EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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86 EW GLAUCOMA February 2011 February 2012 New materials expand surgical options for glaucoma by Tony Realini, M.D., M.P.H. "One common issue with mito- mycin-augmented trabeculectomy is that the edges of the bleb can fibrose and form a so-called ring of steel that limits the size of the bleb," said Steven R. Sarkisian Jr., M.D., clini- cal associate professor of ophthal- mology, Dean McGee Eye Institute, University of Oklahoma College of Medicine, Oklahoma City. "Ologen guides fibroblasts to grow through the scaffolding so they don't create a ring of steel, resulting in a lower profile and more diffuse blebs. It offers an opportunity for wound modulation while avoiding the most dreaded complications of mitomycin-c." Ologen is available as a disc An example of a failed trabeculectomy. Surgeons are looking into augmenting the procedure with new materials in an effort to avoid common issues Source: Leon W. Herndon, M.D. Pig-derived material, amniotic membrane, and others are now used S ince its initial description over 40 years ago, the Cairns trabeculectomy has undergone numerous modifications to improve both its efficacy and safety in lower- ing IOP in eyes with glaucoma. The procedure remains imperfect, plagued with issues such as early and late bleb leaks predisposing to blebitis and endophthalmitis, as well as scarring and fibrosis leading to failure. At the 2011 annual meeting of the American Glaucoma Society in Dana Point, Calif., several sur- geons presented their novel meth- ods of performing trabeculectomy augmented with a variety of both familiar and new materials. Glaucoma continued from page 85 Grafts of 8-8.5 mm are suitable for patients with open angles, a deep chamber, and glaucoma controlled only with medication, said Dr. Ayyala. Patients with narrow angles or those with 360 degrees of periph- eral anterior synechiae and irido- corneal adhesions should have smaller grafts in the 6-7 mm range, depending on the size of the central cornea. "In patients with 360-degree PAS and shallow chambers, it is very easy to penetrate the iris with the air injection needle," he said. "Care should be taken not to inject air under the iris as it will induce papil- lary block." Short- and long-term results vary from person to person, said Dr. Lehrer, noting that he's had a num- ber of successes and a number of failures as well. "I had one patient who had two DSEKs that failed and went on to a full thickness corneal transplant and then did well," he said. "I think the problem that patient had was due to hypotony. If you can address hy- potony in a filtering patient prior to DSEK or during DSEK that may help the graft adhere better." EW Editors' note: Drs. Ayyala and Lehrer have no financial interests related to this article. Contact information Ayyala: rayyala@tulane.edu Lehrer: rlehrer@ohioeye.com Artificial extracellular matrix One key limitation of trabeculec- tomy is that a significant minority of procedures fails due to post-op scarring at the level of the conjuncti- val or Tenon's capsule. The utiliza- tion of antimetabolites such as 5-fluorouracil and mitomycin-c have significantly reduced the rate of fail- ure due to scarring, but this has come at a cost. Antimetabolite-aug- mented blebs tend to be more cystic and thin-walled and have a greater tendency to leak and predispose to blebitis and endophthalmitis. A new product may offer sur- geons a new option for the modula- tion of would healing. Ologen (Aeon Astron Corporation, Taipei City, Taiwan) is an artificial pig-derived extracellular matrix material com- posed of collagen matrix and colla- gen gel approved by the U.S. Food and Drug Administration for wound healing. measuring 12 mm in diameter and 1 mm thick. It is placed over the scle- ral flap and under Tenon's capsule at the completion of the filtration pro- cedure, just before wound closure. "Because the Ologen tampon- ades the scleral flap, you don't have to tie the flap sutures so tightly," said Dr. Sarkisian. "It's thin enough to provide visibility for laser suture lysis using the Hoskins lens [Ocular Instruments, Bellevue, Wash.] if necessary." The implant has not been evalu- ated in human glaucoma yet, he said, but a prospective clinical trial is ongoing. Amniotic membrane Amniotic membrane has been used for a number of ophthalmology ap- plications, including wound modu- lation after pterygium excision, non-healing corneal epithelial de- fects, and acute repair of caustic corneal burns. Derived from the in- nermost of the three-layered fetal membrane, amniotic membrane tis- sue exhibits several features that are attractive in the setting of conjuncti- val wound healing, including excel- lent epithelialization, a slow and low-grade healing response, and ef- fective integration with surrounding ocular tissues. "Amniotic membrane tissue may also be a useful adjunct in glaucoma filtering surgery," said Michael James Pro, M.D., glaucoma service, Wills Eye Hospital, Philadel- phia. "One application might be to use it at the time of trabeculectomy in high-risk eyes." These might in- clude eyes with significant ocular surface disease or a history of prior failed trabeculectomy, he said. Another potential role for amni- otic membrane tissue is in the repair of late-onset bleb leaks. "Bleb exci- sion and conjunctival advancement are the mainstay of surgical therapy for this problem," he said, "but this procedure can result in bleb thicken- ing and loss of intraocular pressure control." Replacing the bleb tissue with amniotic membrane can result in a slower, less exuberant healing process, he said. "But one does tend to get a cystic, avascular bleb as a result." He recommended reserving the use of amniotic membrane for eyes in which conjunctival advancement or even autografting are impractical or impossible. "In some eyes, such as those with cicatricial disease, incor- porating amniotic membrane may be an excellent solution when native conjunctiva isn't available." Tissue glue Wound closure is a fundamentally important step in glaucoma surgery. A watertight closure can make the difference between a smooth post-op course and a long, dark, rocky road continued on page 88