47   Combined Phacoemulsification and Glaucoma Procedures

More than 12 years have passed since the publication of the first edition of this book, and in those years much has changed in the realm of glaucoma surgery, just as it has with phacoemulsification. Preferred techniques have evolved; new surgical implants and adjunctive devices have been developed. The surgeon wishing to combine a glaucoma procedure with cataract surgery has more and, arguably, better options today. Nonpenetrating canal-based procedures such as deep sclerectomy and viscocanalostomy have mostly given way to canaloplasty. Glaucoma drainage devices, or tube shunts, are gaining popularity. Microinvasive glaucoma surgery (MIGS) is rapidly progressing (see Chapter 47). Even the time-honored trabeculectomy, which remains the gold standard for surgical intraocular pressure (IOP) reduction, has seen significant improvements over the last decade.

Preoperative Consideration and Factors that Predispose to Complications

Surgeons must recognize and manage complications as they arise, but avoidance of complications is always preferable. Awareness of potential issues enables the surgeon to take the necessary steps preoperatively to limit intraoperative complications and achieve a successful outcome.

Bleeding

Although not normally a concern in routine cataract surgery, bleeding can be a significant problem during glaucoma procedures. Bleeding complications range from a substantial nuisance during conjunctival and scleral dissection to severe intraocular or subconjunctival bleeding that can affect other aspects, or even the ultimate success, of the procedure. Numerous systemic medications routinely used by patients contribute significantly to risk of intraoperative bleeding. All forms of blood thinners, including warfarin, aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), platelet aggregation inhibitors, and even perhaps vitamin E in high doses potentially increase bleeding during surgery.¹ Warfarin exerts its anticoagulant effect via interference with vitamin K–dependent synthesis of clotting factors II, VII, IX, and X.² Aspirin irreversibly inhibits platelet aggregation for the 8- to 10-day life span of the affected platelets.³ Oral NSAIDs, such as ibuprofen and naproxen, reversibly prevent platelet aggregation via inhibition of cyclooxygenase, with platelet function restored as the medication is eliminated from the body.⁴ Vitamin E interferes with platelet adhesion by reducing stimulation-induced pseudopodia formation, and may further exacerbate the effects of other blood thinners.⁵ Medications such as Ticlid (ticlopidine), Plavix (clopidogrel), and Effient (prasugrel) are thienopyridines, which selectively target the adenosine diphosphate (ADP)-2 receptor on the platelet surface, thereby preventing platelet activation.⁶ Newer anticoagulants continue to be developed, with variable mechanisms of action. Pradaxa (dabigatran) directly inhibits thrombin, whereas Xarelto (rivaroxaban) and Eliquis (apixaban) inhibit factor Xa.⁷

Bleeding is undesirable in glaucoma surgery, as it increases postoperative inflammation and scarring, and may also temporarily occlude the flow of aqueous at the surgical site. Some surgeons routinely recommend discontinuing some or all anticoagulant medications for several days to 2 weeks prior to glaucoma surgery, depending on the drug type and anticipated duration of action. This practice, however, must be cautiously considered, as discontinuation of such treatment could lead to thromboembolic events with potentially serious consequences.⁸ Hemorrhagic complications may occur more commonly in patients taking warfarin than in patients taking aspirin, with a greater risk of surgical failure in the former.⁹ There is little good data on risks associated with other anticoagulant medications. A survey of British glaucoma specialists found that approximately one third of surgeons routinely stopped warfarin or aspirin prior to glaucoma procedures, whereas the majority stopped neither.¹⁰ There is clearly no consensus on this issue. We generally prefer to discontinue aspirin and NSAIDs, but not warfarin or other agents, with the consent of the patient’s primary physician or cardiologist.

The effects of previous ocular surgery must be taken into account when planning a glaucoma procedure. Prior procedures involving the conjunctiva and sclera may limit options and increase the risk of certain complications. Significant conjunctival and episcleral scarring can impede conjunctival dissection and creation of a flap, with the risk of tears or buttonholes. Scleral dissection may also be affected, with the risk of thin or torn flaps. Evidence also suggests that prior surgery that violates the conjunctiva may limit the success of future trabeculectomy.¹¹ Conjunctival biopsies taken distant from the site of apparent scarring in patients having undergone prior surgery were noted to contain more fibroblasts, macrophages, and lymphocytes in the conjunctival stroma.¹² Additionally, alterations in the composition of aqueous humor and exposure of the conjunctiva to aqueous may permanently alter the tissue, leading to more vigorous wound healing and scarring.¹³ Extensive superior scarring, therefore, might lead the surgeon to choose a drainage device over trabeculectomy. Inferior trabeculectomy should be avoided, as the risk of complications, particularly blebitis/endophthalmitis, is significantly higher with an inferior limbal bleb.^14,15 Nonpenetrating procedures, such as canaloplasty, generally do not lead to the formation of significant blebs and can be positioned more freely, including temporally or even inferiorly, although operating inferiorly can be technically and ergonomically more challenging.

Prior use of topical ophthalmic medications, particularly chronic use, may increase postoperative inflammation and influence surgical success.^16,17 Studies have shown increased numbers of conjunctival fibroblasts, macrophages, and lymphocytes, as well as a decrease in goblet cell density and loss of epithelial cell microvilli, in conjunctival tissue exposed to topical medications.^18–20 The majority of the evidence implicates benzalkonium chloride, the most commonly used preservative in topical ophthalmic preparations, as the primary cause of these changes.^21,22 Decreased success of trabeculectomy in patients previously treated with topical glaucoma medications has indeed been noted.^16,23 One recent study, however, failed to identify any effect of either number of topical medications or duration of use on the outcome of trabeculectomy.²⁴ Thus, the degree to which topical glaucoma therapy affects surgical outcome remains somewhat unclear. It seems reasonable to treat an inflamed eye that has received numerous injections with topical steroids for 1 to 2 weeks preoperatively to reduce the risk of failure due to possible chronic conjunctival inflammatory changes.

Young age and darkly pigmented skin may also be risk factors for failure of filtering surgery.^25,26 Surgical considerations that may improve success include increased dose or application time of intraoperative antimetabolite, as well as more frequent and aggressive postoperative follow-up, with early lysis or removal of scleral flap sutures and injections of subconjunctival 5-fluorouracil, as indicated.

Spectrum of Glaucoma Procedures

Before entering into a discussion of complications, it is first necessary to review the current spectrum of glaucoma surgery as well as the details of the newer procedures. Following its introduction by Cairns²⁷ in 1968, trabeculectomy quickly became the procedure of choice for IOP reduction that could not be achieved by nonsurgical therapy, and it remains the gold standard today. Nonetheless, even modern, guarded filtration surgery entails substantial risk of complications, including hyphema, conjunctival leaks, hypotony with possible maculopathy, suprachoroidal hemorrhage, and endophthalmitis.²⁸ The relatively high rate of complications in filtering surgery has prompted the development of nonpenetrating techniques such as nonpenetrating trabeculectomy/deep sclerectomy,²⁹ vicsocanalostomy,³⁰ and canaloplasty.^31,32 The hunt for safer, less technically challenging, and more effective surgery continues with the introduction of the MIGS series of procedures. Ideal for combination with phacoemulsification and generally performed through a clear corneal incision, these procedures are addressed comprehensively in Chapter 47.

