Minimally invasive glaucoma surgery (MIGS) refers to a diverse group of non-penetrating procedures that are safer and less invasive than traditional filtration surgeries (i.e., trabeculectomy and drainage implant devices).
The two approaches are bypassing the trabecular meshwork or accessing the suprachoroidal space. There are no blebs created with MIGS, therefore, these techniques do not suffer from the dreaded bleb-related complications of bleb-leak, hypotony, shallow anterior chamber, blebitis, and endophthalmitis, which may occur even years after penetrating filtration surgery.
The major limitation of MIGS is the more modest reduction in IOP as compared to traditional glaucoma surgery. Also, the IOP lowering effect is not as reliable as the response achievable with filtering procedures. Although the gold standard remains trabeculectomy with or without an antimetabolite (5-fluorouracil or mitomycin-C), MIGS procedures offer an excellent alternative for the surgical treatment of glaucoma, particularly in patients with mild to moderate disease. In addition, MIGS is often used in combination with cataract surgery, which is advantageous because it avoids a separate glaucoma procedure.
Glaucoma surgery is typically classified by the surgical approach: ab externo (outside in) or ab interno (inside out). MIGS techniques are varied and include both types of procedures.
Ab externo MIGS:
Ex-PRESS Glaucoma Filtration Devicefrom Alcon:
This mini glaucoma shunt is a 0.4 x 3 mm piece of stainless steel with a 50 micron or 200 micron lumen that is used in conjunction with trabeculectomy surgery to divert aqueous fluid into the subconjunctival space. Instead of creating a sclerectomy and iridectomy, the device is simply inserted into the anterior chamber under the scleral flap. Once in place, the Ex-PRESS shunt produces uniform filtration to more precisely regulate IOP. The surgery is safer and helps standardize results by causing a more predictable outcome. Patients also benefit from more rapid visual recovery and fewer postoperative visits than after traditional trabeculectomy surgery.
Canaloplasty from Ellex:
This procedure uses the iTrack 250A Canaloplasty Microcatheter to facilitate 360 degree catheterization and viscodilation of Schlemm’s canal and placement of a tensioning suture to enlarge the canal. The prolene suture is tied tightly to keep the canal open. The disadvantages of the technique are that it is technically challenging and there is a risk of perforating Descemet’s membrane.
Endolaser Cyclophotocoagulation from Endo Optiks:
ECP utilizes an 810 nm diode laser to decrease aqueous production by precisely and selectively ablating the pigmented ciliary epithelium under direct visualization with a 23 gauge video endoscope. The procedure usually involves a 270 to 360 degree treatment of the ciliary processes at the time of cataract surgery. There is an increased risk of CME owing to the associated inflammation, but this complication is rare as is hypotony, which often occurs after transscleral cyclophotocoagulation (TCP).
SOLX Gold Shunt from SOLX:
This is another supraciliary device used to increase uveoscleral outflow. The 24-karat gold shunt is composed of two leaflets joined vertically. It contains nine channels connecting the anterior and posterior openings, measures 5.2 mm long and 2.4-3.2 mm wide, and has a thickness of less than 0.1 mm. It is inserted through an external scleral incision so the anterior portion of the shunt lies in the anterior chamber, the body resides intrascleral, and the posterior portion is in the suprachoroidal space.
Ab interno MIGS:
iStent Trabecular Micro-Bypass Stent from Glaukos:
This minishunt is a small transtrabecular titanium stent that drains aqueous fluid into Schlemm’s canal. The device is implanted under direct visualization with a gonioprism at the conclusion of cataract surgery in patients with mild to moderate open angle glaucoma. However, some surgeons advocate inserting two devices to create a larger IOP reduction.
Hydrus Microstent from Ivantis:
This stent is an intracanalicular scaffold that dilates Schlemm’s canal for several clock hours in the nasal quadrant. It is 8 mm long and composed of an elastic biocompatible alloy called nitinol. The device is designed with a pointed tip, snorkel tail, fenestrated windows on the anterior surface, and is open on the posterior surface to increase aqueous outflow through the canal. Similar to the iStent, it is placed using a gonioscopy lens under direct visualization through a small corneal incision.
CyPass Micro-Stent from Transcend Medical:
This small, fenestrated, polyamide stent is inserted with a guide wire in a supraciliary location to improve uveoscleral outflow by essentially creating a controlled cyclodialysis. The device is 6.35 mm long and 0.51 mm in diameter. Like the aforementioned devices, it is introduced through a clear corneal incision and can be used in combination with cataract surgery.
Trabectome from NeoMedix:
This is a thermal cautery unit used to ablate a 2- to 4-clock hour portion of trabecular meshwork and Schlemm’s canal under direct visualization with a gonioprism. The device contains irrigation and aspiration functions as well as a protective footplate. It is utilized through a clear corneal incision and can be combined with cataract surgery. The major advantages of this procedure are that it is less traumatic and safer than trabeculectomy surgery. Another benefit is that it is faster and easier to perform.
The varied array of MIGS techniques offers surgeons many new options to customize glaucoma management on an individual basis for each patient. I am delighted that these new procedures have expanded our treatment armamentarium with safer alternatives.