Hard lenses were the first contact lenses available. Although they are not often prescribed now, they had several advantages. They were easy to put in and take out and easy to care for. They did not cost very much and lasted a long time. For many people, they provided very good vision.
However, the original hard lenses were often uncomfortable during the first week or two of wear. Also, they did not allow much oxygen to reach the cornea. (The cornea is the clear outer layer on the front of the eyeball.) Not getting enough oxygen can damage the cornea. Gas permeable lenses have the same benefits but allow more oxygen to get to the cornea.
Gas permeable lenses are made of a type of plastic that allows oxygen to reach the cornea. They are easier to care for than soft contacts. They are also easier to put in and take out. Gas permeable contacts can correct many vision problems related to abnormal cornea shapes. At first, most people need a few days to get used to them. Some of the newest gas permeable lenses are approved for extended wear. Most contacts should not be worn during sleep. Follow your eye care provider's advice about how long you can leave in extended wear lenses.
Soft contacts are lenses made of flexible plastic that absorbs liquids. Unlike gas permeable or hard lenses, they usually do not cause discomfort when you first wear them. They can correct many vision problems. Regular soft lenses do not correct astigmatism (distorted vision caused by an unevenly curved cornea) as well as gas permeable lenses do. However, special soft lenses called toric lenses are available for people with astigmatism.
Putting soft contacts in and taking them out may take a little practice. Also, soft contacts must be cleaned and sterilized very carefully. You must sterilize daily-wear soft lenses every night. You must sterilize extended-wear soft lenses each time you take them out.
Soft lenses cost more than gas permeable lenses. They may wear out and need to be replaced more often. You may have more problems with allergies if you wear soft lenses. Also, you may develop eye infections more often, especially if you wear your contact lenses while you sleep. An eye infection called a corneal ulcer can be serious and possibly cause a loss of sight. If you have dry eyes, you may not be able to wear soft contacts.
Disposable contacts are soft contact lenses that you wear for a certain amount of time, then throw out. The lenses are replaced before proteins and other deposits can build up on them. Do not wear disposable lenses longer than directed. Wearing them longer than you should can cause a severe infection.
Disposable lenses provide good vision and comfort. Cleaning costs are less and they are easier to care for than regular soft contacts. If a lens is lost or torn, you usually have a replacement lens on hand. However, disposable contacts cost more than other contact lenses.
Bifocal contact lenses have both your distance prescription and your reading prescription in each lens. They are available as gas permeable or soft lenses, and as daily wear or extended wear types. You may need to try bifocal contact lenses to decide if they are right for you. Not everybody likes bifocal contacts.