Trabeculectomy Procedure

Since its introduction by Cairns, the trabeculectomy has undergone numerous modifications, including use of antimetabolites, adjustable and releasable scleral flap sutures, and the EX-PRESS™ shunt.

Although traditionally performed with a retrobulbar block, topical anesthesia augmented with intraoperative sub-Tenon’s anesthetic is gaining popularity. Initially, a conjunctival flap is fashioned in either fornix-based or limbus-based fashion, extending posteriorly toward the superior fornix, with care to avoid tears or buttonholes. Light cautery is applied to avoid excessive bleeding. An approximately one-half scleral thickness flap is created, based at and extending into the limbus, maintaining even thickness throughout. There is no consensus on the size or shape of flap necessary to provide adequate IOP control,³³ and this remains the surgeon’s preference. Antimetabolite, if indicated, is applied. Alternatively, antimetabolite may be injected into the subconjunctival space prior to the procedure, a technique that is becoming popular with some surgeons. The ocular surface is irrigated and a paracentesis is created to allow for instillation of balanced salt solution (BSS) or viscoelastic into the anterior chamber (AC). If desired, scleral flap sutures can be pre-placed for quick closure of the flap following sclerectomy.

At this point the surgeon may choose to proceed with traditional trabeculectomy or consider the use of the EX-PRESS glaucoma shunt. If the traditional approach is taken, the AC is entered at the base of the scleral flap and a block sclerectomy is made with a blade, a scissors, or a Descemet’s punch. It is generally recommended that an iridectomy be made to avoid incarceration of peripheral iris within the sclerostomy, although this may not be necessary in the pseudophakic patient if the chamber is fairly deep. Alternatively, if the EX-PRESS shunt is to be implanted, the surgeon creates a tract for the device using a needle or blade, starting at the scleral blue line and remaining parallel with the iris plane. The EX-PRESS device can then be easily implanted via the inserter by turning it sideways and using gentle rocking pressure until the flange is captured by the internal scleral wall. An iridectomy is not necessary with the EX-PRESS. Scleral flap sutures are then placed and tied, the tightness adjusted to facilitate appropriate transscleral flow of aqueous. The conjunctiva is then sutured, with care taken to achieve a completely watertight closure. This is best achieved with a running double-layer closure of a limbus-based flap, or a running horizontal mattress closure of a fornix-based flap. The AC is pressurized with BSS and a bleb should form. The wound is checked for leaks, and these are repaired as necessary.

Releasable Suture Techniques

Various releasable suture techniques have been reported, initially by Shaffer et al,³⁴ and subsequently by Cohen and Osher,³⁵ Wilson,³⁶ Shin,³⁷ Johnstone and coworkers,³⁸ Hsu and Yarng,³⁹ and Maberley and coworkers.⁴⁰ These suture techniques may be used with either limbus- or fornix-based conjunctival flaps. The Cohen and Osher technique consists of multiple four-throw slipknots of 10-0 or 9-0 nylon, which are used to close the trabeculectomy flap (Fig. 47.1). This suturing technique consists of taking three bites and proceeding from the cornea posterior through the scleral flap and emerging from the sclera. The free end of each slipknot is buried within the corneal stroma. In our experience, 9-0 nylon is less likely to break during removal and is preferred.

Fig. 47.1 (a) Cohen and Osher externalized releasable sutures to close a trabeculectomy flap. The first suture bite is a 2- to 3-mm superficial intracorneal bite that is almost parallel to the limbus. The second suture bite enters the cornea one-half millimeter away from the exit site of the first suture bite. The suture passes into the cornea, into the corneoscleral limbus and out through the trabeculectomy flap (close to the base of the flap). The third suture bite passes through the edge of the trabeculectomy flap into the adjacent sclera. (b) The suture is then tied tightly with a four-throw slipknot. The loop is made smaller by pulling on the corneal aspect of the suture. This will facilitate later release. (c) All sutures are in position. The excess suture is excised at the entrance of the intracorneal bite to ensure epithelialization of the suture.

The Wilson releasable technique also involves taking three suture bites with a square knot (3–1–1–1). This is tied on the epithelial surface of the cornea (Fig. 47.2). It is important to cut off the excess suture flush with the knot with a 15-degree blade. This promotes epithelialization of the knot, which is important for patient comfort postoperatively. This suture often produces some astigmatism until it is either released or the nylon relaxes. However, it may achieve a tighter closure, and is easier to release, than the Cohen and Osher suture. The Wilson suture cannot be easily used at the apex of a triangular trabeculectomy flap, whereas the Cohen and Osher suture can. Therefore, it may be helpful to use both suturing techniques in closing trabeculectomy flaps.

In addition to releasable sutures, an adjustable suturing technique has been introduced by Peng Khaw’s group.⁴¹ Rather than the absolute approach of releasable sutures, this technique allows for a titrated increase in transscleral aqueous flow postoperatively. It does, however, require the use of a specially designed forceps (the Khaw Transconjunctival Adjustable Suture Forceps No. 2–502, Duckworth and Kent, Baldock, United Kingdom) to adjust tension on the sutures. The required manipulation can lead to conjunctival injury and buttonholes, particular where the conjunctiva is thin and Tenon’s is minimal. The technique is best avoided in these cases.

Fig. 47.2 Wilson externalized releasable suture. A, bite 1 enters the cornea 1 mm from the conjunctival reflection and passes into the corneoscleral limbus and out the sclera adjacent to the trabeculectomy flap. B, bite 2 enters the sclera of the trabeculectomy flap near the edge of the flap and into the sclera adjacent to the trabeculectomy flap. C, bite 3 enters the sclera adjacent to the trabeculectomy flap, passes through the corneoscleral limbus, and exits the cornea 1 mm posterior to the conjunctival reflection and 1 to 2 mm nasal to the entrance site for bite 1. D, the suture is tied with a 3–1–1–1 throw pattern. E, excess suture is cut on the knot with a 15-degree blade to ensure epithelialization.

When combined with trabeculectomy, phacoemulsification can be performed either superiorly, under the trabeculectomy flap, or via a separate incision, most commonly by the clear-corneal temporal approach. The single-site technique offers the advantage of not shifting surgeon and microscope positions during the procedure, saving time. However, this approach requires that phacoemulsification be performed superiorly, a position that may be ergonomically challenging for the surgeon not accustomed to doing so (Fig. 47.3).

