MicroMT GLAUCOMA IMPLANT

 

The MicroMT is a novel membrane-tube (MT) type glaucoma shunt device developed by Ahn and colleagues in Korea.

The MicroMT consists of an expanded polytetrafluoroethylene (e-PTFE) membrane and a silicone tube with an intraluminal stent, which allows aqueous drainage from the anterior chamber through a lamellar scleral flap in a similar fashion as conventional trabeculectomy surgery. The intraluminal stent prevents excessive aqueous drainage and allows additional IOP reduction through retraction or removal of the stent.

The MicroMT consists of (1) a 2 × 2-mm area, 0.2 mm thick e-PTFE membrane, by which the tube is anchored to the scleral flap bed using a suture, and (2) a silicone microtube with an external diameter of 200 μm and an internal diameter of 100 μm, which is attached to the membrane using silicone adhesive. The tube is 6 mm long, and is trimmed during the operation.

The silicone tube has an intraluminal stent, which is a 7-0 nylon suture. The more the stent (suture) is pulled out of the silicone tube, the more is the aqueous outflow.

 

SURGICAL TECHNIQUE:

A fornix-based conjunctival incision is made, Tenon’s capsule is dissected, a partial-thickness lamellar scleral flap is formed, eyes are treated using either 0.02% or 0.04% mitomycin-C for 2–4 min, and a sclerostomy is performed into the anterior chamber using a 30-gauge needle.

The tube’s length is adjusted, and is placed in the anterior chamber; aqueous drainage is confirmed when droplets appeared at the end of the microtube. The MicroMT membrane is anchored to the scleral flap bed using a 10-0 nylon suture. The scleral flap is sufficiently closed to prevent exposure of the MicroMT, and the post-luminal part of the stent is fixed with a suture to restrict its movement. After the conjunctival incision is closed, the distal end of the stent is placed on the conjunctival surface and fixed using a 10-0 nylon suture.

During the early postoperative period (<4 weeks), if the amount of aqueous drainage through the tube needs to be increased, the post-luminal part of the stent, which is located on the conjunctival surface, is retracted using forceps under a slit-lamp biomicroscope in an outpatient clinic. To further reduce IOP in a stepwise fashion, all intraluminal stents are completely removed 4 weeks after surgery.

CLINICAL STUDY:

In a study reported by Ahn and colleagues, the MicroMT was implanted in 43 eyes of 43 subjects (11 female and 32 male).

The mean (SD) follow-up period after the surgery was 27.9 (13.7) months (range, 7–47 months). The mean (SD) IOP before the operation was 22.5 (6.9) mmHg. After the surgery, the mean IOP decreased to 14.8 (9.0) mmHg, 12.6 (4.8) mmHg, and 11.1 (3.6) mmHg at 1, 2 and 3 years, respectively, after the operation (34.2%, 44.0%, and 50.7% reduction, respectively, from baseline; P<0.01).

Complete removal of the stent 4 weeks after the operation reduced mean IOP from 17.9 (6.3) to 12.2 (4.9) mmHg (an additional 40.2% reduction, P<0.01).

The mean (SD) number of IOP-lowering medications decreased from a preoperative value of 2.6 (0.6) to 0.5 (0.9), 0.5 (0.8) and 0.4 (0.8) at 1, 2 and 3 years, respectively, after the operation (P0.05; Table 2). The cumulative survival rate (standard error) was 89.5% (5%) 3 years after the surgery (Fig. 4). Failure was observed in four eyes at 7, 9, 10, and 20 months after the operation.

When visual acuity was compared between before and after the surgery, no significant change was observed at any of the postoperative visits (P>0.05).

The only observed complication was conjunctival wound leakage, which was found in one (2.3%) eye with avascular bleb 7 months after the operation; this was successfully resolved by conjunctival suturing.

WEBLINK: https://onlinelibrary.wiley.com/doi/10.1111/ceo.12772