Most corneal transplants performed in the U.S. involve replacing the entire thickness of the diseased cornea with a healthy donor cornea (called penetrating keratoplasty or PK). In partial-thickness corneal transplants (LK), only the anterior (surface) layers of the cornea are removed. The donor cornea is then attached to the host corneal bed, containing only posterior (deeper) layers. LK is less risky, but tends to result in somewhat inferior vision vs. PK and cannot be performed if the disease process (e.g. scar) involves the deeper layers of the cornea.