In recent years, many cataract and anterior segment surgeons have joined the minimally invasive glaucoma surgery (MIGS) revolution and have adopted various MIGS procedures into their surgical armamentarium. But, as MIGS technology experiences rapid growth, we face a “paradox of choice” in this sphere. We have more surgical options for our patients, but we must consider many preoperative, intraoperative and postoperative factors to optimize surgical strategies and choose the best option for each patient. A new MIGS device or procedure is seemingly added (or retracted) every day, requiring MIGS surgeons to constantly be up to date with current technologies and recommendations.

Before I continue, I must make a small confession: I am not a glaucoma fellowship–trained surgeon; nor, as the saying goes, do I play one on TV. As a cornea fellowship-trained anterior segment surgeon with a vibrant cataract surgery practice, I, like many of my colleagues, have enthusiastically adopted MIGS procedures into my surgical practice over the past few years.

The advice that follows, therefore, is a summary of what I have learned during this time, including tips for patient and procedure selection as well as advice on when to refer to a glaucoma specialist.

GONIOSCOPY’S ROLE IN SELECTION

For many non-glaucoma specialists, in-office gonioscopy is not commonly employed in practice. Given that many MIGS procedures involve complex bimanual maneuvers in the anterior chamber angle, a thorough and detailed preoperative examination with slit-lamp gonioscopy is an essential skill for all of us to brush up on. Gonioscopy allows you to not only differentiate between primary open-angle glaucoma (POAG) and narrow-angle glaucoma (and its variants) but is also crucial in the decision-making process, which includes whether a MIGS procedure(s) may be appropriate for a given patient.

For example, a patient with a healthy angle with good visualization of anatomical landmarks (especially the trabecular meshwork [TM]) may be better suited for TM-preserving MIGS procedures, such as trabecular micro-bypass stent (iStent, Glaukos) or ab-interno canaloplasty (ABiC). A patient with poor angle anatomy (eg, peripheral anterior synechiae) may be a better candidate for tissue-destructive procedures (eg, ab-interno goniotomy [Kahook Dual Blade, or KDB, New World Medical], Trabectome [NeoMedix]) or procedures not involving the angle at all (eg, endoscopic cyclophotocoagulation [ECP]). MIGS surgeons should gain an intimate understanding of the angle prior to surgery lest they chose a surgical procedure that may be challenging or ineffective on the day of surgery.

I have made this mistake, and now I make sure that I have performed in-office gonioscopy prior to choosing a MIGS procedure.

KNOW WHAT’S ON THE MENU

Following the withdrawal of the CyPass device from the global market in August 2018, the current menu of available MIGS options are as follows:

• Angle-based procedures
  • Tissue-preserving procedures: iStent, ABiC
  • Tissue-destructive procedures: KDB, Trabectome, gonioscopy-assisted transluminal trabeculotomy (GATT)
• Ciliary space–based procedures: ECP
• MIGS “plus” procedures: Xen (Allergan)

Like me at a French restaurant, the menu choices can seem overwhelming, and you may even need a quick Google search to even know what some of the terms mean. A full discussion of the exact mechanism(s) of each of these procedures is beyond the scope of this article, but suffice it to say that you should be somewhat familiar with how a given procedure works. This will allow you to slowly adopt or not adopt a given procedure.

Some of these procedures are easier to perform than others, and it’s perfectly acceptable if you are not able to perform all of them. See which procedure(s) you can easily learn in a wet-lab/dry model situation, especially if your local company rep can help set this up (Figure 1). And, if there is a certain procedure that you feel you can’t do, don’t be afraid to refer that patient to your friendly neighborhood glaucoma specialist.

IOP AND MEDICATIONS GOALS

A given patient’s target IOP for effective control of his or her glaucoma is a vital part of the decision-making process. For example, a patient with mild POAG controlled on one topical medication will have different target IOP and medication goals than a patient with moderate POAG with poor IOP control on three topical medications.

Remember, the goal with MIGS is to not only lower the IOP but also to reduce the number of topical medications a patient requires for effective IOP control, allow for rapid healing time and preserve ocular tissue for further procedures that may be needed in the future. Oftentimes, the quantitative reduction of IOP in a POAG patient may be minimal after a MIGS procedure, but if that also reduces (or eliminates) the number of topical medications then we must consider that procedure a success.

WHAT TO BUY

The technology and equipment needed for a given MIGS procedure is also important to consider. Some MIGS procedures, such as iStent and KDB, require little additional equipment to perform effectively, making them an attractive choice for those of us new to the MIGS arena. Other MIGS procedures, such as ABiC, ECP, Trabectome and Xen, require the purchase and use of additional surgical instruments, devices, medications, disposables or a combination of them that may present a financial and logistical barrier to adoption. Given the varying reimbursement rates for each procedure, surgeons may wish to give consideration to these financial implications as well.

COMBINED VS. STAND-ALONE PROCEDURES

Another factor to consider is that some MIGS procedures (such as iStent) have to be performed in conjunction with cataract surgery. MIGS procedures may be performed as stand-alone procedures but usually require patients to pay out of pocket. Other procedures (such as ABiC, KDB, Trabectome) may be performed either in conjunction with cataract surgery or as standalone.

WHICH PROCEDURE(S) SHOULD I DO FOR THIS PATIENT?

