Penetrating keratoplasty (PKP) or optical penetrating keratoplasty (OPK) is a technique of performing full-thickness corneal transplantation where a diseased cornea is removed and replaced with a healthy and viable donor corneal button. This operation is sometimes called keratoplasty. The cornea is the transparent, dome-shaped surface of the eye. Light enters the eye through the cornea. It plays a large role in the eye's ability to see clearly.