Publications

REPEAT TRABECULECTOMY

AHMED M. ABDELRAHMAN, YASMINE EL SAYED. 

THE ISGS TEAXT BOOK OF GLAUCOMA SURGERY 

INTRODUCTION

The current operation of choice in glaucoma is trabecu- lectomy, which produces a guarded filtration between the anterior chamber and the subconjunctival space.1 Since its introduction, trabeculectomy underwent modifications, including the size, the shape, and the thickness of the scleral flap, limbal or fornix-based conjunctival flaps, fixed or adjustable sutures and the use of antimetabolites and other antiscarring agents all aimed at optimizing the result of the operation.2

Success rate of filtration surgery (alone, or with adjunctive medical therapy) in a previously unoperated eye is reported to be up to 90% at 2 years with large differences in the criteria used for the definition of success.3-5 Following trabeculectomy, complete success is commonly defined as a controlled intraocular pressure (IOP) without antiglaucoma medications, qualified success is achieving a controlled IOP with topical eye drops, and failure is usually defined as the inability to maintain such a pressure despite maximum tolerated medical treatment, hence necessitating another surgical intervention.6

Healing and scarring are the main determinants of long-term IOP control after trabeculectomy.7 Eyes which are at higher risk of scarring are less likely to have a successful trabeculectomy. Those include eyes with neovascular glaucoma, eyes that underwent recent ocular surgery of less than 3 months duration or a conjunctival surgery, aphakics, inflammatory eye diseases like uveitis and ocular cicatricial pemphigoid, and chronic use of topical antiglaucoma medications. Other factors such as

race and age also influence the scarring response. It is therefore worthwhile analyzing the risk profile for each patient preoperatively in order to determine whether the use of cytotoxic agents would be beneficial or necessary.8,9

SUBSEQUENT MANAGEMENT OPTIONS AFTER FAILURE OF THE INITIAL TRABECULECTOMY

After the first operation, if the target IOP is not achieved and the visual field continues to deteriorate, then adding a tolerable topical antiglaucoma medication becomes an option; otherwise a second intervention is needed. There is currently no consensus among glaucoma surgeons on what to do when the first trabeculectomy fails. The surgical options in case of uncontrolled IOP following a previous trabeculectomy are needling, excision of encapsulation tissue, revision of the original trabeculectomy, re-do trabeculectomy at another site, deep sclerectomy with mitomycin C (MMC), a tube or, usually in cases with poor visual potential, cyclodiode.

Needling is a relatively minor procedure that can help save many failed or failing blebs especially if combined with antimetabolites10 and is usually the first resort when the IOP starts to rise. The success rate ranges from 45% to 90%10-12 and is higher when needling is performed within 4 months of the initial trabeculectomy.11 Risk factors for needling failure include preneedling IOP greater than 30 mm Hg, an IOP greater than 10 mm Hg immediately after needling and lack of MMC use in the initial filtration surgery.12 The procedure can be performed at the slit lamp

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16

Repeat Trabeculectomy

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Ahmed M Abdelrahman, Yasmine El Sayed

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2

Trabeculectomy: Technique and Rescue Operations

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and has been combined with an ab interno approach resulting in a success rate of 77% at 1 year.13 It can be repeated several times but usually if the first two needlings are unsuccessful an alternative surgical option is needed.

Surgical excision of Tenon’s cyst may be performed if multiple needlings result in temporary success with re-encapsulation of tissues. Careful dissection of overlying conjunctiva is followed by the excision of the dome- shaped encapsulated tissues then watertight closure of the conjunctiva.

Revision of a pre-existing scleral flap to re-establish filtration together with MMC application has shown a success rate in the range of 38% without antiglaucoma medications and 64% with medications and/or needling. However, the risk of complications was high with delayed suprachoroidal hemorrhage occurring in 5.6% of eyes, delayed bleb leaks in 9.3%, and blebitis in 3.7%.14 The authors prefer a posterior fornix approach for conjunctival dissection. Mitomycin C 0.2% is applied for 2–3 minutes before removal of the fibrous tissue overlying the scleral flap to reduce the risk of its intraocular penetration. This posterior approach has shown a success rate of 85% at 5 years and with minimal complications.15 We believe the success depends on the proper choice of cases. The authors do not revise trabeculectomies in which the bleb is too injected, flat rather than encapsulated or when the surgical details of the initial procedure are unknown. In these cases an alternative intervention is resorted to.

