Managing glaucoma with surgical procedures (plural)

By Robert J. Noecker, MD, Special to Ophthalmology Times

Dr. NoeckerThere is a shift in mindset happening in regard to glaucoma. It is a chronic disease, and like most chronic diseases, treatment is not a one procedure that controls the disease for the remainder of the patient’s life. The advent of low-risk surgical options is moving this from a pharmaceutically managed disease to one controlled via a series of surgical procedures, and the outcome appears to be highly beneficial for patients.

Though topical glaucoma medications have excellent results in clinical studies, in the real world less than 50% of patients use their medications as prescribed.

Essentially, the result is a therapy in which the physician has zero control, and the tendency is to sit back and wait until there is serious damage to the optical nerve before proposing a risky surgical alternative. Finding myself in a similar mode, I deliberately embraced the myriad low-risk surgical therapies for glaucoma.

Safety first

I regularly perform MicroPulse laser trabeculoplasty (MLT, Iridex) for patients in the early stages of glaucoma. Similar to selective laser trabeculoplasty, MLT lowers IOP about the same as a single prostaglandin¹, but the laser causes no anatomical changes to the trabecular meshwork.² 

If a glaucoma patient needs cataract surgery, I will always consider performing a combination procedure and implant a device (iStent Trabecular Micro-Bypass, Glaukos) at the same time. As experience with this stent has increased, surgeons have seen dramatic improvements in results compared with the pivotal trials.

A study by Tobias Neuhann, MD, followed patients for 36 months who received the stent in conjunction with small-incision cataract surgery and found a mean reduction in IOP from 24.1 mm Hg at baseline to 14.9 mm Hg.³

This was accompanied by a reduction in mean medications from 1.8 at baseline to 0.3 medications at 3 years, with no intraoperative or postoperative complications typically seen with conventional glaucoma surgeries. The upside is very good, and the downside is very small, so it is always my next step in intervention.

The trabecular meshwork is dynamic and is always adjusting in response to changes in pressure with new configurations of cells and structures. The problem with glaucoma is that the system starts to stiffen up a little, and no longer responds as easily to changes in pressure. The trabecular meshwork is a system that needs continuous flow to keep the cells and sensors within it open and functioning.

If fluid is shunted away to another space, studies have found that the system starts to atrophy, thus losing its elasticity and ability to move aqueous away from the anterior chamber.⁴

Recent studies also demonstrate that treatment with trabecular bypass stents after trabecular meshwork disuse atrophy can re-establish conventional outflow.⁵

Whenever possible I try to maintain an active trabecular meshwork before moving on to other treatments to mitigate the risk of a post-fibriotic pressure spike.

Moving to next pathway

Moving to next pathway

With the recent approval of another device (CyPass Micro-Stent, Alcon Laboratories), the suprachoroidal space may be the next step for patients who need additional control following an iStent. While natural drainage is known to occur through the uveoscleral pathway and attempts have been made at cyclodialysis for over 100 years, overall it is a space that is not well understood and comes with a higher risk-to-benefit ratio for the glaucoma patient.

Initial data for a CyPass inserted at the time of cataract surgery in patients with IOP >21 mm Hg show a mean IOP at baseline of 25.5 mm Hg reduced to a mean of 15.8 at 24 months of follow-up.⁶

Medications also reduced from a mean of 2.2 at baseline to a mean of 1.0 at 24 months. Transient hypotony occurred in 15.4% of subjects and micro-stent obstruction, typically due to iris overgrowth, occurred in 8.8% of subjects.

One concern with utilizing the suprachoroidal space is the chance of scarring. We do not yet have long-term data to show if this pathway retains patency over the long-term but the rate of secondary procedures (18.5%⁷, 11%⁶) required to manage glaucoma noted in published studies needs to be taken into consideration. Early hypotony is likely the biggest initial concern.

By definition, this device is making a cyclodialysis and holding it open so that it cannot heal spontaneously. An implantation with too many lateral movements may allow extra flow resulting in transient hypotony.

Although early hypotony is not usually severe, patients can expererience blurred vision and are less happy.

