What Is a Corneal Transplant? DMEK, DALK, and DSAEK Explained

Corneal transplantation has undergone a revolution in the past two decades. What was once a single procedure (full-thickness penetrating keratoplasty) has evolved into a family of techniques, each designed to replace only the specific layer of the cornea that is diseased while preserving the healthy layers. Understanding which technique is appropriate for which condition helps patients and referring practitioners make sense of what can seem like a confusing set of acronyms.

The layers of the cornea

To understand corneal transplantation, it helps to know the basic anatomy of the cornea. The cornea has five main layers: the epithelium (surface cells), Bowman layer (a thin structural layer), the stroma (the thick central layer making up 90 per cent of corneal thickness), Descemet membrane (a thin basement membrane), and the endothelium (a single layer of cells on the inner surface that pumps fluid out and keeps the cornea clear).

Different diseases affect different layers. Keratoconus affects primarily the stroma, causing it to thin and bulge. Fuchs dystrophy affects the endothelium, causing cells to die off gradually. Corneal scarring from infection or trauma may involve the epithelium and stroma. The appropriate transplant technique depends on which layer is affected.

Full-thickness transplant — PKP (Penetrating Keratoplasty)

PKP replaces the entire thickness of the cornea with donor tissue. For many decades it was the only corneal transplant technique available, and it remains appropriate in some situations: when multiple layers are diseased, when there is significant corneal scarring extending deep into the stroma, or when anatomy makes partial-thickness techniques difficult.

The main disadvantages of PKP are a long visual recovery (often twelve to eighteen months), high levels of post-operative astigmatism, a significant risk of rejection, and a wound that remains a structural weakness in the eye indefinitely.

Endothelial transplant for Fuchs dystrophy

When only the endothelium is diseased, as in Fuchs dystrophy or bullous keratopathy, there is no need to replace the entire cornea. Endothelial keratoplasty techniques replace only the inner layer, leaving the healthy anterior cornea intact.

DSAEK (Descemet Stripping Automated Endothelial Keratoplasty) was the first widely adopted endothelial transplant technique. A disc of donor tissue roughly 100 to 150 microns thick including stroma and Descemet membrane is inserted and supported against the recipient cornea with an air bubble. DSAEK is technically accessible and has good outcomes, but the retained donor stroma slightly limits final visual quality.

DMEK (Descemet Membrane Endothelial Keratoplasty) replaces only the Descemet membrane and endothelium, a graft approximately 10 to 15 microns thick. The absence of donor stroma means better optical quality, faster visual recovery, and a lower rejection rate than DSAEK. Most patients with Fuchs dystrophy are now offered DMEK where a surgeon with sufficient experience is available. DMEK is technically more demanding than DSAEK and requires specific training.

Anterior transplant for keratoconus — DALK

DALK (Deep Anterior Lamellar Keratoplasty) is the procedure of choice for advanced keratoconus and anterior corneal scarring where the endothelium is healthy. In DALK, the epithelium and stroma are replaced with donor tissue while the patient's own Descemet membrane and endothelium are preserved. Because no donor endothelium is transplanted, the risk of endothelial rejection is eliminated. The long-term graft survival of DALK is significantly better than PKP for keratoconus.

DALK is technically demanding and requires the surgeon to separate the stroma from Descemet membrane at a precise plane. In experienced hands the success rate of full-depth DALK is high.

Which technique for which patient?

• Fuchs dystrophy, bullous keratopathy, failed endothelial graft: DMEK (preferred) or DSAEK.
• Advanced keratoconus, anterior corneal scarring with healthy endothelium: DALK.
• Deep stromal scarring, multiple layer disease, complex anatomy: PKP.

The decision requires specialist assessment including specular microscopy, corneal topography, tomography, and anterior segment OCT.

For patients with both a cataract and Fuchs dystrophy, combined cataract and corneal transplant surgery allows both conditions to be addressed in a single anaesthetic, shortening the overall treatment pathway.

Dr MacIntyre performs DMEK, DALK, DSAEK, and PKP, as well as combined cataract and corneal transplant procedures. He undertook subspecialty fellowship training in cornea, complex cataract, and refractive surgery at the Wilmer Eye Institute at Johns Hopkins Hospital in Baltimore, and subsequently moved to Australia to complete a cornea fellowship at the Royal Victorian Eye and Ear Hospital in Melbourne, where he continues to hold a staff specialist appointment.

Consultations are available at Northern Eye Consultants, Suite 5, Northpark Private Hospital, 135 Plenty Road, Bundoora, and at Bass Coast Eye Centre, Wonthaggi. To book or refer a patient, contact Northern Eye Consultants on (03) 9466 8822 or refer via HealthLink EDI nthneyec.