Deep Sclerectomy with Mitomycin C

Twenty eyes with a previously failed trabeculectomy were treated with deep sclerectomy with 0.2 mg/mL MMC application under the conjunctiva and the superficial scleral flap. Sixty percent of the cases achieved an IOP less than or equal to 15 mm Hg with and without medication. No cases of shallow or flat anterior chamber, endophthalmitis, or leakage developed.16

The Tube versus Trabeculectomy study is currently the major, multicenter, randomized clinical trial designed to answer the question of whether insertion of a 350 mm2 Baerveldt implant or a re-do trabeculectomy with MMC should be performed in eyes with medically uncontrolled glaucoma that have previously undergone filtering surgery and/or cataract extraction with intraocular lens implantation. Both the 3 years and 5 years results showed comparable IOP reduction and need for antiglaucoma medications. Patients who had a re-do trabeculectomy

were more likely to need additional glaucoma surgery. Early complications were more common with the trabeculectomy group, but the incidence of late post- operative complications and serious complications was similar for both procedures.17-19

The authors prefer to implant a tube rather than repeat the trabeculectomy in refractory cases of glaucoma, namely aphakic, neovascular, uveitic, postkeratoplasty, iridocorneal endothelial syndrome and in pediatric age groups.

The choice of treatment following a failed trabe- culectomy is often individualized to each patient where factors such as age, the visual potential of the eye, the ocular anatomy and details of the primary procedure as well as the condition of the other eye may guide the decision.

RISKS AND TECHNICAL CONSIDERATIONS DURING REPEAT TRABECULECTOMY

Repeating trabeculectomy in an eye that had previously undergone the same surgery carries its own risks and complications in addition to the usual complications of trabeculectomy surgery. Extra care and planning should be implemented to help reduce these risks and achieve optimal results.

Surgical Location

Deciding the site of the repeat surgery is probably the first to consider. Usually the primary trabeculectomy would be at 12 o’clock. Accordingly the surgeon is left with two quadrants to choose from for the re-do, either the superonasal or superotemporal. In an eye that had failed an initial trabeculectomy, there may be a need to consider a tube in case the repeat trabeculectomy fails. Superonasal blebs were found to be associated with higher risk of bleb dysesthesia,20 so it is better to avoid the superonasal quadrant. However, if a tube surgery is likely to be needed later on, then leaving the superotemporal quadrant untouched may be the more reasonable option, to improve the chances of tube success. Of course if the primary trabeculectomy was decentered superonasally or superotemporally then the superotemporal or superonasal quadrant, respectively, would be the next choice (Figs 16.1 and 16.2). The inferior quadrants should be avoided because of the higher risk of infection and endophthalmitis.21

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Fig. 16.1: Shows a repeat trabeculectomy in the upper nasal quad- rant following a failed trabeculectomy at 12'o clock position in a pseudophakic eye

Conjunctival and Tenon’s Capsule Incision

Conjunctival dissection is more difficult in re-do cases namely because of scarring at the conjunctival-episcleral interface. It may be useful to “hydrodissect” the conjunctiva through subconjunctival injection of balanced saline solution to facilitate its dissection. The conjunctiva is also more likely to be friable with a higher risk of inducing buttonholes and bleeding during its dissection. In some cases it may be worthwhile revising the original bleb especially if thin and cystic in addition to creating the new trabeculectomy (Figs 16.3A and B). However, extra care

Repeat Trabeculectomy 3

Fig. 16.2: Three trabeculectomies

should be taken as inadvertent opening of the previous trabeculectomy may lead to hypotony making it difficult to proceed further with the operation (Fig. 16.4).

Antimetabolites

Because eyes undergoing re-do trabeculectomy are at a higher risk of failure than with primary trabeculectomy, the use of adjunctive antimetabolites is strongly advocated.22-24 Although intraocular penetration of anti- metabolites through the previous trabeculectomy is at least a theoretical risk that should be avoided by cautious

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AB

Figs 16.3A and B: (A) Conjunctival dissection to repeat a trabeculectomy adjacent to an old failed ischemic bleb; (B) Postoperative appearance after the re-do in addition to excision of the old bleb and conjunctival reconstruction resulting in a diffuse, healthier-looking bleb

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4

Trabeculectomy: Technique and Rescue Operations

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Fig. 16.4: Shows uveal tissue prolapse as a result of accidental

 

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