Not a week goes by in clinic without hearing this question from a trainee on the glaucoma service. Medical students, residents, and even fellows are easily lost in the rising sea of Micro-invasive Glaucoma Surgeries (MIGS) available to lower intraocular pressure (IOP) and reduce medication dependence in glaucoma patients. To be fair, even we find ourselves torn at times between two or more seemingly equal options for a particular patient.
Keep in mind, however, that if our biggest problem is option overload from so many MIGS, this is a very good problem to have. Remember it was not that long ago that the only viable surgical options for glaucoma patients were either a large glaucoma drainage device, a trabeculectomy, or a cycloablation procedure. While these more traditional glaucoma surgeries may offer supreme IOP lowering, they come with the risk of severe, vision-threatening complications and long, complicated post-operative courses. The advent of MIGS procedures was a welcome addition to our previously limited armamentarium, particularly for patients with mild to moderate disease or those who struggle with topical therapy due to compliance, cost, or troubling side effects.
So now that we have all of these wonderful minimally invasive procedures at our disposal, how do we decide which one to use? Well, the answer is simple: it depends. It depends on a lot of things, actually. It would be nice to have a well laid out decision tree that anyone can follow in order to arrive at the undisputed best option for a patient. Unfortunately, it’s not that black and white. Anyone who treats glaucoma knows there is a serious amount of gray zone in practice. The same is true when deciding the best MIGS procedure for your patient.
However, there are a number of important factors and considerations that you should take into account in order to arrive at the best possible decision and resultant outcome for your patient. As you become more comfortable with each procedure and how they perform in your hands and your patient population, the decision making process will become more fluid and almost occur subconsciously as you process all of these factors on the fly.
One of the primary factors that should be considered in deciding which MIGS procedure to perform is lens status. Most MIGS are employed at the time of cataract surgery in patients with coexisting glaucoma and visually significant cataracts. And if this is the case, virtually any procedure is applicable. However, outside of cataract surgery, there are some limitations. Certain MIGS devices, such as the iStent and Hydrus, are only approved to be implanted at the time of cataract surgery.
Therefore, if the patient is already pseudophakic or does not need or want cataract surgery, these procedures can only be performed if the patient is willing to pay out of pocket for an off-label use of the device. In these scenarios, a goniotomy/trabeculotomy procedure, endoscopic cyclophotocoagulation (ECP), or XEN gel stent may be a better choice, as they are all approved for stand-alone use.
IOP Lowering or Medication Independence?
Perhaps this is stating the obvious, but it is vital to keep in mind what the primary goal of a MIGS procedure is for a particular patient. Specifically, are you trying to decrease their medication burden, or does the patient need a significant IOP reduction to achieve their treatment goal regardless of how many drops they require? Additionally, consider the magnitude of change you are aiming for, both in terms of medications and IOP reduction. MIGS procedures can vary in terms of efficacy and risks and this should be tailored to the patient and clinical scenario. A patient with mild glaucoma and controlled pressures on a single medication looking for drop independence is a different animal than a patient with an IOP above goal despite 3 topical medications. The patient in the former scenario will likely achieve the treatment goal with almost any MIGS procedure, therefore choosing one with the lowest risk profile is most appropriate. Conversely, the more severe patient with uncontrolled IOP would be better served by the procedure with the greatest efficacy, accepting a higher chance of adverse events along with it.
You can even consider combining MIGS in these scenarios to maximize efficacy and decrease the odds of needing a more invasive surgery down the line. As with any operation, the risk to benefit ratio should be carefully weighed when choosing a surgical plan.
Anatomy is paramount when considering any surgical procedure and a careful preoperative assessment is no less important in MIGS. Most MIGS target the anterior chamber angle structures, specifically the trabecular meshwork (TM) and canal of Schlemm. In turn, most MIGS require an open angle and are contraindicated in eyes with some degree of angle closure, neovascularization, or peripheral anterior synechiae (PAS). Specifically, trabecular bypass stents like the iStent and Hydrus are contraindicated for use in eyes with angle closure glaucoma. However, other goniotomy/trabeculotomy procedures may still be considered in cases where PAS are relatively fresh or small in number and/or size. In such cases, goniosynechiolysis can be performed to open the angle first, followed by the goniotomy/trabeculotomy procedure.
