contact lens - Contact lenses are small plastic discs shaped to correct an eyesight problem such as nearsightedness, farsightedness, or astigmatism. These are called refractive errors. They may also be used by people who have had surgery for cataracts. Contacts are placed directly on the eye, where they float on a film of tears in front of the cornea. Correct design and fitting of the lenses are essential for comfort, safety, and accurate correction. Improvements in contact lenses have made them more comfortable and easier to wear. In the United States, 29 million people wear contact lenses; most wear soft lenses. For these people, contact lenses offer a relatively safe and effective way of correcting vision problems. Several types of contact lenses are available to correct nearsightedness. Contact lenses are needed after cataract surgery if an artificial lens cannot be implanted in the eye.