Not Your Father’s Filtration Surgery

Seven ways to bring your approach to trabeculectomy into the 21st Century.

FRANK COTTER, MD

At the 2013 American Glaucoma Society meeting, one ophthalmic company had several poster advertisements displayed around the hotel that read “The 1960s called. They want their filtration surgery back.” The message, of course, is that trabeculectomy is an obsolete, 50-year-old procedure that needs to be retired and replaced.

Most glaucoma specialists would agree. Postoperative management of trabeculectomy is often difficult, time consuming and fraught with potential complications. Severe short-term complications include flat chambers, malignant glaucoma, choroidal effusions and choroidal hemorrhage. Long-term complications such as bleb dysesthesia, dellen, bleb migration over the cornea, bleb leaks and late endophthalmitis have been a major concern.

So, why were approximately 47,000 trabeculectomy procedures (including 16,000 express shunts) performed in the United States last year? This article will explore the answer to that question.

Lower Target IOP and Safer Techniques

Part of the answer lies in the conclusions drawn from a variety of well-designed clinical trials including AGIS, CIGTS and others. These studies strongly have suggested that patients with advanced glaucomatous field loss do best with IOPs in the high single digits or low teens. Currently, trabeculectomy is the glaucoma procedure that can most reliably achieve an IOP of 12 mm Hg or lower.

In the Tube Versus Trabeculectomy Study, long-term IOP control was similar in both groups.¹ However, experienced glaucoma surgeons can modify their technique with trabeculectomy to reach a target IOP in the high single digits when necessary. A surgeon can modify the duration and concentration of mitomycin application, excision of tenon’s fascia, 5fu injections, suture lysis and the sclerostomy and scleral flap size to create added filtration and lower IOP. In contrast, IOP modulation with tube shunts is mainly done with adjunct drop therapy.

Several micro-invasive glaucoma surgeries (MIGS) have been developed. Viscocanalostomy, canaloplasty, trabectome and the trabecular micro-bypass shunt (iStent, Glaukos, Laguna Hills, Calif.) are currently approved with widely varying degrees of adaptation. Trials are currently underway with at least one other trabecular micro-bypass shunt (Hydrus microstent, Ivantis, Irvine, Calif.) and two suprachoroidal microstents (CyPass Micro-Stent, Transcend Medical, Menlo Park, Calif.; and Solx Gold Shunt, Solx Inc., Waltham, Mass.).

Figure 1. A thin, cystic, limbal bleb at the limbus is prone to causing bleb dysesthesia and late complications.

MIGS have significantly lower complication rates than trabeculectomy. However, MIGS procedures tend to lower IOP only into the mid-teens at best. If a patient requires sustained IOP of 12 mm Hg or lower, then a MIGS procedure is unlikely achieve the target IOP.

Another reason trabeculectomy remains popular is that it’s a very different procedure than the trabeculectomy we performed 10 years ago. Several modifications have helped trabeculectomy surgery become safer and more reliable. The following seven features characterize the “new” trabeculectomy.

Wide, posterior application of mitomycin

1 This, in my opinion, is the most significant modification of the procedure. The goal is to avoid small, thin, cystic blebs at the limbus (Figure 1) that can break down and cause late onset endophthalmitis. Blebs develop this appearance when surgeons apply a single sponge containing high concentrations of mitomycin (0.4 mg/cc or greater) directly over the scleral flap with a small area of conjunctiva draped over the sponge. Removing tenon’s fascia from the area compounds the problem.

Wide application of lower-dose mitomycin is now recommended. My technique utilizes three mitomycin-soaked sponges approximately 6 mm in length and 2 mm in width. I place them under the fornix-based flap between the sclera and tenon’s fascia (Figure 2, page 56). I push the sponges posteriorly to create a wide arc and connect them with a 6-0 silk suture (the other half of the corneal traction suture) so that the sponges cannot get lost (Figure 3, page 56). The mitomycin concentration is usually 0.2 mg/cc with an application time of one to three minutes, depending on conjunctival appearance, risk factors and target IOP. I copiously irrigate the subtenon’s space with BSS after I remove the sponges.

Many surgeons are rapidly adopting an intriguing alternative to mitomycin application. Long-term comparative results of almost 250 patients were presented at the AGS meeting this year by Michele Lim, MD, and James Brandt, MD, of University of California, Davis.² I have performed this technique on about 10 cases and I like it.

The technique involves diluting the mitomycin to 0.05 to 0.1 mg/cc and then drawing it up into a TB syringe. It’s critically important to dilute the mitomycin to avoid an overly ischemic bleb. At the beginning of the case and before the conjunctival incision is initiated, 0.1 cc of mitomycin is injected with a 30-g needle through and underneath the superior conjunctiva as far posterior as possible (10-12 mm) (Figure 4, page 57). A small bleb is created and the mitomycin is dispersed using a muscle hook (Figure 5, page 57). The procedure is then initiated as usual.

Results reported at AGS were comparable to the method utilizing sponges. This technique has several advantages, including a more precise dosing of the mitomycin, elimination of “lost sponges” and shorter surgical time. Further, without having to place three large sponges under the conjunctiva, much less stress is placed on the conjunctival wound edges. This results in far fewer conjunctival tears, especially in patients with thin, diaphanous conjunctiva.

