Ординатура / Офтальмология / Английские материалы / Shields Textbook of Glaucoma, 6th edition_Allingham, Damji, Freedman_2010

Figure 38.18 Typical appearance of an encapsulated bleb, characterized by an elevated, smooth-domed conjunctiva with large vessels but intervening avascular areas and no microcysts.

Encapsulated blebs are common, occurring in 3.6% to 28% of eyes (404, 405, 406, 407, 408 and 409), typically developing within the first 2 months after the surgery. Long-term topical glaucoma therapy may be a risk factor for failure of trabeculectomy (119, 120), and it has been associated with increased inflammation of the conjunctiva and Tenon capsule after filtering surgery (410). Reports are conflicting regarding the influence of argon laser trabeculoplasty (404, 411, 412). In the Advanced Glaucoma Intervention Study, encapsulated blebs were found in 18.5% of eyes after previously failed argon laser trabeculoplasty and in 14.5% of eyes without previous laser procedure, but the difference was not statistically significant (408). Higher frequencies of encapsulated bleb have been reported in males and in patients undergoing trabeculectomy alone versus trabeculectomy combined with cataract surgery (408, 413, 414). Adjunctive 5-FU may reduce the incidence of encapsulated blebs (415). Use of MMC was suggested to increase it, on the basis of a 29% incidence in one series (413), although other studies have not confirmed that finding (409, 416). Encapsulation appears to develop more often (33% to 44%) in eyes with congenital and juvenile glaucoma (407).

In managing the encapsulated bleb, the physician should be aware that most begin functioning well within a few months (409). It is generally agreed that the mainstay of treatment is to resume the use of glaucoma medication until the improvement occurs (417). Opinions differ, however, on whether steroids and digital pressure should be used. One study suggested that prolonged steroid therapy may actually increase the incidence of encapsulated blebs (418), and digital pressure may further reduce aqueous flow through the encapsulated bleb by compressing the subconjunctival layer of tissue (406). Some surgeons prefer early needling (discussed later) of the encapsulated bleb. However, because this is more invasive and may be associated with severe complications, most surgeons believe that medical treatment with digital pressure should be used as the initial treatment in eyes with encapsulated blebs (419).

Blebs that do not respond to conservative medical management may be restored surgically. One such technique is called needling, in which a 25to 30-gauge needle is passed beneath the conjunctiva about 5 to 10 mm from the bleb, is used to balloon up the conjunctiva, and is then passed into the bleb to puncture and incise the fibrous episcleral tissue (420). An effective modification is to inject 5 mg of 5- FU (0.5 cc of 10 mg/mL, or 0.1 cc of 50 mg/mL) subconjunctivally at the time of the needling (421, 422, 423, 424 and 425), although higher doses should be avoided because they can cause corneal endothelial toxicity (426). Subconjunctival injection of MMC at the time of the needling has also been advocated (427, 428 and 429). A more involved, but possibly more definitive, technique is to dissect the conjunctiva from the fibrous tissue, completely excise the latter, and resuture the conjunctiva (430). P.507

Other Early Postoperative Complications Uveitis and Hyphema

Anterior uveitis is seen to some degree in the early postoperative period in all patients. It is routinely managed with topical corticosteroids and a mydriatic-cycloplegic. When the inflammation is excessive (3 + cell and flare, or fibrinoid iritis), increasing the frequency of steroid administration to every hour or two is usually sufficient; only rarely is stronger antiinflammatory therapy required. Hyphema is less common and is usually managed conservatively, with elevation of the head and limited activity. The incidence of postoperative hyphema appears to be reduced by placing the sclerostomy anterior to scleral spur (431). Some surgeons place the sclerostomy in clear cornea anterior to the Schwalbe line, which essentially eliminates bleeding from the angle tissues, although iris bleeding from an iridectomy is still a risk.

Dellen

Dellen adjacent to large filtering blebs may occur in the early or late postoperative period. Most heal uneventfully with tear film replacements or bandage contact lens. Corneal ulcers can complicate dell formation if not adequately treated (432). Persistent dellen formation or discomfort from overhanging blebs may require surgical revision.

