Trabeculectomy, tube shunts remain relevant, despite growth of less invasive techniques

Ophthalmologic opinions vary on the role and effectiveness of minimally invasive surgeries for treatment of early to moderate glaucoma. Surgeons agree that trabeculectomy and tube shunts are still preferred for advanced glaucoma and that they will continue to play a major role until the efficacy of other treatments is firmly demonstrated.

“While there is a lot of excitement over these newer procedures, I don’t know if we have clearly established what their role is in the surgical management of glaucoma,” Steven J. Gedde, MD, OSN Glaucoma Board Member, said. “There are still lots of surgeons who feel that transscleral procedures are certainly an appropriate, and maybe even a preferred, option for surgical treatment of glaucoma, including in people with mild to moderate disease.”

When open-angle glaucoma is diagnosed, medication or laser treatment is usually started. Glaucoma surgery is indicated when maximum-tolerated medical therapy and appropriate laser treatment are not adequate to control IOP.

In the U.S., treatment of early to moderate disease has been increasingly associated with minimally invasive procedures such as ab interno trabeculectomy with Trabectome (NeoMedix), canaloplasty (iScience Interventional), endoscopic cyclophotocoagulation (ECP), and phacoemulsification with or without other minimally invasive procedures. The iStent (Glaukos), a trabecular micro-bypass system inserted ab interno and implanted into Schlemm’s canal, has introduced another option for patients; surgeons are gaining clinical experience with this device to determine its effectiveness, but the U.S. Food and Drug Administration has not approved the device for commercial use

During his presentation at OSN New York 2010, Thomas W. Samuelson, MD, OSN Glaucoma Section Editor, said that the minimally invasive procedures enhance the natural outflow system of the trabecular meshwork, rather than create a new drainage system, and are not associated with the severe complications that may result from trabeculectomy and tube surgery.

Steven J. Gedde, MD, reviews images with former Bascom Palmer resident Vivian Schiedler, MD. Image: Victor D

“Unfortunately, transscleral procedures carry more risk than some of the newer, more minimally invasive procedures, and therefore, while still very relevant, they should be reserved for patients with more serious levels of glaucoma,” Dr. Samuelson said in a subsequent telephone interview.

Some surgeons think that the new procedures should be used only in patients with early disease. Others suggest that prospective randomized clinical trials be conducted to compare them with transscleral procedures and further determine their efficacy. Still others think that the minimally invasive procedures are appropriate for the treatment of moderate disease and that their safety may even warrant usage in cases of advanced glaucoma.

Minimally invasive glaucoma surgeries

Even though the role and effectiveness of minimally invasive surgeries remain debatable, most surgeons agree that these procedures are safer than transscleral surgeries.

“The minimally invasive glaucoma surgeries offer lower risk but at the cost of less intraocular pressure-lowering efficacy,” Joel S. Schuman, MD, OSN Glaucoma Board Member, said.

According to Dr. Schuman, ab interno trabeculectomy is one of the least invasive, but also least effective, procedures. Because of the mediocre success rate of this procedure when used by itself, Dr. Schuman nearly always performs ab interno trabeculectomy only in combination with phacoemulsification. The combined procedure often lowers IOP to the mid-to-high teens and may relieve patients of the need to use medication.

Hyphema is a common complication after ab interno trabeculectomy but can be avoided with high-quality wound construction, Dr. Schuman said. He cautioned that surgeons should avoid extending the Trabectome device too far posteriorly to avoid cyclodialysis.

Canaloplasty, a more invasive procedure, is performed much like nonpenetrating surgery, such as viscocanalostomy or deep sclerectomy, and is prescribed to patients who require target IOP in the mid-to-high teens, Dr. Schuman said. He usually combines phacoemulsification with a procedure that is less invasive than canaloplasty. He does not perform phacoemulsification alone as a glaucoma treatment if he needs to lower IOP by more than 1 mm Hg or 2 mm Hg.

Canaloplasty shares the risks of other nonpenetrating surgeries.

Dr. Schuman said he avoids performing ECP alone because it does not dramatically lower IOP and can cause significant postoperative inflammation. He said he also hesitates to combine this procedure with phacoemulsification because recovery time is longer than for phaco alone. In addition to destroying the ciliary body and causing inflammation, ECP increases the risk of macular edema, Dr. Schuman said.

