New York -Five potential causes of failure of glaucoma filtration surgery include excessive subconjunctival fibrosis, tight scleral flap sutures, encapsulated bleb, occluded internal ostium, and intraocular obstruction, according to James C. Tsai, MD.
He elaborated on one of these causes-subconjunctival fibrosis-during the Glaucoma 2004 meeting.
"We would like to limit excessive bleb scarring following filtration surgery," said Dr. Tsai, associate professor of ophthalmology and director of the glaucoma division at Columbia University's Edward S. Harkness Eye Institute, New York. "If the surgeon is usinga limbus-based conjunctival flap, he or she should avoid making very small anterior conjunctival incisions, because these appear to incite more subconjunctival fibrosis. The surgeon should also avoid using large reactive sutures and manipulating the conjunctiva excessively."
When the first signs of a failing bleb appear, such as normal or high IOP, a thick and localized bleb, and prominent vascularization around the bleb, "ocular massage is a very useful technique early on," Dr. Tsai said. "I use a digital technique (or a cotton-tip applicator) to ensure a controlled release of fluid through the fistula."
Pharmacologic treatment An intensive course of topical corticosteroids is usually part of the pharmacologic treatment.
"In rare cases, the clinician may need to use a subconjunctival depot injection of steroids or systemic steroids, or consider postoperative supplementation of antimetabolite therapy (e.g., 5-fluorouracil injections) or tissue plasminogen activator use (for a clot around the fistula)," Dr. Tsai said.
In implementing antimetabolite therapy in the postoperative period, Dr. Tsai most commonly places a subconjunctival injection of 5 mg of 5-fluorouracil approximately 90° from the bleb site, using a 30-gauge needle. However, he defers placement of these injections if he observes large conjunctival wound leaks or significant corneal epithelial defects. A subconjunctival injection of low-dose mitomycin-C can also be used.
A low bleb and the appearance of an episcleral cap is an indication for use of laser suture lysis to increase bleb filtration.
"If I have a patient who has undergone a mitomycin-C-augmented trabeculectomy, I try to avoid performing suture lysis on the first several days following surgery," Dr. Tsai added. "Use of intraoperative mitomycin-C allows one to get a good effect from laser suture lysis even when performed months after filtration surgery."
For a 5-fluorouracil-augmented trabeculectomy, "I will try to perform suture lysis within the first month or so," Dr. Tsai said. "On the rare cases that I do not use any antimetabolite therapy at all, I will try to do laser suture lysis even earlier, certainly within the first 2 weeks. I would caution that only one suture should be cut per visit to prevent inadvertent excessive lowering of IOP."
Dr. Tsai usually performs laser suture lysis with an argon laser using the Hoskins or Ritch lens, with a spot size of 50 µm, energy of 400 to 800 mW, and duration between 0.05 and 0.10 seconds. Following the laser procedure, he often delivers a subconjunctival injection of 5-fluorouracil.
"Releasable sutures are certainly an attractive alternative when the surgeon has no ready access to a laser or the patient has thick Tenon's tissue," he said.
Dr. Tsai also noted that needling of the glaucoma bleb could be done for excision of dense fibrotic tissues to enhance filtration. Success is more probable if the bleb is elevated, but the procedure must often be repeated, and there are risks of infection and conjunctival leakage, he said. One woman he operated on developed an encapsulated filtration bleb months after receiving a mitomycin-C-augmented trabeculectomy.