Advances in treatment for primary open-angle glaucoma are reducing the use of trabeculectomy as first-line treatment for the disease worldwide.
"We are seeing greater use of [selective laser trabeculoplasty (SLT)], tube-shunt procedures, and other non-penetrating treatments as first-line treatment for glaucoma in earlier stages," reported Derek Cunningham, OD, director of optometry at Dell Laser Consultants, Austin, TX. "In some patients these approaches are effective in arresting progression sufficiently to avoid major surgery."
In his experience, Dr. Cunningham prefers SLT to medication to avoid the many side effects associated with drops. SLT uses selective photothermalysis to target intracellular melanin granules, which activate the pigmented cells while preserving surrounding normal tissue. Activated cells release cytokines that trigger a targeted macrophage response to the trabecular meshwork cells. The macrophages reactivate the meshwork, thereby enhancing aqueous outflow and lowering intraocular pressure (IOP).
Among the non-laser therapeutic approaches, Dr. Cunningham considers tube-plate drainage systems the most promising for management of advanced glaucoma. In this procedure, the tube shunts aqueous to a plate that acts as a point of fibrous encapsulation, forming a reservoir with an overlying filtration bleb. The potency of the fistula is mechanically maintained. Channeling off excess fluid reduces IOP, often to near-normal levels.
Shunts success rate
"Shunt surgery has a high success rate and a low complication rate," he said. "Although this intervention tends to be more expensive than SLT, it may have a role in as an alternative to trabeculectomy."
Shunts are gaining acceptance among glaucoma surgeons and patients, Dr. Cunningham added. Drainage devices originally were limited to patients with a failed trabeculectomy or secondary glaucoma. As technology has improved and evidence for the long-term success of drainage devices has been published, the number of tube-shunt procedures is growing each year.
Success rates vary between 50% and 80%, depending on what tube is being used and the diagnosis. Best results are obtained in patients with primary open-angle glaucoma and angle-closure glaucoma. Tubes can successfully reduce IOP from the 30 mm Hg to 50 mm Hg range to the low teens, he said. "Consequently, we are starting to see tube-shunts used more often as first-line treatment of advanced disease," he said.
This acceptance has led to the development and testing of several new drainage devices, such as collagen implants that are smaller or can be placed in a non-penetrating procedure.
Meanwhile, trabeculectomy remains the gold standard for treatment of end-stage primary, open-angle glaucoma.
Debate over trabeculectomy
"Unfortunately, 30 years after its introduction, trabeculectomy still is associated with a significant risk of complications," Dr. Cunningham noted. "The procedure's side effect profile means that these patients require a lot of postoperative time for wound care."
In the landmark Tube versus Trabeculectomy Study, both techniques resulted in comparable IOPs after 3 years. Trabeculectomy had a higher complication rate (57% versus 34%). Tubes required more adjunctive medical therapy, but trabeculectomy was twice as likely to fail.
"Trabeculectomy in the United States traditionally is reserved for the patient who has failed medical treatment, defined as a patient using drops two to three times a day and still losing vision," Dr. Cunningham said.
Several recent studies have suggested that earlier operation not only reduces side effects but also is associated with lower costs. However, attention in the United Sates has been focused more on developing treatment alternatives that have equal efficacy with fewer side effects, he said.
"We still lack a good understating of the disease process. Our limited knowledge of what causes glaucoma, and how and why it progresses, impacts the ability to advance treatment," Dr. Cunninghamsaid.
The bottom line, he noted, is that "we haven't seen significant progress in treatment in 30 years. We need to move the field ahead if we are going to do a better job in preventing vision loss from glaucoma."