Does the temperature of an artificial tear affect its comfort?

Background: Refrigerated eye-drops have been advocated in cases of ocular allergies to provide a soothing effect upon instillation. This notion continues to be promoted by practitioners for artificial tears (AT) in the management of dry eye (DE) with little support in the literature. To further substantiate claims of a soothing effect of cold eye-drops, the aim of this study was to determine if refrigeration of an AT enhanced the subjective comfort upon instillation.
Methods: Participants with mild to moderate DE participated in an open label contralateral study of two weeks duration. Each participant instilled Systane Ultra (Alcon Laboratories) in the morning (between 6.00-10.00 hours) and in the evening (between 18.00-22.00 hours). Participants were asked to report the subjective comfort immediately after both of these instillations, on a scale from 1 (poor) to 10 (excellent). This was done for ambient (aAT) and refrigerated (rAT) drops. An in vitro study evaluated if there were any changes in eye-drop pH and osmolarity with refrigeration.
Results: Participants (n = 18, three male, 15 female, age 22-28 years, average 24.4 ± 1.6) reported mean comfort scores (± standard deviation) of 7.8 ± 0.9 and 7.6 ± 1.4, for the aAT and the rAT, respectively. Mean comfort scores (± standard deviation) for morning and evening, were 7.7 ± 1.2 and 7.8 ± 1.1, respectively. A non-parametric Friedman test of differences among repeated measures was conducted and rendered a chi-squared value of 3.74, which was not statistically significant (p = 0.29). The pH remained stable at 8.0 and the osmolality did not vary significantly with refrigeration.
Conclusion: There is no advantage, with respect to patient perceived comfort, in refrigerating the Systane Ultra (Alcon Laboratories) AT for mild to moderate DE.
(© 2018 Optometry Australia.)