Contact lenses made from materials of low-oxygen permeability (Dk) do not meet the oxygen requirements of the cornea for overnight wear. Long-term extended wear of these lenses results in chronic changes to all layers of the cornea, many of which are associated with hypoxia. High-Dk silicone hydrogel and gas permeable lenses are now available for 30-night continuous wear. The high-oxygen transmissibilities of these lenses have enabled the development of a successful continuous wear modality by eliminating the hypoxic effects of long-term wear. Presently, the focus is on improving lens performance by developing lenses that are more biocompatible, provide greater comfort, and maintain a stable tear film without inflammatory or mechanically induced adverse events.