Penetrating keratoplasty (PKP) is the longest-established corneal transplant technique, with over a century of clinical experience. For many conditions, PKP has been superseded by more targeted lamellar techniques — DMEK for endothelial disease, DALK for anterior disease — that replace only the diseased layers of the cornea and offer faster recovery with lower rejection rates. PKP remains essential, however, when disease involves multiple corneal layers or when lamellar surgery is technically not feasible.
What Is Penetrating Keratoplasty?
Penetrating keratoplasty (PKP) is full-thickness corneal transplant surgery in which the entire central cornea — all five layers from front to back — is removed and replaced with donor tissue from a deceased human donor. PKP has been performed for over a century and remains a well-proven and highly effective procedure, though for many conditions it has been superseded by more targeted lamellar techniques. PKP remains the procedure of choice when disease affects multiple layers of the cornea, or when lamellar surgery is not technically feasible.
Unlike DALK, which preserves the recipient's endothelium, or DMEK and DSAEK, which replace only the inner cell layer, PKP transplants the entire corneal disc — including epithelium, Bowman's layer, stroma, Descemet membrane, and endothelium — and secures it with fine sutures. This comprehensiveness is both its strength (it addresses all layers simultaneously) and its limitation (all layers of the donor tissue can be rejected).
When Is PKP Used?
PKP is indicated when corneal disease is present throughout the full thickness of the cornea, or when the anatomy does not allow for a lamellar approach. Common indications include advanced keratoconus where DALK is not possible due to previous hydrops or deep scarring; full-thickness corneal scarring from infection, perforation, or chemical injury; failed prior grafts requiring regrafting; and certain corneal dystrophies affecting multiple layers.
The decision between PKP and a lamellar technique is made at the pre-operative assessment and occasionally finalised intraoperatively — for example, if a Descemet membrane perforation occurs during a planned DALK procedure, conversion to PKP may be required to achieve a safe outcome.
The PKP Procedure
PKP is performed under general or local anaesthesia. A circular trephine — a precision cutting instrument — removes a disc of the recipient's central cornea, typically 7.5–8.5mm in diameter. A matching disc of donor tissue is then sutured into place using extremely fine nylon sutures (10-0 nylon) placed at 16 or more points around the circumference of the graft. The donor button is often cut slightly larger than the recipient opening to create gentle positive tension in the wound.
The surgery takes approximately 60–90 minutes. The sutures remain in the eye for a prolonged period — typically twelve to eighteen months for interrupted sutures, or longer for running sutures — while the graft heals and optically stabilises. Selective suture removal is used to reduce astigmatism during this period, guided by keratometry and corneal topography.
Most patients require cataract surgery at some point during their lifetime, and those with a PKP graft present a specific challenge for IOL power calculation due to the altered corneal curvature. Pre-operative planning must account for the post-graft corneal shape when calculating the intraocular lens power.
Recovery After PKP
Recovery after PKP is the longest of any corneal transplant technique — typically twelve to eighteen months before the corneal shape stabilises sufficiently to assess the final refractive outcome. This is substantially longer than after DMEK (3–6 months) or DALK (12–18 months for visual stabilisation after suture removal).
Even after full recovery, most patients require glasses, rigid contact lenses, or scleral lenses for best corrected vision, as the sutured graft introduces irregular astigmatism that is difficult to fully correct with spectacles alone. In some patients, suture-induced astigmatism can be addressed with selective suture removal, laser vision correction, or astigmatic keratotomy after the graft has stabilised. Lifelong topical steroid use at a low maintenance dose is recommended after PKP to reduce the risk of rejection.
Graft Rejection After PKP
Rejection is the most common cause of PKP failure. The immune system recognises the donor cornea as foreign tissue and mounts an immune response that, if not promptly treated, can permanently damage the donor endothelium and cause graft failure. Signs of rejection include a red eye, pain, photophobia, and blurred vision — symptoms that should prompt the patient to seek urgent ophthalmic review, regardless of the time since surgery.
Rejection is treatable with intensive topical steroids if recognised early. The risk of rejection is highest in the first two years after surgery but persists throughout the patient's lifetime. Patients with a history of rejection, vascularised corneas, or multiple prior grafts are at higher risk and require more intensive monitoring and immunosuppression. The substantially lower rejection rate of DMEK (~1–3%) compared with PKP (~15–25% over 5 years) is the primary driver of the shift to lamellar techniques for appropriate indications.
Long-Term Outcomes After PKP
PKP has excellent long-term outcomes for appropriate indications, with graft survival rates exceeding 90% at five years for keratoconus and similarly low-risk conditions. For higher-risk indications — regrafts, vascularised corneas, or prior infections — survival rates are lower, and patients require more intensive monitoring and immunosuppression.
Even in the event of graft failure, a repeat PKP or conversion to a lamellar technique is often possible. The outcomes of repeat grafting have improved with modern tissue preparation and surgical technique, and patients who have experienced one graft failure should not be discouraged from considering a second procedure.
Dr Ross MacIntyre BA (Chemistry) MD FRANZCO is a cataract, corneal and refractive surgeon practising in Melbourne. He completed subspecialty fellowship training in cornea, complex cataract and refractive surgery at the Wilmer Eye Institute, Johns Hopkins University, and holds a public appointment at the Royal Victorian Eye and Ear Hospital.