Corneal requirements for extended wear: an update.

The current status of extended wear is reviewed in terms of the ability of available rigid and soft contact lens materials to provide: oxygen to the cornea, lens movement, and resistance to deposit formation and corneal desiccation. Current hydrogel lenses seem unsuitable as a modality for extended wear due to limited oxygen transmissibility, except when the frequency of overnight wear is reduced. Rigid gas permeable lenses, while not without problems, show greater promise for extended wear at this time.