In more chronic cases of angle closure, ECP can be an effective alternative to angle procedures as it does not require an open angle and can even serve to further open an anatomically narrow angle. Application of laser energy to the ciliary processes can shrink and rotate them posteriorly producing a deepening of the angle. This form of endocycloplasty can be very effective in eyes with plateau iris syndrome where enlarged or anteriorly rotated ciliary processes are the most significant driver of angle closure.
Intraoperative gonioscopy is also necessary to visualize the angle during most MIGS. Any corneal opacity may obscure visualization and should be assessed preoperatively as it may preclude safe completion of angle-based procedures. Here again though, ECP may be a great option as a clear view through the cornea is not required. A XEN gel stent may also be a viable option depending on the location and severity of the opacity.
Anatomical considerations for a subconjunctival procedure like the XEN focus more on conjunctival integrity and angle status in the targeted quadrant of implantation. Using the ab interno approach, the device is typically directed to the superonasal quadrant. The angle should be open at least at this location and the conjunctiva should be free of scarring or thinning from prior surgery to increase the likelihood of success. Another unique consideration for XEN is facial anatomy. Patients with prominent cheekbones, deep set eyes, or narrow fissures can greatly affect the ease of implantation using an ab interno approach temporally. Adapting surgeon body and hand position can help to work around these obstacles; however, you may want to avoid these patients for your first few cases and consider another MIGS if possible until you are comfortable with the basics of the procedure.
Type of Glaucoma
Along the lines of ocular anatomy, the sub-type of glaucoma may similarly help direct your choice of MIGS. Some of the common types of secondary open angle glaucoma, such as pigmentary or pseudoexfoliation, may respond particularly well to trabecular bypass procedures. Both goniotomy/trabeculotomy procedures as well as bypass stents have been shown to be at least as effective, if not more so, in these cases than in primary open angle glaucoma. Intuitively this makes sense, as these are conditions where the resistance to aqueous outflow is most certainly at the level of the trabecular meshwork, such that removing or bypassing the site of obstruction will result in a significant drop in IOP. Perhaps our biggest MIGS home runs have been a TM bypass procedure in these eyes. The increased pigmentation in these patients also makes visualization of the trabecular meshwork easier, which may be particularly useful in your first few cases. Also of note: in pseudoexfoliative patients, ECP should generally be avoided, as the fibrillar deposits on the ciliary processes can impede adequate laser uptake in these eyes.
Patients with uveitic glaucoma are known to be at high risk of hypotony and other complications after filtering surgery. While some MIGS devices may be contraindicated in these patients, we have seen excellent results with goniotomy/trabeculotomy procedures, particularly in younger patients. Similar to pigmentary and pseudoexfoliative cases, in uveitic glaucoma, the TM is often pathologic such that incision and/or removal can be very effective at controlling IOP and they can be performed in phakic patients as well. The inflammation should ideally be well controlled however with appropriate steroid or steroid sparing management perioperatively.
As discussed above, for angle closure patients, TM bypass stents should be avoided. However, new studies have demonstrated that goniosynechiolysis and goniotomy with the Kahook Dual Blade can be a very effective option in these cases. A word of caution: if you are just learning this procedure, we would not recommend attempting this in your first few cases as the anatomy can be deceiving.
In conditions where elevated episcleral venous pressure (EVP) is suspected, such as Sturge-Weber Syndrome or thyroid eye disease, a goniotomy/trabeculotomy procedure may not be the best option. By removing the TM as a barrier in a system with high EVP, significant blood reflux and hyphema may result. Further, as the resistance to aqueous outflow is further downstream in these patients, you may not obtain the IOP lowering results you were hoping for with an angle based procedure. In such cases, consider other MIGS such as ECP or a Xen gel stent.
In addition to closely analyzing ocular features, a patient’s systemic health, medications, and comorbid conditions should be factored into your surgical plan. While most of these procedures by definition have minimal impact on a patient’s quality of life, they may not all work well in every scenario. First, all TM bypass procedures carry the risk of intraoperative blood reflux and resultant hyphema postoperatively. The risk may be greater with goniotomy compared to bypass stents or with greater degrees of angle treated, though any patient may experience this. Patients on blood thinners and anticoagulants may have an even greater risk of intraoperative blood reflux which can obscure your view during the case or result in a more profound hyphema after surgery. While this does not preclude performing a TM based procedure, the risk should be considered and thoroughly discussed with patients ahead of time.