Surgeons also have to worry about the sequela of low pressure and sequela that can negatively affect visual outcomes including choroidal effusions and hyphemas.

The device is also placed closer to the iris, making it more susceptible to trauma. Simply put, the risk of working in the suprachoroidal space is a step up from that of working in the trabecular meshwork space.

The CyPass may also be an option for initial therapy in a person who is not a candidate for an iStent. Patients that had a lot of argon laser trabeculoplasty and have little spots throughout the trabecular meshwork, or perhaps have visible scarring from other causes, often cannot restore sufficient flow in this area.

Having another lower-risk option is helpful, and this remains true for other therapies (Xen Gel Stent, Allergan; the InnFocus Micro-Shunt, Transcend Medical).

Re-thinking success

Re-thinking success 

In many ways, we are improving at diagnosing and treating glaucoma earlier, which always offers the best prognosis. But we are still not where we need to be. We do not have a single glaucoma procedure that is a cure-all.

I am frequently making adjustments to shunts that were placed 10 years previously. However, all of these options are much safer than in the past, and I find myself performing far fewer filtering surgeries and tube shunts now. 

Excellent safety profiles have changed my criticism of efficacy. While patients may have to undergo more procedures, they are seeing well, their lives are not adversely affected by the recovery, and they are generally better off.

Reducing medication is a big deal. Even patients who understand the importance and have good compliance still find it a daily burden. The ability to minimize in a meaningful way or replace medical therapy is a big advance. 

Changes in mindset never happen quickly, but as convincing evidence builds, we always get there. It is true that most of these MIGS procedures are not designed to deliver home-run IOP reductions for end-stage glaucoma, but they do deliver solid singles and doubles for mild-to-moderate glaucoma patients where these devices offer significant advances in therapy.

If we can hit a single every time and work our way around the bases while eliminating the really bad events, we have won the game. 

References

Fea AM, Bosone A, Rolle T, et al. Micropulse diode laser trabeculoplasty (MDLT): a phase II clinical study with 12 months follow-up. Clin Ophthalmol. 2008;2:247-252.

Fudemberg SJ, Myers JS, Katz LJ. Trabecular meshwork tissue examination with scanning electron microscopy: a comparison of micropulse diode laser (MLT), selective laser (SLT), and argon laser (ALT) trabeculoplasty in human cadaver tissue. Invest Ophthalmol Vis Sci. 2008;49(5):ARVO e-abstract 1236.

Neuhann TH.  Trabecular micro-bypass stent implantation during small-incision cataract surgery for open-angle glaucoma or ocular hypertension:  Long-term results. J Cataract Refract Surg. 2015; 41:2664-2671.

Johnson DH, Matsumoto Y.  Schlemm's canal becomes smaller after successful filtration surgery. Arch Ophthalmol. 2000 Sep;118(9):1251-6.

Traverso C. iStent Trabecular Micro-Bypass Stent: 18-Month Interim Analysis on Refractory Open-Angle Glaucoma Patients. Presented at the 2015 American Academy of Ophthalmology Meeting, Atlanta. November 2015.

Höh H, Grisanti S, Grisanti S, Rau M, Ianchulev S. Two-year clinical experience with the CyPass micro-stent: safety and surgical outcomes of a novel supraciliary micro-stent. Klin Monbl Augenheilkd, 2014. Vol. 231(4), pp. 377-81.

García-Feijoo J, Rau M, Grisanti S, et al. Supraciliary Micro-stent Implantation for Open-Angle Glaucoma Failing Topical Therapy: 1-Year Results of a Multicenter Study. Am J Ophthalmol. March 2015.

Robert J. Noecker, MD

E: noeckerrj@gmail.com

Dr. Noecker practices at Ophthalmic Consultants of Connecticut in Fairfield, CT. He is currently assistant clinical professor of ophthalmology at the Yale University School of Medicine and is clinical professor of surgery at the Frank Netter School of Medicine of Quinnipiac University. Dr. Noecker is a consultant to Alcon Laboratories, Allergan, Glaukos, Innfocus, and Iridex.