DALK, hydrops
& decision algorithm

DALK — deep anterior lamellar keratoplasty

Deep anterior lamellar keratoplasty is indicated in advanced keratoconus and PMD when scars or stromal opacities degrade vision while the endothelium remains healthy — that is, as long as there is no extensive cicatricial hydrops having compromised Descemet's membrane. Its value rests on a simple principle: by replacing the pathological stroma while preserving the recipient's Descemet and endothelium, it eliminates the risk of endothelial rejection, the main cause of late failure in penetrating keratoplasty. The graft is thus safer in the long term, at the cost of a technically more demanding surgery, whose whole difficulty concentrates on dissecting the pre-Descemetic plane.

The cleavage plane and the "big bubble"

Anwar's technique transformed DALK by making this plane reproducible. By injecting air (or a fluid) into the deep stroma, one detaches Descemet from the residual stroma and creates a bubble exposing a bare membrane on which the lamellar graft will rest. Dua's work then showed that this bubble does not always form in the same plane, and this distinction has direct surgical consequences.

Manual techniques

In its manual form, big-bubble DALK chains a partial trephination, the insertion of a cannula or needle to two-thirds or three-quarters of stromal depth, then air injection that creates the bubble. It is then punctured, the stromal roof is cut, and dissection is completed down to bare Descemet, if needed under viscoelastic protection. When the bubble does not form — a frequent case in heavily scarred corneas — one falls back on layer-by-layer dissection, longer and sometimes leaving a less regular interface. It is precisely the depth uncertainty and the "blind" nature of needle insertion that expose to perforation, and that femtosecond assistance seeks to reduce.

Femtosecond assistance and double docking (DD-DALK)

The femtosecond laser first served to standardise the geometry of the donor-recipient junction, drawing interlocking side profiles — zigzag, mushroom, top-hat — that improve apposition and biomechanical strength of the scar. But the central difficulty of DALK is not the peripheral cut: it is entering the deep stroma and opening the bubble roof without injuring Descemet.

This is the logic of the double docking (DD-DALK) technique we described (Guindolet, Nguyen, Doan, Cochereau, Gabison), then evaluated on a consecutive series of 37 eyes published in Cornea in 2023. Rather than performing everything in a single applanation, the procedure is split into two successive dockings framing the air injection. During the first docking, under control of the laser-integrated intraoperative OCT — which allows the cuts to be visualised and calibrated directly on a cornea of irregular thickness — the anterior lamellar cut and the circular side cut are performed to remove the anterior stroma. One then undocks and injects air per Anwar into the residual posterior stroma to detach Descemet and obtain the big bubble. Finally comes the second docking: the residual posterior stroma is brought back into the docked position, and the laser performs a penetrating vertical cylindrical cut that opens the bubble roof in a controlled way, where the manual gesture would be freehand. The benefit is twofold: the precision of the stromal cuts is entrusted to the laser, and OCT guidance of the air injection increases the bubble-formation rate. In the 37-eye series, a big bubble was obtained in about two-thirds of cases, the remaining third requiring manual dissection; bubble failure was associated with the presence of stromal scars — a useful reminder that even a standardised technique remains dependent on the state of the stroma it crosses.

Complications and management

Descemet perforation remains the feared complication. A micro-perforation usually allows the procedure to continue, tamponading with an anterior-chamber air bubble and avoiding any over-pressure; a macro-perforation mandates conversion to penetrating keratoplasty. Postoperatively, a Descemet detachment presents as a double anterior chamber, corrected by air re-injection. The other pitfalls concern the interface — fibrosis, haze, folds, irregularities, especially after manual dissection — and the possibility of stromal or epithelial rejection, bearing in mind that the absence of endothelial rejection remains the cardinal advantage of the technique.

Sutures and astigmatism management

Closure follows the same principles as penetrating keratoplasty. Interrupted sutures — classically sixteen 10-0 nylon sutures — are adjustable sector by sector and removed selectively according to topography; the running suture, single or double, in 10-0 or 11-0, distributes tension more harmoniously; the two are often combined. Sutures are passed at about 90 % depth, straddling the donor-recipient junction, without transfixing Descemet. Astigmatism reduction then plays out over time: early keratometry and topography guide loosening or selective removal of tight sutures on the steep meridian, with complete removal staged over twelve to eighteen months.

Acute corneal hydrops

• Mechanism: acute rupture of Descemet + endothelium at the cone apex → aqueous influx into the stroma → massive acute stromal oedema, abrupt visual loss, pain/photophobia.
• Background: very advanced cones, Down syndrome, VKC, rubbing.

Management

Treatment now relies on posterior stromal sutures (pre-Descemetic compression sutures), most often combined with an intracameral gas injection (SF6 20 % or C3F8 14 %): they appose the edges of the Descemet tear and markedly accelerate resorption of the oedema, shortening the course and limiting extensive scarring. This has become the mainstay of modern management, ahead of a purely conservative approach.

Synthesis decision algorithm

Diagnosis → Background (rubbing/atopy/familial) + Placido + Pentacam (posterior elevation + pachymetry + BAD-D) + Corvis TBI + epithelial mapping (doughnut) → ABCD staging.