If you choose one of these procedures, it is also important to discuss with your patients how bleeding, if it occurs, may affect their vision postoperatively. While a hyphema should not affect eventual outcomes, it could certainly worry your patient if they weren’t aware of this possibility. Furthermore, if a patient is monocular, procedures with a high risk of hyphema may significantly limit their function until the blood clears—which may take several days or longer. Ab interno canaloplasty or smaller TM bypass stents like the iStent may minimize the risk of bleeding and should perhaps be considered over TM removal in such cases. ECP is another procedure that is typically bloodless and may be a preferred option in high risk individuals.
In patients at high risk for macular edema, such as those with an epiretinal membrane, a history of macular edema, or vein occlusion, ECP should generally be avoided, as this can be more inflammatory than other MIGS procedures and can stir up or worsen pre-existing edema. Because of this, you may also want to avoid using ECP in patients with a history of uveitis or in darkly pigmented patients as they have been shown to have more persistent postoperative inflammation.
It is also important to consider what is required of the patient during MIGS procedures. For instance, angle or TM based procedures often require that a patient tilt their head and remain still for several minutes to provide you, as the surgeon, visualization of angle structures. This may be difficult or impossible for some patients to do. You should consider this and possibly avoid these procedures in patients with dementia, difficulty remaining still and following instructions, or in patients with head and neck disease which may preclude adequate rotation. In such instances, procedures like the Xen gel Stent or ECP, which don’t require significant intraoperative patient participation or head rotation, may be better suited.
In an ideal world, the patient and surgeon would together decide the most appropriate procedure based on the medical literature, clinical experience, and patient wishes. Unfortunately, insurance companies and managed care plans have a significant say in what we can and cannot do. Newer procedures, like many in the MIGS category, are not always covered immediately by every plan. Some companies require several years of data before coverage is provided. Thus, we must keep a patient’s medical insurance coverage in mind when selecting which MIGS to perform. Failure to do so may result in a large out of pocket expense for your patient.
Of course, your best medical judgement should always be used to decide which procedure to perform, but when several options are similarly viable and coverage is only available for one, this may steer you and the patient toward the covered procedure. Keep in mind some manufacturers may offer free devices or samples in cases where insurance coverage is lacking. Several companies also provide reimbursement services to help with denials or designation of a non-covered procedure. Alternatively, if you feel strongly about a particular procedure that is not covered, a cash-pay option can be considered.
Availability and Device Costs
When deciding which MIGS to adopt and offer in your practice, the startup and ongoing costs to perform the procedure must be considered. For example, ECP requires a substantial startup expense for equipment, but probes are reusable, keeping ongoing costs minimal. Trabecular bypass procedures require very little initial investment but require ongoing costs for each device or implant used. These costs vary from one device to the next and are sometimes based on region and surgical setting as well. Further, financial margins may vary widely from a hospital based operating room to an ambulatory surgery center. All of these factors may influence which procedures are approved for you to use and may limit your access to certain procedures. But do not be afraid to fight for a new device that you think will greatly benefit your patients regardless of the financial or administrative barriers you may encounter.
We would recommend having at least two MIGS options at your disposal. More options may add to the complexity of your treatment algorithm but will allow you significantly more flexibility to customize your treatment and adapt to any clinical scenario you may face. Consider choosing procedures that are unique to each other which will allow you the most diverse treatment options. For example, one implant-based procedure and one that is not, one outflow and one inflow procedure, or one TM-based and one subconjunctival procedure.
As the available MIGS options continue to expand, we are all forced to constantly learn and expand our knowledge and surgical skills. Don’t be afraid to try new MIGS and expand your surgical wheelhouse through practice, training and mentorship. It is also important to remember that your comfort level as the surgeon, especially as a new graduate, is paramount.
The success of any procedure, to some extent, depends on the surgeon, and the best choice may be the one that you are most comfortable with. Just keep in mind that the brand new procedure you’ve never performed before may not be the best option for your high risk patient.
The advent of MIGS has forever changed the treatment of glaucoma for physicians and patients alike. By offering effective yet safe procedures with rapid recovery, MIGS has helped to fill the treatment gap that existed between conservative therapies such as medication or laser and the more invasive, traditional filtration surgery. Offering these attractive treatment options to our glaucoma patients can be incredibly rewarding to surgeons and have a dramatic impact on a patient's quality of life. The choice of which MIGS procedure to perform is one that requires thoughtful consideration of several ocular and patient factors that vary from one patient to the next. Appropriate discussion and involvement of the patient in the decision-making process is essential as well.
The decision is not always straightforward, but with practice, it can become like second nature to an experienced MIGS surgeon.