Trabeculectomy

Trabeculectomy, the most prevalent of all glaucoma surgeries, is known for reliably lowering IOP. Douglas J. Rhee, MD, OSN Glaucoma Board Member, said that the primary indication for this procedure is a target pressure of less than 14 mm Hg.

Dr. Rhee does not perform trabeculectomy if the conjunctiva has previously been operated on, such as with trabeculectomy, vitrectomy or canaloplasty. Moreover, the advent of minimally invasive procedures has prompted him to limit his surgical indications because of the risks associated with trabeculectomy.

Intraoperative and perioperative risks include infection, retinal detachment, expulsive hemorrhage and suprachoroidal hemorrhage, all of which may have devastating effects on visual acuity, Dr. Rhee said. He also discussed bleb leak, blebitis and infection as potential long-term risks.

“It would not be rare to have a patient do beautifully for 5 years … and then all of a sudden, a severe bleb-related infection could threaten eyesight. That could happen anytime in the lifetime of that bleb, 5 years later, 10 years later,” Dr. Samuelson said. “There are very few surgeries that subject patients to unending, serious risk.”

However, despite potential complications, some surgeons think transscleral procedures such as trabeculectomy are more reliable than the newer surgeries because extensive testing and clinical experience have made them more predictable.

“They [trabeculectomy and tube shunts] are the operations that remain the most popular, and with good reason, because they are quite efficacious and we certainly have a wealth of experience with both of these types of operations spanning over 4 decades,” Dr. Gedde said.

According to Dr. Rhee, in the realm of clinical practice, there are generally two schools of thought regarding trabeculectomy. Some prefer to tie the sutures tighter and gradually reduce pressure by either using a laser to cut one of the internal sutures or using releasable sutures; this preference stems from a strong desire to avoid hypotony.

Other surgeons, Dr. Rhee said, seek to achieve low IOP immediately and use either atropine or a small amount of viscoelastic in the anterior chamber or allow for postoperative leaks.

In the case of tighter sutures, surgeons can avoid flat anterior chambers but must invest significant time into postoperative care, George L. Spaeth, MD, OSN Glaucoma Board Member, said. This requirement limits the approach to patients who are able and willing to attend follow-up exams.

Trabeculectomy with shunt

Another option for patients who undergo transscleral surgery is trabeculectomy with the Ex-PRESS mini glaucoma shunt (Alcon). In his presentation at OSN New York, Dr. Samuelson said that the device does not enhance the efficacy of a standard trabeculectomy but does enable more surgical control and improves safety.

Thomas W. Samuelson

“You make a tiny little incision, and the anterior chamber doesn’t shallow, and the iris doesn’t prolapse, and you do not get bleeding from the ciliary body. … There is more wound control. There is less induced astigmatism,” Dr. Samuelson said, adding that there is less choroidal effusion and postoperative hypotony.

“You still need very good trabeculectomy techniques, but it’s safer, it’s more elegant, it’s reproducible, and it’s less invasive,” he said.

In the follow-up interview, Dr. Samuelson again distinguished between standard trabeculectomy and trabeculectomy with the Ex-PRESS shunt by stating that the first surgery requires surgeons to excise tissue and the second surgery does not, meaning that the device eliminates the possibility of excising too far posterior and causing bleeding from vascular tissue.

Dr. Gedde said that despite solid evidence that the device may be an improvement over traditional trabeculectomy, it still produces a bleb at the limbus, and Dr. Rhee said he thinks that the Ex-PRESS shunt does not actually lower the rate of postoperative hypotony.

“I think what determines the rate of postoperative hypotony is still how tight you tie the sutures of the flap for the trabeculectomy. … However, if there is hypotony, I have found that the Ex-PRESS shunt maintains the chamber much better and, in doing so, limits some of the consequences of hypotony,” Dr. Rhee said.

