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The first minimally invasive glaucoma shunt was developed by AqueSys, which led to the company’s acquisition by Allergan in 2015. Not long after, the product was launched in Europe as the Xen transscleral gelatin stent.
The Xen stent is a 6-mm long hydrophilic gelatin stent, with an inner diameter of 45 micrometers.
It is inserted with a preloaded injector, through a corneal incision, and exits into the subconjunctival space to form a bleb. Usually, mitomycin C is injected prior to stent insertion.
The insertion can be performed as a standalone procedure or combined with cataract surgery.
In the United States, Xen is licensed as a treatment for refractory glaucoma in cases where previous glaucoma surgery may have failed or in cases that have become nonresponsive to maximum tolerated medical therapy.
In Europe, however, the stent was launched for use as a primary surgical intervention that may prevent or delay the need for trabeculectomy and that can be performed at the same time as cataract surgery.
Hari Jayaram, MD, PhD, of the Glaucoma Service at Moorfields Eye Hospital in London, recently presented the results of a study of 7 years of data on surgical experience at Moorfields.
The majority of the cases were of the second type mentioned above, as a primary intervention, which indicates that Xen is suited to primary open-angle glaucoma (POAG) when drops are not enough or previous medical treatments have failed.
The investigators performed a retrospective review of all ab-interno Xen procedures that had been performed at Moorfields.
In extracting the data, they paid special attention to the patient’s ethnic origin and primary underlying diagnosis, their IOP and medication history over the time of follow-up, whether or not bleb needling had been performed, and whether or not the patient required further glaucoma surgery.
They also looked at the incidence of complications, in particular hypotony and infection, as well as loss of vision.
Failure was determined using a generous composite outcome, including an IOP definition of less than 20% reduction of IOP from the highest recorded pressure in the patient’s medical record, either with or without the use of eye drops.
Outcomes measured included whether or not a patient was using drops, and failure also included reoperation for glaucoma, endophthalmitis, or loss of light perception vision. Importantly, the need for bleb needling was not included among the criteria for failure.
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The study looked at Xen insertions performed at Moorfields from May 2012 to June 2019. This included a total of 426 eyes from 375 patients.
Five percent of the patients had undergone prior surgery for glaucoma. Almost two-thirds of the patients had an underlying diagnosis of POAG, and about a quarter had an underlying diagnosis of either uveitic glaucoma or another form of secondary open-angle glaucoma.
There was a wide age range of patients receiving the stents, from 16 to 95 years, with a mean age of 67. The patient population was typical of the ethnic diversity seen in London, with around 44% of patients coming from nonwhite British ancestry.
Sixty percent of the cases were performed as standalone procedures and 40% were combined with cataract surgery. Mitomycin C was used almost universally. Some surgeons also used anti-VEGF treatments, and long-acting corticosteroid therapies.
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The graph at left shows the long-term outcomes, using the above-mentioned definition for failure. At 1 year, 64% of the procedures were found to be successful. This reduced to 41% after 4 years.
One interesting thing noted by the investigators is that almost a third of patients failed within the first postoperative year.
Comparing standalone to combined surgeries showed no significant difference in the survival curve of the 2 groups.
The researchers also looked at the impact of ethnicity. Patients of nonwhite British ancestry showed a trend in increase in late failure, but when viewed over the entire time course this did not reach statistical significance.
The authors believe this is in keeping with the understanding that there is a more aggressive wound healing response in these ethnic groups. However, when successful, and further surgery was not required, patients with the Xen achieved a mean IOP of around 15 mm Hg.
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There was a mean reduction in medication use from 3 drops prior to surgery to about 1.3 drops over long-term follow-up in patients classified as successes.
In terms of achieving drop independence, about 40% of patients who did not require further glaucoma surgery were drop free beyond a 2-year period.
Hypotony occurred in about 1 in 5 patients but responded well to conservative management.
There was only 1 case of cleft formation that required surgical intervention. Bleb needling was very common, with 26% of patients needing at least 1 bleb needling procedure within the first 3 months after surgery.
The need for further surgery was the cause of failure in around a third of patients. Over half of these were revision procedures, which tended to be necessary early on in the postoperative course with a median time to reoperation of 4 months.
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The overall infection rate was 1.6%. This is lower than that reported in the trabeculectomy group in the Tube Versus Trabeculectomy (TVT) Study (NCT00306852), which was 1.9%.
However, it is higher than for all ocular surgery at Moorfields performed in 2018 (0.02%) and higher than the infection rate (0.3%) derived from annual core trabeculectomy outcome audits performed at the hospital.
The authors concluded that when stent insertion is successful, and further revision surgery is not required, the Xen stent can effectively lower pressure and reduce the need for medications.
They noted, however, that surgeons should be aware of potentially high rates of reoperation and the long-term risks of bleb-related infection, and said that refining surgical technique and careful patient selection in the future may help optimize outcomes.
Read more by Steve Lenier
Hari Jayaram, MD, PhD
Dr Jayaram has no financial disclosurers related to this content.