A U.S. technology that improves nearsightedness by just getting some shut-eye is catching on around the world and has moved into the clinical testing stage in Japan.

The technology -- orthokeratology -- is designed to correct nearsightedness through the use of special contact lenses while a person sleeps. The lenses change the shape of the cornea overnight so the wearer can see clearly after the lenses are removed.

The effect is temporary, lasting for about a day or two, unlike a Lasik operation, which reshapes the cornea using a laser and is a popular method of correcting nearsightedness, although the effects are permanent.

Orthokeratology has so far been authorized for use in the United States, many European countries, China, South Korea and Taiwan, with people attracted to the fact that they can improve their vision without undergoing an operation.

Some Japanese ophthalmologists are now using it in clinical tests pending official approval, but eye specialists said guidelines are needed to avoid problems in their usage.

Orthokeratology was developed in the United States during the 1960s, but Dr. Kenichi Yoshino, director of Yoshino Ophthalmologic Clinic in Taito Ward, Tokyo, said the first lenses were unusable.

The technology took off only after third-generation lenses became available for clinical testing in the 1990s. They had much better oxygen permeability and shape.

They were approved by the U.S. Federal Drug Administration in 2002.

Yoshino, whose clinic has so far handled 66 orthokeratology cases, has repeatedly examined his patients and had them insert the lenses before going to bed in an effort to choose the right ones.

The procedure costs about 150,000 yen to 300,000 yen in Japan because eye specialists must import the lenses themselves and hand out prescriptions. The national medical insurance system does not cover the treatment.