Loss of Central Vision

Loss of central vision (“snuff out” syndrome) may o ccur after glaucoma filtering surgery. Most studies have shown this to be uncommon (433, 434, 435, 436 and 437). In one study, snuff out occurred in 4 of 508 eyes (0.8%) (436). Risk factors included older age, preoperative macular splitting in the visual field, and hypotony. Although a small central island or split fixation is not considered to be a contraindication to glaucoma filtering surgery (433, 434, 435, 436 and 437), these patients appear to be at greater risk of losing central vision postoperatively (438). The patient should be informed of the risk, and efforts should be made to minimize postoperative extremes in IOP.

Ocular Decompression Retinopathy

Ocular decompression retinopathy is a term that was used to describe eyes of patients who developed intraretinal hemorrhages immediately after trabeculectomies (439, 440, 441, 442, 443 and 444). An especially high preoperative IOP with sudden decompression and alteration in the configuration of the lamina cribrosa may lead to retinal vein obstruction and cause this complication. This may occur more commonly in children.

Late Postoperative Complications Late Failure of Filtration

The most common late complication of any filtering procedure is eventual failure to maintain a low IOP. This may develop within months to years after an initially successful operation. It is hard to predict on the basis of the appearance of the bleb which eyes will ultimately experience failure, although persistent inflammation, along with preoperative and postoperative factors that predispose to an inflammatory response, appears to play an important role.

The mechanism of late bleb failure may be closure of the fistula, although it is more commonly related to fibrosis of the scleral flap or scarring of the conjunctival portion of the bleb. A histopathologic study of failed blebs revealed a marked inflammatory response, abundant fibroblasts, and deposition of new collagen in the first few months after surgery (445). In eyes with failure in the later postoperative period, a hypocellular capsule of fibrous tissue lined by a thick layer of fibrin was seen beneath relatively normal conjunctiva and Tenon capsule.

These cases rarely respond to digital pressure or pharmacologic agents to suppress inflammation or fibrosis. When the pressure cannot be controlled medically and the bleb appears to be encapsulated, it may be possible to revise the bleb surgically by using the techniques described earlier.

When clinical evaluation suggests that the procedure has failed because of closure of the fistula by membranous tissue, it may be possible to re-establish patency by incising the tissue with a knife or needle through an ab externo or ab interno approach. It may also be possible to remove the obstructing element with laser surgery. Argon laser treatment has been reported to be effective for this purpose when the membrane is pigmented (446, 447), while pulsed Nd:YAG lasers have been used successfully to eliminate nonpigmented tissue from the fistula or to loosen or penetrate the scleral flap through the fistula (448, 449, 450, 451 and 452). These techniques, however, are usually only successful in eyes with previously well-established filtering blebs, in which failure has occurred abruptly and the bleb is still moderately elevated.

When the aforementioned measures are ineffective in reestablishing a failed filtering procedure, it is usually necessary to revise the bleb with incisional surgery, to repeat the operation in the other superior quadrant with use of adjunctive MMC or 5-FU, or to consider performing glaucoma drainagedevice surgery. Revision is usually more successful when dealing with encapsulated blebs rather than those that are flat and scarred down to underlying episclera (453).

A Leaking Filtering Bleb

A bleb wall that has become too thin may rupture, leading to loss of the anterior chamber and possible endophthalmitis (Fig. 38.19). Blebs with a large avascular area are at increased risk for leaks (454). Severe coughing, for example, is a potential cause of late posttrabeculectomy bleb leaks (455). Small, focal cystic blebs under tension are also thought to be at increased risk for leaks.

Bleb leaks seem to occur more often after full-thickness procedures or when antimetabolites are used (456). Transconjunctival oozing and point leak at least 3 months after trabeculectomy with use of 5-FU

or MMC occurred in 11.9% and 2.0%, respectively, in one series (457). Oozing was significantly more common after use of 5-FU than MMC, and point leak was associated with a larger avascular area. The defects are usually small, and the Seidel test is often helpful in confirming the

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leak (Fig. 38.20). If the leak is small, aqueous suppressants and observation alone may be sufficient. In some cases, the defect will close beneath a soft bandage contact lens (458), which can be left in place for a few weeks. Coverage with a topical antibiotic is advisable during the course of treatment for bleb leaks.

Figure 38.19 Leaking of a filtering bleb, associated with a shallow to flat anterior chamber and low IOP. This slitlamp photograph shows an eye with an avascular, thin-walled filtering bleb, which was found to be leaking near the limbus.

