Trabeculectomy

Indications

Trabeculectomy is indicated for eyes with open angle glaucoma that have an intraocular pressure (IOP) that is inadequate despite maximum tolerated medical therapy and appropriate use of laser trabeculoplasty. Indications include progressive (or the high likelihood of progressive) functional or structural glaucomatous injury. Patients without access to medical treatment or laser surgery may require trabeculectomy as an option to these therapies. Primary surgery may also be indicated on the basis of socioeconomic or logistical constraints. Individual patient factors, such as an inability to comply with the prescribed medical therapy, inability to instill eye medications, and low target IOP may also influence the decision to proceed to surgery.

Trabeculectomy has been, and remains, the most widely performed incisional surgical procedure for glaucoma worldwide. This is a result of its high success rate, efficacy at IOP lowering, and technical advances over the past thirty years designed to enhance surgical success and minimize complications.

Many factors may affect the success rate of trabeculectomy. These include type of glaucoma, race,1,2 age,3,4 prior history of failed trabeculectomy,1 aphakia or pseudophakia, intraocular inflammation,3 the use of antifibrotic agents,1,5,6 and co-morbidities requiring combination surgeries such as cataract,1,7 retinal disease, and corneal disease. In general, individuals with risk factors that may lead to excessive scarring, such as African ancestry, prior incisional surgery or glaucomas associated with intraocular inflammation, are at increased risk for filtration failure.

Preoperative evaluation and risk assessment

The risks of trabeculectomy can be categorized as intraoperative, early postoperative, and late postoperative. Intraoperative complications include hyphema, suprachoroidal hemorrhage and effusion, iridodialysis, cyclodialysis, conjunctival injury, scleral flap or conjunctival dehiscence, vitreous hemorrhage, and vitreous loss. Early postoperative complications include wound leak, shallow/ flat chamber, endophthalmitis, hypotony maculopathy, corneal abrasions, suprachoroidal effusion and hemorrhage, malignant glaucoma, and overand underfiltration. Late complications include, cataract, bleb related ocular infection, bleb leak, bleb dysesthesia, and filtration failure (including Tenon’s cyst, and scarring at the conjunctiva-Tenon’s fascia-episcleral interface).

One can use topical, local infiltration, peribulbar, retrobulbar (used with caution in those with advanced field loss), or general anesthesia. These methods can be augmented with a lid block. The choice depends on the patient and the surgeon’s comfort level. Topical anesthesia with local infiltrative supplementation offers an excellent approach for cooperative patients. Surgical exposure can be enhanced by instructing the patient to look in a position of gaze and does not require the use of corneal or superior rectus traction sutures. While topical

anesthesia is useful for the experienced surgeon, the surgeon who performs glaucoma surgery on a less regular basis may find the use of regional anesthesia more comfortable. Poorly cooperative or uncooperative patients are better candidates for regional anesthesia than topical anesthesia.

Preoperative assessment includes considering the discontinuation of anticoagulants (aspirin, warfarin, etc.) prior to surgery whenever possible to minimize the risk of intraocular hemorrhage. Medications known to increase conjunctival hyperemia also may be discontinued provided that IOP remains satisfactorily controlled.8 One may choose to start preoperative antibiotics and/ or steroids (for inflamed eyes) prior to surgery. This might include a topical antibiotic administered four times daily to both eyes commencing three days prior to surgery and topical prednisolone acetate 1% to the operative eye beginning one week preoperatively. The latter causes a decrease in conjunctival hyperemia and may help reverse glaucoma drug-induced changes in conjunctival morphology.

Procedure

Trabeculectomy reduces IOP by bypassing the outflow tract9 and allowing aqueous humor to exit through the internal ostium, beneath the scleral flap and under the conjunctiva where it forms a filtering bleb.10 This fluid is then absorbed into the periocular tissues.

After the correct eye is identified and confirmed with the patient, the patient is prepped and draped in the usual fashion for intraocular surgery. A single drop of Betadine 5% should be administered in the operating room for bacterial prophylaxis. A superior corneal traction or superior rectus bridle suture may be placed if required for adequate exposure11 or the patient should be instructed to infraduct the globe if topical anesthesia is used. Depending on the choice of a limbusor fornix-based flap, the conjunctiva is incised approximately 10 mm behind the limbus or at the limbus, respectively.12,13 A fornixbased conjunctival flap offers the theoretical advantage of a more diffuse, posterior bleb. A limbus-based conjunctival flap is technically more difficult, may limit the posterior extent of filtration due to scarring at the suture line, and requires more operating room time, but often provides for an easier watertight closure. Creation of the conjunctival flap should be performed with blunt dissection to create a plane in the episcleral space. Toothed forceps should be avoided or used with caution when handling conjunctiva to minimize trauma and prevent creation of an inadvertent buttonhole. Hemostasis is controlled with focal light cautery to minimize bleeding.

