Mechanical Characterization of a Convex Shell (Contact Lens) with Meridional Thickness Variation

Contact lenses are hydrogel shells of spherical cap geometry, and their meridional thickness variation determines their optical power. To characterize the lens mechanical behavior, a rigid shaft was used to apply a quasi-static load to the apex while the central displacement and deformed profile were monitored in-situ. Loading-unloading cycles were performed. In contrast to classical shells of uniform thickness, contact lenses show distinct mechanical response signatures, depending upon their optical power. Typical hyperopic lenses show a local maximum and minimum, attributable to the expanding-contracting dimple across the changing meridional thickness. In addition, deformation-driven water efflux-influx suggest poroelastic behavior of the gel. The measurements have significant impacts on contact lens design.