Some leaks can be sealed with cyanoacrylate glue (341) or autologous fibrin glue (459). When these measures fail, surgical revision of the leaking bleb may be required (460). Results of a retrospective analysis of patients with late bleb leaks suggest that bleb revision is associated with more successful outcomes and less serious intraocular infections than in those managed more conservatively (461). Bleb revision techniques include resection of the bleb and creation of a new conjunctival flap posterior to the defect or a rotational conjunctival flap to cover the defect (461, 462). When there is insufficient conjunctiva for a flap, autologous conjunctival grafts can be obtained from the fornix and placed over existing de-epithelialized leaking blebs (463).

A retrospective analysis of various surgical techniques for bleb revision demonstrated a high success rate with few postoperative complications, and it was suggested that choosing different techniques for specific clinical situations may enhance the success of surgical bleb revision (464). Histologic examination of 10 leaking filtering blebs revealed an epithelial tract running from the surface of the bleb to the episclera in eight cases, and it was suggested that the bleb should be excised before bringing down the new flap to prevent epithelial downgrowth (465). Autologous Tenon and partial-thickness scleral patch grafts have been found adequate, safe, and effective for closing excessively draining fistulas (466). Bleb excision and repair of the scleral defect with a full-thickness scleral graft, followed by coverage with the advancement of a conjunctival flap or by a free conjunctival autograft, have also been useful for

Figure 38.20 Leakage from the filtering bleb can be clearly documented by using the Seidel test: Fluorescein is applied to the area in question and observed at the slitlamp with a cobalt blue light; leaking aqueous will be seen as bright yellow fluid flowing from the leaking site.

Amniotic membrane transplantation has been considered as a substitute for conjunctiva in the revision of glaucoma filtration blebs (468, 469 and 470). Although a prospective, randomized clinical trial failed to support the value of amniotic membrane transplantation (471), the simplicity of the technique may make it useful in certain clinical situations (472).

Bleb-Related Infections

Infection after glaucoma filtering surgery is rare in the early postoperative period but tends to occur months or years after the surgery. It typically begins as a bleb infection (blebitis), in which the bleb is white and surrounded by intense conjunctival injection (Fig. 38.21). There are usually variable degrees of anterior chamber reaction, but the vitreous is clear (473). Blebrelated endophthalmitis is characterized by the addition of vitreous involvement. The two forms of bleb-related infection are clinically distinct, with different presentations, prognoses, and outcomes. Although blebitis is considered a limited form of bleb-related infection in which inflammation is limited to the bleb and the surrounding conjunctiva, with or without cells in the anterior chamber, bleb-related endophthalmitis is the virulent form of bleb-related infection with rapidly worsening vision, redness, and pain with diffuse conjunctival injection. When associated with endophthalmitis, blebs usually have a white “milky” appearance, with or without epithelial defects; fibrin or hypopyon is usually seen in the anterior chamber; and vitritis is present (Fig. 38.22) (474, 475).

Figure 38.21 Slitlamp view of an eye with early bleb infection (blebitis), with characteristic intense conjunctival injection around a whitish bleb.

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Figure 38.22 Bleb-associated endophthalmitis occurring 2 years after glaucoma filtering surgery. A: Marked purulence of the bleb, hypopyon, and fibrin in the pupil. Visual acuity was reduced to hand motion. The patient was treated with a vitreous tap and injected with intravitreal antibiotics. B:

Coagulase-negative staphylococcus was isolated from the vitreous. Final visual acuity was 20/400 because advanced glaucomatous disease limited visual recovery. (From Scott IU, Flynn HW Jr., Han DP. Endophthalmitis: categories, management and prevention. In: Tasman W, Jaeger EA, eds. Duane's Clinical Ophthalmology. Vol 6. Philadelphia:Lippincott, Williams & Wilkins;chap 64.)

Blebitis

Incidence

A record review has found that the incidence of delayedonset, bleb-related infection after trabeculectomy with antiproliferative treatment is similar to that after trabeculectomy without antimetabolites: 1.1% to 1.3% (476). Bleb-related infection was reported to develop an average of 3.1 years after trabeculectomy (476).

