Penetrating keratoplasty (PK / PKP)
The historic procedure, now reserved for situations where no selective approach is possible: opacity involving the full thickness, a highly irregular or thinned cornea, perforation, or multiple lamellar failures.
Principle & technique
Trephination of a recipient button (often 7.5-8.25 mm) and of a slightly larger donor graft, then suturing (interrupted, running, or a combination) under the microscope. Managing post-graft astigmatism — through suture tension, intraoperative keratometry and selective suture removal — is the central challenge of visual recovery.
Contribution of the femtosecond laser
The femtosecond laser allows profiled cuts (zig-zag, mushroom, top-hat edges) that increase the healing surface, improve apposition and junction strength, and can speed visual rehabilitation compared with a vertical trephine cut.
| Advantages | Limitations |
|---|---|
| Universal solution (any layer), tectonic | Frequent irregular astigmatism |
| Maximum track record and standardisation | Highest endothelial rejection; long-term sutures |
| Essential for perforation/total opacity | Slow visual recovery; tectonic fragility (lifelong risk of traumatic dehiscence) |
▶ Watch corneal graft videos (surgical technique & reports) on egabison.com
Anterior lamellar keratoplasty (ALK / DALK)
When the endothelium is healthy but the stroma is diseased — the emblematic case of keratoconus — DALK replaces the stroma down to Descemet's membrane while preserving the native endothelium. The cardinal benefit: elimination of endothelial rejection and therefore potentially lifelong graft survival.
Anwar's big bubble
The reference technique: after partial trephination and stromal dissection, air/viscoelastic is injected to cleave the deep stroma from Descemet's membrane.
- Type 1 — central bubble, cleavage at the Dua / pre-Descemet layer: robust bed, the most favourable.
- Type 2 — large peripheral bubble beneath true Descemet: more fragile wall, increased perforation risk.
- Mixed — coexistence of both, to be recognised to avoid rupture.
Alternatives: viscodissection, manual layer-by-layer dissection (Melles), femtosecond assistance for trephination and cutting planes.
Learning curve & conversion
DALK is technically demanding: micro-perforation of Descemet's membrane is the key intraoperative complication and may force conversion to penetrating keratoplasty. Visual results, when dissection reaches the pre-Descemet plane, equal those of PK, without the endothelial risk. Main indications: keratoconus, ectasias, stromal scars and dystrophies, post-infectious opacities not reaching the endothelium.
For keratoconus, a growing share of cases now falls to CAIRS (allogenic corneal intrastromal ring segments): human corneal tissue is added within a stromal tunnel to remodel the surface, with no synthetic material and no penetrating graft. Planning relies on dedicated nomograms (e.g. Jacob, Istanbul). See also Ch. 10.
▶ Watch the “double docking” DALK technique videos (egabison.com)