Clinical Investigation of New Glaucoma Procedures

Kateki Vinod; Steven J. Gedde

Disclosures

Curr Opin Ophthalmol. 2017;28(2):187-193. 

In This Article

Targeting the Subconjunctival Space

The subconjunctival space is the site of aqueous drainage in traditional glaucoma surgery. Newer procedures utilizing this pathway (XEN Gel Stent; AqueSys, Inc., Aliso Viejo, California, USA and InnFocus MicroShunt; InnFocus Inc., Miami, Florida, USA) resemble filtering surgery, but are designed to be less invasive and safer. Tube-like devices have been engineered with set lengths and inner luminal diameters that provide restriction to flow and attempt to minimize hypotony, in contrast to the variably-sized scleral flaps and sclerostomies involved in trabeculectomy.

Although both the XEN Gel Stent and InnFocus MicroShunt are designed to provide flow restriction, they may be subject to similar early hypotony-related and late bleb-associated complications as trabeculectomy, particularly with the use of intraoperative antifibrotics. Furthermore, the need for additional antifibrotic injections may complicate the postoperative course. Future studies will be critical to evaluate whether the degree of IOP-lowering is worth the risk of potential early and late complications. These new subconjunctival procedures merit direct comparison to trabeculectomy more so than Schlemm's canal-based and suprachoroidal techniques.

Xen Gel Stent

The XEN Gel Stent is an investigational 6 mm gelatinous tube that softens and conforms to tissue once hydrated. The device is inserted through a corneal incision using a preloaded 27 gauge needle inserter. An ab-interno scleral tunnel is made to access the subconjunctival space and a bleb is formed after device insertion. Multiple models have been developed with different inner lumen diameters (45, 63, and 140 microns) that provide restriction to aqueous outflow to minimize hypotony and its sequelae.

A prospective noncomparative pilot study[31] of 37 eyes evaluated two models of the XEN Gel Stent (XEN140 and XEN63) in combination with phacoemulsification. Mean IOP was reduced from 22.4 ± 4.2 mmHg using 2.5 ± 1.4 medications at baseline to 15.4 ± 3.0 mmHg on 0.9 ± 1.0 medications at 1 year. Complete success (IOP < 18 mmHg and >20% reduction from baseline without medication) was achieved in 47.1% of patients, and qualified success (IOP < 18 mmHg and >20% reduction from baseline) in 85.3%. Two (5%) patients with the XEN140 implant required anterior chamber reformation during the first postoperative week, but no patients experienced prolonged hypotony beyond the first postoperative month. Twelve (32%) patients required postoperative needling with antifibrotics. The contribution of phacoemulsification to IOP lowering was unclear given the absence of a control group. In a similar prospective trial, 49 eyes underwent XEN140 implantation alone, 22 (45%) of which had prior glaucoma surgery.[32] Mean IOP dropped from 23.1 ± 4.1 mmHg at baseline to 14.7 ± 3.7 mmHg at 1 year, and mean number of medications decreased from 3.0 to 1.3. Complete success was achieved in 40.0% and qualified success in 88.9% using the same definitions above. Four (9%) patients required anterior chamber reformation within the first postoperative week, and 21 (47%) patients required needling with antifibrotics. Neither of these studies used antifibrotics at the time of initial stent placement, but the use of mitomycin C during XEN implantation is currently under investigation.

InnFocus MicroShunt

The investigational InnFocus MicroShunt is an ab-externo, bleb-forming procedure that involves insertion of an 8.5 mm poly(styrene-block-isobutylene-block-styrene) tube with a 70 micron lumen through the limbus into the anterior chamber. This procedure requires dissection of a scleral pocket large enough to accommodate two fins on the tube that are designed to prevent anterior migration. Intraoperative antifibrotics are used as in trabeculectomy. Overall qualified success (IOP ≤ 14 mmHg and IOP reduction ≥20%) was 95% at 3 years in 23 patients who underwent microshunt placement with or without cataract surgery.[33] Mean IOP decreased from 23.8 ± 5.3 mmHg at baseline to 10.7 ± 3.5 mmHg at 3 years, and mean number of medications fell from 2.4 ± 0.9 to 0.7 ± 1.1. Complications included transient hypotony (13%) and choroidal effusion (8.7%), which resolved spontaneously.

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