Penetrating Keratoplasty: When Full-Thickness Corneal Transplant Is Still the Answer

The cornea was the first human tissue ever transplanted successfully, and it remains the most transplanted tissue in the world.

Penetrating keratoplasty (PK) replaces the full thickness of the cornea with donor tissue.

For most of the last century it was the only corneal transplant on offer.

Lamellar techniques have since taken over much of its former workload, because replacing only the diseased layer is safer and heals faster.

But PK has not disappeared – it remains the operation when the full thickness of the cornea is damaged, and nothing else will do.

Knowing when full-thickness surgery is still the right answer, and how to recognise rejection early, is essential for anyone following these patients.

What Is Penetrating Keratoplasty?

Penetrating keratoplasty is full-thickness corneal transplantation, in which a circular disc of the patient’s cornea is removed and replaced with a matching donor button secured by sutures.

It sits within a family of corneal transplant procedures:

Penetrating keratoplasty (PK) – all corneal layers replaced
Deep anterior lamellar keratoplasty (DALK) – stroma replaced, the patient’s own endothelium retained
Descemet stripping automated endothelial keratoplasty (DSAEK) – posterior stroma and endothelium replaced
Descemet membrane endothelial keratoplasty (DMEK) – Descemet membrane and endothelium alone replaced

The general principle of modern corneal surgery is to replace only what is diseased, which is why PK is now reserved for full-thickness pathology.

Epidemiology

Corneal transplantation is by a wide margin the most commonly performed transplant procedure worldwide.

The cornea is avascular and immune-privileged, which is why graft survival compares favourably with solid organ transplantation and systemic immunosuppression is not routinely required
The proportion of transplants performed as PK has fallen substantially as endothelial and lamellar techniques have been adopted
Endothelial failure – Fuchs dystrophy and pseudophakic bullous keratopathy – was historically the leading indication and is now largely managed by DSAEK or DMEK
Keratoconus, once a common PK indication, is increasingly treated with DALK or stabilised earlier with corneal cross-linking
Access to donor tissue remains the principal limiting factor in many parts of the world

The shift away from PK is one of the clearest examples in ophthalmology of a procedure being narrowed rather than abandoned as better-targeted alternatives arrived.

Indications

When Full-Thickness Replacement Is Needed

Full-thickness corneal scarring, whether from infection, trauma or chemical injury
Advanced keratoconus with significant scarring or previous hydrops, where DALK is not feasible
Failed previous grafts
Corneal perforation or descemetocele requiring tectonic support to restore globe integrity
Severe infectious keratitis unresponsive to medical therapy – a therapeutic rather than optical graft
Corneal dystrophies affecting all layers

When a Lamellar Procedure Is Preferred

Isolated endothelial disease – Fuchs dystrophy, pseudophakic bullous keratopathy – where DSAEK or DMEK gives faster recovery and lower rejection risk
Anterior stromal disease with a healthy endothelium, where DALK avoids the risk of endothelial rejection entirely

The decisive question at the planning stage is whether the patient’s own endothelium is healthy – if it is, a lamellar procedure is almost always the better operation.

Surgical Principles

The operation follows a well-established sequence.

Donor tissue is assessed for endothelial cell density and clarity before use
A trephine cuts the recipient bed, and a slightly larger donor button is punched to allow a good fit
The donor button is secured with interrupted sutures, a continuous suture, or a combination
Because the eye is open at the point of trephination, PK is an “open sky” procedure with a risk of suprachoroidal haemorrhage and expulsion
Sutures remain for many months and are adjusted or removed selectively to manage astigmatism

That open-sky step is the fundamental reason lamellar surgery is safer – it never fully opens the globe.

Clinical Presentation and Postoperative Findings

Expected Course

Visual recovery is slow, typically over many months, and is limited early on by suture-induced astigmatism
Topical corticosteroids are continued long-term, often at a low maintenance dose
Refractive outcome is frequently irregular, and many patients need rigid gas-permeable contact lenses for best vision

Examination Findings

A circular graft-host junction with visible sutures in the early postoperative period
A clear graft with a compact stroma when the endothelium is functioning well
Loose, broken or vascularised sutures, which are a route to infection and a trigger for rejection
Stromal oedema and folds in Descemet membrane if the endothelium is failing
Neovascularisation crossing the graft-host junction, a significant risk factor for rejection

Any suture that has loosened or become vascularised should be dealt with promptly, because it is one of the commonest preventable triggers of both infection and rejection.

Graft Rejection

Recognising Rejection

Redness, pain, photophobia and blurred vision – the classic warning symptoms patients must be taught before discharge
A Khodadoust line – a linear front of inflammatory cells advancing across the endothelium
Keratic precipitates on the graft endothelium, with anterior chamber activity
New graft oedema, often the first objective sign
Subepithelial infiltrates or an advancing epithelial rejection line in anterior forms

Managing Rejection

Intensive topical corticosteroids started urgently – outcome depends heavily on how quickly treatment begins
Systemic or periocular steroids in severe episodes
Steroid-sparing systemic immunosuppression in high-risk or repeatedly rejecting grafts
Rejection is reversible if caught early; a graft left untreated may fail irreversibly

Every PK patient should leave the clinic knowing that a red, painful or newly blurred eye means being seen the same day, not at the next routine appointment.

Complications

Beyond rejection, the recognised complications include:

High and irregular postoperative astigmatism, the commonest limit on visual outcome
Wound dehiscence, since a full-thickness wound never regains normal corneal strength and remains vulnerable to trauma for life
Suture-related infiltrates and microbial keratitis
Steroid-induced ocular hypertension and glaucoma from prolonged topical steroid use
Late endothelial cell loss leading to gradual graft failure years after successful surgery
Recurrence of the original disease within the graft, particularly with corneal dystrophies

The permanent weakness of the full-thickness wound is a point worth making explicitly to patients, who should use eye protection for contact sports and manual work indefinitely.

Prognosis

Graft survival depends heavily on the indication and on the vascularity of the recipient bed.

Keratoconus and corneal dystrophies in an avascular, uninflamed eye carry the best long-term graft survival
Grafts placed in vascularised, inflamed or chemically injured eyes have a substantially higher rejection and failure rate
Repeat grafts carry a poorer prognosis than primary grafts
Endothelial cell density declines steadily after surgery, so late graft failure can occur even after years of clarity
Visual outcome is often limited by astigmatism rather than by graft clarity itself

A clear graft and a good visual result are not the same thing, which is why refractive rehabilitation is as much a part of success as surgical technique.

References

Tan DTH, Dart JKG, Holland EJ, Kinoshita S. Corneal transplantation. The Lancet. 2012.
Williams KA, Lowe M, Bartlett C, et al. Risk factors for human corneal graft failure within the Australian corneal graft registry. Transplantation. 2008.
Price MO, Price FW. Endothelial keratoplasty – a review. Clinical and Experimental Ophthalmology. 2010.
Penetrating Keratoplasty. EyeWiki, American Academy of Ophthalmology.
Corneal Graft Rejection. StatPearls, NCBI Bookshelf.