#14: Endothelial Corneal Transplantation

Until nearly the start of the 21^st century, full thickness corneal transplantation – or penetrating keratoplasty (PKP) – was commonly considered the surgical standard of care for patients with pseudophakic bullous keratopathy and Fuchs' dystrophy. While PKP had a long track record of success dating back nearly 100 years, the procedure required several months of refractive adjustments for patients to achieve stable vision.

Starting with the advent of posterior lamellar keratoplasty in the late 1990s, a number of procedures have been developed, refined, and widely adopted in the opththalmology community that have improved upon some of the basic tenets of PKP. These advances have allowed patients to recover faster from surgery and improved globe stability.

Anterior segment optical coherence tomography (AS-OCT) and in vivo confocal microscopy are among the tools commonly used in the follow-up of corneal transplantation. These tools allow ophthalmologists to evaluate graft adhesion in the immediate postoperative period and measure graft and corneal thickness.

Descemet's membrane endothelial keratoplasty (DMEK) in a case of Fuchs' endothelial dystrophy as seen with Heidelberg Engineering's SPECTRALIS Anterior Segment Module

Here is a brief timeline of recent progress in corneal transplantation:

• 1998: Dr. Gerrit Melles of the Netherlands Institute for Innovative Ocular Surgery describes a new technique called posterior lamellar keratoplasty (PLK) that involves dissection of the posterior lamella, Descemet's membrane, and endothelium through a 9-mm sclerocorneal incision. This is then followed by insertion of a donor button consisting of posterior stroma, Descemet's membrane, and endothelium.

• 2001: PLK is introduced into the United States as deep lamellar endothelial keratoplasty (DLEK) by Dr. Mark Terry. The 9-mm incision is reduced to 5 mm, but the procedure is not adopted on a widespread basis due to factors such as a high degree of technical surgical difficulty, significant risk of tissue loss in donor graft preparation, and variably smooth donor-host interface that limited visual recovery.

• 2004: Dr. Melles develops an alternate technique to PLK called Descemet’s stripping endothelial keratoplasty (DSEK) by manually peeling away the host endothelium and Descemet’s membrane. This allows the posterior stroma of the host cornea to remain intact. Further modifications to this procedure were introduced that simplified the procedure and improved the graft-host interface. This modified procedure, called Descemet’s stripping automated endothelial keratoplasty (DSAEK), is the most commonly performed keratoplasty procedure performed today.

• 2006: Dr. Melles develops another surgical modification, called Descemet’s membrane endothelial keratoplasty (DMEK), where only the thin layer of Descemet’s membrane and its associated endothelial cells are transplanted. This is then further modified with a combination of elements that simplify the procedure and is now termed Descemet’s membrane automated endothelial keratoplasty (DMAEK). In this procedure, instead of transplanting bare donor Descemet’s membrane and endothelium, a rim of stroma is left at the periphery of the donor lenticule to increase tissue stability.

The future of treating Fuchs' dystrophy may involve another surgical modification called Descemet’s membrane endothelial transfer (DMET), where a free-floating Descemet-endothelial graft in placed partly in contact with the recipient posterior cornea after removing host Descemet’s membrane. There is some evidence that corneal clearance can be achieved with this procedure.