In-vitro method for determining corneal tissue friction and damage due to contact lens sliding

It is postulated that frictional energy due to contact lens rubbing against corneal tissue correlates positively with cell damage; where the damage is due to a fatigue mechanism (repeated stressing). Efforts were made to develop a relatively rapid in-vitro method capable of exploring this postulate. Measurements of the dynamic coefficient of friction (DCoF) between corneal epithelium and contact lenses, associated frictional forces, frictional energy, and corresponding cell damage were made using SkinEthic (Lyon, France) human corneal epithelial (HCE) constructs and commercially available contact lenses. Five silicone hydrogels (SiHs) and two polyhydroxyethlymethacrylate (p-HEMA) lens types were employed. Frictional forces were measured while the lens was rubbed against a construct that was moistened using a tear-like fluid. The exposed constructs were stained, imaged, and processed using a custom Matlab code. The range of DCoF values observed here extended from about 0.04 to 0.07. The frictional energy varied from about 0.03 mJ to 0.08 mJ. The results indicated a moderate correlation (Pearson's R = 0.79, P = 3.4%) between the frictional energy and cell damage. The authors believe that these results support the notion that cell damage can be caused by fatigue. Future efforts should explore how cell damage relates to a potentially more relevant metric, power density.