Pros and cons of shunts for IOP control

Two glaucoma specialists explore when to use shunts, trabeculectomy or both.

By Hylton R. Mayer, MD, and Alan L. Robin, MD

About the Authors
	Hylton R. Mayer, MD (top), practices with Eye Doctors of Washington in Chevy Chase, Md. Disclosures: Dr. Mayer is a consultant to Alcon and Allergan, and is a speaker for those companies and Bausch + Lomb.
	Alan L. Robin, MD, is associate professor of ophthalmology and international health at Johns Hopkins University, Baltimore. Disclosures: Dr. Robin holds stock options in Glaukos, is a consultant to and has stock options in Aerie Pharmaceuticals, is a consultant to Cipla pharmaceuticals, and has spoken for Merck and Allergan.

Successful frontline glaucoma treatment, whether via trabeculectomy, medication, micro-invasive glaucoma surgery (MIGS) or another variation of glaucoma drainage implant surgery (GDIS), increases hope for patients and provides formidable debate material for doctors.

While trabeculectomy remains the most frequently performed glaucoma operation worldwide, other treatments have gained traction. They include drainage device surgery, which involves placing a flexible plastic tube with an attached silicone reservoir to help drain aqueous fluid, usually after a failed trabeculectomy, and mini-shunts implanted beneath a scleral flap.

Figure 1. The Ex-Press mini-shunt is placed under a scleral flap to prevent erosion and allow a diffuse bleb to form.

COURTESY: ALCON

The Tube vs. Trabeculectomy (TVT) Study,¹ while not demonstrating clear superiority of one over the other, suggested that ophthalmologists should expand the role of drainage devices in managing glaucoma. The 2012 follow-up study indicated that tube-shunt surgery had a higher success rate compared to trabeculectomy with mitomycin (MMC) during five years of follow-up to the TVT study.²

A 2013 study of outcomes of the Ex-Press Glaucoma Filtration Device (Alcon, Fort Worth, Texas)³ — a device with which we are both familiar — placed under a partial-fitness scleral flap with trabeculectomy, found no clinically significant differences either early or late compared with trabeculectomy alone.

Q Considering the results of the 2009 TVT study and the 2012 follow-up, which treatment you prefer — trabeculectomy or tube shunt?

Dr. Mayer: Historically, tube shunts were intended for people with glaucoma for whom trabeculectomy was predicted to fail. More recently, people started having the tube shunt as an earlier surgery.

Both are good at lowering IOP. If you want the lowest pressures with the fewest postoperative medications, I would go with trabeculectomy, but patients may need more postoperative care. If you don't need the lowest IOP, the TVT trial showed the tube works well after a failed trabeculectomy. I tailor that information to the patient and her or his individual clinical positions, and highlight which surgery has a higher complication rate.

In my practice, a trabeculectomy requires more intensive postoperative follow-up. I typically prefer trabeculectomy first for vision-threatening glaucoma for patients who have not had previous conjunctival surgery. If patients are not good at taking their drops and presenting for follow-up visits, I go with a tube.

In addition, people in tropical and subtropical environments may be at higher risk for bleb-related endophthalmitis. Frequent swimmers or patients in Florida may benefit from avoiding trabeculectomies.

Dr. Robin: After considering patient history, my choice is trabeculectomy because the TVT study showed that the two are almost comparable and that fewer IOP medications are needed following trabeculectomy than tubes.

Adherence to medical therapy is an important issue, and I believe that lack of adherence is associated with progressive visual disability, so I would like to avoid IOP-lowering medications after glaucoma surgery. IOP was lower in the trabeculectomy group in those taking no IOP-lowering medications.

Q What concerns do patients have about mini-shunt implantation, and how do you address them?

Dr. Mayer: The mini-shunt is a variation of trabeculectomy; it can enable a more controlled intraoperative experience, with a more stable anterior chamber. The Ex-Press device also allows the surgeon to create a more uniform and predictable fistula at the time of trabeculectomy.