Risk Factors

Early, chronic, intermittent bleb leaks are risk factors for the bleb-related infection (477). Increased axial length, conjunctivitis, upper respiratory infection, winter season (477), intraoperative use of MMC, and antibiotic use after the postoperative period have also been associated with an increased risk for blebrelated infection (478).

Treatment

Blebitis usually responds well to intensive topical antibiotic treatment, returning visual acuity and IOP to preinfection levels (474, 479). Most patients with blebitis are treated as outpatients. With prompt, aggressive therapy at this stage, the prognosis for visual recovery is much better than for fulminant endophthalmitis. Prophylactic antibiotic use is not recommended for patients with filtering surgery. A survey of American Glaucoma Society members, published in 2001, has shown that methods of the managing blebitis continue to differ among specialists. More than two thirds do not ask their patients to keep topical antibiotics in their homes for early symptoms of blebitis but prefer to examine a patient with symptoms of blebitis within 1 hour of an onset of symptoms, or as soon as possible. Most glaucoma specialists prescribe a topical fluoroquinolone, alone or in combination with one or two other antibiotics, as the initial empirical treatment of isolated blebitis. Twenty-one percent choose a combination of fortified topical agents, usually including a fortified aminoglycoside, vancomycin, or cephalosporin. Only a minority of patients use an oral antibiotic in cases of blebitis, and approximately two thirds use topical corticosteroids in conjunction with antibiotic treatment. Most glaucoma specialists perform surgical bleb revision in eyes with a persistently leaking bleb (480). Oral fluoroquinolones have good vitreous penetration and may be considered in the treatment of blebitis or endophthalmitis (481). Prognosis

With aggressive treatment, blebitis has much better prognosis for visual recovery than endophthalmitis does (473). In one retrospective study, the majority of patients who developed blebitis retained their preinfection visual acuity (475).

Bleb-Related Endophthalmitis

Bleb-related endophthalmitis is usually associated with a thinwalled filtering bleb. Bleb-related endophthalmitis is a virulent form of bleb-related infection with a poor visual prognosis despite aggressive immediate treatment with topical, systemic, and intravitreal antibiotic administration combined with core vitrectomy (474).

Early Postoperative Endophthalmitis

Differentiation of early (approximately first 3 months) versus late endophthalmitis is based not only on the time of onset but also on the pathogenesis. A retrospective analysis of 1100 consecutive trabeculectomies revealed an incidence of fewer than 0.1% for early and 0.2% for late endophthalmitis (482). The 7- to 10-year incidence of early endophthalmitis has been reported to be 0.05% to 0.09% for overall intraocular surgery, with higher rates of 0.12% to 0.2% for glaucoma procedures and 0.11% for combined cataract and glaucoma surgery. However, visual acuity outcomes were better with glaucoma surgery than with other types of surgery (483, 484). Another retrospective analysis from a large referral eye center showed that, in early

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endophthalmitis, Staphylococcus epidermidis was isolated from vitreous culture in 4 of 6 cases, whereas in late endophthalmitis, this organism was isolated in only 1 of 27 cases (479).

Incidence

The incidence of endophthalmitis in one study was the same with thermal sclerostomy and trabeculectomy (485). In a retrospective review of primary trabeculectomy with MMC and laser suture lysis, bleb leak occurred in 14.6% of eyes, blebitis occurred in 5.7% of eyes, and endophthalmitis occurred in 0.8% of eyes during 1 to 3 years of follow-up (486). The incidence of endophthalmitis per year was 1.3% after trabeculectomy with MMC in another retrospective review. The 5-year probability of developing a bleb leak, blebitis, or endophthalmitis was 17.9%, 6.3%, and 7.5%, respectively. An isolated bleb leak seems to be a relatively benign condition, in that three fourths resolved with office-

based methods (487). In a retrospective analysis of trabeculectomy performed with adjunctive use of MMC, 2.1% of patients developed bleb-associated endophthalmitis, an average of 18 months after the surgery. The incidence of bleb-related endophthalmitis was significantly greater after inferior trabeculectomy than after superior trabeculectomy. The cumulative incidence was 13% for inferior limbal blebs and 1.6% for superior limbal blebs. Streptococcus sanguis and Haemophilus influenzae were the most frequently found organisms. The incidence of bleb-related endophthalmitis is higher with adjunctive antimetabolites than the reported rate in eyes undergoing filtering surgery without the use of antifibrotic agents (0.2% to 1.5%) (488). In a retrospective review of trabeculectomies with adjunctive use of MMC, the overall incidence of bleb-related endophthalmitis was 2.6% (489).

