limbus­ (as commonly seen with limbus-based flaps), thus reducing the risk of serious complications such as leaks or endophthalmitis. The advantage of diffuse, low blebs with fornix-flap closure, when combined with mitomycin usage and releasable (or adjustable) flap sutures, makes it a technique of increasing and compelling popularity.41

Excision of tenon’s capsule

Some studies have suggested that excision of Tenon’s capsule in young people, in African-Americans, or in people who require reoperations may enhance filtration success.42–45 Evidence for this is not conclusive, and the use of antimetabolites has made much of the issue moot.46 If excision of Tenon’s capsule is desired, the dissection can be

facilitated by injecting xylocaine or saline between the capsule and conjunctiva; care must be taken to avoid conjunctival buttonholes.

Guarded Filtration Procedure

Trabeculectomy

Trabeculectomy, with its many modifications, is the most commonly used guarded filtration procedure. Cairns introduced the modern-day trabeculectomy in the 1960s.47 It was initially believed that aqueous escaped through the cut ends of Schlemm’s canal, but it subsequently became obvious that the major effect of the surgery

occurred via filtration of aqueous into the subconjunctival space.48 The reduced incidence of hypotony and flat anterior chambers made trabeculectomy attractive to glaucoma surgeons.

Indications

Trabeculectomy has become the standard glaucoma procedure, with excellent results for most forms of open-angle and chronic angle-clo- sure glaucoma. Aphakic, inflammatory, traumatic, and other secondary

forms of uncontrolled glaucoma also are treated by trabeculectomy; success rates are good when wound-healing retardants are used,49–51

although success rates tend to be lower than in uncomplicated cases. So long as mobile conjunctiva is available superiorly, despite a history of prior surgeries, the predictability of the trabeculectomy and its long-term efficacy at maximally lowering IOP make it the procedure of choice for the majority of uncontrolled glaucoma eyes.

As discussed more extensively in Chapter 37, trabeculectomy can be successfully combined with cataract extraction under a variety of circumstances. The most important advance allowing combined surgeries at one sitting has been the advent of the small-incision cataract/intraocular lens procedure. Thus modern techniques have broadened the indications52,53 for combining these procedures, and many surgeons report excellent results.54–57

Standard technique

There is a wide variety of surgical preferences and techniques developed in the last half-century of the trabeculectomy’s development, and we begin with a generalized approach, and conclude with the specifics of a successful fornix-flap technique from the Moorfield’s Eye Hospital in London.

The initial trabeculectomy procedure is usually performed at a site superiorly and slightly nasal.58 (This preserves the superotemporal area for repeat trabeculectomy or tube surgery if needed.) A corneal traction suture (e.g. 7-0 or 8-0Vicryl) is preferable to a superior rectus suture, so as to minimize conjunctival perforation superiorly, an area of potential bleb formation. In aphakic or pseudophakic glaucoma, the surgical area selected should have minimal conjunctival scarring. This can be determined by attempting to move the anesthetized conjunctiva with an instrument or by injecting xylocaine with epinephrine under the conjunctiva at the time of surgery. If the conjunctiva is tightly adherent to the globe, another site should be selected, based on the response to subconjunctival fluid dissection. In the face of inoperable superior conjunctival scarring, an alternative procedure, such as an inferonasal glaucoma shunt, can be selected.

The episcleral surface planned for the scleral flap is lightly cauterized (Fig. 34-8) to reduce bleeding. Excessive cauterization should be avoided, however. Cauterization can be done with wetfield cautery or with a microdiathermy instrument. Microdiathermy offers the advantage of pinpoint cauterization, which is useful when cauterizing individual vessels during the early parts of the procedure, and later in the operation for persistent microhemorrhage from the iris, ciliary body or deep sclera after excising the trabeculectomy specimen.

The scleral flap is usually one-third to one-half the scleral thickness, rectangular or triangular in shape, and dissected anteriorly towards the limbus (Fig. 34-9). Antimetabolites may be administered before or after the scleral flap is developed, but usually before any opening is made into the anterior chamber (Fig. 34-10). It is important to place a paracentesis at the peripheral limbus using a super-sharp blade after preparing the scleral flap but before otherwise entering the globe (Fig. 34-11). The paracentesis site is used to fill the chamber in the course of the procedure (e.g., with intra­ cameral miotic or saline), or to re-form a flat anterior chamber with saline or viscoelastic during the first postoperative weeks.

Fig. 34-8  Unipolar cautery to a scleral bleed in preparation for developing a scleral flap.

Fig. 34-9  Scleral flap.

Fig. 34-10  Mitomycin-C-soaked sponge (arrow) being removed from the subconjunctival space after 3–5 minutes of scleral contact.

After the scleral flap is extended past the limbus into the cornea and the paracentesis site has been made, the anterior chamber is entered under the flap (Fig. 34-12) and a block of tissue approximately 1.5–2.5 mm wide is removed with a Descemet’s punch just anterior to the scleral spur. Removal of the trabeculectomy block too posterior to the scleral spur offers no advantage and increases the risk of hemorrhage.

