LAUSR

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.