Risk Factors

The increased use of adjunctive antimetabolites in trabeculectomy has caused an increased concern about the risk of blebrelated endophthalmitis (490), although reports show that use of antifibrotic agents is not always associated with an increased risk of bleb-related endophthalmitis (476, 491). Other risk factors for bleb-related infections include an inferior or nasally located bleb, presence of a high bleb or blepharitis, development of a late-onset bleb leak, diabetes mellitus (492), chronic antibiotic use, and performance of a trabeculectomy alone versus a combined procedure. Glaucoma procedures that provide the lowest IOP are often those that predispose to bleb-related infections (493). Contact lens use may increase the risk of bleb-associated infection (478). The risk of endophthalmitis in eyes with filtering blebs makes it imperative that any evidence of external infection, such as conjunctivitis, be treated aggressively.

Causative Organisms

The most common causative organisms of delayed-onset blebassociated endophthalmitis are Streptococcus and Staphylococcus species and H. influenzae (488, 494, 495, 496, 497, 498, 499). Staphylococcal species may be associated with better visual outcomes (499). The infection may rapidly progress over a few days (496), and despite successful treatment of the infection, visual outcomes are generally poor (495). Moraxella species, Acremonium filamentous fungi, Neisseria meningitidis, Pseudomonas aeruginosa, and Aspergillus niger have been reported as causes of delayed-onset endophthalmitis in patients with filtering blebs (500, 501, 502, 503, 504, 505, 506, 507, 508, 509 and 510).

Clinicopathologic Features

Common pathologic features of the eyes enucleated for endophthalmitis include inflammation involving the anterior segment, lens, and choroid, with one eye showing evidence of focal granulomatous uveitis (496). In one case-control study, eyes with endophthalmitis had hypopyon, cells in the anterior vitreous cavity, or a positive vitreous biopsy sampling result. The risk of endophthalmitis is increased if vitrectomy is performed in conjunction with glaucoma surgery (511). In a significant number of patients, prodromal signs or symptoms were documented by ophthalmologists days or weeks before the blebitis or endophthalmitis was diagnosed (475).

Treatment

As noted previously, most of these cases are caused by virulent organisms, such as gram-negative rods and streptococci, which require prompt, aggressive management (512). When vitreous involvement is present or suspected, a recommended approach is to establish the diagnosis with aqueous and vitreous aspirates and then to begin treatment with high-dose, broad-spectrum parenteral and periocular antibiotics, such as gentamicin and cefazolin, and intravitreal antibiotics, such as vancomycin and gentamicin—with adjustment of the treatment, if nec essary, according to culture and sensitivity results (512, 513, 514 and 515). In the Endophthalmitis Vitrectomy Study, which involved endophthalmitis after cataract surgery or secondary intraocular lens implantation, a vitrectomy (rather than a vitreous tap or biopsy) was beneficial only in eyes with initial light perception vision, and the use of systemic antibiotics had no benefit (516). Corticosteroid therapy should also be used after antibiotic therapy has been established. However, the results of the Endophthalmitis Vitrectomy Study cannot be simply projected to the posttrabeculectomy endophthalmitis because of the difference in pathogenesis and spectrum of organisms (479).

Prognosis

Despite successful treatment of the infection, visual outcomes are generally poor (495). Patients in whom endophthalmitis develops after trabeculectomy do poorly, even with aggressive medical and surgical intervention.

Cataracts

Patients undergoing glaucoma surgery are at increased risk for the development and progression of cataracts, which are reported to occur in approximately one third of eyes after filtering surgery (433, 517). The mechanism of this complication is uncertain, but possible factors include (a) patient's age, (b) duration of miotic therapy, (c) surgical manipulation, (d) postoperative iritis, (e) prolonged flat anterior chamber, and (f) nutritional changes (517, 518 and 519).

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Figure 38.23 Excessive filtering bleb extending over cornea as a late complication of glaucoma filtering surgery.

