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

Anterior migration of the tube can occur due to the dislocation of the external plate.

In pediatric patients, the tube may retract out of the anterior chamber or even erode through the cornea (106, 107, 108 and 109). Extrusion of the implant was the most common reason for repeated surgery in children who received an Ahmed glaucoma drainage device (110). This may occur as the eye grows, requiring repositioning of the tube from the original site (111). The tube may also need to be repositioned when it is blocked by the cornea, iris, or vitreous (64). If the tube end is too short to allow for repositioning, a silastic sleeve or silastic extension tube may be used (112). A 22-gauge angiocatheter and a piece of pediatric lacrimal tubing, with a 0.3-mm internal diameter and 0.64-mm external diameter, may be used for this purpose (113).

Avulsion of an implant after blunt trauma may force the tube against the cornea, causing corneal melting and requiring explantation of the implant and possibly corneal grafting. Placing the connecting tube of a double-plate Molteno implant under the superior rectus muscle might decrease the risk for shunt avulsion after trauma (114).

Figure 39.12 Exposed silicone tube posterior to the limbus in a patient with a Baerveldt glaucoma implant device. The patient had undergone penetrating keratoplasty and implantation of a glaucoma drainage device for treatment of essential iris atrophy.

Erosion of the silicone tube through the overlying conjunctiva is a recognized complication of glaucoma drainage devices (Fig. 39.12). A partial-thickness scleral flap does not prevent erosion of the tube, and (as previously described) the tube and fistula site should be covered with preserved sclera, dura, fascia lata, or pericardium. However, pericardial graft thinning, melting, and conjunctival erosion despite the patch graft have occurred (115, 116 and 117).

If a scleral graft is too thick, it may elevate the limbal conjunctiva enough to produce dellen formation. Conversely, a thin scleral patch graft may predispose the tube to erosion. In addition, immune reactions resulting in scleral melting have been reported (118). The use of preserved sclera also has the disadvantages of dependence on eye bank supplies, precluding its use in emergency cases; possibly

greater cost; and concerns about infectious disease transmission, despite donor screening (119, 120). Studies using polymerase chain reaction have shown evidence of the human immunodeficiency virus (HIV) genome in sclera obtained from HIV-1-seropositive donors, despite treatment with heat, alcohol, or formalin, but not after irradiation (120).

Solvent-preserved cadaver pericardium (Tutoplast) offers several advantages, including availability, lower cost, uniformity in size and tissue quality, and enhanced sterility. A dehydration process leaves the graft devoid of antigenic stimuli yet preserves the tissue's inherent strength and flexibility (121). Tissue sterilization is achieved through the treatment with organic solvents followed by low-dose radiation, which inactivates bacteria, fungi, and viruses, including HIV and Creutzfeldt-Jakob disease virus (120, 122, 123).

Thin (0.25 mm) polytetrafluoroethylene patches were well tolerated in rabbit eyes and may be an alternative to donor sclera for reinforcement in glaucoma drain surgery (124).

If the plate of an implant migrates toward the medial rectus muscle insertion, myositis may develop. This was reported to resolve after removal of the implant (125).

Endophthalmitis

As mentioned previously, endophthalmitis may develop after needling of the implant (102). P.534

Recurrent Propionibacterium acnes endophthalmitis has been reported after surgical revision of a Molteno drainage device, based on a positive culture of anterior chamber needle aspirate. The response to repeated intraocular vancomycin injections was poor, and explantation of the device was required to achieve complete resolution of the infection. Reinsertion of the drainage device into the anterior chamber resulted in recurrence of the infection (126).

Removal of the glaucoma drainage device in cases of endophthalmitis may be necessary to remove the contaminated foreign body. Early postoperative endophthalmitis after placement of a glaucoma drainage device may be successfully treated by immediate removal of the implant and surgical management of the infection, with subsequent placement of a new device (127).

Endophthalmitis may also occur in the late postoperative course. Exposure of the tube seems to be a major risk factor for these infections. Surgical revision with a patch graft in all cases in which a tube is exposed is indicated to prevent this potentially devastating complication (128).

Sterile endophthalmitis was also described approximately 1 month after discontinuation of postoperative corticosteroid therapy (129).

Visual Loss

In one series of 41 patients after Molteno device implantation, the incidence of reduced visual acuity was 22%, with hypotony and shallow anterior chambers being the most commonly associated events (130). Other reported mechanisms of visual loss include retinal detachment, vitreous hemorrhage, cystoid macular edema, and operating microscope-induced retinal phototoxicity (130, 131, 132, 133 and 134). These complications often occurred despite successful control of IOP.