There has been some debate regarding the outcome of trabeculectomy via the one-site versus two-site approach. Several studies have found no difference in efficacy in terms of IOP reduction and the postsurgical requirement for glaucoma medication use.^42,43 Others, however, have concluded that two-site surgery offers better long-term IOP reduction and surgical success.⁴⁴ In the absence of conclusive data, the surgeon’s comfort and familiarity with technique should dictate the surgical approach.

Fig. 47.3 A cataract incision made under a trabeculectomy flap should enter the anterior chamber 1 mm anterior to the anterior edge of the flap to avoid iris prolapse.

At this point it is helpful to use blunt dissection to disinsert Schwalbe’s line and carry the flap into the cornea, forming the trabeculo-Descemet’s window. The window should extend at least 500 µm anterior to Schwalbe’s line, as this is the primary means by which aqueous will drain into the scleral lake and canal. The deep flap is then excised, with care taken to not perforate the window. Next, a microcatheter (iTrack-250, Ellex iScience, Menlo Park, CA) is introduced into a cut end of Schlemm’s canal, passed 360 degrees, and retrieved from the opposite side (Figs. 47.4 and 47.5).

Fig. 47.4 The microcatheter is introduced into Schlemm’s canal.

A 9-0 or 10-0 Prolene suture is tied to the end of the catheter, which is then withdrawn as viscoelastic (Healon GV, Abbott Medical Optics, Santa Ana, CA) is slowly but steadily injected to dilate the canal. The suture is cut from the catheter and the ends tightly tied, creating a cerclage-like stent within Schlemm’s canal. The tension on this suture is critical, with studies showing that the ultimate IOP reduction correlates with this tension.³² The superficial scleral flap is sutured back into place, creating a watertight closure. Finally, the conjunctiva is closed.

Glaucoma Drainage Device Procedure

Drainage devices, or tube shunts, come in two basic forms: valved and nonvalved. Valved shunts offer the advantages of immediate IOP control and, theoretically, prevention of early hypotony. However, the valve mechanism does not always function as intended, sometimes causing hypotony due to excessive flow or late failure due to valve malfunction. Furthermore, early flow of aqueous into the subconjunctival space may cause a more robust encapsulation to develop around the plate, leading to poorer IOP control.^45–47 Nonvalved shunts must be occluded to prevent early flow of aqueous, achieved via placement of ligature sutures that either dissolve or can be removed by the surgeon after plate encapsulation has occurred. These shunts may suffer higher early postoperative IOPs and require more early medication use, but long-term IOP control may be better, with the need for fewer glaucoma medications.^45,46 It has further been suggested that larger plates may lead to lower IOP, but the data on this are unclear. Surgeons must ultimately choose the type of implant with which they are most comfortable and that will achieve the specific treatment goals for the patient.

Fig. 47.5 As the catheter passes though Schlemm’s canal, the beacon tip can be visualized through the sclera to assist catheter advancement.

Direct repair of a conjunctival buttonhole can usually be achieved using a 10-0 or 9-0 polyglactin or nylon suture on a tapered needle, either via a purse-string or interrupted technique. If possible, Tenon’s capsule should be incorporated into the repair for added strength. For holes or small tears near the limbus in a fornix-based flap, the area may simply be excised and the flap pulled forward for standard closure. Care must be taken, however, with holes in very thin conjunctiva, where Tenon’s may also be thin or absent. These holes may form over the scleral flap, particularly when mitomycin has been applied, and must be meticulously repaired to prevent early leaks and hypotony. Thin tissue may be difficult to suture, with “cheese-wiring” and enlargement of the defect. Several novel techniques have been described for dealing with conjunctival holes in such cases. Tissue adhesives, either cyanoacrylate or fibrin-based, have been successfully employed to seal small defects.^48–50 Additionally, intra-bleb injection of sodium hyaluronate 2.3% (Healon 5, Abbott Medical Optics) has been efficacious at closing small buttonholes in thin conjunctiva in a small series.⁵¹ For defects that are not amenable to direct repair by suturing or the use of adhesives, amniotic membrane grafting may enable effective closure.⁵²

Scleral Flap Complications

Trabeculectomy

As the primary determinant of aqueous flow and IOP in the early postoperative period, the scleral flap must be fashioned with care. As noted earlier, flap shape is relatively unimportant, but its thickness should be at least one-third to one-half the scleral depth to avoid tearing or avulsing the tissue and to prevent cheese-wiring of sutures. The flap should be dissected anteriorly into clear cornea to create a reasonably anterior sclerostomy, avoiding the ciliary body. However, care should be taken to avoid cutting the lateral flap margins too far beyond the limbus, as this may result in overfiltration and early hypotony.⁵³ If implanting an EX-PRESS shunt, the flap does not need to be dissected as far anteriorly, as the insertion point is at the scleral spur, posterior to the limbus. Nonetheless, the dissection must be continued slightly beyond the point of insertion to avoid excessive compression of the device and poor resultant flow.

Many complications involving the scleral flap can be avoided by paying attention to risk factors preoperatively and by careful surgical technique. Prior surgery at the intended flap site has already been discussed. In such cases, Tenon’s capsule is often scarred and adherent to sclera, and identifying the correct tissue plane can be challenging, leading to irregular flap thickness and margins. High myopia, known to be associated with scleral thinning,⁵⁴ may require dissection of a thinner flap, which is more prone to tears or buttonholes, and requires very delicate handling. Other conditions affecting scleral thickness or strength, including scleritis and other autoimmune inflammatory disease, as well as genetic abnormalities such as Ehlers-Danlos and Marfan’s syndromes, may predispose to flap complications, and extra care, therefore, must be taken.

The surgeon should attempt to maintain a consistent depth throughout the dissection of the scleral flap. Superficial dissection results in a thin and more easily damaged flap. Overly deep dissection, particularly anteriorly, may lead to premature, posterior entry into the globe with possible bleeding from the ciliary body or iris prolapse. Proper repair of a damaged scleral flap allows the procedure to proceed without significant difficulty in most cases. A thin flap, although not truly a complication, must be handled carefully, as previously noted, to avoid inadvertent tearing or buttonholing. Suture tracts should be a bit longer than usual to prevent cheese-wiring through the edges of the flap. Should the flap prove too thin to adequately tamponade the flow of aqueous, a patch graft may be necessary to more effectively restrict flow. Small tears, and even complete dehiscence of the scleral flap, can be repaired primarily by suturing using a horizontal mattress technique.⁵⁵ The use of donor sclera to create a functional scleral flap has also been described.⁵⁶ Again, if primary repair does not adequately strengthen the flap and lead to flow restriction, patch grafting should be performed. Donor scleral or corneal tissue, or a commercially available preparation of sclera, cornea, or pericardium, may be used for this purpose. The use of tissue adhesive, as described in the prior section on conjunctival repair, may also serve as an adjunct to achieving a functional scleral flap.⁵⁷