Surgically, Dr. Samuelson recommends injecting lidocaine 1% or 2% with epinephrine anteriorly, broadly diffusing mitomycin C on either side of the lateral rectus and at the incision site, creating an adequate bed to support the shunt and an adequate flap to cover it, and rotating the device during insertion. A reasonably thick posterior margin of the scleral flap is important to control flow as the egress of aqueous is more posterior with the Ex-PRESS, especially the “P” design. An incompetent scleral flap can be particularly problematic as the Ex-PRESS ensures flow. A small peritomy and a fornix-based approach are also preferred.

Tube shunts

The indications for inserting tube shunts vary, depending on the surgeon. Most agree that a failed conjunctival filtration surgery or high risk for bleb infection are consistent indications. According to Dr. Gedde, certain types of secondary glaucoma that tend to have a poor prognosis with trabeculectomy, such as neovascular glaucoma, iridocorneal endothelial syndrome, fibrous and epithelial downgrowth, and uveitic glaucoma, are also common indications.

Conjunctival scarring from ocular operations, such as retinal detachment surgery or ruptured globe surgery, generally suggests the need for tube surgery, Dr. Rhee said.

“Tubes are much less labor intensive from the point of view of patient care, especially postoperatively,” Dr. Spaeth said, comparing the procedure to trabeculectomy. “There are certain parts of the world where that is an important consideration.”

Some surgeons encounter complex patient histories that may lend themselves to implantation of tube shunts.

“A tremendous number of patients in my practice have had grafts and stem cell transplants and just very complicated situations, and tubes have been a lifesaver in those patients,” Dr. Samuelson said at OSN New York.

Moreover, research conducted by Dr. Gedde and colleagues in the Tube Versus Trabeculectomy (TVT) Study suggests that patients with less refractory glaucoma, such as those who have undergone cataract extraction through phacoemulsification, may also be treated with tube shunts.

The primary risk associated with this procedure is diplopia, Dr. Samuelson said, but Dr. Spaeth said that the number of patients who suffer from this complication is less than 5%.

Aside from some minor modifications, Dr. Gedde’s technique is nearly universal for the implantation of all tube shunts. He prefers a fornix-based flap during surgery to improve exposure and ease closure. He attaches the plate to the sclera at a distance of 10 mm posterior to the limbus and thinks this tactic is particularly important when using the Baerveldt glaucoma implant (Abbott Medical Optics), so the plate does not crowd the muscle insertions.

“I would say having the reservoir well centered between the muscles is important to try to reduce or eliminate the risk for diplopia,” Dr. Samuelson said.

According to Dr. Gedde, complete restriction of flow is necessary when using non-valved implants and can be achieved by ligating the tube with a 7-0 Vicryl suture. He also thinks that tube fenestration is an effective means of lowering IOP in the early postoperative period.

Related studies

The TVT Study is a multicenter randomized clinical trial that enrolled lower-risk patients than have traditionally received tube shunts, such as those who already underwent cataract extraction or a trabeculectomy that failed.

“At least when the study was designed, this was a population of patients in which about 95% of glaucoma surgeons favored trabeculectomy,” Dr. Gedde said.

Even though the study has not demonstrated clear superiority of one procedure over the other, 3-year results showed a higher success rate for surgery with a 350 mm² Baerveldt implant than trabeculectomy with mitomycin C. IOP control, medication use and rates of serious postoperative complications were similar for the two treatment groups, but the cumulative probability of surgical failure for the 107 patients in the tube group was 15.1%, compared with 30.7% for the 105 patients in the trabeculectomy group.

“The TVT Study has given us a lot of excellent information that indicates that tubes are the preferred procedure after failed conjunctival procedure,” Dr. Rhee said.

Five-year results will be presented at the American Glaucoma Society annual meeting in March, and Dr. Gedde said these results are similar to the 3-year results.

Dr. Gedde also runs the Primary Tube Versus Trabeculectomy Study, which is enrolling patients who have not yet had ocular surgery and have low-risk glaucomas such as primary open-angle glaucoma, pigmentary glaucoma and pseudoexfoliation glaucoma.

Another study focusing on transscleral procedures, specifically tube shunts, is the Ahmed Baerveldt Comparison Study, a multicenter randomized prospective clinical trial comparing the Ahmed glaucoma valve (New World Medical) with the Baerveldt implant. The study enrolled 276 patients and after 1 year has shown a slightly higher average IOP in patients treated with the Ahmed glaucoma valve but also fewer early and severe postoperative complications in those patients.

