Eyeworld

EW FEATURE 42 Facing complicated glaucoma cases • February 2019 AT A GLANCE • Glaucoma itself can have damaging effects on the corneal endotheli- um. Factors include increased IOP, mechanical forces, and the altered aqueous environment. • Glaucoma surgery combined with DMEK/DSEK is feasible, with extreme caution. • Dr. Ayyala chooses ab externo canaloplasty in his glaucoma patients to best protect the corneal endothelium. • Dr. Berdahl first performs glaucoma surgery to stabilize IOP and control bleedings before proceeding to DMEK. by Stefanie Petrou Binder, MD, EyeWorld Contributing Writer tion but preservation of these cells is paramount due to their limited regenerative capacity. Understand- ing how glaucoma and glaucoma surgery impact the endothelium is important for protecting corneal clarity in affected patients. "Most devices that we put into the anteri- or chamber are glaucoma devices, however, sometimes phakic IOLs are placed there, too," Dr. Berdahl explained in his interview with We think that this is due to a nu- tritional deficiency as the aqueous humor circulation in the anterior chamber is disrupted. Rabbit studies we conducted suggested significant hypoxia and nutritional deficiency in the GDD eye compared to the unoperated eye." 3 The corneal endothelium is crit- ical in maintaining a healthy and clear cornea. Corneal endothelial cells have a significant reserve func- indurated, leading to a loss in transparency and compromising clear vision. As endothelial cells do not regenerate, it is paramount to protect this fragile layer of cells. Normal corneas lose 0.6% of endothelial cells (2,500–3,000 cells per square millimeter in adults) per year. In conditions that predispose to endothelial cell damage, such as glaucoma, endothelial cell loss is enhanced. Glaucoma—and its management—can have deleterious effects on the corneal endothelium. Increased IOP, mechanical forces, and the aqueous environment have been implicated in endothelial cell loss, as have glaucoma surgery or a history of glaucoma surgery, which present a particularly significant risk for endothelial cell health and cornea transplant graft survival. 1 Endothelial cell damage "Corneal issues in glaucoma patients mostly have to do with endothelial decomposition, with resulting corneal edema," Dr. Ayyala told EyeWorld. "Corneal diseases and glaucoma are seen together in almost 50% of glaucoma patients." Precisely how the endothelium is damaged in glaucomatous eyes is incompletely understood. In a pub- lished study he conducted on pene- trating keratoplasty and glaucoma, Dr. Ayyala observed that glaucoma issues in corneal patients were mul- tifactorial in origin, usually due to angle closure, steroid response, and inflammation. 2 In his experience, endothelial cell damage can result from glauco- ma surgery, as well as from bouts of acute or sustained elevated intraoc- ular pressures. "Acute angle closure glaucoma is an outstanding exam- ple of increased IOP that can cause damage to endothelial cells," Dr. Ayyala explained. "Some glaucoma surgeries increase the risk of corneal decompensation more than others. For instance, glaucoma drainage devices (GDD) are associated with a 20–30% risk of corneal decompensa- tion. The exact reason is unknown. Direct contact of the silicone tube of a GDD with the corneal endo- thelium can cause endothelial cell death and sequential endothelial decompensation. In the majority of the cases, the tube is kept away from corneal endothelium, but it still develops corneal decompensation. G laucoma patients will frequently have a reduced endothelial cell count due to various changes that come along with the disease. Glaucoma surgery, which is performed to reduce IOP in these in- dividuals, will likely compound the problem by causing further endo- thelial cell loss. The ensuing corneal decompensation adversely affects vision and is best addressed by Descemet's membrane endothelial keratoplasty (DMEK) or Descemet's stripping endothelial keratoplasty (DSEK), procedures that replace the endothelium using donor corneal endothelium. Patients will often require both, however, combining glaucoma surgery with DMEK/DSEK warrants a great deal of caution. EyeWorld spoke to glaucoma specialists Ramesh Ayyala, MD, FRCS, University of South Florida, Tampa, Florida, and John Berdahl, MD, Vance Thompson Vision, Sioux Falls, South Dakota, about what they have learned with respect to managing glaucoma in the setting of a damaged corneal endothelium in patients with glaucoma. The endothelium The corneal endothelium is a single layer of squamous cells lining the posterior surface of the cornea that plays a unique role in the regulation of hydration through a system of active ion transport. When this reg- ulation becomes impaired through damage to the endothelium, corneal cells can become edematous and Glaucoma surgery and managing the corneal endothelium Figures 1 and 2. A 2.4-millimeter keratome is used to create a wound angle for the stent followed by lidocaine and viscoelastic. Figure 3. On gonioscopy you can see several rings of the stent are visible and it is near the cornea.

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