Canaloplasty/Viscocanalostomy

Superficial Flap

As in trabeculectomy, proper dissection of the scleral flaps, both superficial and deep, is vital in nonpenetrating procedures. The superficial flap is intended to create a watertight closure, eliminating the filtering bleb and its attendant complications. It is therefore important that this flap be of adequate and relatively uniform depth, preferably about one-half scleral thickness. Although the precise size and shape of the flap are not critical, the tangential length should be large enough to allow a reasonably sized scleral lake. At least 4 mm is recommended. Too thin a flap may lead to poor closure, buttonholes, cheese-wiring of sutures, and leaks. An overly thick flap, particularly at the anterior aspect, may cause perforation into the AC. Given the typically large size of this flap, extra care should be taken to maintain the proper tissue plane. A crescent blade may be useful for this dissection, and the surgeon should pay attention to the thickness of the flap margins as well as the central flap. If the flap appears translucent with the blade visible beneath, dissection should be directed more deeply. Tight closure of this flap is necessary at the end of the procedure to prevent formation of a bleb. However, in our experience, a low bleb does occasionally form. These blebs cause no problems, having not been exposed to antimetabolites, and may slightly augment the effect of the procedure.

Deep Flap

Creation of the deep scleral flap necessitates an understanding of and comfort with the surgical anatomy of the AC angle. Dissection of the flap should commence as posteriorly as possible, so that proper depth can be achieved well before Schlemm’s canal is approached. Proper depth is determined by either noting the underlying dark choroid though a thin bed of scleral fibers, or by exposing choroid slightly and then backing up 50 to 100 µm. Maintaining this depth as the dissection is carried forward essentially guarantees entry into the canal.

The most common mistake made as the procedure is being learned is dissecting the deep flap too shallowly and passing over the canal. If this occurs, a deeper plane must be established posteriorly. Therefore, dissection should be performed slowly, maintaining a depth just over the choroid. As the limbal blue zone is approached, the deep scleral fibers appear to change direction and become more organized. At this point, the surgeon should create a paracentesis and decompress the eye, thus preventing the soon-to-be-exposed Descemet’s membrane from bulging and reducing the risk of inadvertent perforation. Dissection can then be very carefully continued anteriorly, unroofing the canal and exposing trabecular meshwork and Descemet’s membrane. The walls of the deep flap should be maintained as vertical as possible at this point, to produce clean Schlemm’s canal ostia.

Creation of the trabeculo-Descemet’s window is the most delicate aspect of the procedure and involves cautious, sharp dissection of the lateral deep flap margin into clear cornea, while bluntly separating the corneal stroma from Schwalbe’s line with a rounded spatula or moistened surgical sponge. Dissection of the lateral margins can be aided by use of a vertically cutting diamond with a specially designed footplate, known as a ZIP blade (model SPDM ZP, Mastel Precision Surgical Instruments, Rapid City, SD), that protects Descemet’s membrane as the incision is advanced into the cornea. Blunt dissection is continued until the window is of adequate size, generally at least 400 to 500 um anterior to Schwalbe’s, and the deep flap is excised with a blade or Vannas scissors. A very small perforation of Descemet’s at this stage may not be a problem, and the case may proceed normally. Postoperative use of topical pilocarpine may be useful to prevent iris incarceration into the trabeculo-Descemet’s window caused by increased flow.⁵⁸ A macro-perforation, however, usually necessitates conversion to a trabeculectomy.

Anterior Chamber Entry in Trabeculectomy: Sclerectomy Versus EX-PRESS Shunt

When performing trabeculectomy, the surgeon has the option of standard block/punch sclerectomy or implantation of the EX-PRESS shunt. Block excision, performed with a blade and scissors, offers the least reproducibility and control of sclerectomy size. More commonly, a scleral punch is employed to create an opening of uniform size. Care should be taken to ensure that the full thickness of the scleral lip is engaged, with the punch then turned perpendicularly to the eye so that a clean, non-shelved sclerectomy is created. Positioning the punch centrally will help avoid excessive filtration and early hypotony. It has been suggested, however, that the sclerectomy be decentered toward one edge of the scleral flap to improve the likelihood that releasing a flap suture during the postoperative period will result in improved flow and reduced IOP.⁵⁹ In this case, care must be taken to ensure adequate flap suture tension to avoid excessive leakage. More recently, Peng Khaw et al⁶⁰ have advocated the use of a smaller, 0.5-mm punch to better control aqueous egress, prioritizing the avoidance of early postoperative hypotony.

The development of the EX-PRESS shunt has provided the surgeon with even greater regulation of aqueous flow. Available in two models, with either a 50- or 200-µm lumen, the shunt offers more standardized control of aqueous egress than a sclerectomy. The smaller, 50-µm lumen appears to be adequate in the majority of cases. A prospective randomized study comparing EX-PRESS with standard trabeculectomy reported significantly better control of IOP during the first 3 years of follow-up, with 66.7% of EX-PRESS eyes versus 38.5% of standard trabeculectomy eyes demonstrating an IOP less than 15 mm Hg at 3 years.⁶¹ The trend continued at 5 years, but was not statistically significant. Furthermore, fewer glaucoma medications and postoperative interventions for complications were required following EX-PRESS surgery throughout the 5-year follow-up. Additional studies have confirmed IOP reduction with EX-PRESS that is equal to or better than that with trabeculectomy alone, with significantly reduced rates of complications, particularly early hypotony, as well as fewer required glaucoma medications.^62–64 Our personal experience reflects these findings, with less hypotony, fewer hyphemas, and an overall smoother postoperative course.

Implantation of the EX-PRESS device is relatively straightforward but requires careful attention to anatomic landmarks. The scleral spur and limbal blue zone must be identified, and a 26-gauge needle used to create an entry tract at the junction of these structures, parallel with the iris. Angling the entry anteriorly or posteriorly results in the implant potentially contacting the cornea or iris, respectively. The needle should be inserted and withdrawn smoothly, as excessive lateral movement may allow fluid to escape around the shunt. Additionally, the scleral bed should be of adequate thickness to support the device, as a thin bed may either tear during insertion or may allow for too much movement of the shunt, risking injury to adjacent structures or even a rare dislocation of the device.⁶⁵ If a thin bed and unstable shunt are noted after insertion, the shunt should be removed and a standard sclerectomy performed.

Bleeding and Hyphema

Intraoperative bleeding is a common complication in glaucoma surgery, and can range from a mere nuisance to a vision-threatening hemorrhage, though the latter is uncommon. Conjunctival and episcleral bleeding is usually mild and self-limited, but may be greater in patients on anticoagulants, as noted previously. A combination of judicious cautery and localized pressure with a cotton-tipped applicator usually suppresses the bleeding. The development of extensive subconjunctival hemorrhage should be avoided in filtering surgery, as this may plug the scleral flap and hinder bleb formation, increase inflammation, and potentially lead to surgical failure. In the case of canaloplasty, cautery of the scleral surface should be minimized, as this may damage the episcleral vessels that drain the aqueous collector channels, decreasing the efficacy of the procedure.⁶⁶ Surface bleeding is primarily a nuisance in drainage device surgery, although significant thickening of Tenon’s fascia due to hematoma, although uncommon, can cause difficulty with conjunctival closure.