Antifibrotic agents such as mitomycin C or 5-flurouracil on a sponge may be placed at this time or after the dissection of the partial thickness scleral flap. The antifibrosis agent is best placed between Tenon’s fascia and episclera and should cover a wide area to reduce the risk of creating a small, focal bleb.

Although adjunctive antifibrosis agents enhance the success of trabeculectomy, their risk/benefit ratio should be assessed for each individual patient prior to use. This applies to initial and repeat surgeries.

Eyes undergoing trabeculectomy should have a paracentesis to allow reformation of the anterior chamber and to test the security of the scleral flap and conjunctival closure. It is important to avoid lens touch when forming the paracentesis.

Following dissection of the partial thickness lamellar scleral flap into clear cornea, the anterior chamber is entered at the base of the scleral flap with sharp blade, diamond knife or similar instrument. A punch or other instrumentation is used excise a section of cornea and trabecular meshwork. An iridectomy is performed. To close the flap, 10-0 nylon sutures, which can be preplaced are used. The anterior chamber is reinflated, flow through the flap is adjusted to allow egress of aqueous while maintaining adequate pressure, and the sutures are tied. The conjunctiva is brought back to the limbus in a fornix-based flap and sutured. A limbus-based flap requires a running closure. A fluorescein strip can be used to test for leaks. Cycloplegia is placed in phakic patients to help maintain the depth of the anterior chamber. Subconjunctival injection or topical steroids and antibiotics may be given.

Although operating time may vary depending on experience of the surgeon and the technique used, the surgical technique is within the ability of most ophthalmic surgeons. Identification and management of postoperative complications requires significant experience, and may be more important than even the surgery to obtain a successful outcome.

Postoperative management

Postoperative medications are begun on the day of surgery. These include postoperative antibiotics qid for one week, long-acting cycloplegia, when indicated, to maintain anterior chamber depth and frequent dosing of topical prednisolone acetate 1% for several weeks after surgery. Cycloplegics help maintain anterior chamber depth by relaxing the ciliary muscle, tightening the zonular apparatus, and pulling the lens posteriorly.

Suppression of inflammation is critical to success.3 Topical steroids are tapered based upon the anterior chamber response initially, but later based upon conjunctival hyperemia. The duration of topical steroid therapy varies widely, and some patients require continuation for four or more months. Supplemental 5-fluorouracil may be used as necessary to limit scarring14 and is typically given in 5.0 to 7.5 mg doses several times per week as required. Minimizing aqueous suppressant use may enhance bleb formation.

Laser suture lysis or removal of releasable sutures, if necessary, is often performed within several weeks of surgery to enhance aqueous drainage. With planned sequential suture release, initial postoperative hypotony and excessive

filtration can be avoided. Suture release should be performed within one week in eyes not receiving antifibrosis agents, but may be postponed for a few weeks after 5-fluorouracil surgeries and for even longer after mitomycin-C.

Interventions are needed as complications arise. Early recognition of postoperative complications and timely, appropriate intervention enhances the success rate of surgery and minimizes patient morbidity. The surgeon must be prepared and equipped to manage post-filtration surgery complications such as hypotony, anterior chamber shallowing, and malignant glaucoma, among others. Adjunctive techniques to limit excessive filtration include patching, large diameter contact lenses, and symblepharon rings. Anterior chamber shallowing may require reformation. Choroidal effusion typically resolves with elevation of IOP, but may upon occasion necessitate drainage.

Late complications of filtering surgery include prolonged hypotony associated with hyptony maculopathy and bleb-related ocular infection. Loss of vision due to hyptony maculopathy is more common in younger, myopic patients and may require surgery to repair the hypotony and restore normal IOP. Thinwalled blebs, often associated with focal leakage, are more prone to late blebrelated ocular infection. Conjunctivitis in the presence of a filtering bleb or bleb infection should be treated as a medical emergency as it may lead to infectious endopthalmitis and loss of vision or the eye. Patients that have had trabeculectomy should be warned of the signs and symptoms of late bleb-re- lated ocular infection and should be counseled to seek immediate attention should these occur.

