Recently a new porcine gel stent (Xen45, Allergan) has become available to shunt aqueous humor from the anterior chamber to the subconjunctival space in patients with refractory glaucoma. Several years ago, we saw the availability of a trabecular microbypass stent (iStent, Glaukos), and earlier in 2016 the first supraciliary stent (Cypass, Alcon) became available. When new stents become available, clinicians must learn the technique, enhance the success rate, and determine which patients are most likely to respond. The subconjunctival stent is a hybrid procedure that blends microinvasive glaucoma surgical techniques with trabeculectomy. As such, a bleb is created by the procedure. The bleb, however (I call it a “xleb” for xen-bleb), may behave differently due to the standardized, limited amount of aqueous flow and bleb location. Ideally the xleb will be more posterior, given the scleral exit site of the stent 3 mm posterior to the limbus. As such, the question of xleb management arises. With standard trabeculectomy, bleb needlings to break scar tissue are commonplace. With the subconjunctival stent, questions immediately arise. Can the passage of a needle into the xleb cause damage the Xen stent? Should needle revision be avoided? How might we alter or enhance the technique?
In the January JAMA Ophthalmology issue, a technique is described for needle revision of a bleb (or xleb) after placement of a subconjunctival stent. The technique involves needle revision with mitomycin C and a bent 27-gauge needle with 2 unique features. First, viscoelastic is placed in the subconjunctival space to maintain the bleb. Second, the gel stent itself is intentionally amputated to allow the distal stent access to a new region of subconjunctival space. Clinical images provided with the article describing the technique demonstrate a healthy-appearing bleb/xleb several weeks after the procedure.
I spoke with Matt Schlenker, a co-author of the article, to further discuss his approach to managing the xleb. I was happy to hear that he frequently recommends that the patient employ direct ocular compression, which I have found also works, particularly when the xleb is only slightly elevated but rises when you compress the eye. He cautions to carefully examine the internal ostium for blockage from blood or fibrin prior to needling. Once the decision to needle is made, he recommends aiming for success. Pick a conjunctival entry site that will allow you to incise the scar tissue, knowing that a small-gauge needle entry site is unlikely to leak.
What other innovations will come along with new surgical implants? Hopefully many. What is important is that we share our ideas and outcomes and continue to push the era of microinvasive glaucoma surgery forward.