There are two general types of contact lenses: hard and soft. The hard lenses most commonly used today are rigid, gas-permeable lenses (RGP for short). They are made of plastics and other materials such as silicone or fluoropolymers. Hard lenses hold their shape, yet allow the free flow of oxygen through the lenses to the cornea.
Soft lenses are the choice of most contact lens wearers. These lenses are comfortable and come in many versions, depending on how you want to wear them.
Daily-wear lenses are the least expensive, are removed nightly and are replaced on an individualized schedule. They should not be used as an extended-wear lens.
Disposable-wear lenses are more expensive but convenient. They are removed nightly and replaced on a daily, weekly, bi-weekly, or monthly basis.
Colored lenses are contacts that change your eye color, the appearance of your eye, or both. And in the case of circle lenses, they can also make your iris appear bigger.
Toric soft lenses can correct astigmatism, but sometimes not as well as RGP lenses do. They usually cost more than other contact lenses.
Bifocal or multifocal lenses are available in both soft and RPG varieties. They can correct nearsightedness, farsightedness, and astigmatism in combination with presbyopia. Cleaning and disinfection are specific to the lens material.
When To Replace Your Contact Lenses
Daily disposable lenses — Discard after a single day of wear
Disposable lenses — Discard every two weeks, or sooner
Frequent replacement lenses — Discard monthly or quarterly
Traditional (reusable) lenses — Discard every six months or longer