Glaucoma is treated with medication, laser, and surgery. Until recently, the surgical options were limited and primarily consisted of filtration surgery with
trabeculectomy or drainage implant (i.e., Ahmed, Baerveldt, Molteno). The gold standard has been trabeculectomy with or without an antimetabolite (5-FU or mitomycin-C). However, a variety of new techniques are emerging that will expand our options for the surgical management of glaucoma. These have collectively been referred to as minimally invasive glaucoma surgery (MIGS).
The main advantage of MIGS is that these procedures are non-penetrating, so they are less invasive and safer. These alternative techniques are blebless, thus avoiding bleb-related complications which have been the major problem associated with trabeculectomy surgery, such as bleb-leak, shallow anterior chamber, hypotony, blebitis, and endophthalmitis. Infection is the most dreaded complication and can occur at any time even years after surgery.
The main limitation of MIGS, however, is that these procedures do not produce as large a pressure lowering effect as trabeculectomy does. In addition, the resulting effect is not as reliable as that achieved with traditional filtering procedures. Therefore, MIGS is generally reserved for patients with less advanced disease or used in combination with cataract surgery.
MIGS procedures can be classified as ab externo (outside in) or ab interno (inside out).
The ab externo surgeries include:
- Ex-PRESS glaucoma filtration device (Alcon): this 0.4 x 3 mm stainless steel mini-shunt drains aqueous fluid into the subconjunctival space and is used in conjunction with standard trabeculectomy surgery. It is placed under the scleral flap and into the anterior chamber so no sclerectomy or iridectomy is required. This makes the surgery safer and provides some resistance to flow. It also helps to standardize what has been a surgeon dependent procedure with variable results by making one step of the surgery constant—the size of the outflow hole (50 microns). Another advantage is that the Ex-PRESS shunt procedure provides faster visual recovery than traditional trabeculectomy surgery.
- Canaloplasty (iScience Interventional): the goal of this procedure is to enlarge Schlemm's canal. This is accomplished by passing a 9-0 or 10-0 prolene suture 360 degrees through Schlemm's canal with the aid of a microcatheter and viscoelastic to dilate the canal. The suture is tied tightly in order to keep the canal open. One drawback of this procedure is that it is technically challenging, and there is a risk of puncturing Descemet’s membrane.
- ECP (Endo Optiks): endolaser cyclophotocoagulation is used for selective ablation of the pigmented ciliary epithelium to reduce aqueous production. The procedure is performed under direct visualization with a video endoscope in order to control the precise placement of the laser applications. ECP is typically used to treat 360 degrees of the ciliary processes. It can be used in conjunction with cataract surgery for additional reduction in IOP. The procedure causes some inflammation so there is a potential increased risk of CME; however, this is uncommon with ECP. The other potential complication, hypotony, is rare. These complications are more commonly associated with TCP (transscleral cyclophotocoagulation).
The ab interno surgeries include:
- iStent trabecular micro-bypass (Glaukos): this small transtrabecular titanium stent drains aqueous fluid into Schlemm's canal. The device is placed through a clear corneal incision with the aid of a gonioscopy lens. Because it provides less IOP reduction than the Ex-PRESS shunt, some surgeons are investigating placement of more than one iStent to further lower pressure. This device is used for early to moderate glaucoma and can also be combined with cataract surgery.
- CyPass (Transcend Medical): this supraciliary microstent increases uveoscleral outflow. It is implanted through a clear corneal incision and can be combined with cataract surgery.
- Gold micro-shunt (SOLX): this is a 3 x 6 mm device that is less than 0.1 mm thick. It is placed into the supraciliary space through a 3 mm incision to increase uveoscleral outflow.
- Trabectome (NeoMedix): this is a thermal cautery device with irrigation and aspiration and a protective footplate. It is used to ablate a 2- to 4-clock hour segment of trabecular meshwork and Schlemm’s canal under direct visualization with a gonioscopy lens. This procedure is less traumatic and safer than trabeculectomy surgery. It also has the advantages of being quicker and technically easier to perform. The trabectome is inserted through a clear corneal incision and can be used in combination with cataract surgery. Like the other MIGS procedures, the main disadvantage of this technique is the limited effect on IOP reduction.
This variety of minimally invasive options for glaucoma surgery should allow for better customization of treatment to individual patients.