Patients ask if it can fall out. The Ex-Press is tiny, and inside the eye it should not be felt or seen, other than through a microscope. It can erode or migrate outside of the eye and have to be removed. Some worry about MRIs or going through airport scanners; these are false fears.

Dr. Robin: As for the Ex-Press mini shunt, investigators have found no proven advantage over trabeculectomy. A recent article in the American Journal of Ophthalmology³ found no difference at two years in the group prospectively randomized to the Ex-Press shunt compared to the trabeculectomy group with regards to IOP, success rate, number of medications required for IOP control or visual recovery.

Trabeculectomy alone has a very high success rate and costs about $900 less when unaccompanied by an Ex-press mini-shunt. The Ex-Press mini shunt is also only approved in situations where a conventional shunt would be appropriate, not as a primary surgical procedure. Patients and doctors should be aware that the Ex-Press is not approved for primary glaucoma surgery; its only FDA approval was a 510(k) for advanced glaucoma. I personally realize that there are finite health-care dollars, and try not to waste our resources.

As for the iStent (Glaukos, Laguna Hills, Calif.), the only approved use is for patients with open-angle glaucoma also requiring simultaneous cataract surgery. It has been shown to be very safe and offers a modest advantage in terms of lowering IOP; for most of my patients with advanced glaucoma with advanced damage, this may be insufficient to prevent progressive optic neuropathy.

My patients, mostly in the mid-Atlantic area, are not aware of this device.

Q Can mini-shunt therapy replace eyedrops as first-line therapy?

Dr. Robin: The iStent can perhaps replace some medications in early glaucoma in patients undergoing cataract surgery. It appears to lower the IOP a few more millimeters of mercury than cataract surgery alone.

So in someone with early glaucoma who requires a single medication, such as an alpha-agonist or beta-blocker, and also cataract surgery, the iStent plus cataract surgery could sufficiently lower IOP to prevent the need for postoperative IOP-lowering medications.

Dr. Mayer: In the future, the iStent or similar devices may become first-line options. If the devices are safe and the efficacy persists, earlier use will probably be a no-brainer. Patients will have options: Take one more drop every day, undergo laser trabeculoplasty that can provide constant IOP-lowering effect for up to five years and hopefully one day have the option to undergo a safe and efficacious incisional surgery, such as the iStent, to provide a more permanent IOP-lowering effect. Currently we don't have the data to support this option for the iStent.

Q How do the risks of trabeculectomy — mainly failure of the filtering bleb — stack up against those of other therapies?

Dr. Mayer: I consider the mini-shunt a variation of trabeculectomy, so it has most or all of the potential problems associated with trabeculectomy. The mini-shunt is reputed to have lower rates of postoperative hypotony. Some surgeons feel the perioperative experience, stability and predictability are greater with the shunt. There are no good long-term comparisons of the Ex-Press and traditional trabeculectomy.

Dr. Robin: Compared to an Ex-Press shunt, the risks are no different, and the shunt is $900 more. In conjunction with cataract surgery, the iStent is far safer and probably would contribute to an improved quality of life compared to combined phacoemulsification and trabeculectomy in the right person.

Q What types of patients would SLT/ALT or medications serve best vs. other approaches?

Dr. Robin: SLT is used as a primary therapy for many patients with glaucoma. A mini-stent may be useful for people with cataracts requiring surgery who have early, easily controlled glaucoma.

For many patients, one medicine is inadequate in controlling IOP and they have trouble instilling eyedrops or don't have the coordination. Eighteen percent have trouble with eyedrops, and two-thirds have trouble starting with ALT or SLT, depending on their situations, and require cataract surgery. In these patients, depending upon the circumstances, either procedure could easily reduce the medication burden.

Figure 2. The iStent allows aqueous to flow directly into Schlemm's canal, bypassing the trabecular meshwork.