Intraoperative hyphema is a relatively common complication in filtering surgery, occurring in 8% of trabeculectomies in one large multicenter clinical trial.⁶⁷ Bleeding develops most commonly during iridectomy, but may also occur during creation of the sclerectomy or implantation of an EX-PRESS shunt or drainage device tube. When possible, bleeding from the iris base or sclerectomy margins should be cauterized, which is best performed with a fine needle-tipped probe. Direct pressure with a cotton-tipped applicator may also be useful. In most cases, hemorrhaging stops spontaneously, but closing the eye and elevating the IOP, either with BSS or viscoelastic, may be required to tamponade the offending vessels.

Limited hyphema during canaloplasty is also quite common.^32,68 The main source of bleeding appears to be reflux from Schlemm’s canal into the depressurized eye.⁶⁶ One recent study found that surgical success and degree of IOP reduction correlated positively with presence and height of microhyphema on postoperative day 1, with 88% with hyphema versus 38% without hyphema achieving a 30% or greater reduction in pressure at 24 months.⁶⁹ The authors suggest that hyphema in this context should not be considered a complication, but rather an indicator that the collector system is functioning. Small hyphemas in canaloplasty are nearly always self-limited with no adverse consequences, and blood seldom remains in the AC beyond 1 week.

Vitreous Prolapse

The risk factors, etiologies, and management of vitreous loss due to capsular tears or zonular defects are addressed in more detailed discussions in many other chapters in this book. When combined with a glaucoma procedure, care must be taken to remove all lens fragments, cortex, and vitreous according to the principles discussed. This is necessary to minimize postoperative inflammation, which may cause increased scarring and failure of the glaucoma procedure. If vitreous is present in the AC postoperatively, it may block or form anterior synechiae to Descemet’s window in a canaloplasty or to the sclerectomy in a trabeculectomy. In this case, an additional surgical intervention with anterior vitrectomy and lysis of vitreous bands may be required. Sometimes vitreous bands can be lysed with the yttrium-aluminum-garnet (YAG) laser. However, this frequently requires high energy and a large number of pulses. This can increase the inflammation in the AC with a resultant increased risk of failure of the glaucoma procedure. Subconjunctival Depo-Medrol or Kenalog (triamcinolone 20 to 40 mg) should be routinely given after combined phaco–glaucoma procedures, but especially after cases in which more inflammation is anticipated.

If the anterior capsular rim is intact, and a posterior capsular rent cannot be converted into a continuous tear by capsulor-rhexis, then a posterior chamber intraocular lens (IOL) should be placed in the ciliary sulcus. If the diameter of the anterior capsulotomy is smaller than that of the IOL optic, the optic of the IOL should be captured within the anterior capsule. This ensures a snug fit between the edge of the capsulorrhexis and the posterior edge of the optic and makes herniation of vitreous into the AC unlikely. Additionally, it also stabilizes the lens implant, making anterior displacement of the lens less likely if postoperative hypotony occurs. The haptics of a posterior chamber lens placed in the ciliary sulcus should be oriented in a meridian perpendicular to the meridian of the glaucoma operation. This prevents iris from being pushed anteriorly at the site of Descemet’s window (in a canaloplasty) or the sclerectomy (in a trabeculectomy), thereby reducing the risk of synechiae. If there is an anterior capsular rent in conjunction with an intact posterior capsule, a posterior chamber (PC) IOL can usually be gently placed in the capsular bag. If both the anterior and posterior capsules have been damaged to a significant degree, then a suture fixated PC IOL in the ciliary sulcus or an AC IOL may be necessary. If either a ciliary sulcus suture-fixated PC IOL or an AC IOL is used, it is best to place the haptics away from Descemet’s window or the sclerectomy. This helps to minimize inflammation in the immediate area and makes the occurrence of peripheral anterior synechiae, with subsequent failure of the glaucoma procedure, less likely.

Less commonly, vitreous may present during trabeculectomy if the sclerectomy is made too far posteriorly. This typically occurs following iridectomy when the scleral flap has not been dissected far enough into clear cornea, or occasionally if a canaloplasty must be converted to trabeculectomy due to macroperforation of Descemet’s window. Vitreous may also present at this location through a zonular defect during an otherwise normal case. Regardless, the principles of meticulous vitreous cleanup must be maintained to prevent vitreous from plugging the sclerectomy and possibly causing surgical failure. Although anterior vitrectomy via the sclerostomy is most straightforward in this situation, it seems reasonable to suggest that a pars plana approach might be more successful, maintaining vitreous posteriorly rather than pulling it anteriorly. Ultimately, this issue is best avoiding by ensuring adequate scleral flap dissection and anterior placement of the sclerectomy.

Intraoperative Complications Unique to Canaloplasty

Although canaloplasty shares many potential complications with other glaucoma surgeries, some problems are unique to the procedure, related to the microcatheter, viscodissection, and stent suture placement.

Although Schlemm’s canal has been properly unroofed, the ostia may be difficult to identify and catheterize. This may be due to irregular dissection of the deep flap walls, or simply due to collapse of the canal, causing the ostia to appear as tiny slits. Careful dissection along the lateral flap margin may improve visualization of an ostium. Additionally, there is often slight reflux of blood from the canal ostia, as the IOP has been reduced below episcleral venous pressure. Using the scleral spur and pigmented trabecular meshwork as a landmark and moving laterally, a 30-gauge viscocanalostomy cannula can be used to enter an ostium. Gentle injection of BSS causes blanching of episcleral vessels if the canal has been entered properly. Injecting a small amount of viscoelastic to maintain patency aids in placement of the microcatheter.

Viscodilation of Schlemm’s canal is performed as the catheter is retracted, with care taken to ensure slow, steady release of viscoelastic. Excessive viscodissection may lead to Descemet’s detachment, in which the sub-Descemet’s space is filled with viscoelastic or blood, a finding noted in numerous studies.^32,58,70 The occurrence rate of this complication is generally low, with one recent report of 7.4% (12 of 162 eyes).⁷⁰ The majority of these were small, measuring less than 3 mm, and resolved spontaneously over 4 to 6 weeks, with no significant sequelae. Three required drainage at the slit lamp, and two of these resolved completely. The final patient ultimately developed corneal decompensation requiring penetrating keratoplasty. Thus, although a relatively uncommon and usually benign complication, Descemet’s detachment is best avoided by slow and gentle viscodilation of the canal. Small detachments can be observed and they usually resolve, whereas larger occurrences may require drainage.

