Complications associated with minimally invasive glaucoma surgeries (MIGS), are infrequent and, for the most part, transient.1 However, they can occur with any of the available devices on the market. In the case that a patient is unsatisfied or experiences lasting deleterious effects, ophthalmologists have the skills to right the course.

Ophthalmology Advisor asked 2 experts in glaucoma surgery to offer their guidance in the postoperative management of patients who have undergone a MIGS procedure and may be experiencing complications. Here, Noureen Khan, MD, of Northern Virginia Ophthalmology Associates, P.C., and Monisha Vora, MD, of Wills Eye Hospital, discusses how to recognize and treat those patients. 

1. MIGS implantations are notably safe, but no procedure or medical device is without complications. What is the likelihood a patient will experience any complications at all and what kind of preoperative signs might indicate a patient is more likely than others to experience one? Do you have any advice regarding MIGS patient selection?

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Monisha Vora, MD: MIGS is traditionally well suited for patients who have mild to moderate amounts of open-angle glaucoma, and are typically on 1 or 2 glaucoma medications.

Both primary and secondary open-angle glaucomas are indicated for MIGS. In particular, pseudoexfoliation or pigment dispersion glaucoma respond well to trabecular meshwork (TM) bypass and goniotomy/trabeculotomy procedures.2  

Those with advanced disease are less well-suited, as it is not likely that MIGS alone can lower the intraocular pressure (IOP) to an adequate level to prevent optic nerve damage and progression of disease. Of course, there is debate in the ophthalmic community on the efficacy of certain MIGS over others and some surgeons will utilize specific MIGS for more advanced glaucoma. 

The lens status of the patient is an important consideration when choosing which MIGS device to use.  Most of the MIGS devices on the market require concomitant cataract surgery, and so phakic patients with mild to moderate amounts of glaucoma tend to be the most ideal candidates for surgery.

During preoperative evaluation, gonioscopy of the angle to ensure that the angle is free from any pathology (such as synechiae, neovascularization, prior hardware) and is open wide enough to allow for adequate intraoperative visualization is imperative. Without the typical en face view of the TM, MIGS is much more difficult. It is important to remember that the risk of procedure should not exceed the risk of the disease. For patients with narrow-angle glaucoma, MIGS is limited to goniosynechialysis, rather than implant-based procedures.

Noureen Khan, MD: 

In general, MIGS are designed as first-line therapy for mild to moderate open-angle glaucoma patients to aid in pressure reduction. Just as choosing the ideal patient is important, it is equally essential to identify which patients may be poor candidates for MIGS procedures. This is a difficult task, because MIGS have so many benefits with their atraumatic, low complication rate profile.

From a patient selection standpoint, be cautious with any patient who wants only 1 glaucoma surgery. The devices to make IOP reduction attainable, but the effect is no comparison to the amount of IOP reduction obtained with bread-and-butter glaucoma surgeries, such as trabeculectomy or tube shunts. However, the complication risks with MIGS are much lower.2 I have found that patients are typically more likely to try the least invasive, less risky option even if it may require a second surgery in the future.

Additional candidates to attentively select include rapidly progressing, high-IOP, severe-disease patients. This is a hot button topic as there are always exceptions, but likely if a patient had advanced disease the amount of pressure reduction obtained from a single MIGS procedure may not be sufficient to halt glaucomatous vision loss. There is an argument to offer multiple combined MIGS; however, insurance does not cover off-label use that trickles down into an out-of-pocket expense for the patient. Additionally, multiple MIGS will increase the complication risks and, if there is advanced disease, the patient needs a long-standing procedure that will maintain long-term IOP reduction.

Exam wise, it is imperative to perform gonioscopy to distinguish if the patient is open, narrow, or closed-angle to allow for visualization of clearly delineated angle structures where MIGS can be performed. If there is any synechiae, neovascularization, or previous MIGS hardware implanted, this will limit which MIGS the surgeon can choose, and the options for sites to implant another device.

