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Studies of aqueous shunts for glaucoma failed to demonstrate consistent advantages over standard surgery, authors of a systematic review concluded.

"Most surgeons in the USA reserve aqueous shunts until one or more standard procedures have failed, and controversy persists regarding when aqueous shunts should be used in the sequence of glaucoma surgeries as well of the effectiveness of different aqueous shunts," Victoria Tseng, MD, PhD, of UCLA, and colleagues wrote in the . "[And we found that] information was insufficient to conclude whether there are differences between aqueous shunts and trabeculectomy for glaucoma treatment."

The analysis comprised 27 randomized controlled trials involving a total of 2,099 patients with mixed diagnoses treated with a variety of procedures or shunts. The authors compared the safety and efficacy of aqueous shunts versus trabeculectomy for lowering intraocular pressure (IOP).

Four trials compared an aqueous shunt (Ahmed or Baerveldt) with trabeculectomy and demonstrated no clear difference in IOP at 1 year. Two additional studies compared the Ahmed and Baerveldt implants and showed that the mean IOP was 2.60 mmHg higher with the Ahmed device (95% CI 1.58 to 3.62).

A comparison of the Ahmed and Molteno implants showed a higher mean IOP at 2 years among patients who had received the Ahmed implant (1.64 mmHg, 95% CI 0.875 to 2.43 mmHg). Two studies comparing the double-plate Molteno implant and Schocket shunt showed a 2.50 mmHg lower mean IOP at 6 months with the Molteno implant (95% CI -4.60 to -0.40 mmHg).

The remaining 18 trials evaluated modifications to aqueous shunts, including 14 trials of Ahmed implants. Collectively, the trials showed a few differences. Specifically, the Baerveldt and Molteno implants were associated with lower mean IOPs and less need for additional antiglaucoma medications as compared with the Ahmed implant. The evidence also suggested that the Molteno implant may be superior to the Schocket implant. Overall, the level of evidence supporting various modifications to aqueous shunts remained inconclusive, the authors said.

The review identified a possible benefit of early initiation of aqueous suppression at lower IOP levels after Ahmed valve placement for more effective long-term IOP control. The authors found that patients with neovascular glaucoma may achieve long-term IOP control with adjunctive intravitreal anti-VEGF therapy, in addition to aqueous shunt placement.

"The role of aqueous shunts in the surgical management of glaucoma is a complicated and controversial subject," Tseng and colleagues concluded. "With the increasing use of aqueous shunts worldwide, further adequately powered trials that compare aqueous shunts to each other and to other types of surgical interventions for glaucoma are needed for improved patient care."

Asked to comment on the review, Andrew Iwach MD, clinical spokesman for the American Academy of Ophthalmology, noted that aqueous shunts and glaucoma drainage devices are increasingly being used to treat the disease, as opposed to surgery, a development that helped provide a rationale for the systematic review.

"Technically, both of these approaches are delicate surgeries," he told 麻豆传媒. With trabeculectomy, ophthalmologists weaken part of the eye wall to let fluid flow through, and when they do this, "we create a small blister area we call a bleb, and that's what keeps the pressure down."

However, blebs are a potential source for trauma or infection over time, an inherent risk associated with the "gold standard" glaucoma surgery. Implants or glaucoma drainage devices take advantage of the fact that there is a space between the eye muscle where ophthalmologists can suture in a plate and then tunnel a tube into the eye.

"Even done perfectly, there is a risk that some patients will develop double vision, because of the eye muscle involved, and this can be quite symptomatic," added Iwach, who is executive director of the Glaucoma Center of San Francisco.

Given that neither approach is perfect, ophthalmologists should individualize treatment to individual patient and clinical characteristics, he said. "Patients are living longer now, and if we can find solutions that reduce these bleb-related complications, that could influence us in that direction."

Recent developments in laser technology can complement some of the glaucoma drainage devices used, and an emerging field of minimally invasive surgery can be directed towards the treatment of glaucoma as well.

"Early on, many patients with glaucoma actually don't have any symptoms," Iwach said. "So we are looking for ways to help glaucoma patients see through the long-run while minimizing the impact [of our intervention] in the short-run. Individually, these advances are shifting how we approach all of this."

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