In the Advanced Glaucoma Intervention Study, a trabeculectomy increased the risk for cataract development by 78%, compared with those who did not have a trabeculectomy. The risk decreased to 47% when the glaucoma surgery was uncomplicated, and it approximately doubled with complications, such as marked inflammation and a flat anterior chamber (520). In the Collaborative Interventional Glaucoma Study, cataract extraction was required more often (521).

Overhanging Filtering Blebs

In some cases, a large bleb may gradually extend down over the cornea, possibly because of the effect of eyelid movements (Fig. 38.23). These blebs can be bothersome to the patient, especially when overhanging the cornea. In some cases, these can be reduced by applying argon laser energy to the bleb (522), whereas others require incisional surgical correction by lifting the bleb from the cornea with an iris spatula, excising it near the limbus, and suturing the free edges (523). Excision of the excessive bleb near the limbus does not lead to a bleb leak and generally does not require suturing (524, 525). Bleb window cryopexy has also been reported to be an effective treatment for selected patients with large, symptomatic, overhanging blebs (526).

Spontaneous Hyphema

Spontaneous hyphema may occur weeks to years after filtering surgery (527). The bleeding may come from one of the cut ends of Schlemm canal or from abnormal vessels near the internal portion of the fistula (528, 529). Argon laser photocoagulation can be effective if the source of bleeding can be visualized.

Hypotony and Ciliochoroidal Detachment

Hypotony and ciliochoroidal detachment may occur at any time after a filtering procedure. Some may be chronic and recurrent, and inflammation is frequently present (530, 531). Other apparent risk factors include drugs that can incite ocular inflammation and aqueous suppressants (530, 532). Management in these cases involves discontinuing use of the responsible drugs and initiating aggressive antiinflammatory therapy. Cataracts are common with this condition, and cataract extraction may be associated with resolution of the choroidal detachments (530). Tearing of the retinal pigment epithelium can be a sequela of hypotony and choroidal or serous retinal detachment after glaucoma surgery (533). Corneal Changes

Patients with glaucoma appear to have a decreased corneal endothelial cell count, particularly when exfoliation is present or when patients are taking three or more glaucoma medications (534, 535). Corneal endothelial cell count has been shown to be further reduced after glaucoma filtering surgery, which is influenced by early postoperative iridocorneal touch but not by the use of adjunctive MMC (536, 537). However, severe endothelial damage after trabeculectomy with MMC was reported in two eyes with pre-existing cornea guttata (538). The trabeculectomy procedure can also alter corneal topography, although it may be undetectable without topographic analysis and usually does not persist (539, 540). Limbal stem cell deficiency can also occur in patients receiving 5-FU after trabeculectomy, which can be treated with amniotic membrane transplantation. However, for total limbal stem cell deficiency, limbal transplantation has been suggested as an alternative to restore the corneal surface (541).

Eyelid Changes

Upper eyelid retraction after glaucoma filtering surgery was described in two patients and was thought to result from the adrenergic effect of aqueous humor on Müller muscle (542). Ptosis has also been reported after trabeculectomy in 6% to 12% of patients and was not significantly affected by combined cataract surgery, type of conjunctival flap, or previous ocular surgery (543). Ptosis may be related to surgical trauma to the levator muscle and adjacent tissue.

Sympathetic Ophthalmia

Sympathetic ophthalmia after glaucoma surgery is a rare complication. Studies suggest that this is unrelated to the type of operation, but rather to the preoperative condition of the eye, in that it occurs more commonly when operating on a blind, painful eye or after a uveal trauma (544, 545). OUTCOMES OF FILTERING PROCEDURES

Trabeculectomy versus Full-Thickness Procedures

As previously noted, most surgeons prefer some form of trabeculectomy rather than a full-thickness procedure. Studies that have specifically compared trabeculectomies and fullthickness operations have shown both types of procedures to have similar glaucoma control (546, 547). Some surveys suggested slightly better IOP control with full-thickness procedures (67, 548, 549, 550, 551 and 552), although these studies were done before the advent of adjunctive antimetabolite therapy. In general, the IOP results were similar to those that had been previously described for various full-thickness procedures, with variable reductions in the incidence of complications (553, 554, 555, 556, 557 and 558).

