Open angle glaucoma (OAG) is a disease affecting an estimated 2.8 million people in the United States as of 2010, accounting for an approximate cost of $1.5 billion per year. Initial therapy for OAG typically consists of eye pressure reducing medications that can aid in decreasing aqueous humor production or increasing aqueous humor outflow. Additionally, laser trabeculoplasty is another option for the treatment of early, mild, open angle glaucoma, though long-term efficacy has been found to be similar to medical management. Traditionally, pharmacologic and laser treatment have been the mainstays of therapy until the disease progresses to a stage that warrants the need for surgical trabeculectomy. This procedure is typically reserved for those with moderate to advanced cases of glaucoma due to the invasiveness of the procedure and possible complications. While there had previously been limited surgical options for patients with mild-moderate glaucoma, developing micro invasive glaucoma surgery (MIGS) procedures are creating new options for those who do not meet the criteria for surgical trabeculectomy. These procedures have a higher safety profile with fewer complications and a more rapid recovery time than other invasive techniques. They have been shown to be effective in decreasing intra-ocular pressure (IOP) as well as a patient’s need for medications, which is important given a typically low compliance rate for medication adherence.
All patients should have a pre-operative comprehensive eye exam including gonioscopy and a detailed medical history. Patients that are candidates for microinvasive glaucoma surgery are:
- Patients with mild-moderate glaucoma
- Primary open-angle glaucoma, pseudoexfoliation glaucoma, or pigmentary dispersion glaucoma
- Glaucoma is uncontrolled with maximum pharmacologic treatment or there are barriers preventing adequate medication dosing
- Age greater than 18
- Patients with clinically significant cataract, as surgery may be performed simultaneously.
Relative contraindications for this procedure may include angle-closure glaucoma, secondary glaucoma moderate-advanced glaucoma, previous glaucoma surgery, or severely uncontrolled IOP. Other considerations include patients with previous refractive procedures (LASIK or RK) as well as monocular patients.
MIGS Procedures available
A) Trabecular Meshwork Bypass
- Trabectome: Trabectome is a surgical system developed by NeoMedix (Tustin, CA). The system works by removing a strip of trabecular meshwork and the inner wall of Schlemm’s canal in order to create a path for the drainage of aqueous humor thus reducing eye pressure.
- Kahook Dual Blade: Goniotomy, such as that performed with the Kahook Dual Blade (KDB) is a minimally invasive surgical option for glaucoma. The procedure does not violate the scleral wall and is not associated with a bleb. By removing a section of trabecular tissue, the KDB gives aqueous direct access to the collector channels and the distal outflow system.
- OMNI: The OMNI Glaucoma Treatment System is the only device that combines two well-established micro-invasive glaucoma surgery (MIGS) procedures into one using a single device and single clear corneal incision. OMNI treats all three points of resistance: the trabecular meshwork, Schlemm’s Canal and the distal collector channels to reduce IOP. It viscodilates up to 360° of Schlemm’s canal and unroofs up to 360° of the trabecular meshwork.
- iStent and iStent inject: The iStent Trabecular Micro-Bypass Stent (Glaukos, Laguna Hills, CA) received FDA approval in 2012. The device is a heparin-coated, non-ferromagnetic titanium (MRI safe) stent with a snorkel shape to facilitate implantation. The device is placed using a single-use, sterile inserter through a 1.5mm corneal incision. The applicator is inserted into the anterior chamber and across the nasal angle. The pointed tip allows penetration of the trabecular meshwork and insertion into Schlemm’s canal and three retention arches ensure that the device will be held in place. The iStent itself is the smallest FDA approved device.
- Hydrus stent: This microstent is made from a super-elastic, biocompatible, nickel-titanium alloy and is MRI safe. The “intracanalicular scaffold” is inserted into Schlemm’s canal to maintain patency and establish outflow. The procedure can be performed in conjunction with cataract surgery and uses the same corneal incision.
- Gonioscopy assisted transluminal trabeculotomy
B) SupraChoroidal Shunt
- CyPass MicroStent: Overall, the device has shown in initial trials that there can be a significant decrease in number of medications used as well as a significant decrease in uncontrolled IOP or maintenance of a controlled IOP. The device is currently on a recall hold due to possible corneal cell loss several years after implantation.
C) Reducing Aqueous Production
- Endocyclophotocoagulation (ECP): ECP is an exciting development in the management of many types of glaucoma including the more common open-angle glaucoma and narrow-angle glaucoma. ECP is performed on an outpatient basis. In this procedure, the ciliary body of the eye, which creates fluid, is treated with a laser. This reduces fluid production that in turn, reduces intra-ocular pressure. The ciliary body is a small gland running around the circumference of the eye located behind the iris.
D) Subconjunctival filtration
- XEN gel stent: The implant itself is made out of a soft, collagen-derived, gelatin that is known to be non-inflammatory. The goal of implantation is to create an aqueous humor outflow path from the anterior chamber to the subconjunctival space creating a bleb. The implant is injected through a small corneal incision with the use of an inserter similar to those used for IOLs. Similar to other implants, it can be performed in conjunction with cataract surgery. This device is currently on a recall hold due to trace amounts of residual polishing compounds on some lots of the device.
E) Gonioscopy Assisted Transluminal Trabeculotomy (GATT): Under the guidance of a gonioscopy lens, a goniotomy is made in the nasal trabecular meshwork which serves as the entry point for the iTrack microcatheter. This surgical technique lowers IOP by cleaving the trabecular meshwork, thereby improving aqueous outflow through the normal conventional pathway.
Conclusion: In patients with mild-moderate glaucoma with an IOP that has been unable to be controlled by medications or who have poor medication compliance, micro invasive glaucoma surgery appears to be a viable option. Clinical trials have shown there to be a significant decrease in IOP over periods of up to 24 months along with a significant decrease in medication usage. The procedure has maintained a high safety profile with minimal adverse effects. While the Trabectome and iStent are currently the only FDA approved devices, there are multiple new devices pending. Micro invasive glaucoma surgery can provide a method of treatment for glaucoma patients that decreases reliance on medications without the safety risks of more invasive procedures.