The surgeon may excise the block with Vannas scissors, a trephine, a scleral punch, or thermal cautery (Fig. 34-13).The success rate of these approaches is similar. A peripheral iridectomy should be performed in all phakic eyes, with care taken to avoid the iris base and ciliary body to prevent hemorrhage. (In an effort to avoid encountering vitreous prolapse through the trabeculectomy site, some surgeons omit an iridectomy in aphakic or pseudophakic eyes if another iridectomy is already present, or if laser iridotomy is readily available in the postoperative setting.)59

The scleral flap is reapproximated with 9-0 or 10-0 nylon sutures placed so that the anterior chamber is maintained after injection of saline, with a slow leak of fluid through the scleral wound indicating adequate filtration flow (Figs 34-14 and 34-15). In a simulation of the patient’s natural blinking effect on filtration, flow adequacy

Fig. 34-15  A slow leak of fluid from beneath the flap may be detectable under the operating microscope.

at the site can be checked by gently ‘burping’ or depressing posterior to the scleral flap with a surgical instrument. Based on clinical experience, the surgeon tightens the flap, anticipating future adjust-

ment with either releasable sutures or with laser suture lysis during the follow-up period.60–64b Since the surgeon’s careful assessment

of flow is critical before closing the eye, intracameral viscoelastic

– which temporarily interferes with fluid flow – is rarely helpful during uncomplicated filtering surgery.

The conjunctival flap is closed as described above, depending on the use of the fornix-based or limbal-based approach.The conjunctival flap should be water tight, as assessed by intracameral filling and inspection of the bleb (Fig. 34-16). Especially if an antimetabolite has been used, intraoperative leaks should be scrupulously identified (with either high-magnification inspection or fluorescein drops) and then closed; a #10-0 nylon or a #10-0 Vicryl suture on a tapered BV vascular needle works well for this. Most filters show quiet tissue after healing has completed (Fig. 34-17).

Moorfields Safer Surgery System technique

The technique popularized as the ‘Moorfields Safer Surgery System’  36,36b,36c,65 has been meticulously developed for consistent

results in a wide range of complicated glaucomas. The hallmark features of this technique as originally described are a fornix-based conjunctival flap, an anterior chamber maintainer, a standardized punch technique, and a combination of adjustable and releasable sutures. It is also compatible with a single-site combined phacoemulsification/intraocular lens procedure, with minimal modification.

A fornix flap is prepared, with careful posterior dissection lateral to the superior rectus muscle, in preparation for a dispersed application of mitomycin-C-soaked sponges for a diffuse, posterior bleb (Fig. 34-18). Next a 4–6 mm wide half-thickness scleral tunnel is prepared 4 mm from and centered at the 12 o’clock limbus. Only partial (1–2 mm) lateral incisions of the tunnel flap are made, but not extended to the limbus itself; this inhibits any lateral aqueous accumulation at the limbus and instead encourages its posterior flow superiorly (Fig. 34-19A).

The recommended applicators for antimetabolite are bisected, 6-mm polyvinyl-alcohol round, corneal sponges (used in LASIK surgery), whose advantages include a predictable release of anti­ metabolite as well as resistance to shredding under the conjunctiva. (Alternative applicators can be cut free-hand as longitudinal strips of triangular-shaped cellulose sponges, which when cut thin enough will, with hydration by antimetabolite, become flat rectangular strips, easily insinuated and removed from the subconjunctival space (Fig. 34-19B,C,D). Either mitomycin-C (0.2 mg/cc) or 5-FU as 5 mg/0.1 cc is applied to the sponge strips. As many as six hemi-sponges are carefully insinuated posteriorly beneath the conjunctiva, adjacent to the superior rectus muscle and laterally (Fig. 34-20). While the sponges are in place, the conjunctival edges are carefully suspended away from the mitomycin. A small sponge (or strip fragment) is placed beneath the trabeculectomy flap in the bed of the scleral tunnel (Fig. 34-21). After 3 minutes the sponges are all removed, a sponge count is performed, and subconjunctival irrigation performed.

Next a Lewicke anterior chamber maintainer is placed through a microvitreoretinal (MVR)-blade incision at the 6 o’clock periph-

Fig. 34-16  Water-tight conjunctival closure. A diffuse bleb has begun to form immediately.

Fig. 34-17  Filtering bleb 1 year after trabeculectomy.

Fig. 34-18  Fornix flap allows posterior undermining of conjunctiva adjacent to superior rectus.

(Fig. 34-22A,B). A relatively small trabeculectomy stoma (0.5–1 mm) is created with a scleral punch beneath the flap, and a peripheral iridectomy performed (Fig. 34-23). The flap is closed with two or more ‘adjustable’ sutures, using a 4-loop slip-knot closure­ (Figs 34-24 and 34-25).The conjunctival flap is then closed at the limbus using lateral phimotic stitches and corneal ‘scratch’ incisions to bury #10-0 Vicryl mattress sutures (see Fig. 34-7C,D). The merit of the ‘adjustable’ sutures is that postoperatively at the slit lamp, a blunt forceps (e.g., fine needle driver) can transconjunctivally wiggle and loosen them, effecting an incremental drop in IOP (Fig. 34-25).

The typical postoperative course following trabeculectomy surgery is characterized by little discomfort, several weeks of improving vision, and frequent office visits. Unless severe hypotony, a flat anterior chamber, or a hyphema is present, there is little reason to limit the patient’s activity beyond the routine restrictions common to outpatient eye surgery. Although hospitalization may be useful for the convenience or medical access of the patient, it is not warranted on the basis of the procedure’s healing course: trabeculectomy is considered an outpatient operation. Subconjunctival steroids and antibiotics are injected at the end of surgery, and topical steroids are usually instilled 4–8 times per day during the first