Keratoplasty Types: PK vs DALK vs DSAEK vs DMEK
Last updated: October 2026
Corneal transplantation has moved from replacing the whole cornea to replacing only the diseased layer. Knowing which layer is sick tells you which operation to choose. This page compares PK, DALK, DSAEK and DMEK in the way examiners like to ask about them.
The principle: replace only what is diseased
- Full-thickness disease (scar through all layers, perforation): penetrating keratoplasty
- Anterior disease with healthy endothelium (keratoconus, stromal scars, stromal dystrophies): deep anterior lamellar keratoplasty
- Endothelial disease with a clear stroma (Fuchs dystrophy, pseudophakic bullous keratopathy, failed endothelium): endothelial keratoplasty (DSAEK or DMEK)
Comparison at a glance
| PK | DALK | DSAEK | DMEK | |
|---|---|---|---|---|
| What is replaced | All layers | Epithelium and stroma, down to Descemet's membrane | Posterior stroma, Descemet's membrane and endothelium | Descemet's membrane and endothelium only |
| Typical indications | Full-thickness scars, perforation, combined disease | Keratoconus, anterior stromal scars and dystrophies | Fuchs, bullous keratopathy, especially complex eyes | Fuchs, bullous keratopathy |
| Endothelial rejection | Possible; highest risk | Not possible (own endothelium) | Possible; lower than PK | Lowest risk |
| Visual recovery | Slow (often a year or more); high and irregular astigmatism | Slow; astigmatism similar to PK | Faster; small hyperopic shift | Fastest and best quality vision |
| Wound strength | Weak for life; risk of dehiscence after trauma | Weak (full-diameter wound) but globe less open during surgery | Strong (small incision) | Strong (small incision) |
| Main surgical challenge | Open-sky surgery: risk of expulsive haemorrhage | Baring Descemet's membrane without perforating it | Graft centration and attachment | Handling the scroll-like graft; graft detachment needing re-bubbling |
DALK pearls
- The big-bubble technique injects air into the deep stroma to separate it from Descemet's membrane.
- If Descemet's membrane perforates, a small tear can be managed with air tamponade. A large tear may need conversion to PK.
- A double anterior chamber (fluid between donor and recipient Descemet's) is treated with an air or gas injection.
- Because there is no endothelial rejection, DALK is ideal for young keratoconus patients who need a graft to last for decades.
Graft rejection: recognise it early
- Endothelial rejection (the most serious): a line of keratic precipitates moving across the graft (Khodadoust line), with graft oedema behind it.
- Stromal rejection: subepithelial infiltrates or stromal haze.
- Epithelial rejection: an elevated epithelial line.
- Risk factors: corneal vascularisation, previous rejection, large or eccentric grafts, young age, active inflammation, and herpetic disease.
- Treatment: intensive topical steroids, with systemic or periocular steroids in severe cases. Teach every patient the warning signs: redness, sensitivity to light, reduced vision and pain.
Other things examiners ask
- Donor tissue: eye banks check endothelial cell density; many surgeons want around 2000 cells/mm² or more for PK and endothelial grafts.
- Graft failure vs rejection: primary graft failure is a graft that never clears after surgery (usually donor endothelial failure); rejection is an immune attack on a previously clear graft.
- Keratoprosthesis (e.g., Boston KPro) is considered when repeated grafts have failed.
- Suture-related astigmatism after PK can be reduced by selective suture removal guided by topography. See topography tips.
Related: Fuchs dystrophy, keratoconus, Descemet's membrane detachment, and eye donation.
📘 Want more exam-ready material? See iNotes 2027: Cornea and Refractive on Kindle, or browse all my books.
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