The American Optometric Association estimates 30 million Americans wear contact lenses. Two-thirds of them are women. The majority of contact lens wearers are 25 and older, with 50 percent of them between 25 and 44.

There are two main types of contact lenses: gas-permeable and soft. Gas permeable contacts (technically referred to as rigid gas permeables) are made of rigid, yet slightly flexible plastic that allows oxygen to pass through the lens to the eyes. Most people find them comfortable to wear, but they may take a short period of adjustment. Gas permeable lenses are more durable than soft lenses and can correct many different types of vision problems.

Soft contacts are thin, gel-like lenses that contain water to maintain a flexible shape. Since they are so soft, many people can wear them without any period of adjustment. Daily wear soft contacts are designed to be taken out each night, cleaned and stored. These are the most popular kind of contacts, used by 80 percent of contact lens wearers in the U.S. Extended wear contacts are worn continuously (including at night), usually for up to seven days. Disposable contacts are lenses that are used for a specified number of days and then discarded. They must be removed each night.

The High Tech Contact Lens

Contacts are mainly designed to correct vision. Now, researchers at the University of Washington are trying to find ways to incorporate complex technology into the lenses. A device under development, referred to as a "bionic lens" or "e-lens," integrates a miniature electronic circuit and LED lights between layers of polyethylene terephthalate (PET). It's powered through radiofrequency energy transmitted to an antennae incorporated into the lens.

Electrical Engineering Researcher, Babak Parviz, Ph.D., says there are several possible uses of the high tech lens. Biosensors embedded into the lens could monitor a patient's health (like glucose levels or intraocular pressure). Computer images could be sent to the circuit, enabling the wearer to see virtual displays, like a map, warning signal or message. Parviz says the technology may also be picked by the video game industry, allowing a wearer to play games or surf the net without the need for a display monitor. He envisions the computer generated images as being semi-transparent. Thus, as they are projected onto the visual background, they wouldn't interfere with sight.

The high tech lenses are still in development. The current prototype has been tested in a rabbit eye and has been shown to be well tolerated without any side effects. A fully functional lens (i.e., one with working circuitry) has not yet been produced.

For general information on contact lenses:

American Optometric Association

The Foundation of the American Academy of Ophthalmology

Food and Drug Administration