Evaluation of 18 artificial tears based on viscosity and pH

Introduction: Different polymers used in artificial tear formulations influence their physical properties, such as viscosity and pH, hence affecting their bioavailability. There is limited data available from manufacturers specifying the physical properties of artificial tears, even though these data can contribute to their efficacyand effectiveness. Purpose: The aim of this study was to evaluate 18 artificial tears available in the Malaysian market based on their physical properties. Methodology: Viscosity and pH of 18 artificial tears were evaluated using rheometer and compact pH-meter, respectively, at standard room temperature (25°C). The amount of fluid used for both tests of each artificial tear was standardised using micropipette. The Kruskal-Wallis test was employed to compare the viscosity median between the three groups (low, medium, and high viscosity) of artificial tears, while the independent t-test was used to compare the pH between preservative and non-preservative artificial tears. A p-value of 0.05 was set as the level of significance. Results: The mean viscosity for all 18 artificial tears was 12.05 cP ± 10.21 within a range of 0.55 cP to 34.49 cP. There was a significant difference observed in viscosity between low- (n = 7), median- (n = 8), and high- (n = 3) viscosity groups, χ2(2) = 14.474, p = 0.001. The mean pH for all 18 artificial tears was 7.21 ± 0.43, with a range of 6.19 to 7.85. pH for preservative artificial tears was slightly alkaline compared to non-preservative artificial tears (7.26 ± 0.47 vs 7.14 ± 0.38, respectively). Conclusion: Rheological findings indicated that different formulations of artificial tears have different viscosities, with most artificial tears falling within the recommended values. There was no difference in terms of pH between preservative and non-preservative artificial tears.