shows higher viscosity at low shear rates and lower viscosity at higher shear rates. Of the eight solutions tested, one solution, containing sodium hyaluronate, showed distinct non-newtonian character, one solution, containing carboxymethylcellulose, showed a trend toward non-newtonian behavior, and the remaining six solutions showed little to no non-newtonian traits. Conclusion: The choice of the appropriate polymer can impart non-newtonian character to lens comfort drops. Only the investigational solution showed distinct non-newtonian behavior. This formulation contained sodium hyaluronate at a sufficient concentration that the solution mimicked closely the non-newtonian viscosity curve of normal human tears.
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