Descemet Membrane Endothelial Keratoplasty: Update on Endothelial Transplantation Techniques

Abstract

The cornea remains in a state of deturgescence, maintained by the endothelial cell Na+/K+ ATPase and by tight junctions between endothelial cells that limit the entrance of fluid into the stroma. By maintaining an optimum level of corneal hydration, endothelial cells preserve the ordered arrangement of collagen fibers, which is crucial for corneal transparency. Fuchs' endothelial corneal dystrophy (FECD) was initially described by Fuchs in 1910 as a combination of epithelial and stromal edema in older patients. It manifests itself as bilateral, albeit asymmetric, central corneal guttae, corneal edema, and reduced vision. The Descemet membrane thickens and develops excrescences known histopathologically as guttae. Stromal edema develops, and the corneal thickness may increase to over 1,000 μm. When the edema is severe, the corneal epithelium can detach from its basement membrane, creating painful bullae on the anterior surface of the cornea. FECD is the most common endothelial dystrophy and is usually seen beyond the fifth decade of life, although not all cases are in the elderly. Pseudophakic bullous keratopathy is a term used to describe endothelial cell loss caused by surgical manipulations in the anterior chamber (usually due to pseudophakic intraocular lens (IOL) implantation, but it may be related to any other intraocular surgical procedure, obviously including phakic IOL implantation). If the corneal endothelium is damaged during surgery (as often occurs during cataract extraction, phakic IOL implantation and other procedures), the same spectrum of symptoms as found in FECD can develop, although the histological phenotype of both diseases is different and, usually, there is no guttata in pseudophakic bullous keratopathy. Full-thickness grafts have been the standard of care for treating medically uncontrollable endothelial disease for a significant number of years worldwide. However, although the success rate is 90% in low-risk patients, it is only 30-50% in more complex, higher-risk cases, and overall, 30% of cases have a rejection episode. Moreover, regrafting has become the most common indication for corneal transplantation in the US and in some places in Europe. The more recently developed lamellar keratoplasty techniques are designed to overcome some of the problems of corneal transplantation by leaving as much of the healthy cornea in place as possible. For example, endothelial keratoplasty procedures replace only the endothelium but leave the patient's cornea's refraction as well as most of its biomechanical properties fairly intact. In this chapter, we will review the actual techniques for endothelial transplantation and provide an update on the surgical strategy (mostly for Descemet membrane endothelial keratoplasty) and its clinical results and complications.