Types of contact lenses Rigid contact lenses, originally created over 25 years ago, are still used by some people. Made of hard plastic, they are very durable but some brands do not allow oxygen direct access to the cornea. A lack of oxygen over an extended period of time can change the shape of the cornea. Newer rigid lenses combine the hard plastic with other molecules that allow oxygen to pass through to the cornea. These are called gas-permeable lenses.
Rigid lenses are often the least comfortable choice.
Extended wear contact lenses designed to be left in the eye overnight may be either soft or rigid gas-permeable lenses. Soft lenses, the choice of most contact lens wearers, are also made of plastic but incorporate water, allowing softness and flexibility. Disposable lenses are designed for daily or extended wear and are discarded or replaced each week. These lenses are convenient and may reduce the chance of infection or deposit formation. Risks Rigid, nongas-permeable lenses are more likely to scratch the cornea if left in overnight or if used without a proper fit.