Contact lenses are lenses placed directly on the top of the cornea in the eye. The lenses are used to correct vision just as eyeglasses do. In recent years, tinted contact lenses have become a way to change eye color.

There are both hard and soft contact lenses. They're usually made from some type of polymer that contains silicone hydrogel. The lens itself is made to fit the vision problem. This is especially helpful for people who have a different vision condition in each eye or who only have a vision problem in one eye, but not the other.

When using contact lenses, knowing how long to leave them in is of the utmost importance. Again, there are different types available, normal and extended wear. Extended wear contact lenses can be worn up to 30 days and nights before needing to come out. This is because they allow oxygen to freely move from the outside into the eye. At the end of 30 days, they're thrown away and a new set of contacts is used. Hard contacts are taken out and cleaned daily.