Why Repeat Pk? Hydrodissection-Assisted Dalk-On-Pk For Rim Ectasia

Deep anterior lamellar keratoplasty (DALK) on a prior penetrating keratoplasty (PK) is technically challenging due to scarring at the graft–host junction and uncertainty regarding the posterior stromal interface. In graft rim ectasia, marked peripheral thinning further increases the risk of perforation during trephination, often prompting consideration of repeat PK. Proposed approaches for DALK-on-PK include manual dissection or Big Bubble formation, both potentially hazardous in previously grafted corneas. We describe a hydrodissection-assisted technique using balanced salt solution (BSS) to reinforce thinned ectatic stroma and exploit a PK-specific plane of separation, confirmed with intra-operative OCT.

James Paget University Hospital NHS Foundation Trust, United Kingdom.

A 66-year-old woman with keratoconus had undergone PK in 1997. She presented with progressive graft failure characterised by severe inferior rim ectasia, stromal scarring, and marked irregular astigmatism (ΔK 15.6D). Best-corrected visual acuity was 6/19 (pinhole 6/9.5). Endothelial cell count remained preserved at 2618 cells/mm², supporting an endothelial-sparing approach.

DALK-on-PK was undertaken using hydrodissection rather than Big Bubble formation. A 9.0mm trephination to approximately 400µm depth was centred over the ectatic graft–host junction. Due to marked inferior thinning, BSS was injected intrastromally along the inferior junctional region to locally thicken and stabilise the diseased stroma, reducing the risk of perforation during trephination.

Given the extreme thinning, the injection likely entered the posterior stromal layers, estimated to be within the final 100µm of stroma. Fluid tracking at this depth produced a visible wave propagating through the posterior stroma, indicating creation of a cleavage plane between posterior stroma and the pre-Descemet’s layer complex across both donor and host tissue. Intra-operative OCT confirmed a continuous fluid-defined separation plane without breach of Descemet’s membrane. The anterior stroma was removed along this interface, revealing an intact posterior lamellar bed spanning the PK–host boundary. No macro- or micro-perforation occurred. A donor anterior lamellar graft was secured with interrupted 10-0 nylon sutures.

Hydrodissection with BSS can safely facilitate DALK on a previous PK by exploiting a cleavage plane that appears unique to grafted corneas. In cases of rim ectasia, extreme thinning may permit deep intrastromal injection into the posterior stromal layers, enabling controlled separation of the posterior stroma from the pre-Descemet’s layer without air injection. This manoeuvre provides dual benefits of tectonic stromal thickening and plane creation, reducing the risk of Descemet’s membrane perforation and conversion to repeat PK. The intraoperative fluid wave and OCT confirmation provide objective indicators of successful separation, supporting this endothelial-preserving alternative to repeat PK in selected cases.