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Long-Term Outcomes with Trabeculectomy

Several studies in the late 1970s and 1980s reported outcomes after various forms of trabeculectomy. More recent studies, with up to 12 years of follow-up, have shown a gradual decline in the probability of successful IOP control over time, although the actual numbers vary considerably (559, 560 and 561). In one study of 75 patients followed up for 6 to 12 years, IOP control of 21 mm Hg or less was achieved in

90% at 5 years and the final visit (559), whereas in another study of 43 eyes with COAG, 67% maintained an IOP below 21 mm Hg during a 7- to 10-year follow-up (560). Yet a third study, in which success was defined as an IOP of 20 mm Hg or less and a minimum reduction of 20%, revealed a probability of success after a single operation of 48% and 40% at 3 and 5 years, respectively (561). Of greater significance are visual field outcomes. One study of 54 patients revealed further loss of visual field in 28% during the first 5 years (562), whereas another study of 239 patients followed up for up to 10 years revealed progressive glaucomatous damage in 25%, 30%, 43%, and 58% at 1, 2, 5, and 10 years, respectively (563). Consistent with previous reports, the reported incidence of cataract formation ranged from 22% to 78% (520, 559, 560 and 561). For uncertain reasons, when primary trabeculectomies were performed in both eyes of patients, encapsulated blebs and hypotony occurred slightly more frequently in the second operated eye, despite a similar clinical course (564). Trabeculectomy versus Nonpenetrating Procedures

Nonpenetrating procedures may reduce the complication rate, but they do not typically achieve IOPs as low as trabeculectomy does. In a randomized trial comparing viscocanalostomy and trabeculectomy without intraoperative use of antimetabolites, trabeculectomy provided only slightly better IOP control after 2 years (320). Other studies have also found that trabeculectomy is more effective than viscocanalostomy in reducing the IOP, whereas viscocanalostomy has a lower incidence of complications (565, 566 and 567). Trabeculectomy also decreases the IOP more than the nonpenetrating deep sclerectomy technique does, although the complication rate again seems to be lower with the latter procedure (568). Deep sclerectomy may be combined with phacoemulsification (569), achieving an IOP reduction similar to that achieved with phacoemulsification combined with trabeculectomy, but with lower complication rates (570).

Deep sclerectomy with collagen implantation provided pressure results similar to those with trabeculectomy but with a lower rate of early postoperative complications (571, 572). One study has shown that when a deep sclerectomy is complicated by perforation of the trabeculo-Descemet membrane, the long-term success rate is similar to that of trabeculectomy, but the likelihood of immediate postoperative complications, such as hypotony and hyphema, is increased (573). Outcomes in High-Risk Populations

For most filtering procedures, glaucoma control is generally thought to be poorer among black patients than white patients, although this has not been substantiated in all studies. With trabeculectomies, success rates in black patients have mostly been in the same range as those for white patients (574, 575, 576, 577 and 578), although in some series standard trabeculectomies were successful in fewer than 75% of black patients (82, 579, 580). The difference in outcome, if it truly exists, may be explained by an increase in macrophages and fibroblasts and a decrease in mast cells and goblet cells in the conjunctiva at the time of filtering surgery, compared with white patients (580). Some surgeons have noted improved pressure control in black patients when the trabeculectomy technique is modified to enhance filtration around the scleral flap (82, 581). Comparative studies of trabeculectomies and fullthickness filtering procedures in black populations have given conflicting results (552, 582, 583 and 584).

Children, when compared with adults, generally have worse outcomes with filtering procedures (585), including trabeculectomies (586, 587 and 588). In one study, trabeculectomy was no better than other procedures for advanced pediatric glaucomas (589), although the results are probably different with the addition of adjunctive antimetabolite therapy. Patients aged 15 to 40 years have outcomes similar to those in older patients (590), unless additional risk factors are present (591). A retrospective analysis of primary trabeculectomy has shown that primary infantile glaucoma had a better outcome than secondary developmental glaucoma, and that the visual outcome depends on early and sustained control of IOP and aggressive treatment of the amblyopia (592).

In patients with glaucoma after congenital cataract surgery, trabeculectomy controlled IOP in only slightly more than one third of aphakic eyes after 3 years, regardless of MMC use (103). A retrospective review revealed that with trabeculectomies in children with aphakia, aniridia, anterior segment dysgenesis, and other secondary glaucomas, IOP control and stabilization of visual acuity and optic disc