Postoperative Complications Common to All Surgeries

Hyphema

Postoperative hyphema is common in glaucoma surgery. Although rates in the literature vary, studies suggest the occurrence of significant bleeding in up to 25% of trabeculectomies.^28,67,71 The incidence of hyphema in drainage device surgery appears to be less, with the majority of hyphemas occurring in patient with neovascular glaucoma.^72,73 Small hyphemas after canaloplasty, a normal and self-limited occurrence, have been discussed previously.

Preoperative considerations regarding anticoagulant use have already been addressed, as has the importance of hemostasis intraoperatively. Nonetheless, significant hyphema continues to plague the surgeon following filtering surgery, although there may have been no evidence of bleeding at the end of the procedure. These delayed hemorrhages may be caused by postoperative hypotony, or may be due to Valsalva maneuver or eye rubbing. Additionally, manipulations performed by the surgeon during the postoperative period, such as digital massage of the bleb, suture lysis/removal, or needle revision of a failing bleb at the slit lamp may cause undesired bleeding.^74,75

In the event of significant hyphema, the patient should be instructed to limit physical activity and to sleep with the head of the bed elevated to maintain better vision. An eye shield should be worn at all times to prevent accidental trauma. Blood thinning medications must be avoided. The IOP may need to be controlled with topical medications, or possibly with oral carbonic anhydrase inhibitors. Increased topical steroids may be useful to limit the inflammatory reaction and fibrin production stimulated by the blood. With such conservative measures, the majority of smaller hyphemas resolve, usually within 1 to 2 weeks, as the clot hemolyzes. A larger hyphema that is not clearing, however, may require surgical intervention with AC washout. Prolonged presence of blood in the AC may cause elevated IOP due to clogging of the sclerostomy, EX-PRESS shunt, or tube, ultimately leading to surgical failure. Anterior synechiae or corneal blood staining may also result. The amount of blood and the IOP dictate the urgency of intervention.

Hypotony

Although the goal of glaucoma surgery is reduction of the IOP to a low enough level to preserve vision, an overly low tension is not well tolerated by most eyes, leading to changes within ocular structures that can adversely affect visual acuity, including maculopathy and corneal edema.⁷⁶ Achieving the appropriate balance surgically can be difficult, and early postoperative hypotony is quite common following filtration surgery, occurring in as many as one third of procedures.^28,77,78 Hypotony may be statistically defined as an IOP below 6 mm Hg, or 3 standard deviations below the mean.⁷⁹ As the adverse clinical manifestations of low IOP often occur below this level, 6 mm Hg shall be considered the definition of hypotony for this discussion. The use of antimetabolites, primarily in trabeculectomy, has certainly improved surgical success, but it has also resulted in a significant increase in early hypotony.^78,80 Uncommonly, low IOP is due to decreased aqueous production, which may occur in cases of intraocular inflammation, in the presence of a large choroidal or retinal detachment, or with the concomitant use of aqueous suppressants, such as oral carbonic anhydrase inhibitors or β-blockers.⁸¹ Such conditions are usually easily ruled out. In most cases, hypotony is caused by excessive aqueous outflow. Thus, many cases of postoperative low IOP can be avoided by careful attention to detail during surgery.

Trabeculectomy Hypotony

Overfiltration

The primary determinant of early postoperative IOP following trabeculectomy is the resistance created by the scleral flap.⁸² Therefore, strict attention should be paid to the tension on flap sutures prior to closure of the conjunctiva. Inflating the AC with BSS to physiological pressure enables the surgeon to check the rate of transscleral flow as well as the maintenance of chamber depth and globe firmness. It is often best to leave the flap somewhat tight with minimal flow and to make adjustments to sutures postoperatively, particularly in patients at increased risk for hypotony and its complications, such as high myopes or older patients with vascular disease.⁸³ The use of an AC infusion line has been advocated as a means of maintaining rigidity of the globe intraoperatively, minimizing the risk of choroidal effusions, and facilitating estimation of scleral flow after suturing of the flap.⁶⁰ If the chamber fails to remain well formed as flow is monitored, additional sutures should be placed until adequate pressurization of the globe is maintained. Of course, watertight conjunctival closure is also vital to surgical success and the avoidance of hypotony, and any conjunctival defects, whether buttonholes or wound leaks, must be meticulously closed before the procedure is completed.

Beyond the early postoperative period, episcleral and conjunctival healing begin to have a greater impact on aqueous outflow and IOP, and the effects of mitomycin C become more pronounced. A scleral flap that fails to adequately restrict flow initially typically heals via episcleral fibrosis, but this process may be inhibited by mitomycin, leading to more prolonged hypotony.⁸³ Additionally, postoperative manipulations of the scleral flap, such as suture lysis or removal, or needling of an encapsulated bleb or fibrotic flap, can cause a precipitous drop in IOP that is slow to return to acceptable levels.^75,84–87 Hypotony in these circumstances typically presents with a diffuse, intact, functional bleb. In most cases, resolution comes about with nothing more than routine postoperative care, though more frequent follow-up is recommended to monitor for complications. Some patients tolerate prolonged hypotony with no discernible adverse effects or complaints, and may be monitored indefinitely as long as visual acuity does not suffer. If, however, visual symptoms or significant AC shallowing are present, then treatment is indicated.

Early hypotony may respond to more rapid reduction in topical steroid dosing, allowing episcleral and conjunctival fibrosis to develop. Pressure patching or the use of a scleral shell or large-diameter contact lens flattens the conjunctiva and scleral flap and may promote fibrosis, leading to elevated IOP.^88,89 Autologous blood injection into the bleb, possibly combined with conjunctival compression sutures, may also cause fibrosis and raise IOP.^90–92 As long as the AC remains deep, these relatively conservative measures may suffice. However, if the chamber shallows significantly, additional action may be required. In general, it has been our experience that AC shallowing in pseudophakic eyes is less severe and better tolerated than in phakic eyes, and may be monitored for a more extended period as long as the central chamber is not flat. Pharmacological measures, such as use of topical atropine or other cycloplegics, may help deepen the chamber by restoring the normal anatomy of the iris and ciliary body, lessening iridocorneal contact. If necessary, AC reformation with a viscoelastic, injected via a paracentesis at the slit lamp, is easily performed and may lead to resolution of hypotony, though multiple injections may be required.^93,94

Ultimately, if persistent hypotony causes continued poor vision, shallow chamber, or evidence of hypotony maculopathy such as choroidal folds or macular edema, then surgical revision is indicated. This may be achieved by opening the conjunctiva and placing additional sutures to tighten the scleral flap.^95,96 Transconjunctival suturing of the scleral flap, as has been recently described,^97,98 has been found to be safe and effective, is less invasive, and can be performed at the slit lamp. Eyes suffering late hypotony, which is often due to progressive thinning of the scleral flap and conjunctiva following exposure to mitomycin, may not be amenable to these techniques. In such cases, more complex revisions involving patch grafts to reinforce the sclera, and either conjunctival advancement or free conjunctival grafts will be required.^99–101 Drainage of choroidal effusion is also often necessary.

