XEN Implant, A Minimally Invasive Glaucoma Surgery (MIGS)
One of the new and exciting prospects in the treatment of glaucoma is called MIGS, or Minimally Invasive Glaucoma Surgeries. These procedures are exciting from a patient’s perspective because they are generally safer with quicker recovery times.
Before discussing specific MIGS procedures, it would be helpful to define what constitutes “MIGS.” There are quite a few definitions of MIGS, but the American Glaucoma Society, which is the largest society of glaucoma specialists in the United States, provides the following working definition:
- IOP, or intraocular pressure, should be lowered by improving outflow of eye fluid. This is the same mechanism used by traditional glaucoma surgeries, such as trabeculectomy or tube shunt surgeries.
- The device or procedure can either be approached from inside the eye (ab-interno) or outside the eye (ab-externo). As an example, both trabeculectomy and tube shunt procedures are performed from outside the eye, or an ab-externo approach. MIGS procedures using an approach from inside of the eye are described below in the iStent and Trabectome sections.
- There should be limited surgical manipulation of the sclera, which is the thick white wall of the eye. Trabeculectomy involves quite a bit of extensive cutting of the sclera, and that includes trabeculectomy modified with the Ex-PRESS shunt surgeries.
- MIGS should have little manipulation of the conjunctiva, which is the transparent outermost layer of the eye. By contrast, non-MIGS procedures, such as trabeculectomy and tube shunt procedures involve extensive cutting of the conjunctiva.
In meeting these criteria, MIGS procedures do not preclude the possibility of future, more traditional surgical approaches, such as trabeculectomy or tube shunt surgery.
There have been a plethora of abstracts, presentations, papers in recent years detailing the use of MIGS procedures. However, there is still a lack of consensus, even among clinical trials, as to what constitutes a MIGS device, which patients are most appropriately suited for these procedures, and what constitutes surgical success. The purpose of this article is not to provide an exhaustive or comprehensive list and details about all of the FDA approved and not yet approved MIGS procedures that are under development, but to give patients an overview of the MIGS procedures and some questions you will want to ask your ophthalmologist to find out if a MIGS procedure is right for you.
Overall, MIGS procedures have been touted as safer than our traditional trabeculectomy or tube shunt surgeries. This is because they do not have some of the associated complications from trabeculectomy and tube shunt procedures, such as low eye pressure (hypotony) and bleb infection. However, doctors do not yet have long-term safety or effectiveness data. Currently, there are also no randomized clinical trials comparing MIGS procedures to the “gold standard” procedure of trabeculectomy.
Shorter Surgery Time
Many of the MIGS procedures involve implantation of small devices. MIGS procedures are generally faster than trabeculectomy and tube shunt surgeries, and shortened surgical time can be very important for the safety of the patient. Many MIGS procedures are combined with cataract surgery, adding a short amount of time to the total surgical procedure. This is an important point to understand as well, since many clinical trials will compare a MIGS procedure combined with cataract surgery to cataract surgery alone.
Lowering of Eye Pressure
Lastly, an important point is that the majority of MIGS procedures are safer than trabeculectomy, but they are also not as effective in lowering eye pressure. The eye pressure in the majority of MIGS clinical trials is typically in the mid-teens range (approximately 15). Many ophthalmologists do not think MIGS procedures are appropriate for patients who have advanced glaucoma and need much lower eye pressures.
XEN Gel Implant
The current approach in the management of patients with glaucoma begins with laser trabeculoplasty followed by medications, and then either a trabeculectomy or a glaucoma drainage device. Both are highly effective, yet invasive and complication-prone solutions.
Traditional trabeculectomy and tube shunt procedures require substantial dissection of the ocular tissues, and have a relatively high complication rate (up to 50% at one year). Unfortunately, these procedures are not only invasive, but also have a high degree of variability that can lead to too little or too much intraocular pressure reduction (IOP). Despite these high complication rates and variability, these procedures are still the most common glaucoma surgeries performed globally due to the need for significant efficacy.
Worldwide, doctors accept that the subconjunctival outflow pathway delivers the greatest IOP reduction because it has been proven in millions of cases during 50+ years of usage. AqueSys has developed a new technology that is designed to have similar efficacy as the invasive gold standard procedures yet through a standardized minimally invasive procedure that has the potential to significantly lower traditional complication rates.
A minimally invasive approach to the gold standard mechanism of action for the treatment of glaucoma
The XEN Gel Stent is made of a permanent, soft, collagen-derived, gelatin. Upon implantation, it creates a gentle, diffuse outflow of aqueous from the anterior chamber into the non-dissected tissue of the subconjunctival space. The AqueSys gelatin is well accepted by the human body, and is non-inflammatory. The pliability and softness allows it to conform to the ocular tissue, which may be shown to minimize many of the issues seen with synthetic materials (e.g., migration, erosion, corneal endothelial damage).
The 6mm XEN implant positioned next to an Ahmed Glaucoma Valve (New World Medical, Inc.)
Anterior segment OCT image shows the soft XEN implant conforming to tissue in a human eye
The XEN Gel Stent is 6mm long and about the width of a human hair. It is injected through a small self-sealing corneal incision using a simple, preloaded IOL-like injector.
XEN Injector, showing implant, needle and sleeve
Potential benefits of the XEN Gel Stent include:
- Significant and sustained reduction of IOP through the globally accepted and well-studied subconjunctival outflow pathway
- Minimally invasive subconjunctival approach bypasses all potential aqueous outflow obstructions
- Soft gelatin material minimizes complications related to synthetic materials
- Significant ocular tissue available after the procedure, leaving all other treatment options available for the patient’s future care
The AqueSys XEN Gel Stent has Health Canada approval and CE mark internationally, and is intended to reduce intraocular pressure in patients with primary open angle glaucoma where previous medical treatments have failed.
In the United States, the XEN Gel Stent is an investigational device, which means that it has not been approved by the US Food and Drug Administration (FDA). The company is currently enrolling subjects under an approved IDE for its first indication in the United States.
Dr. Youssef started implanting the XEN implants January 2017 at the PVSC.