Radial keratotomy (RK) is a surgical procedure designed to cure myopia (nearsightedness). In this operation, the surgeon makes a small number of radially-oriented incisions in the cornea of the eye. These incisions cause a decrease in the strength of the cornea and may increase the risk of serious injury if the eye is subjected to subsequent trauma, including barotrauma such as a facemask squeeze. Despite this theoretical risk, there have been no reports of which I am aware involving a traumatic rupture of the cornea resulting from diving after RK.
Divers who have had this procedure should wait at least three months after the surgery before returning to diving and should be careful to avoid a facemask squeeze - it's important to avoid imposing the "Boyle's Law Stress Test" on these corneal incisions.
If you are a diver and considering having this procedure done, I would recommend that you also ask your eye surgeon to discuss the potential advantages of photorefractive keratectomy, the alternative refractive surgical procedure discussed below.
For more information on vision issues, see the complete article by Frank K. Butler Jr., Captain, Medical Corps, United States Navy on High-Pressure Ophthalmology from Alert Diver.