Future of transscleral surgeries

Despite the lack of consensus regarding minimally invasive glaucoma surgeries, most surgeons agree that transscleral procedures will continue to play a role in the treatment of certain diseases, such as uveitic glaucoma, neovascular glaucoma, and advanced glaucoma that has either been diagnosed late or failed to respond to less invasive procedures.

“These transscleral procedures have been around for a long time, and until we have some clear evidence that other options are better, they are going to continue to play a major role in the surgical management of glaucoma patients,” Dr. Gedde said. He thinks that randomized prospective clinical trials would be necessary to establish minimally invasive procedures as the preferred surgical approach for managing glaucoma.

Dr. Spaeth does not think these newer procedures will be efficacious as treatment for more advanced disease.

“There is fairly good pathologic evidence demonstrating that, with people who have had glaucoma for a long time, the resistance to outflow is no longer in the trabecular meshwork but in the collector channels. Clearly, if what you are trying to do is shunt aqueous from the anterior chamber to the collector channels, and the collector channels are not working, that operation is not going to work,” Dr. Spaeth said.

Nevertheless, Dr. Spaeth shares the popular opinion that these procedures are appropriate for patients with early disease or those who are highly susceptible to infection from a bleb. Excitement for the newer surgeries is stronger in other surgeons who foresee the use of transscleral procedures as being more limited in the future.

“I think [minimally invasive glaucoma surgeries] give us access for the first time to tissues that we were not able to access before. We are operating within Schlemm’s canal itself. … We are operating on the site of the pathology,” Dr. Schuman said.

Despite such enthusiasm, most surgeons agree that the continued need for an operation that can reliably achieve low IOP will maintain the relevance of transscleral procedures, no matter what the future of minimally invasive surgery holds. — by Michelle Pagnani

Do you prefer implants or trabeculectomy when treating patients with advanced glaucoma?

References:

• Budenz DL, Barton K, Feuer WJ, et al. Treatment outcomes in the Ahmed Baerveldt Comparison Study after 1 year of follow-up [published online ahead of print Oct. 7, 2010]. Ophthalmology. doi:10.1016/j.ophtha.2010.07.016
• Gedde SJ, Heuer DK, Parrish RK 2nd; Tube Versus Trabeculectomy Study Group. Review of results from Tube Versus Trabeculectomy Study. Curr Opin Ophthalmol. 2010;21(2):123-128.

• Steven J. Gedde, MD, can be reached at Bascom Palmer Eye Institute, 900 NW 17th St., Miami, FL 33136; 305-326-6435; e-mail: sgedde@med.miami.edu.
• Douglas J. Rhee, MD, can be reached at Massachusetts Eye and Ear Infirmary, 243 Charles St., Boston, MA 02144; 617-573-3670; e-mail: dougrhee@aol.com.
• Thomas W. Samuelson, MD, can be reached at Minnesota Eye Consultants, 701 E. 24th St., Suite 100, Minneapolis, MN 55404; 612-813-3628; fax: 612-813-3656; e-mail: twsamuelson@mneye.com.
• Joel S. Schuman, MD, FACS, can be reached at UPMC Eye Center, University of Pittsburgh School of Medicine Dept. of Ophthalmology, Eye and Ear Institute, 203 Lothrop St., Suite 816, Pittsburgh, PA 15213; 412-647-2205; e-mail: schumanjs@upmc.edu.
• George L. Spaeth, MD, can be reached at Wills Eye Institute, 840 Walnut St., Philadelphia, PA 19107; 215-928-3197; e-mail: gspaeth@willseye.org.
• Disclosures: Drs. Gedde and Spaeth have no direct financial interest in any of the products discussed in this article, nor are they paid consultants for any companies mentioned. Dr. Rhee is a consultant and has research support from Alcon. Dr. Samuelson is a consultant for AMO, Alcon Surgical, Glaukos, AqueSys, Ivantis and Endo Optiks. Dr. Schuman receives royalties for intellectual property licensed by MIT to Carl Zeiss Meditec.