Research considerations

The IOP measurement for research studies should include a mean pressure at different time points after the surgery. A successful surgery should be defined as one that achieves a target IOP that prevents, or will likely prevent, further damage to the visual field or optic nerve/ganglion cells. One can include success rates exclusive and inclusive of additional medical therapy. The progression of glaucoma can also be followed by assessing the RNFL/ONH. No study of surgery should include results that are less than 12 months for an initial report and should preferably be longer than 2 years. Long-term success (greater than 5 years) should be reported whenever possible.

The quality of life can be measured by detailed questionnaires,15 that can be internet based in the future. Complications can be measured by considering separately intraoperative, immediate postoperative, and late complications.

Levels of evidence

There is no evidence on the relationship between the size/shape of the scleral flap and the success of the operation. There is a higher chance of success with antifibrotics; however, the incidence of postoperative complications is greater than without antifibrotics.1,5,16 In general, lower pressure measurements with less IOP fluctuation can be achieved with filtering surgery than with medical therapy.17-21

References

1.The Fluorouracil Filtering Surgery Study Group. Five-year follow-up of the Fluorouracil Filtering Surgery Study. Am J Ophthalmol 1996; 121: 349-366.

2.AGIS Investigators. The Advanced Glaucoma Intervention Study (AGIS): 9. Comparison of glaucoma outcomes in black and white patients within treatment groups. Am J Ophthalmol 2001; 132: 311-320.

3.AGIS Investigators. The Advanced Glaucoma Intervention Study (AGIS): 11. Risk factors for failure of trabeculectomy and argon laser trabeculoplasty. Am J Ophthalmol 2002; 134: 481-498.

4.Ederer F, Gaasterland DA, Dally LG, Kim J, VanVeldhuisen PC, Blackwell B, Prum B, Shafranov G, Allen RC, Beck A; AGIS Investigators. The Advanced Glaucoma Intervention Study (AGIS): 13. Comparison of treatment outcomes within race: 10-year results. Ophthalmology 2004; 111: 651-664.

5.Liebmann JM, Ritch R, Marmor M, Nunez J, Wolner B. Initial 5-fluorouracil trabeculectomy in uncomplicated glaucoma. Ophthalmology 1991; 98: 1036-1041.

6.WuDunn D, Cantor LB, Palanca-Capistrano AM, Hoop J, Alvi NP, Finley C, Lakhani V, Burnstein A, Knotts SL. A prospective randomized trial comparing intraoperative 5-fluo- rouracil vs mitomycin C in primary trabeculectomy. Am J Ophthalmol 2002; 134: 521528.

7.Jampel HD, Friedman DS, Lubomski LH, Kempen JH, Quigley H, Congdon N, LevkovitchVerbin H, Robinson KA, Bass EB. Effect of technique on intraocular pressure after combined cataract and glaucoma surgery: An evidence-based review. Ophthalmology 2002;

109:2215-2224.

8.Lavin MJ, Wormald RP, Migdal CS, Hitchings RA. The influence of prior therapy on the success of trabeculectomy. Arch Ophthalmol 1990; 108: 1543-1548.

9.Taylor HR. A histologic survey of trabeculectomy. Am J Ophthalmol 1976; 82: 733-735.

10.Cairns JE. Trabeculectomy. Preliminary report of a new method. Am J Ophthalmol 1968;

66:673-679.

11.Caronia RM, Liebmann JM, Friedman R, Cohen H, Ritch R. Trabeculectomy at the inferior limbus. Arch Ophthalmol 1996; 114: 387-391.

12.Traverso CE, Tomey KF, Antonios S. Limbalvs fornix-based conjunctival trabeculectomy flaps. Am J Ophthalmol 1987; 104: 28-32.

13.Shuster JN, Krupin T, Kolker AE, Becker B. Limbusvs fornix-based conjunctival flap in trabeculectomy. A long-term randomized study. Arch Ophthalmol 1984; 102: 361-362.

14.Lama PJ, Fechtner RD. Antifibrotics and wound healing in glaucoma surgery. Surv Ophthalmol 2003; 48: 314-346.

15.Janz NK, Wren PA, Lichter PR, Musch DC, Gillespie BW, Guire KE, Mills RP; CIGTS Study Group. The Collaborative Initial Glaucoma Treatment Study: interim quality of life

Robert Weinreb, Franz Grehn, Jeff Liebmann (speaker)