EyeWorld Asia-Pacific June 2019 Issue

32 EWAP JUNE 2019 SECONDARY FEATURE 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 decompensation. The exact reason is unknown. Direct contact of the silicone tube of a GDD with the corneal endothelium 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. We think that this is due to a nutritional `iwVˆi˜VÞ >à ̅i >µÕiœÕà humor circulation in the anterior chamber is disrupted. Rabbit studies we conducted ÃÕ}}iÃÌi` È}˜ˆwV>˜Ì…Þ«œÝˆ> >˜` ˜ÕÌÀˆÌˆœ˜> `iwVˆi˜VÞ ˆ˜ the GDD eye compared to the unoperated eye.” 3 The corneal endothelium is critical in maintaining a healthy and clear cornea. Corneal endothelial cells have > È}˜ˆwV>˜Ì ÀiÃiÀÛi v՘V̈œ˜ but preservation of these cells is paramount due to their limited regenerative capacity. Understanding how glaucoma and glaucoma surgery impact the endothelium is important for protecting corneal clarity in affected patients. “Most devices that we put into the anterior chamber are glaucoma devices, however, sometimes phakic IOLs are placed there, too,” Dr. Berdahl explained in his interview with EyeWorld . “If these devices come into contact with the corneal endothelium, it will lead to a decreased endothelial cell count. We also know that low intraocular pressures alone, hypotony, can cause a loss of endothelial cells. I think we have to be extra diligent in making sure devices are not in contact, or in too close proximity, to the corneal endothelium. We also need to ensure that the surgeries that we are doing are at a very low likelihood of creating hypotony.” Combining surgeries Ophthalmic surgeons always need to take the altered endothelium into account in patients with glaucoma or with a history of glaucoma surgery. Often individuals will require both glaucoma surgery and partial or full thickness keratoplasty. According to Dr. Berdahl, the biggest challenge in these eyes is how the anterior chamber will behave during surgery. “The anterior chamber is the challenge. You have to retain the air bubble long enough to ensure attaching the graft,” he said. “I generally put some viscoelastic in the lumen of the tube shunt or the ostium of the trabeculectomy in an effort to keep air in the anterior chamber and not going into the bleb. This is only modestly successful, so I do think that endothelial transplants are more challenging in these eyes. Some surgeons advocate for DSEK only, although there is literature to support that DMEK does just as well in these scenarios. I generally make a judgment call on how the eye is going to behave, and if I think it is going ̜ Li “œÀi `ˆvwVՏÌ] ̅i˜ `œ > DSEK,” Dr. Berdahl said. In Dr. Ayyala’s extensive experience with penetrating keratoplasty and glaucoma over many years that includes a number of publications, what a successful surgery comes down to is eye pressure and the donor corneal graft. “I had the opportunity to operate on a lot of penetrating keratoplasty glaucoma (PKPG) cases over the past 20 years. There are two main things to consider in these cases; ̅i wÀÃÌ ˆÃ "* Vœ˜ÌÀœ >˜` ̅i second is saving the graft. One at the exclusion of the other is not good for the patient,” 4 he said. According to Dr. Ayyala, most glaucoma surgeries are going to be detrimental to the survival of the corneal graft. “GDD controls IOP but increases the risk of graft rejection by 30–50%. Cyclo- Figure 3. On gonioscopy you can see several rings of the stent are visible and it is near the cornea. Figure 4. Additional viscoelastic is used to create space above and below the stent and to protect the cornea during removal. Figure 5. Large MST scissors are then used to trim the stent. The angle of approach is very important in order to avoid trauma to the cornea and iris and to avoid moving the stent to the side and creating a cyclodialysis cleft. In this case the wound needed to be enlarged slightly to provide an optimal angle.