DALK (Deep Anterior Lamellar Keratoplasty) is the corneal transplant procedure of choice when the front layers of the cornea are diseased but the inner endothelial layer remains intact. By replacing only the diseased tissue, DALK avoids the main cause of long-term graft failure after traditional full-thickness transplantation: endothelial rejection. For patients with advanced keratoconus or anterior corneal scarring where contact lens wear is no longer possible, DALK offers durable visual rehabilitation with a more favourable long-term graft survival profile than PKP.
What Is DALK?
DALK (Deep Anterior Lamellar Keratoplasty) is a partial-thickness corneal transplant that replaces the front layers of the cornea — the epithelium, Bowman's layer, and stroma — while preserving the patient's own Descemet membrane and endothelium. Because the recipient's own inner cell layer is retained, DALK carries a significantly lower risk of endothelial rejection than full-thickness penetrating keratoplasty, and patients do not require lifelong immune suppression to the same degree.
The endothelium is the single-cell layer on the inner surface of the cornea responsible for pumping fluid out of the corneal stroma and maintaining corneal clarity. When this layer is preserved — as in DALK — the principal driver of long-term graft failure after full-thickness transplantation is eliminated. Even if the donor stroma is eventually rejected immunologically, the recipient endothelium survives and the cornea may remain clear with appropriate treatment.
When Is DALK Used?
DALK is used for conditions affecting the anterior cornea where the endothelium remains healthy. The most common indication is advanced keratoconus where contact lens wear is no longer possible or tolerated, and where the corneal thinning and irregular shape cannot be adequately managed with non-surgical approaches including corneal cross-linking. DALK is also used for anterior corneal scarring from infection, trauma, or dystrophies affecting the anterior stroma.
DALK is not appropriate when the endothelium is also diseased — in those cases, DMEK or DSAEK is required. Careful pre-operative assessment including endothelial cell count and specular microscopy determines whether DALK or a full-thickness procedure is most appropriate.
The DALK Technique
DALK surgery aims to dissect as close as possible to Descemet membrane — leaving only the thinnest possible residual stroma between the donor tissue and the recipient's own membrane. The deeper the dissection, the better the visual quality achievable after surgery, as the optical interface between donor and recipient tissue is minimised.
The most widely used approach is the big-bubble technique, in which air or viscoelastic is injected into the deep stroma to separate it from Descemet membrane, creating a large bubble that facilitates safe, controlled dissection to the deepest possible level. When successful, this produces a cleavage plane directly above Descemet membrane, allowing almost all recipient stroma to be removed.
In some cases, complete pre-Descemet dissection is not achievable, and the surgeon proceeds with a near-complete dissection leaving a thin residual stromal bed. This is called a partial-thickness or non-big-bubble DALK and still carries the endothelial preservation advantage over PKP, though visual outcomes may be slightly less predictable. The donor corneal tissue is sutured into place with interrupted or running sutures, which remain in the eye for at least twelve months while the graft heals.
Recovery After DALK
Recovery after DALK is slower than after endothelial keratoplasty procedures such as DMEK or DSAEK, reflecting the full-thickness anterior dissection and the need for suture healing. Most patients notice meaningful visual improvement within three to six months, with best corrected vision achieved at twelve to eighteen months — after which glasses, contact lenses, or in some cases laser vision correction can be used to refine the refractive outcome.
Suture removal is performed in stages, guided by refraction and corneal topography, and can itself improve vision as suture-induced astigmatism is released. Final refraction is typically not assessed until at least twelve months after the last suture removal, when the corneal shape has stabilised.
Advantages of DALK Over PKP
The principal advantage of DALK over full-thickness PKP is the preservation of the patient's own endothelium, which eliminates the risk of endothelial rejection — the most common cause of graft failure after PKP — and means patients require less intensive long-term topical steroid use than PKP recipients.
Because the recipient's Descemet membrane and endothelium are retained, even if the donor stroma is eventually rejected, the endothelium survives and the graft may remain clear with appropriate medical treatment. Graft failure rates after DALK are lower than after PKP over long-term follow-up, making it the preferred option for keratoconus and anterior scarring in appropriately selected patients. DALK also avoids the intraoperative risks of opening the eye to atmospheric pressure, which is associated with a small risk of suprachoroidal haemorrhage in PKP.
DALK vs PKP — When Each Is Preferred
DALK is preferred when the endothelium is healthy and disease is confined to the anterior cornea. PKP is required when the endothelium is also diseased, when previous deep corneal scarring extends to Descemet membrane, or when prior surgery makes lamellar dissection unsafe. The decision is made at pre-operative assessment and may occasionally be finalised intraoperatively if a Descemet membrane perforation occurs during DALK dissection — in which case conversion to PKP may be required.
For patients with combined endothelial and anterior disease — where both layers of the cornea are compromised — PKP may be the only appropriate option, or a staged approach (DALK followed by DMEK at a later date) may be considered in selected cases.
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.