If the eye is unable to correctly focus incoming light on the retina, vision may be corrected with spectacles or with  contact lenses. 

Alternately, vision can be corrected by changing the shape of the cornea itself.  Orthokeratology (also known as OK or ortho-k) uses custom fitted gas permeable lenses to gently reshape the cornea while you sleep. In the morning, these lenses are removed, allowing clear vision throughout the day without glasses or contact lenses.

Unlike refractive surgery, Orthokeratology is completely reversible – simply stop wearing your lenses and your cornea will return to its original shape.