Conjunctival Leaks

Wound leaks may occur early following surgery due to inadequate conjunctival closure, or may develop subsequently due to poor healing, particularly following exposure to mitomycin C. Furthermore, mitomycin-exposed conjunctiva may become progressively avascular and thin over time, leading to late bleb leaks and hypotony.⁸³ All patients with hypotony, particularly when IOP has dropped substantially from the prior visit, must be checked for the presence of conjunctival leaks via the Seidel test, using either moistened fluorescein strips or 2% fluorescein solution. If using a strip, care should be taken to “paint” the entire bleb. Leaks in the hypotonous eye may be intermittent and not immediately apparent, possibly requiring prolonged observation to be identified. Gentle pressure on the globe will raise IOP and may reveal an occult leak. Management of leaks is dependent on the location and the condition of the surrounding tissue.

An early leak, whether a buttonhole or wound-related, can be observed as long as the AC remains formed. Small leaks may respond to conservative therapy, including a decrease in the frequency of topical steroids to allow more rapid fibrosis and wound healing. Aqueous suppressants, including oral carbonic anhydrase inhibitors and topical β-blockers, can decrease the flow of fluid through the leak and may improve the chances of closure.^77–79 Additionally, a large-diameter bandage contact lens or Simmons Shell will cover the defect, protecting it from trauma, and can lead to complete resolution of the leak.^89,102,103 Topical antibiotics should be continued until the leak is fully resolved, and topical steroids increased in frequency to normal levels as soon as possible to diminish inflammation and avoid surgical failure.

Another conservative approach is the use of cyanoacrylate tissue glue, as noted previously for management of intraoperative conjunctival defects.^48–50,103 Care must be taken to apply only a small amount of glue with the wooden end of a cotton-tipped applicator, a small plastic micropipette, or a thin glass rod. The conjunctival surface must be fairly dry to enable the glue to stick, which can be difficult to achieve in the presence of a leak. Finally, a bandage contact lens should be placed to avoid both traumatic dislocation of the adhesive and patient discomfort, and multiple reapplications of glue may be required to achieve resolution.¹⁰⁴

Fibrin tissue adhesive may also be used to seal an early or late conjunctival leak.^50,105,106 Two products, Tisseel (Baxter International, Deerfield, IL) and Evicel (Johnson & Johnson, Somerville, NJ), are Food and Drug Administration (FDA)-approved and readily available for use in the United States. Both are produced from pooled plasma and share the threat of transmission of blood-borne pathogens, but such risk has been largely mitigated by improved plasma fractionation practices.¹⁰⁷ Alternatively, autologous fibrin can be employed, but production requires equipment and reagents not typically found in the ophthalmologist’s office or surgery center, making this approach inconvenient.⁵⁰ Compared with cyanoacrylate-based adhesives, fibrin sealants have the advantages of greater ease of application, in layers if necessary, improved biocompatibility with creation of a scaffold for cellular adhesion for improved wound healing, and a nonirritant nature, obviating the need for a bandage contact lens.

Failure of more conservative measures to heal a leak will necessitate surgical repair. An early leak, particularly of the wound margin, can usually be repaired by directly suturing the defect, as the tissue has not become ischemic and thin. As noted previously, conjunctiva is best sutured using 8-0 or 9-0 Vicryl on a tapered needle, which minimizes the size of the holes created. We have found that a running horizontal mattress technique improves the odds of successful closure. When suturing conjunctiva to either sclera or cornea, such as when repairing the dehiscence of a fornix-based flap, a needle with a small cutting tip (Ethicon VAS 100–4) is helpful, as a tapered needle is quite difficult to pass through firmer tissue. Buttonholes are repaired using a purse-string or interrupted technique, as noted previously.

Late conjunctival leaks often develop in the presence of thin, avascular conjunctiva due to the long-term effects of mitomycin C, and are usually not amenable to direct repair given the friable nature of the tissue. These cases require revision with conjunctival advancement flaps or free autografts, and may necessitate scleral reinforcement with a patch graft if aqueous flow is found to be excessive.^99–101 The conjunctiva should be cut posterior to the area of thinning, within healthy, vascular tissue, followed by blunt dissection posteriorly and laterally to mobilize as much conjunctiva as possible. The atrophic bleb can be retained, but all epithelium should be removed from the ischemic conjunctiva and limbus to promote adhesion and avoid formation of epithelial cysts. The advancement flap is then sutured anteriorly to the limbus. If excessive tension is noted, a relaxing incision can be made posteriorly in the conjunctiva, which can then be sutured to underlying Tenon’s fascia. If it is determined that enough healthy conjunctiva does not exist for adequate closure, then a free autograft, typically taken from inferiorly in the same eye, will be necessary. As a whole, these techniques are quite successful at eliminating leaks, resolving hypotony, and maintaining IOP control, but additional glaucoma medications are often necessary.^108,109

Glaucoma Drainage Devices Hypotony

Hypotony following drainage device surgery may be due to overfiltration, aqueous hyposecretion, or, less commonly, wound leak. The causes of aqueous hyposecretion are the same as those following trabeculectomy, including choroidal or retinal detachment, excessive inflammation, or use of aqueous suppressants. In such cases, treatment of the underlying condition promotes resolution of hypotony.

The primary etiology of hypotony in the early postoperative period following tube shunt surgery is overfiltration, the causes of which vary slightly by type of shunt. Independent of shunt design, leakage around the tube may lead to very low IOP in the days immediately following the procedure, and careful surgical technique will mitigate the risk.¹¹⁰ Scleral entry with a 23-gauge needle usually results in a tightly fitting tube, with low risk of significant leakage. Creation of a fairly long intrascleral track, preferably at least 2 to 3 mm, also reduces the risk of peritubular leakage.¹¹¹ Use of a larger diameter needle, or lateral movements of the needle tip to widen the tract for easier tube insertion, may lead to excessive flow. Occasionally, creation of a second entry tract may be necessary due to poor tube positioning in the AC. In such cases, care must be taken to properly close the initial sclerostomy tightly. Absorbable sutures, such as Vicryl, work well in this role, as any induced astigmatism will resolve as the sutures dissolve. Areas of thin sclera, such as adjacent to a prior trabeculectomy flap, should be avoided when possible, as there is greater risk for aqueous leakage.

