This patient-education article is written by the cornea service at Suraj Eye Institute, Nagpur.

What Are PK and DALK?

Penetrating keratoplasty (PK) and deep anterior lamellar keratoplasty (DALK) are two corneal transplantation operations in which the diseased cornea of the patient is replaced with healthy donor tissue. The difference between them is how much of the cornea is replaced:

  • PK — the whole thickness of the central cornea is removed and replaced. All five layers of the cornea (epithelium, Bowman, stroma, Descemet membrane, endothelium) come from the donor.
  • DALK — only the anterior layers of the cornea (epithelium, Bowman, stroma) are replaced. The patient’s own Descemet membrane and endothelial layer are preserved.

DALK is preferred wherever the patient’s own endothelial layer is healthy — for example, in most cases of keratoconus, anterior corneal scars and stromal dystrophies. Preserving the patient’s endothelium avoids the small but life-long risk of endothelial rejection that follows a full-thickness graft.

PK vs DALK — Anatomical Cross-Section

PK vs DALK — Cross-Section Through the Cornea

PENETRATING KERATOPLASTY (PK) Full thickness — all 5 layers replaced

Epithelium Bowman Stroma Descemet Endothelium

Anterior chamber

DONOR BUTTON HOST HOST

Donor tissue (pink) replaces all 5 layers Wound margins (red) cut through full thickness Held by ~16 sutures around the circumference

DEEP ANTERIOR LAMELLAR KERATOPLASTY (DALK) Anterior layers only — host endothelium kept

HOST’S OWN Descemet + endothelium CONTINUOUS — no wound, no junction

DONOR (front layers only) HOST HOST

Donor tissue (pink) replaces only the front 3 layers Wound margins stop above Descemet membrane Patient’s endothelium kept → much lower rejection risk

Total corneal thickness ≈ 540 µm · stroma forms ~90% of thickness · donor button typically 7.5–8.5 mm in diameter

Figure 1. Anatomical cross-section through the cornea showing what each transplant replaces. Penetrating keratoplasty (PK, left): a full-thickness disc of cornea is removed and replaced with donor tissue (pink). The two surgical wound margins (red vertical lines) pass through all five corneal layers, and the graft is held in place by sutures (typically ~16) around the circumference. Deep anterior lamellar keratoplasty (DALK, right): only the front three layers — epithelium, Bowman, stroma — are replaced. The patient’s own Descemet membrane and endothelial layer (green-outlined band) run continuously across the entire diameter, never cut. Preserving the host endothelium nearly eliminates the risk of endothelial rejection, the most serious long-term complication of full-thickness keratoplasty.

Indications

Condition Preferred procedure
Advanced keratoconus with contact-lens intolerance DALK
Anterior corneal scarring (post-infection or trauma) DALK if endothelium healthy; PK if scar reaches Descemet
Stromal corneal dystrophies (lattice, granular, macular) DALK
Endothelial disease (Fuchs, PBK) Endothelial keratoplasty (DSAEK / DMEK) — not PK or DALK
Full-thickness scar after corneal melt or perforation PK
Re-graft after a failed PK / DALK PK

The Big-Bubble DALK Technique

Modern DALK is most often performed using the big-bubble technique introduced by Mohammad Anwar. After partial-thickness trephination, a fine cannula is used to inject air deep into the corneal stroma. The air dissects between the deep stroma and Descemet membrane, creating a smooth pre-Descemet plane that allows clean removal of the anterior corneal layers. The donor tissue (with its endothelium stripped off in the eye bank) is then sutured into place over the patient’s preserved Descemet and endothelium.

What to Expect

PK and DALK are performed under local or general anaesthesia and take 90–120 minutes. The graft is secured with 16 interrupted 10-0 nylon sutures or a running suture. Sutures are usually left in place for 12–18 months for PK and 9–12 months for DALK. Vision improves gradually over 6–12 months as the cornea heals and astigmatism is adjusted with selective suture removal.

Long-term graft care matters. A clear corneal graft can last decades, but life-long topical steroid drops at a low dose, careful suture management and prompt review of any new redness, pain or vision change are essential. Rejection, when caught early, is usually reversible with intensive topical steroid treatment.
✔ Corneal Transplantation at Suraj Eye Institute

Our cornea service performs penetrating keratoplasty and deep anterior lamellar keratoplasty (including the big-bubble technique) for keratoconus, stromal dystrophies, infectious and traumatic corneal scars, and failed grafts. Donor tissue is supplied through our partner eye bank, and structured long-term follow-up reduces rejection and maximises graft survival.

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Frequently Asked Questions

How long does the graft last?
A clear, well-cared-for graft commonly lasts ten to twenty years and often much longer. In keratoconus, DALK has the advantage of preserving the patient’s own endothelium, so there is no risk of endothelial rejection and the eye is left structurally stronger; the final choice between DALK and PK depends on the surgeon’s judgement for each patient. When a graft eventually fails, a regraft is usually possible.

What does rejection feel like?
Rejection causes a new red, painful, light-sensitive eye with reduced vision, usually weeks to years after surgery. Any of these symptoms after a corneal transplant is an emergency — early intensive topical steroid treatment reverses most rejections, while delayed treatment can cause permanent graft failure.

How long is the recovery?
Day-to-day function returns within a few weeks, but the cornea continues to remodel for 6–12 months. Vision improves gradually as the swelling settles and selective suture adjustment reduces post-operative astigmatism. Final spectacles or contact lenses are usually prescribed only after sutures are removed.

Can my body reject the donor cornea?
Yes, but at a much lower rate than other transplanted organs because the cornea has no blood vessels of its own. DALK substantially reduces the risk of the most serious form of rejection (endothelial) because the donor endothelium is replaced by the patient’s own.

Where does the donor tissue come from?
From eyes donated after death by the donor or their family. The tissue is recovered within hours, screened for infection and stored in the eye bank in a special preservation medium. Tissue matching is not required for corneal transplantation because of the cornea’s immune-privileged status.

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