Now we get to the million-dollar question that every MIGS surgeon faces. Depending on whom you ask, there are a dozen different answers (and permutations of these answers) for a given patient. The following list, while not a comprehensive one, highlights factors a MIGS surgeon must consider prior to surgery:

• Severity of POAG: As mentioned previously, mild POAG patients may be effectively treated at a higher IOP target than a moderate POAG patient. Each MIGS procedure has a varying amount of expected IOP reduction. For example, the Xen will likely lower IOP to a much greater degree than the iStent, so the former may be considered for a moderate/moderate-severe POAG patient while the latter may be considered for a mild/mild-moderate POAG patient.
• Phakic versus pseudophakic: Cataract extraction should not be overlooked as the best of all “MIGS procedures.” For phakic patients, cataract extraction, with or without a MIGS procedure, may be an effective option for IOP lowering. However, for pseudophakic patients, the MIGS options may be limited based on indications for usage and insurance company reimbursement policies.
• Repeatability and future procedures: Consideration should be given to the advantages of a procedure, such as ABiC or ECP, that may be safely repeated in the future.
• The condition of the TM and angle anatomy: For example, if a patient has a healthy TM and angle structures, there may be an advantage to proceeding with a TM-preserving procedure, such as iStent or ABiC. This will allow for one to perform tissue-destructive procedures in the future if the need arises. Furthermore, many of the newer topical medications, such as Rhopressa (netarsudil; Aerie Pharmaceuticals), have a mechanism of action that increases TM outflow, so preserving this anatomy will be advantageous for post-MIGS medical therapy as well.
• History and risk of intraocular inflammation: Certain MIGS procedures that are associated with tissue destruction, such as KDB and ECP, may cause significant inflammation that will require considerable anti-inflammatory therapy in the postoperative period (which may also raise the IOP via steroid response). Patients with darker pigmented irises may also have postoperative inflammation that may be challenging to control and may require extensive follow-up by the primary surgeon.
• Uncomfortable head positioning: Many MIGS procedures require the patient to rotate and hold his/her head in an uncomfortable position. This is something to consider, especially in elderly POAG patients who may have a high rate of concordant musculoskeletal and degenerative conditions that may hinder their ability to maintain long periods of required head positioning. In these patients, a procedure that is quick, such as iStent or KDB, may offer an advantage over a longer procedure, such as ABiC. On the other hand, procedures that do not require angular head posturing, such as ECP, may be easier to perform on such patients.
• Performing multiple MIGS procedures: Some procedures may be combined in a “peanut butter and jelly” manner so that the advantages of a given procedure may enhance the outcomes of another procedure. For example, the “ICE” (iStent, cataract, ECP) procedure is a favorite among some MIGS surgeons because it aims to lower IOP through increased TM outflow, deepening of the angular space and reduction of aqueous humor production, respectively. The “CIA” (cataract, iStent, ABiC) is another procedure that symbiotically aims to increase drainage via the TM pathway by increasing TM outflow proximally and drainage via Schlemm’s canal and collector channels distally.
• When to refer: It is OK for a MIGS surgeon to refer a patient to a glaucoma colleague if that is in the patient’s best interests. For example, if a patient would benefit from Xen (or incisional glaucoma surgery), I personally refer that patient because I do not feel comfortable performing glaucoma surgeries that require mitomycin-C and the postoperative bleb management that is often needed. Your patients — and your glaucoma colleagues — will appreciate this in the long term.

Based on my experiences and discussions with glaucoma experts, I created “non-glaucoma specialist’s MIGS decision trees” for patients with mild POAG (Figure 2), moderate POAG (Figure 3) and severe POAG (Figure 4).

POSTOPERATIVE MANAGEMENT CONSIDERATIONS

While many MIGS surgeries are fun and gratifying to perform, surgeons should be aware that not every MIGS procedure is equal in terms of the necessary postoperative management. Some procedures, such as iStent and ABiC, may be considered as “fire-and-forget,” as, aside from their close IOP monitoring, the postoperative course for these procedures is similar to that for routine cataract surgery. Other procedures, such as KDB, Trabectome, GATT and ECP, may incite considerable postoperative inflammation and may warrant close monitoring and slow tapering of topical medications.

Such procedures may require the primary surgeon to personally examine patients postoperatively, which may hinder the ability to comanage patients with other eye-care providers. These procedures may also have a “rebound” IOP spike that occurs a few days to weeks afterward, so the usual routine of postoperative visits may need to be increased accordingly.

Finally, some procedures, such as Xen, not only warrant close follow-up but may also require postoperative intervention, such as bleb needling, that may be beyond the comfort zone of non-glaucoma specialists.

SUMMARY

MIGS procedures are part of an ever-increasing list of options for ophthalmologists to safely and effectively reduce IOP for their POAG patients. Those who are not glaucoma specialists may be interested in learning and incorporating MIGS procedures into their surgical practice. Proper patient-procedure selection, preoperative examination, intraoperative considerations and postoperative monitoring are essential for succeeding at MIGS. In addition, knowing when to refer cases to your glaucoma friends is sometimes the best thing you can do for your patients. OM

About the Author

Kamran Riaz, MD, specializes in cataract, cornea and refractive surgery. He is director of refractive surgery and an assistant professor in the Department of Ophthalmology and Visual Science, University of Chicago.