COURTESY: GLAUKOS

Dr. Mayer: Medication works well for most patients. Short-term medication use is typically not too expensive, especially if covered by insurance. SLT/ALT is an excellent option for those who do not comply with or tolerate medications and for those who cannot afford medications. SLT is a great first- or second-line option whenever patients have issues with topical IOP-lowering drops.

Q What are the costs of mini-shunt vs. SLT/ALT and topical medications?

Dr. Mayer: Short term, medication cost is cheaper. With incisional surgery, you have to look at efficacy over time; SLT might be the most cost-efficient. I have seen a few patients who had ALT 20 years ago and their pressures are fantastic, but these are exceptional patients. For most patients, laser trabeculoplasty works for up to five years, but even this duration can make laser trabeculoplasty more cost-effective than drops.

Dr. Robin: The cost of SLT/ALT is minimal and might have dramatic results in aiding some patients minimize the burden of instilling eye drops. Josh Stein and coworkers⁴ reported SLT may be a cost-effective alternative to medical therapy when considering the lack of adherence in many individuals.

Q What skill level does a doctor need to have to implant mini-shunt devices?

Dr. Robin: For an iStent the surgeon must be efficient with gonioscopy and very capable of maneuvering across the eye using a clear corneal incision. For the Ex-Press the surgeon must be proficient at performing a trabeculectomy.

Dr. Mayer: With the Ex-Press, you must be facile at trabeculectomy and understand aqueous flow and postoperative care. The iStent has a steep learning curve. One needs to be able to visualize and differentiate anterior-chamber angle structures and be facile and skilled with manipulation and implantation of the device. It is a straightforward procedure that is performed at the time of cataract surgery and is well within the abilities of most surgeons.

Q What are some of the complications that can arise after mini-shunt implantation?

Dr. Mayer: With the mini-shunt, there are the typical post-trabeculectomy bleb-related complications. There can also be occlusion of the implant with blood or intraocular material, or migration or erosion of the implant. With the iStent, the complications include scar tissue around the shunt, placement in the wrong location and bleeding or potential corneal trauma. The iStent may also dislocate or migrate. Still, if it was my eye and I had mild to moderate (and possibly even significant glaucoma), I would want the iStent.

Dr. Robin: For the mini-shunt, the complications are the same as trabeculectomy; for the iStent, almost nothing in terms of complications outside of those experienced with cataract surgery alone.

Q Between 1995 and 2004, there was an increase in Medicare claims for tube-shunt surgery of 184% compared to a 43% decrease in trabeculectomy. How does this figure into your opinions of the two procedures?

Dr. Mayer: The TVT study was designed in part to determine whether this trend was appropriate. The results of the study supported earlier tube-shunt surgery for many patients, especially those with previous failed trabeculectomy.

Dr. Robin: There are a lot of factors, with newer classes of medications introduced: The whole surgical rate has decreased overall. The baseline for the number of shunts being performed was low; there weren't that many tube-shunt surgeries done to begin with. OM

REFERENCES

1. Gedde SJ, Schiffman JC, Feuer WJ, Herndon LW, Brandt JD, Budenz DL; Tube Versus Trabeculectomy Study Group. Three-year follow-up of the tube versus trabeculectomy study. Am J Ophthalmol. 2009;148:670-684.

2. Gedde SJ, Schiffman JC, Feuer WJ, Herndon LW, Brandt JD, Budenz DL. Tube versus Trabeculectomy Study Group. Treatment outcomes in the Tube Versus Trabeculectomy (TVT) study after five years of follow-up. Am J Ophthalmol. 2012;153:789-803.

3. Netland PA, Sarkisian SR Jr, Moster MR, et. al. Randomized, prospective, comparative trial of Ex-Press glaucoma filtration device versus trabeculectomy (XVT Study). Ophthalmol. 2013 Nov 7. [Epub ahead of print].

4. Stein JD, Kim DD, Peck WW, Giannetti SM, Hutton DW. Cost-effectiveness of medications compared with laser trabeculoplasty in patients with newly diagnosed open-angle glaucoma. Arch Ophthalmol. 2012;130:497-505.