Penetrating Keratoplasty (PK)

Corneal Transplant

Traditional Penetrating Keratoplasty (PK) 

A corneal transplant involves replacing a diseased or scarred cornea with a new one. When the cornea becomes cloudy, light cannot penetrate the eye to reach the light-sensitive retina. Poor vision or blindness may result.

If the cornea develops visually significant opacities or irregularities, a traditional penetrating corneal transplant, or PK procedure can be performed.

In corneal transplant surgery, the surgeon removes the central portion of the cloudy cornea and replaces it with a clear cornea, usually donated through an eye bank. A trephine, an instrument like a cookie cutter, is used to remove the cloudy cornea. The surgeon places the new cornea in the opening and sews it with a very fine thread. The thread stays in for months or even years until the eye heals properly (removing the thread is quite simple and can easily be done in an ophthalmologist’s office). Following surgery, eye drops to help promote healing will be needed for several months.

Corneal transplant illustration
Illustration by JirehDesign.com

Corneal transplants are very common in the United States; about 40,000 are performed each year. The chances of success of this operation have risen dramatically because of technological advances, such as less irritating sutures, or threads, which are often finer than a human hair; and the surgical microscope.

Corneal transplantation has restored sight to many, who a generation ago would have been blinded permanently by corneal injury, infection, or inherited corneal disease or degeneration.

Postoperative Complications
Even with a fairly high success rate, some problems can develop, such as rejection of the new cornea. Warning signs for rejection are decreased vision, increased redness of the eye, increased pain, and increased sensitivity to light. If any of these last for more than six hours, you should immediately call your ophthalmologist. Rejection can be successfully treated if medication is administered at the first sign of symptoms.

A study supported by the National Eye Institute (NEI) suggests that matching the blood type, but not tissue type, of the recipient with that of the cornea donor may improve the success rate of corneal transplants in people at high risk for graft failure. Approximately 20 percent of corneal transplant patients reject their donor corneas.

What are the differences between PK, DSAEK and DMEK?

PK
(full thickness traditional cornea transplant)
DSAEK
(partial thickness posterior cornea transplant)
DMEK (Single layer of cells and supporting membrane)
Typical time for visual improvement 6-12 months 4-6 weeks 2 weeks
Visits for suture adjustment 6-12 visits 2-3 visits 1
Time of surgery 45-60 mins. 45-60 mins. 15-20 min.
Wound size 7.5 mm diameter circle 5 mm linear Less than 2.4 mm
Sutures 16 2-4 1
Contact lens required Rigid gas permeable (often) Not required None
Induced astigmatism High regular and Irregular astigmatism possible Minimal to no induced astigmatism None
Indications for surgery Cornea scar, keratoconus, pellucid marginal degeneration, corneal ulcer Fuch’s endothelial dystrophy, cornea edema, pseudophakic bullous keratopathy Fuch’s endothelial dystrophy, cornea edema, pseudophakic bullous keratopathy