Chapter 12

Savak “Sev” Teymoorian, MD, MBA

Why would a book about refractive cataract surgery have a discussion about glaucoma procedures? The decision on when to remove a cataract and what, if any, concurrent glaucoma surgery to perform plays a significant role in the long-term care of these patients. All cataract surgeons will inevitably take care of patients with glaucoma. It is estimated that 20% to 25% of patients having cataract surgery have some form of glaucoma or ocular hypertension.¹ Of course there are those refractive surgeons who believe that they will not encounter this problem because these patients may not be candidates for premium lenses. However, glaucoma patients still benefit from astigmatic correction, even with a standard monofocal lens, and therefore still fit into a refractive practice.

In fact, the number and percentage of patients with glaucoma will increase in the future for a few reasons. First, the use of advancing technology including optical coherence tomography allows earlier diagnosis of patients and identification of those at risk.² Second, the average lifespan of patients continues to increase, and glaucoma is more common with older age.^3–5 What was once a disease requiring management for 10 to 20 years now becomes a challenge lasting 20 to 40 years. The thought process of how to care for these patients has changed from a sprint to a marathon.

In glaucoma patients, it is especially critical to achieve the best refractive outcomes. Glaucoma by definition is an optic neuropathy with associated visual field changes.⁶ Glaucoma patients already have or will be having diminished visual fields in the future. It becomes imperative to try to maximize the areas of vision that do remain. Key factors that influence their vision include the use of intraocular pressure (IOP)–lowering eye drops and traditional glaucoma surgery. The use of glaucoma drops help decrease IOP, but at a cost to the corneal surface. It is not uncommon to see patients who have their glaucoma controlled but still have their visual acuity and quality of life decreased because of the corneal adverse effects of these medications.7–8 This leads to frustration for providers, because, at best, we are breaking even with the battle against glaucoma, since it can’t be reversed, but losing the war on retaining functional vision because of adverse effects of therapy.

The other issue is that gold-standard glaucoma surgery still remains with trabeculectomy and tube shunt surgery.^9–13 These procedures are used only when needed because of the high risk-to-benefit profile.¹⁴ Unfortunately, the perfect storm is created when glaucoma is not controlled earlier in the disease process. Not only do these patients have worsening glaucoma as they get older, but they also are subjected to riskier surgical interventions. The ideal care for glaucoma patients is to avoid these larger surgeries if possible. Any intervention that decreases the need for glaucoma eye drops and either delays the performance or even eliminates traditional glaucoma surgery should be considered. It just so happens this exists, and it comes in the form of cataract surgery.

Cataract surgery is now becoming commonplace, with approximately 3 to 4 million surgeries done every year in the United States. With better procedures and intraocular lens (IOL) technology along with longer lifespans, it becomes an almost inevitable part of a patient’s care. Integrating a treatment for glaucoma with a procedure that will naturally be done, like cataract removal, is where micro-invasive glaucoma surgery (MIGS) fits in the paradigm.^15–16

The key to MIGS is the positive benefit-to-risk ratio. The definition of MIGS is evolving, but the core principles remain the same. This involves any surgical procedure that helps decrease IOP with a risk profile that is less than that seen with trabeculectomy or tube shunt surgery. A secondary requirement is that it is conjunctival-sparing, in order to leave this space undisturbed should there be a need for a more gold-standard surgery.¹⁷ A tertiary requirement is rapid recovery.¹⁸ These guidelines generally lead to ab interno procedures done concurrently with cataract surgery. The hope is to give additional IOP reduction beyond that seen with cataract surgery alone, without much additional risk.^15,16

THE PRESENT AND FUTURE OF MICRO-INVASIVE GLAUCOMA SURGERY

The landscape of MIGS is rapidly changing. For providers, this means there are products in the pipeline that are under study or development that will become available for implantation in the near future. The technology that is being currently evaluated can be divided into subgroups depending on their anatomical target.

Trabecular Bypass/Schlemm’s Canal

These MIGS procedures focus on maximizing the conventional outflow of aqueous through Schlemm canal (SC) by bypassing the trabecular meshwork for 2 reasons. The first is to provide an alternative pathway through the juxtacanalicular section of the meshwork that provides the greatest resistance to flow. The second is to reduce the dependence on the need for aqueous to flow through the disease meshwork.¹⁹ These procedures allow for access of aqueous from the anterior chamber directly to SC.

The iStent Trabecular Micro-Bypass (Glaukos Corporation) is the first Food and Drug Administration (FDA)–approved stent to be used in conjunction with cataract surgery for those with mild to moderate glaucoma.20 It is manufactured in both a right and left orientation, allowing the surgeon to point the stent toward the inferonasal quadrant of the surgical eye where the greatest number of collector channels are located^21,22 (Figure 12-1). The tip of the titanium stent is advanced past the trabecular meshwork and into SC, where it is held in place by 3 retention arches (Figure 12-2). Research from the iStent study that compared the use of one iStent in addition to cataract surgery vs cataract surgery alone met its primary and secondary endpoints. It demonstrated the advantage in IOP reduction using the iStent during cataract surgery.23

The iStent Inject, the second generation of this stent, is a 26-gauge injectable system that allows surgeons to place 2 preloaded stents with 1 applicator. The theorized advantages include an easier procedure to position the stent though an injection action and also place multiple stents in rapid progression²⁴ (Figure 12-3). It is currently under investigational trials.

Hydrus

The Hydrus Microstent (Ivantis Inc) is intended to be used as a scaffold placed into SC to enhance aqueous outflow through that pathway.²⁵ The injector system helps direct the 8-mm, crescent-shaped, flexible stent into place²⁶ (Figure 12-4). It is intended for those with mild to moderate glaucoma and is still under investigational trials.

Trabectome

The Trabectome (NeoMedix) is an externally powered unit that uses electrosurgical pulses to bypass through the trabecular meshwork and open the inner wall of SC. Once the instrument is guided into SC, a foot-operated switch is used to turn the pulse, which results in the removal of the tissue at the instrument tip²⁷ (Figure 12-5). This creates a direct path for aqueous to flow from the anterior chamber to the collector channels by SC. The Trabectome is FDA approved at this time and available for use in patients.²⁸

Ab Interno Trabeculotomy

Recent innovations in trabeculotomy procedures allowing for it to be performed through an ab interno approach places this surgical intervention under the MIGS category. The first is gonioscopic-assisted transluminal trabeculotomy. After performing goniotomy to create an opening from the anterior chamber to SC, a suture is guided 360 degrees around the canal. The ends of the threaded object are then pulled from the eye, creating the circumferential opening of the canal.²⁹

The second approach is the use of the Trab360 (Sight Sciences) instrument. It is a hand-held instrument that uses a sharp tip to enter SC. Then, a medical-grade polymer is advanced through the space by rotating the wheel on the instrument (Figures 12-6 and 12-7). Removal of the instrument from the eye then pulls open the area of the canal that the polymer had passed. The polymer can then be recoiled back into the instrument, and then the remaining area of SC can be opened if desired by the surgeon.³⁰

The CyPass Micro-Stent (Alcon) is a 6-mm, polyimide device with fenestrations that is placed into the supraciliary space using an applicator that deploys it into position31,32 (Figures 12-8 and 12-9). It is the second FDA-approved stent and is commercially available.

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