GLAUCOMA EWAP MARCH 2022 55 the pressure points and points where it enters the anterior chamber, she said. This is key, hence her tendency to enter the anterior chamber at 12 o’clock and at least 2 mm posterior to the limbus. Reza Razeghinejad, MD, said that tube exposure can be divided into two groups: early tube exposure and late-onset tube exposure. Early tube exposure, he said, is often caused by a dehiscence of the suture that secures the conjunctiva or conjunctival retraction and dehiscence due to having tension on the conjunctiva. The exact mechanism for late-onset tube exposures is not known, Dr. Razeghinejad said. It’s likely related to an erosion of the overlying conjunctiva and patch graft due to the micromovements of the tube with blinking and eye movements, he said. The reported risk factors for tube exposure are ocular inflammation, neovascular glaucoma, increased number of preoperative glaucoma medications, diabetes mellitus, prior ocular surgeries with conjunctival violation (strabismus surgeries, retinal detachment surgeries, pterygium surgery with free conjunctival flap, etc.), and inferiorly implanted tubes.4–7 Late tube exposure is estimated to occur in 2.5–8.9% of patients and commonly more than 1 year postoperatively.4–7 “As I work in a tertiary eyecare center, I get these patients every month,” Dr. Razeghinejad said. “If you are in a private practice, you won’t see as many as I see and manage.” When tube exposure occurs, prompt surgical revision is highly recommended to prevent endophthalmitis, he added. Dr. Razeghinejad noted that he operated on a patient with a re-exposure who had intravitreal injection and tube revision by her surgeon for tube exposure and endophthalmitis 4 weeks prior. “She had cells in the anterior chamber and exudates around the intracameral portion of the tube,” he said. The retina colleagues recommended tube explantation because they thought the tube was infected. The cause of the tube exposure, he said, was anterior tube insertion, which was not addressed in the first tube revision. In the second revision surgery, Dr. Razeghinejad cut the anterior portion of the tube and used a tube extender and inserted it more posteriorly around 12 o’clock. A cornea patch graft was used. Planning and prevention Dr. Smith noted that tube exposure is generally easy to spot when patients come in for routine visits, and she stressed the importance of actively checking when patients come in. “Being constantly aware that this is possible is one of the important things as you follow patients who have had tube shunts,” she said. Dr. Smith also said she is careful to advise patients who get repeated retinal injections to remind the retinal surgeon about the placement of the tube. Just being alert to the location of the tube is important, she said. To try to plan for this and prevent it from occurring, Dr. Razeghinejad suggested inserting the tube at least 2 mm posterior to the limbus. He also said to have no tension on the conjunctiva when you close it; you may need to undermine the conjunctiva and have the loose conjunctiva covering the whole area of bare sclera before suturing. If you are pulling the conjunctiva toward the limbus with the aid of suture force, Dr. Razeghinejad said there is a good chance that you may get patch and tube exposure. Dr. Myers said that he has used patch grafts in primary surgery to prevent erosions. However, these often dissolve over time. “For those of us who switched to long intrascleral tunnels for tube insertions, it seems the erosions are less common with intrascleral tunnels without patch grafts,” he added, noting that there is not a lot of data to know for sure. “But I haven’t seen a case yet of an erosion in a patient with a long scleral tunnel, 5 mm or more, without a patch graft.” The switch to this approach has been more recent. “A lot of us switched to that when CMS stopped reimbursing the surgery center for patch grafts,” he said. “I think that was about 3 years ago, and since 'ZposWre oH pNate with partiaN eZtrWsion.
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