Penetrating Keratoplasty (PKP)

Modern corneal surgery increasingly favors partial-thickness techniques that replace only the diseased layer, but there are many situations where PKP remains the best or only option. When pathology involves both the stroma and the endothelium simultaneously, partial-thickness procedures cannot address the full extent of the problem. For example, advanced keratoconus with prior hydrops damages both the structural framework and the inner pump layer, making PKP the most reliable path to a clear, stable cornea.

Dense corneal scars from prior infections, chemical burns, or trauma that extend from the surface through to the deeper layers leave no healthy tissue to preserve. In these cases, removing and replacing the entire cornea offers the best chance of restoring useful vision. Therapeutic PKP may also be performed on an urgent basis when a corneal ulcer or melt threatens to perforate the eye.

If a previous DSEK or DMEK graft has failed and repeat endothelial keratoplasty is not feasible because of stromal scarring or other complications, converting to a full-thickness PKP allows the surgeon to start fresh with an entirely new corneal button. Similarly, patients who have had multiple graft failures may benefit from PKP combined with adjunctive immunosuppressive strategies.

When the cornea is perforated or at imminent risk of perforation from autoimmune melting, severe infection, or trauma, an emergency PKP can restore the structural wall of the eye and prevent loss of the globe. In these situations, the primary goal is tectonic repair, with visual rehabilitation addressed once the eye has stabilized.

Recovery after PKP is gradual and longer than after partial-thickness transplants. Most patients notice improved clarity within the first few weeks, but vision continues to fluctuate as the graft heals. Sutures typically remain in place for 12 to 18 months and are removed selectively based on how they influence astigmatism. Best-corrected visual acuity may not stabilize until one to two years after surgery. During the recovery period, topical corticosteroid drops are used to prevent rejection, often for at least 12 months.

Graft longevity depends heavily on the underlying condition. In low-risk eyes such as keratoconus, studies report graft survival rates of approximately 90% or higher at 10 years and 70% to 80% at 20 years. High-risk eyes with vascularization, prior graft failure, or active inflammation have lower survival rates. If a graft eventually fails due to chronic endothelial cell loss, it may be possible to perform a repeat PKP or convert to an endothelial keratoplasty.

The most significant risk is immune-mediated graft rejection, in which the recipient's immune system recognizes the donor tissue as foreign and attacks it. Warning signs include increasing redness, light sensitivity, pain, and worsening vision. Patients are taught to remember the mnemonic RSVP for recognition. Other risks include infection, elevated eye pressure, wound dehiscence from trauma, recurrence of the original disease, and persistent or irregular astigmatism.

Most patients require some form of vision correction after PKP because the full-thickness wound and suture pattern introduce astigmatism. Glasses are sufficient for many patients once sutures are removed and the refraction stabilizes. Patients with high or irregular astigmatism often achieve their best vision with rigid gas-permeable or scleral contact lenses. Additional procedures such as relaxing incisions or excimer laser surface ablation can reduce residual astigmatism once the graft is fully healed.

Rejection rates vary significantly by risk category. In low-risk, non-vascularized first grafts, the overall rejection rate ranges from about 5% to 20%, and most rejection episodes can be reversed if caught early. In high-risk eyes, rejection episodes occur in 30% to 60% of cases. Endothelial rejection, the most threatening form, targets the pump cells and can lead to permanent corneal edema if not treated promptly.

Partial-thickness transplants have become the preferred approach whenever disease is limited to a single corneal layer. Deep anterior lamellar keratoplasty replaces only the stroma while preserving the patient's own healthy endothelium, virtually eliminating endothelial rejection. Endothelial keratoplasty techniques such as DSEK and DMEK offer faster visual recovery and lower rejection rates. PKP remains necessary when disease involves multiple layers simultaneously or when the cornea has full-thickness scarring. For patients weighing options, the page on DMEK versus DSAEK explains the differences in detail.