Orthokeratology is a unique fitting technique that uses rigid gas permeable lenses to temporarily change the curvature of the cornea. Ortho-K lenses change how light focuses inside your eyes and is most commonly used to correct nearsightedness. Ortho-K lenses are typically worn at night while sleeping and are removed in the morning. As the cornea changes shape, nearsightedness improves and some people can go all day without needing to wear their glasses or contact lenses. In some cases, however, vision correction does not last the entire day. If Ortho-K treatment is discontinued, the corneas will eventually return to their original shape and glasses or contacts will again be needed to correct vision.