Complex Endothelial Keratoplasty

Introduction

In a few short years, endothelial keratoplasty (EK) has emerged as the most popular surgical treatment option for corneal endothelial dysfunction, even superseding penetrating keratoplasty (PK) in overall transplant volume in the United States since 2012.

The seminal discovery behind EK was that a posterior corneal graft could be held in place with an intracameral air bubble rather than sutures. Subsequent donor endothelial pump action not only clears stromal edema but simultaneously generates suction that maintains graft adherence. Ideally, this pump activity begins before the intracameral air is resorbed and the air’s applanating and tamponading effects are lost. Both Descemet stripping endothelial keratoplasty (DSEK) and Descemet membrane endothelial keratoplasty (DMEK) require an intracameral air or gas bubble.

EK is straightforward in most eyes with a normal anterior segment and a stable lens–iris diaphragm—be it the crystalline lens or a well-seated posterior chamber intraocular lens (IOL). In these eyes, pupillary constriction effectively sequesters intracameral air or gas in the anterior chamber (AC). The lens-iris diaphragm resists posterior displacement of the bubble, such that intraoperative bubble expansion exerts vector forces anteriorly to more efficiently applanate the graft against the recipient cornea.

It follows that EK becomes technically more complex when the prerequisite bubble cannot be adequately formed or maintained in the AC. This problem may occur when the lens-iris diaphragm is compromised, such as in aphakia and various iris abnormalities. Diaphragmatic patencies provide exit points allowing the bubble (and even the graft) to escape out of the AC. This situation is exacerbated in postvitrectomized, unicameral eyes. The bubble will favor the larger vitreous cavity because it can adopt a more spherical shape there, minimizing surface tension as predicted by Laplace’s law ( Video 138.1 ). The bubble (and even the graft) can also escape anteriorly if pathways exist, for example through a glaucoma shunt or filter.

Video 138.1 Descemet Stripping Endothelial Keratoplasty Under Top Hat Penetrating Keratoplasty (PK) with Laplace Phenomenon. Matthew T. Feng, Francis W. Price Jr., Marianne O. Price.

EK also becomes technically more complex when certain abnormalities of the recipient eye or recipient patient exist. In a crowded anterior segment, both DSEK and DMEK grafts may incur endothelial damage or fail to completely unfold unless steps are taken to create space and/or undersize the donors. Similarly, the rescue of failed PK grafts by both DSEK and DMEK may be complicated by abnormal protrusions of, or synechiae to, the posterior corneal surface.

Nevertheless, because of the well-known advantages of EK over PK, the indications for EK have expanded to include eyes with precisely the aforementioned anterior segment complexities as well as others ( Box 138.1 ). This chapter therefore discusses strategies for performing complex EK—so-called “extreme EK.” While both DMEK and DSEK can be attempted and performed successfully in most of these situations, the decision for DMEK is more reserved owing to its need for a fuller air fill. DMEK grafts demonstrate a seemingly less-inherent ability to stick to the recipient cornea and are more likely to detach if given the chance.

When deciding which type of EK to offer, the visual and immune advantages of DMEK must be weighed against its technical challenges and postoperative requirements in individual case scenarios. Patient factors may require special attention even in the presence of a normal anterior segment. These factors include, but are not limited to, conditions that interfere with supine positioning and, by extension, level positioning of the eye such as kyphosis and congestive heart failure; conditions that counteract graft attachment such as chronic eye rubbing and essential blepharospasm; conditions associated with increased intraoperative posterior pressure such as obesity and thyroid orbitopathy; conditions that may diminish postoperative compliance such as decreased mental capacity and extremely young or advanced age; and conditions that may impair full function of the donor endothelial pump via toxicity associated with their treatment—for example, carbonic anhydrase inhibitors, amantadine, and memantine.