Workup, Diagnosis and Treatment
Octopus visual fields showed dense inferior arcuate defects OU with evidence of progression OS (Figure 1). OCT of the retinal nerve fiber layer showed corresponding superior thinning OU. Given progression of his glaucoma in the left eye in the presence of maximally tolerated medical therapy, it was recommended that the patient have a surgical intervention to lower his IOP. He didn’t want to undergo a trabeculectomy due to the complications he experienced OD, including pain, redness and a lengthy recovery. Since he had a visually significant cataract, minimally-invasive glaucoma surgery options were considered in conjunction with cataract surgery, and the patient decided to proceed with cataract surgery combined with a XEN Gel Stent (Allergan).
The patient underwent an uncomplicated surgery, and at his one-month postoperative visit, his IOP OS was 14 mmHg, and he was taken off all glaucoma medications. At his three-month visit, the IOP was stable. At six months, however, the IOP in his left eye had increased to 23 mmHg, with notable fibrosis over the XEN Gel Stent. He was restarted on latanoprost and timolol OS. He subsequently underwent surgical XEN revision (Figure 2). At his most recent follow-up visits, the IOP was in the low teens, he was off all drops and had stable defects on visual field testing.
MIGS devices can be divided into: 1) trabecular, which increase outflow through Schlemm’s canal; 2) suprachoroidal, which improve uveoscleral outflow via a connection between the anterior chamber and the suprachoroidal space; and 3) subconjunctival, which allow for an alternative pathway of aqueous flow to the subconjunctival space.1,2 Multiple non-randomized studies show that MIGS devices have better safety profiles and faster recovery than traditional incisional glaucoma surgeries, likely due to reduced surgical trauma with minimal scleral and conjunctival dissection.3
The XEN Gel Stent is a subconjunctival MIGS device made with gelatin crosslinked with glutaraldehyde. The XEN has a length of 6 mm with an internal diameter of 45 µm and an outer diameter of 150 µm.4,5 Multiple prospective and retrospective studies have assessed outcomes in patients with XEN implants.2,6-9 The average IOP reduction after XEN placement ranges from 30 to 45 percent. Topical drop class reduction ranges from 85 to 95 percent, with 40 to 90 percent of patients off all drops.2,6-9 In our patient, the IOP reduction at postoperative month one was 33 percent, which is similar to the reported literature.
Common complications after XEN implantation include hypotony (9 to 35 percent), flat anterior chamber requiring refilling (5 to 10 percent), bleb needling (2 to 43 percent), and reoperation (3 to 15 percent).2,4,7-11 Most cases of hypotony occur early in the postoperative period and resolve spontaneously with conservative management. Other less-common complications include corneal edema, choroidal folds, choroidal detachment, and device extrusion, migration or obstruction.2,4,7-11 In our patient, XEN placement was complicated by fibrosis, likely leading to device obstruction, requiring surgical revision with a good eventual outcome. In comparison to other MIGS devices, including iStent and iStent Inject (Glaukos), Hydrus (Ivantis), InnFocus MicroShunt (Santen Pharmaceutical Company) and the recently withdrawn CyPass (Alcon), the XEN carries a comparable IOP lowering effect and topical drop reduction, with a slightly higher needling rate but comparable rate of reoperation.1,3,12-14 In comparison to trabeculectomy, XEN has a better side-effect profile, while approaching a similar IOP-lowering efficacy.15
In conclusion, MIGS devices have become an increasingly utilized alternative to traditional incisional glaucoma surgeries, especially in conjunction with cataract surgery or in the setting of glaucoma progression on maximum medical therapy. MIGS selection is key to achieving the desired target IOP, with disease severity and mechanism of glaucoma as two important factors. Although their safety profile is markedly better than trabeculectomy or tube shunt surgery, MIGS devices aren’t without complications, as demonstrated in our patient. Nevertheless, MIGS represents an exciting innovation in the field of glaucoma and a potential pathway towards safer, yet still effective, surgeries. REVIEW
The authors have no financial interest in any products discussed in the case.
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