To determine if and which standalone microinvasive glaucoma surgery (MIGS) procedure to employ, Mark Gallardo, MD, utilizes an algorithm that begins by asking whether the patient’s glaucoma is controlled or uncontrolled in order to determine the level of severity.
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What factors go into the MIGS algorithm?
As a glaucoma specialist who practices in the desert Southwest, Dr. Gallardo finds dry eye in his patients is a profound concomitant co-morbidity. Therefore, ocular surface disease (OSD) plays a major role in his decision-making to perform surgery on patients who are controlled in order to alleviate the burden and negative effects of drops containing benzalkonium chloride (BAK), which is known to exacerbate OSD. Medication intolerance is also a defining factor for him.
The final piece of the puzzle is whether the patient is phakic or pseudophakic. From here, Dr. Gallardo dives into the specifics of his algorithm for the management of patients with MIGS procedures as standalone tools.
The algorithm in action
In his practice, the vast majority of MIGS procedures are being used in patients with controlled glaucoma who are currently on one to two medications. Given the fact that most MIGS tend to have similar efficacy in his experience, Dr. Gallardo’s goal is to choose the procedure in which he can most effectively minimize the footprint on the nasal angle in preparation for the potential of future procedures that may need to be performed 5 to 10 years down the road to manage glaucomatous progression.
MicroPulse laser therapy
In patients with controlled open-angle glaucoma and severe OSD, who have already undergone selective laser trabeculoplasty and require intervention beyond drops, Dr. Gallardo first addresses whether the individual is phakic or pseudophakic. In phakic patients, it is imperative to limit the intracameral manipulation to avoid causing a cataract. With the goal of reducing the medication burden in controlled patients with a natural crystalline lens, he often opts for diode MicroPulse laser therapy (Iridex).
As with any procedure, there are pros and cons. Perhaps the biggest benefit is the non-invasive nature of MicroPulse, as it does not require entering the anterior chamber. As for cons, over the years, finding the right laser settings has proven a challenge. Associated adverse events include chronic mydriasis or corneal toxicity resulting from an abnormality within the corneal stem cells.
Note: Transluminal viscodilation through an internal approach using the iTrack catheter is an alternative solution.
The case for goniotomy
In patients whose insurance may not cover canaloplasty without tensioning suture, Dr. Gallardo pivots to considering goniotomy as an alternative. However, he limits it to a small focal goniotomy of approximately 2 to 3 clock hours. Knowing glaucoma procedures are seldom permanent, he always makes certain the ostia is very visible, so he can easily return and manipulate the nasal angle in the future.
For phakic patients who might undergo a cataract surgery procedure at a later juncture in time, performing goniotomy ensures they will have ample angle access to either implant a trabecular micro-bypass stent, such as the Hydrus Microstent (Alcon) or iStent inject (Glaukos), or reintubate the canal with either the iTrack catheter or the OMNI Surgical System. As an all-in-one unit, OMNI is very user-friendly and allows the surgeon to introduce the injector through a clear corneal incision, which tends to reduce overall operating time.
In pseudophakic patients for whom implantation of a trabecular micro-bypass stent is not available, a more aggressive treatment with goniotomy is endorsed. In these cases, Dr. Gallardo still focuses on leaving a minimal footprint and opts for viscodilation in the majority of these patients. When possible, he utilizes the iTrack catheter, due to the volume of the ophthalmic viscosurgical device (OVD) that can be injected into the canal.
MIGS for patients with uncontrolled glaucoma
For patients who are uncontrolled with mild to moderate disease, Dr. Gallardo takes a more aggressive approach, while also adding that he takes into account whether they are phakic versus pseudophakic as part of his decision-making.
- In the case of pseudophakic individuals, he sometimes selects a 360° ablation with the iTrack catheter or ablating either 180° or 360° degrees with OMNI.
- With regard to phakic patients, he routinely chooses transluminal viscodilation with the iTrack catheter coupled with a focal goniotomy using the Kahook Dual Blade (KDB GLIDE, New World Medical) limited to 2 to 3 clock hours. He still prioritizes keeping a portion of the trabecular meshwork in the nasal angle visible to allow for future manipulation of the outflow system.
In severe cases where it is integral to maintain the target IOP to protect the optic nerve head integrity and preserve visual fields, he forgoes an angle-based procedure in favor of a filtering procedure, such as the XEN Gel Stent. If the patient is pseudophakic, one has the option of taking either an ab interno or ab externo approach, even though the latter is considered off-label. For phakic individuals, the ab externo approach is preferred, as it will not induce cataract formation since there is no interference with any of the intracameral structures.
When patients are on three to four medications, Dr. Gallardo tends to select the Hydrus Microstent and often may combine it with ab interno canaloplasty. If there are insurance barriers, he might choose more ablative procedures such as KDB or OMNI performing a 180° goniotomy in the superior portion of the angle while reserving the inferior to inferonasal area for future MIGS procedures.
Taking the long view to potentially avoid filtration devices
For uncontrolled patients going into cataract surgery, the primary aim isn't to reduce medication burden, but instead to reduce the intraocular pressure and prevent the patient from needing a filter down the pike.
Prior to the staging now required by insurance carriers with ICD-10 codes, the diagnosis was simply primary open-angle glaucoma (POAG), which allowed him to implant first-generation (G1) iStents in patients even with moderate to severe glaucoma. Dr. Gallardo discovered through a retrospective study of his practice that 88% of the patients undergoing this procedure were moderate to severe. In that subgroup, 90% of patients at 5 years out had been able to avoid a filtration device.
The takeaway: Angle-based procedures can be a very effective tool to control glaucoma when combined with cataract surgery.
In conclusion
For severe, uncontrolled glaucoma, the primary goal should always be to maintain the optic nerve head’s structure and function with as few medications as possible. This is at the forefront of Dr. Gallardo's algorithm when determining which MIGS procedures will best serve his patients.
He encourages each surgeon to develop their own algorithm utilizing the available information and adopting the procedures that work best for their hands and for their patient population.