Fornix-based conjunctval incisions

2 Fornix-based flaps with wide, posterior dissection between the sclera and tenon’s fascia have become much more popular. The posterior dissection, along with the posterior placement of mitomycin, promotes aqueous flow away from the limbus with a more even distribution of the aqueous for absorption. The goal is a low diffuse, and only mildly ischemic bleb with good microcyst formation (Figure 6, opposite page).

Figure 2. Sponges are placed posteriorly between tenon’s fascia and sclera.

Figure 3. The sponges are connected with a silk suture (the other half of the corneal traction suture). This provides for easy removal and prevents lost sponges.

Limbus-based flaps can often create a scar at the incision line that can prevent posterior migration of the aqueous. The result can often be creation of anterior, high, thin, avascular blebs vulnerable to the long-term complications discussed earlier. Limbus-based flaps are also prone to late bleb migration over the cornea, inducing irregular astigmatism and decreased visual acuity. I have not seen this complication with fornix-based flaps constructed with posterior dissection and mitomycin placement.

Express shunt

3 The express shunt is a rather minor adaptation to one part of the trabeculectomy procedure. It allows for a uniform outflow of aqueous which helps with predictability of flow and a slightly lower incidence of flat chambers postoperatively. I perform express shunts in patients with grade III or IV angles and trabeculectomy in cases with grade II or narrower angles.

A peripheral iridectomy is not necessary when utilizing an express shunt. However, many surgeons have already abandoned the peripheral iridectomy during trabeculectomy, especially in pseudophakic patients or phakic patients with Grade III or wider angles.

Tight scleral flap closure with postoperative laser suture lysis

4 Ideally, IOP reduction with trabeculectomy should be controlled and gradual. Postoperative hypotony should be avoided. Fairly tight scleral flap closure with postoperative suture lysis offers the best chance for gradual, controlled IOP reduction into the target range. Many surgeons place releasable sutures.

Meticulous conjunctival wound closure

5 Watertight conjunctival closure is essential for success. Leaks can result in hypotony, loss of bleb architecture and failure. I use an 8-0 vicryl on a BV130 needle to close my fornix-based incision. I make my incision leaving 0.5 mm of conjunctiva attached at the limbus. When re-approximating the conjunctiva, I pull the conjunctiva to one side until the conjunctival edge is flush with the limbus. I close the “dog ear” with a running suture and the limbal conjunctiva with a horizontal mattress suture.

James Wise, MD, described another excellent watertight wound closure technique for trabeculectomy.³ Gary Condon, MD, has popularized and slightly modified it.⁴

Figure 4. A 30-g needle is used to inject 0.1 cc of mitomycin. A small bleb is formed.

Figure 5. A muscle hook is used to disperse the mitomycin.

‘Topical’ anesthesia

6 Most surgeons have adopted some form of “topical” anesthesia for trabeculectomy. My regimen has several steps. In the preoperative area, I apply one drop of Tetravisc (tetracaine, Altaire Pharmaceuticals Inc., Aquebogue, N.Y.) about 10 minutes before surgery. In the OR, I apply topical tetracaine with a tetracaine-soaked weck cell sponge to the superior conjunctiva for about 30 seconds.

After my initial conjunctival incision at the limbus, I inject preservative-free lidocaine 1% subconjunctivally. Before the iridectomy, I inject a few drops of lidocaine intracamerally. This combination provides excellent comfort and avoids the risk of a retrobulbar or peribulbar injection.

Figure 6. The goal of the “new” trabeculectomy is a low, diffuse and only mildly ischemic bleb.

Corneal traction suture

7 The corneal traction suture has clear advantages over the superior rectus bridal suture when performing trabeculectomy. The corneal traction suture provides superior exposure while avoiding bleeding, conjunctival manipulation and the possibility of globe perforation.

Conclusion

The poster at AGS was right. The 1960s can definitely have its filtration surgery back. We have moved on from the days of full-thickness procedures with thin, cystic, limbal blebs. But I want to keep my 2013 version of trabeculectomy for a while. Improvements to this procedure over the past decade have made it much safer and better tolerated. For my patients with advanced glaucoma and a target IOP of 12 mm Hg or less, trabeculectomy still offers the best chance for visual field preservation. OM

References

1. Gedde SJ, Schiffman JC, Feuer WJ, et al. Treatment outcomes in the Tupe Versus Trabeculectomy Study after five years of follow-up. Am J Ophthalmol. 2012;153:789-803.

2. Lim MC, Paul T, Gong MG, Brandt JD, Watnik MR, Samimi SA. A comparison of trabeculectomy surgery outcomes with mitomycin-C applied by intra-tenon injection versus sponge method. Paper presented at: American Glaucoma Society 23rd Annual Meeting; March 7, 2013; San Francisco, CA.

3. Wise, JB. Mitomycin-compatible suture technique for fornix-based conjunctival flaps in glaucoma filtration surgery. Arch Ophthalmol. 1993;111:992-997.

4. Condon GP. Closing the fornix based conjunctival flap. EyeTube.net. Available at: http://eyetube.net/search.asp?q=Condon.

Frank Cotter, MD, is a glaucoma consultant at Vistar Eye Center in Roanoke, Va. He can be reached at jsc1of6@yahoo.com. Disclosure: Dr. Cotter has no conflicts to disclose.