The type of drainage device implanted also impacts the risk of postoperative hypotony. Two basic drainage device styles are available: restricted and unrestricted. Restricted devices, also known as valved shunts, have a mechanism within the plate body meant to limit the early postoperative flow of aqueous humor, theoretically reducing the risk of hypotony.¹¹² Although these shunts offer the advantage of immediate IOP reduction, the flow restrictors do not always function as intended or may be damaged during tube priming, leading to extremely low early postoperative IOP. Unrestricted implants, in contrast, offer no early resistance to aqueous flow and must be completely ligated, typically with an absorbable suture, to avoid early hypotony.¹¹³ The ligature dissolves in 4 to 6 weeks following surgery, allowing the tube to open and drain aqueous. To allow some immediate postoperative flow and avoid significantly elevated IOP, most surgeons create venting incisions within the tube proximal to the ligature using a suture needle or small blade, thus allowing early egress of aqueous. Although generally successful at producing a reasonable postoperative IOP, this practice can lead to excessive flow and hypotony. Furthermore, failure of adequate fibrous encapsulation to develop around the plate by the time the tube opens can cause a sudden drop in IOP.¹¹⁴

Hypotony following drainage device implantation can usually be managed relatively conservatively, as most cases resolve as fibrous encapsulation of the plate develops and resistance to aqueous outflow increases.¹¹⁴ If significant choroidal effusions and AC shallowing develop, injection of a viscoelastic agent into the chamber provides transient deepening, elevation of IOP, and reduced flow through the tube. Repeated injections may be required to stabilize the globe until encapsulation results in maintenance of an adequate pressure. Prolonged instability of the chamber and IOP, particularly in cases at greater risk for more severe hypotony-related complications, should be addressed surgically. Ligature of the tube, although not commonly necessary, is relatively straightforward and effective at resolving hypotony, with greater success found using nonabsorbable versus absorbable sutures.¹¹⁵

Elevated Intraocular Pressure and Surgical Failure

Trabeculectomy

Deep Anterior Chamber

Early elevated IOP following trabeculectomy, in the presence of a deep AC, is nearly always due to underfiltration, caused either by overly tight scleral flap sutures or mechanical obstruction of the sclerostomy or EX-PRESS shunt. Careful examination usually reveals the etiology. Extensive subconjunctival hemorrhage may obstruct the scleral flap. The presence of excessive blood or fibrin within the AC may lead to blockage of aqueous outflow. The configuration of the pupil may suggest iris incarceration at the sclerostomy. Gonioscopy should be performed to confirm these findings.

Relatively mild digital massage in the region of the scleral flap typically produces egress of aqueous in the presence of tight sutures, proving this to be the primary issue. In such cases, improved flow may develop spontaneously as tissues stretch over the first couple of weeks postoperatively. Failure to achieve an adequate IOP will prompt either laser suture lysis or removal of releasable sutures. The direction in which the bleb expands during massage often indicates which suture’s removal is most likely to effect the greatest improvement in flow. Suture lysis or removal is best avoided during the first 2 weeks postoperatively, as this may cause prolonged hypotony, although long-term reduction in IOP may benefit from earlier intervention.^85,116

If digital massage is initially unsuccessful, more direct manipulation of the flap margin can be achieved with a cotton-tipped applicator using the Carlo Traverso Maneuver (CTM), named for the physician who initially described it.¹¹⁷ Under topical anesthesia, a moistened applicator is placed adjacent or posterior to the scleral flap with pressure applied to deform the globe. This maneuver often promotes flow, possibly by dislodging either an internal obstruction or a blood clot at the scleral flap margin. This means of reestablishing aqueous flow may be all that is required to produce effective filtration. In some cases, however, no amount of massage or focal pressure reestablishes outflow. If no clear obstruction is visible on examination, suture lysis or removal should be considered. However, other interventions may be considered if obstructing material is identified. Iris incarceration may be alleviated by use of miotics such as pilocarpine. Blood, fibrin, vitreous, iris tissue, or fragments of Descemet’s membrane may be dislodged via gonioscopically directed YAG or argon laser.^118,119 Additionally, tissue plasminogen activator (tPA; Activase^®, Genentech, San Francisco, CA), in doses of 6 to 25 µg, may be useful to dissolve blood or fibrin that is obstructing the outflow pathway. Such treatment has been reported to reestablish flow and lower IOP when injected either subconjunctivally for an adherent scleral flap,¹²⁰ or intracamerally. Doses less than 12.5 µg appear less likely to cause hyphema.¹²¹ Ultimately, if IOP can be temporarily managed with topical medication, and if the eye can tolerate the level of increased IOP, obstructions due to blood and fibrin tend to resolve spontaneously as reabsorption occurs.

Elevation in IOP may also occur several weeks to months following trabeculectomy due either to fibrous encapsulation of the filtering bleb or to episcleral fibrosis of the flap. Bleb encapsulation tends to present at between 2 and 8 weeks postoperatively as a tense, elevated, often quite vascular elevation of Tenon’s capsule and conjunctiva, associated with a significant increase in IOP that is unresponsive to bleb massage. Rates of encapsulation are reported between 2.5% and 18.5%, although the higher incidence is associated with procedures performed prior to the routine use of antimetabolites, specifically mitomycin C.^122,123 Bleb encapsulation may be managed medically, with topical or oral ocular antihypertensive agents and steroids, often with a gradual decline in IOP and improved bleb morphology occurring over several months.¹²⁴ If more rapid decompression of the encapsulated bleb is necessary, needle revision can be performed with adjunctive 5-fluorouracil.^125,126 Commonly described as “bleb needling,” this procedure can usually be comfortably performed at the slit lamp under topical anesthesia. After placement of a lid speculum and instillation of topical antibiotic and/or povidoneiodine, a 27- or 30-gauge needle is inserted subconjunctivally near the margin of the bleb, outside the encapsulated area. The needle is then advanced into and withdrawn from the encapsulated Tenon’s cyst repeatedly, creating numerous perforations, using the needle tip to incise as much of the capsule wall as possible (Fig. 47.6). It is common to see the area of encapsulation flatten and a much more diffuse bleb form quite rapidly upon decompression. Then 5-fluorouracil, 0.1 to 0.2 mL of 50 mg/mL solution, is injected into the bleb or, alternatively, in the inferior fornix. If necessary, this procedure can be repeated if encapsulation redevelops. One prospective randomized study comparing needling with medical management found that, although both methods were effective at reducing IOP, bleb needling produced a significantly lower mean IOP at 12 months.¹²⁶

Fibrosis of the scleral flap, often occurring months to years following trabeculectomy, is the most common cause of late IOP elevation and surgical failure, and is heralded by flattening of a previously elevated bleb. Bleb needling is an effective means of managing such late failures.^75,127 The procedure is similar to needling an encapsulated bleb, and has been described using either 5-fluorouracil or mitomycin C. In this case, the antimetabolite is often injected subconjunctivally in the region of the bleb and allowed to diffuse prior to needling. The use of mitomycin C, 0.2 mL of a 0.2 mg/mL solution, has been described as safe and effective.⁷⁵ The needle tip is used to perforate the adhesions between the scleral flap and bed, elevating at least one corner of the flap. Some surgeons prefer to introduce the needle into the AC to prove that the sclerostomy is patent, a maneuver that is not possible with an EX-PRESS shunt. Success rates of 64% achieving IOP less than 21 mm Hg⁷⁵ and 71% achieving IOP less than 16 mm Hg¹²⁸ have been reported for revision with mitomycin, which has been found more effective than 5-fluorouracil.¹²⁸

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