Une façon innovante d'évaluer la friction causée par un verre de contact

There are over 140 million contact lens wearers worldwide. However, 50% of those report dry eye symptoms. These symptoms are mostly due to friction between the ocular surface and the eyelid during blinking and are exacerbated with contact lens use. Indeed, friction is the strongest indicator of contact lens comfort, although, there is no industry standard for in vitro evaluation of friction in the contact lens industry.

Furthermore, researchers have recently discovered a lubricating glycoprotein at the ocular surface: Proteoglycan 4 (PRG4, or lubricin). PRG4 functions as a boundary lubricant and appears to reduce friction between human eyelids and commercial contact lenses. The abundant expression of full-length recombinant human PRG4 (rhPRG4) has been possible with recent technological advances. In a clinical trial, rhPRG4 has benn shown to produce significant improvements in signs and symptoms of dry eye disease compared to sodium hyaluronate (HA). This is why researchers A.C.Y Chan and Dr. Tannin Schmidt at University of Calgary were interested in investigating the following question: how do different lens types, lubricants and lens incubation times affect rhPRG4 lubrication? They had the goal of understanding which commercial lenses are compatible with rhPRG4 for friction reduction as a first step for potential clinical use.

This study involved a great challenge however. Namely, that of mimicking the blinking of an eye using a mechanical tester to obtain the kinetic friction coefficient. The researchers turned to the Mach-1 mechanical tester from Biomomentum to perform friction testing on a curved surface. The Mach-1 is a modular mechanical testing machine where a multi-axial load cell (6 degree-of-freedom load/torque) and 3 stages (vertical and horizontals) can be installed. Biomomentum worked together with the researchers to develop an program allowing the synchronization of multiple stages to perform the sliding of an eyelid on a contact lens. The kinetic friction coefficient was calculated dividing the shear forces (tangential forces) by the normal forces obtained through the multi-axial load cell. The test was performed in PBS solution using a sliding path of 10° at a sliding velocity of 0.3 mm/s. Two test sequences were performed: a soak test (overnight cleaning solution) and an eye drop test (eye drop solution).

The researchers found that PRG4 may be useful as a friction reducing lubricant (either as an eye drop solution or as an overnight cleaning solution) on specific silicone hydrogel contact lenses with potential improvement of in vivo contact lens comfort. This study aims to help understand the function and properties of rhPRG4 and thus, help initiate the commercialization of rhPRG4 for treatment of dry eye through improved comfort.