Mechanical Characterization of Contact Lenses by Microindentation: Constant Velocity and Relaxation Testing

Mechanical and fluid transport properties of soft contact lenses may influence clinical performance, e.g., on-eye movement, fitting, and wettability, and may be related to the occurrence of complications, e.g. lesions [1, 2]. In the mechanical assessment of soft hydrated materials, indentation is increasingly being used because of its nondestructive methods for testing these material properties allow for multiple tests to be performed on the same sample, which will speed up the design and testing process for hydrogel contact lenses. [3]. Contact lens hydrogels may be described as a biphasic material. The material properties governing biphasic behavior are the Young’s modulus of the solid phase, Poisson ratio’s, and hydraulic permeability which is measure of fluid conductance in porous media. Previous studies of indentation of biphasic media have been completed by Mow and coworkers [4]. Also, computational finite element (FE) models have also been developed [5].