Physicochemical Properties and Rheological Behavior of Artificial Tears for Dry Eye Syndrome

Purpose: Dry eye syndrome (DES) is a growing global public health problem. The clinical management of DES involves general advice on environmental and lifestyle adaptations, as well as the use of artificial tears. While there are a multitude of tear substitutes and eye drops for DES on the market, with a wide variety of ingredients, there are no specific recommendations on the priority use of one or the other. The aim of this study was to determine and compare physicochemical and rheological properties of ten widely used eye drops for DES, pure or mixed in tears to get closer to the real conditions of use. Methods: Physicochemical characterization was done according to pH, density and osmolarity. Rheological characterization was done according to flow measurements and oscillatory measurements. Results: Three categories of eye drops could be identified according to their rheological behavior: those with significant shear-thinning behavior, those with moderate shear-thinning behavior, and those with Newtonian behavior. Some changed their rheological behavior when mixed with simulated tear fluid. Within each category, differences were identified based on physicochemical criteria or the presence of problematic excipients such as preservatives or phosphates. Conclusions: This categorization could be used to refine prescriptions, particularly when several eye drops are to be combined, in order to avoid redundancy of mechanism of action.