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ment of prostate cancers without endangering the bladder and spinal tissue adjacent to the prostate gland.

Lasers are a much more recent invention, but their therapeutic use is rapidly increasing. Focal tissue coagulation by laser is the standard nonsurgical treatment for a detached retina, and the reforming of the corneal surface shape (laser keratotomy) with laser radiation is a very effective treatment for nearsightedness that is now becoming standard. The use of local laser heating is a microsurgical technique that is finding application in a variety of fields.

Although of more limited use, ultrasound has also found an important place as a nonsurgical treatment for kidney stones and for the cleaning of surgical instruments.

Another revolution in therapy, based on the use of fiber optics, has been developing over the past several decades. Before physicists developed ordered fiber-optic bundles, visualization of internal body surfaces was limited by the requirement that light must follow straight lines; this meant, for instance, that only small portions of the gastrointestinal tract and the airways could be seen by a physician. With fiber-optics and video imaging, the gastroenterologist and otolaryngologist can now see much of the inner surface of humans. A more recent trend has been to use fiber-optics imaging to permit surgery through tiny incisions. Many appendectomies and other surgical procedures—even including heart surgery—are now carried out in this much less invasive way. Because damage caused by large incisions and the exposure of internal organs is minimized, these remote surgical procedures can be less dangerous and patients can recover more quickly and with less discomfort.

New materials have also become available to replace damaged or missing body components. Silicone is used in reconstructive surgery to provide internal support for soft tissues, and new, hard plastic materials are transforming dentistry by permitting better reconstruction of damaged teeth. These materials not only are strong but also bond well to the tooth surface and expand with heat like the natural tooth; this means that a much wider range of tooth damage can be repaired, and that the repairs are much more durable than in the past.