Orthokeratology, or ortho-K, is the process of fitting special contact lenses to reshape the cornea. Ortho-K uses gas-permeable contact lenses designed to be worn overnight rather than during the day.

While the patient sleeps, the lenses gently and gradually reshape the surface of the eye. When the patient wakes up and takes out the contact lenses, he or she should be able to see clearly throughout the day without wearing glasses or other contact lenses.