When people get contact lenses they have two choices. Those choices are gas permeable lenses or soft lenses. Gas permeable lenses are traditionally called hard lenses. People don't often know the difference between the two kinds of lenses and why someone might choose one or the other. 

Gas Permeable Lenses

These lenses are called hard lenses because they are made out of a more rigid material. They are actually made out of a kind of plastic, generally with silicone added, which allows gas through the lenses to the eye. They are also smaller in diameter than soft lenses are, which makes them cover less of the eye. A soft lens will generally cover the entire iris, and usually a little more. The GP lenses generally cover the pupil, plus a little bit of the iris. The coverage into the iris makes sure that your pupil will always be covered by the contact lens.

There are particular reasons why someone may use the GP lenses instead of a soft lens. One of them is astigmatism. Astigmatism is when your eye has an irregular curve to it. That means that soft lenses don't often work well. The GP lenses, because they are more rigid, can correct that curve to the eye better, and make it easier for you to see. Gas permeable lenses also have a benefit for people who need bifocals. These lenses can actually have more than one focus point, like bifocal glasses. 

One problem with these lenses is that since they are made out of a more rigid material, they can be uncomfortable to wear at first. They have a longer breaking-in period and can't be worn as non-stop as soft lenses can be. 

Soft Lenses

Soft lenses are exactly that. They are flexible and conform to the eye very well. The material lets them curve to your eye instead of your eye adjusting more to the lens. 

Soft lenses are much more comfortable right at the start. They don't have a significant break-in period, although it does take a little bit of time to get used to wearing anything directly on the eye. Some soft lenses can actually be worn for several days at a time. You can also get disposable lenses that you can just throw away when you are done wearing them instead of having to clean them daily. 

One drawback to the soft lenses is that they can't be used for multi-focal purposes. You can get some soft contacts and wear some single focus glasses to give you the benefit of bifocals. 

Knowing what the differences are, and some benefits and drawbacks to the different kinds of lenses, can help you choose which are the best for you. To gain more insight into which is the best choice for your unique eyes, consult with an eye specialist, such as those at Dixie Ophthalmic Specialists at Zion Eye Institute.