Focusing the soul's fuzzy window.

Poets call the eyes the window of the soul. But when that window gets blurry, most souls prefer clarity without glasses.

Focusing on this problem are two advanced-materials companies, which are testing corneal implants for people who don't like glasses or contact lenses.

For those with presbyopia, which makes close-up focusing difficult, a tiny lens implanted in the cornea "acts like bifocal," says Cary J. Reich, a chemist with Chiron IntraOptics, Inc., in Irvine, Calif. The cornea is the clear tissue covering the iris and lens of the eye. A surgeon inserts a wafer-thin lens, 2 millimeters in diameter, in front of the natural lens to help it focus on close objects. People with presbyopia, most of whom are over 45, struggle with reading because theirt natural lenses aren't as flexible as once were. Thus, the implanted lenses act like a pair of reading glasses. The Small-Diameter Corneal Inlay, made of a soft, hydrogel polymer, will undergo clinical testing in the United States later this year, Reich says.

For myopia (nearsightedness), a small polymer ring reshapes the cornea and puts distant objects back into fosucs, says Thomas A. Silvestrini, a chemist with KeraVision, Inc., in Santa Clara, Claif. The Intrastromal Corneal Ring, 7 millimeters in diameter, is inserted into the cornea's periphery, around the lens. By flattening the cornea, the ring sharpens distance vision without cutmting into the central optical zone, he says. Testing of the ring in humans began overseas in 1991; a clinical study of 75 patients in three U.S. hospitals is now under way.

Both devices need further clinical evaluation and Food and Drug Administration approval before consumers can sign up for implants, the researchers note.