In the early 1960s, a group of clinicians asserted that myopia could be reduced and possibly corrected by fitting specially designed contact lenses to induce corneal flattening and thereby reduce the refractive power of the eye. This technique, known as orthokeratology, required that the lenses be fitted and then changed progressively until vision becomes normal or nearly normal. Advocates of orthokeratology claimed that corneal changes could be induced in a predictable fashion, were often permanent, and occurred without causing any adverse effects to the cornea. Data on orthokeratology were generally limited, poorly documented, and did not address the issues of control or failure.