Overview of 37 Tear Substitutes in Europe Based on Various Physicochemical Parameters

Dry eye disease (DED) is one of the most prevalent eye conditions worldwide, with artificial tears serving as a primary treatment option. Despite their wide availability on the European market, there is a lack of established classifications based on their physicochemical properties. The aim of our study was therefore (i) to develop an analytical method that measures the concentration and the molecular weight (MW) of the hyaluronic acid (HA) in commercialized products, and (ii) to propose an overview based on their various physicochemical parameters.

The intrinsic viscosity and MW of the HA, as well as osmolarity, pH, rheological profile, and viscosity, were measured or determined. A specific method was developed to measure the average intrinsic viscosity and HA content using a liquid size-exclusion chromatography system. The MW was determined using the Mark-Houwink equation.

Thirty-seven products commercialized in Europe were analyzed, with 21 of them containing HA. The HA MW was lowest (300 kDa) for Thealose^®, Thealoz Duo^® Gel, and Hyabak^®, and highest (1300 kDa) for Vismed^® Multi, Vismed^® Gel, and Neovis^® Gel. The pH values varied between 5.94 for Treovis^® and 8.06 for Systane^® Ultra. Osmolarity ranged between 148 mOsm/L and 325 mOsm/L for Neovis^® and Treovis^®, respectively. Viscosity was highly variable, ranging from 0.38 mPas·s for Hylolipid^® to 337.47 mPas·s for Thealoz^® Duo Gel. Finally, rheological profile analysis revealed different shear-thinning behaviors.

While the perfect eye drop does not exist, a multitude of options are available to choose from. This study improves our understanding of the major tear substitutes available on the European market based on several physicochemical properties. A better understanding and awareness of these parameters is crucial in order to offer the best treatment for patients with DED.