<unk> <unk><unk>  <unk>  A<unk> , also known as an<unk> ,<unk> , or colloquially, a hard contact lens, is a<unk>  contact lens made of oxygen-permeable polymers. Initially developed in the late 1970s, and through the 1980s and 1990s, they were an improvement over prior 'hard' lenses that restricted oxygen transmission to the eye.<unk>  lenses are able to replace the natural shape of the cornea with a new refracting surface. This means that a regular (spherical)<unk>  contact lens can provide good level of vision in people who have astigmatism or distorted corneal shapes as with keratoconus. However, they require a period of adaptation before full comfort is achieved.
Rigid gas permeable lens
Multifocal intraocular lens
Corrective lens
Phakic intraocular lens
Angle-supported intraocular lens
Trifocal lenses
Adjustable-focus eyeglasses
Argus retinal prosthesis