2. While the rate is low, what, specifically, are the likely complications that patients may develop after surgery?

Dr Khan:

Complications associated with MIGS are typically infrequent and temporary. The more common expected complications for iStent/iStent Inject (Glaukos), goniotomy with Kahook Dual Blade (New World Medical) or Trabectome (NeoMedix) are heme reflux leading to hyphema.3 Minimal heme is expected and is actually a good sign because this indicates that blood is refluxing through the device or from the cut edges of the TM and Schlemms, confirming appropriate positioning. However significant heme reflux or recurrent hyphema can be a sign of angle structure trauma or cyclodialysis or iridodialysis. In this situation, although rare, the device may need to be removed.1

Other common complications are IOP spike and formation of peripheral anterior synechia.1,3 IOP spikes may result from retained viscoelastic, iritis, herpetic flare, or chronic inflammation caused by implant malposition. Inflammation can be managed with steroid drops, glaucoma drops, or an A/C tap until removal is possible, if necessary. Uncontrolled chronic inflammation may result in PAS forming over the lumen causing failure of the implant.

Less common complications include corneal injury, including Descemet’s tears and malposition of implant resulting in obstruction or displacement.1 Obstruction can occur if the lumen is not placed parallel to the TM. YAG laser can be attempted at the tip of the lumen to open flow. Complete displacement is rare but has been reported. If displacement is causing cornea decompensating then the implant must be removed immediately.4

More severe, but rare complications are the creation of iridodialysis, cyclodialysis or complete iris disinsertion 360 resulting in an 8-ball hyphema.5 These risks are rare but I have seen them personally during my fellowship training. If a patient is in deep sedation, I wake up my patient to minimize sudden movement and, conversely, if the patient is moving significantly either hold on implanting any MIGS or ask for more sedation from your anesthesia provider.

Dr Vora: Most angle-based MIGS have similar complications. Trabeculotomy-type procedures, such as OMNI (Sight Sciences) and GATT (gonioscopy-assisted transluminal trabeculotomy), can lead to hyphema, iridodialysis, cyclodialysis, and partial goniosynechiae.5 Of course, this can cause IOP to become higher or lower than desired, and lead to potentially the need for additional glaucoma surgery. 

Then, there are the “out-of-the-box” MIGS surgeries, including the Xen gel stent and endocyclophotocoagulation, or ECP. Their complications are a bit more significant as these procedures are straddling the border between minimally and maximally invasive procedures such as traditional trabeculectomy and tube shunt surgery.

The Xen gel stent (Allergan) is a hydrophilic 6 mm porcine-derived tube placed ab-internally to create a subconjunctival bleb. Many surgeons consider Xen to be a MIGS-plus procedure due to the bleb formation, which comes with increased risk of complications compared with other MIGS. Xen is FDA approved for insertion in patients with refractory glaucoma as a standalone procedure or during cataract surgery. Reported complications with the Xen gel stent include malignant glaucoma, conjunctival wound leak, hyphema, vitreous hemorrhage, hypotony maculopathy, choroidal effusion, stent obstruction, exposed stent, and dellen formation.1 

Endocyclophotocoagulation (ECP, BVI Medical) reduces aqueous outflow and is the only MIGS with indications in neovascular and angle-closure glaucoma. Because ECP directly treats the ciliary processes, some surgeons feel it is less traumatic than transscleral cyclophotocoagulation (CPC). ECP can be performed with or without cataract extraction; however, it is better suited for pseudophakic eyes or during cataract extraction because the energy applied to the eye may induce cataract development. Possible complications include inflammation, cystoid macular edema, cataract development, hypotony, and phthisis bulbi.  These complications can be reduced as they are dose-dependent.3      

3. Acknowledging that different devices require different implantation techniques, how can you advise ophthalmic surgeons to perform the initial implantation in a way that helps avoid these complications?

Dr Vora: My tips for successful MIGS implantation start with a central theme: location, location, location! If you are not anatomically aligned with where the MIGS should be happening, you will cause more harm to the patient than good. The view is everything. 

To ensure you have a good view of the angle, first and foremost, make sure you have chosen the right type of patient. A patient with a nice, wide-open angle with minimal pathology, preferably visibly pigmented TM will make it easy to perform MIGS. I prefer to perform all my MIGS (except for Trabectome, MicroSurgical Technology) after cataract surgery because the angle is automatically wider. Some surgeons will advocate performing MIGS at the beginning of phacoemulsification because the cornea is likely to be clearer. 

When I teach MIGS to trainees, I often have them stain the TM with trypan blue. This further enhances the pigmentation and therefore improves the view. It creates what I like to call a “landing strip” for the surgeon.

Another tip is to have plenty of viscoelastic at the ready. When performing MIGS for the first time, it is common to place extra pressure with the non-dominant hand and squeeze out the viscoelastic that is needed to keep the eye, and angle, inflated. If the eye feels soft, come out of it and refill. This will clear your view of potential corneal striae and any heme that could impede your view.