Contact lenses are thin, clear disks of plastic that float on the surface of the eye. They correct vision like eyeglasses do and are safe when used with care. Contact lenses are used to correct the same conditions that eyeglasses do: myopia (nearsightedness), hyperopia (farsightedness), astigmatism (blurred vision due to the shape of the cornea) and presbyopia (inability to see close up).

Millions of people around the world wear contact lenses, more than 24 million in the United States alone. Depending on your lifestyle, your motivation and the health of your eyes, contact lenses may provide a safe and effective alternative to eyeglasses when used with proper care and maintenance.

How They Work

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. RGP lenses may be the best choice when the cornea has enough astigmatism (is shaped like an egg instead of an orange) that a soft lens will not provide sharp vision. They may also be preferable when a person has allergies or tends to form protein deposits on his or her contacts.

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. 
• Extended-wear lenses are worn overnight but are removed at least weekly for thorough cleaning and disinfection. They are being recommended less frequently, since there is a greater risk of corneal infection with any overnight wear of contact lenses. 
• Disposable-wear lenses are more expensive, but convenient. They are removed nightly and replaced on a daily, weekly or monthly basis. Disposable lenses are sometimes recommended for people with allergies and for those who tend to form deposits on their lenses. 
• Colored contact lenses change the appearance of your eye color. 
• Toric soft contact lenses can correct astigmatism, but sometimes not as well as RGP lenses do. They usually cost more than other contact lenses.

Risks

Lenses that are not properly cleaned and disinfected increase the risk of eye infection. Any lens that is removed from the eye needs to be cleaned and disinfected before it is reinserted. Your eye care professional will discuss the best type of cleansing system for you, depending on the type of lens you use, any allergies you might have and whether your eye tends to form protein deposits.

Care of contact lenses includes cleaning their case, since it is a potential source of infection. The case should be rinsed with contact lens solution and allowed to dry. >> Learn more about proper care of contact lenses.

Lenses that are old or not properly fitted may scratch the eye or cause blood vessels to grow into the cornea. Because a lens can warp over time, and the cornea can change shape, the fit of the contact lens and the power should be re-evaluated on a regular basis. Your return visits will be scheduled depending on the condition of your eyes and visual needs.

You may not be a good candidate for contacts if you have: 

• Frequent eye infections,
• Severe allergies,
• Dry eye that is resistant to treatment,
• A very dusty work environment, or
  
• An inability to handle and care for the lenses.

Any eyedrops you use can interact with all types of contact lenses. It is best to avoid the use of eyedrops while wearing lenses, except for wetting drops recommended by your eye doctor.

Homemade saline (salt water) solutions have been linked to serious corneal infections and should not be used.

Last reviewed and updated in February 2009,
by the American Academy of Ophthalmology.