Corneal Decompensation and Graft Failure

The causes of corneal decompensation and graft failure in eyes with glaucoma drainage devices are not completely clear but may be related to the retrograde flow from the encapsulated reservoir to the anterior chamber. Serial corneal endothelial cell counts in 19 patients after uneventful Molteno device implantation revealed slight, clinically insignificant progressive cell loss (135). Tube-cornea touch is another cause of corneal decompensation. In one study of Ahmed glaucoma drainagedevice implantation in pediatric patients, cornea-tube contact occurred in 18.5% (136). When the tube-cornea contact is seen, removal of the tube from the anterior chamber, shortening of the tube, and subsequent reinsertion may be necessary. Because this technique may require extensive revision with possible complications, a simpler technique was described for trimming the silicone tube in situ (137).

In one retrospective review, corneal edema developed on average after 21 months in 50% of patients after Molteno drainage-device implantation, and in 6.7% after multiple eye surgeries, including a trabeculectomy, but not after the trabeculectomy alone (138). In another study, when corneal

complications thought to be unrelated to the implant were excluded from the definition of failure in a cohort of patients with Ahmed drainage devices with a mean follow-up for 30.5 months, only 21.5% of the eyes experienced failure, and cumulative probabilities of success at 1, 2, 3, and 4 years were 87%, 82%, 76%, and 76%, respectively. However, when corneal decompensation and corneal graft failure were included in the definition of failure, 43% of the eyes were considered to have experienced failure, decreasing cumulative probabilities of success at 1, 2, 3, and 4 years to 76%, 68%, 54%, and 45%, respectively. These corneal problems may be secondary to the underlying ocular condition or to the drainage device itself (139). Phosphorylcholine polymer coating of the glaucoma drainage devices was suggested to reduce the rate of corneal endothelial failure (140).

A comparative study showed that although implantation of an additional glaucoma drainage device provided better IOP control than with tube repositioning, the most common complication with this approach was corneal edema (141). Another study showed that device replacement after initial drainagedevice failure has high corneal morbidity, reaching a corneal decompensation rate of 36% (142). However, an IOP less than 21 mm Hg or 20% reduction in IOP after the second tube procedure was achieved in 86.4% with a 3-year follow-up.

Diplopia and Ocular Motility Disturbance

As previously noted, devices with larger plates, especially when implanted in the superonasal quadrant, can interrupt extraocular muscle function and cause strabismus and diplopia (58). Characteristic patterns are exotropia, hypertropia, or limitation of ocular rotations (143, 144, 145, 146 and 147), although a Brown superior oblique tendon-like syndrome has also been described (58, 148, 149). Whereas the

complication is usually associated with the larger plates, such as the 350-mm2 Baerveldt drainage device and the Krupin eye valve with disc (143, 145, 146, 147 and 148), it may also occur with smaller plates, such as the single-plate or double-plate Molteno implants, especially in children (144). Corrective measures may require removal of the device, replacement with a device that has a smaller plate, or transfer of the device to the superotemporal quadrant, which usually relieves the diplopia (143).

In one study, postoperative motility disturbance, including acquired Brown syndrome, superior oblique palsy, and lateral rectus palsy, developed in 11 of 24 eyes (24%) more than 6 months after implantation of a double-plate Molteno drainage device, although this may resolve spontaneously with time (149).

Surgical treatment may require several interventions but can be successful (150). Other Complications

Epithelial downgrowth is an uncommon but potential risk, especially with tubes inserted at the limbus. It can cause failure of the implant function; corneal decompensation; and, when associated with the formation of a true Tenon cyst, significant cosmetic deformity and motility disturbance (151).

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Figure 39.13 Appearance of silicone subconjunctival silicone oil extravasation through a Baerveldt drainage device.

Epithelial invasion into the fibrous capsule with persistent aqueous leak was described in four patients during the early postoperative course following Baerveldt drainage-device implantation (152). All reported cases of epithelial ingrowth occurred in previously operated eyes. In advanced cases of epithelial downgrowth associated with secondary glaucoma, the combination of a glaucoma drainage device and PKP may be indicated to maintain useful vision (153).

Sterile hypopyon has been reported after removal of 4-0 chromic suture stents (154).

Silicone oil drainage from the vitreous cavity to the subconjunctival space through a Molteno drainage device was reported in an eye with an anterior chamber Molteno implant, lensectomy, vitrectomy, and intravitreal silicone oil injection (155). This complication can occur with any device implanted in the superior quadrants (Fig. 39.13). A glaucoma drainage device may thus be inappropriate in eyes with intravitreal silicone oil.

Some patients may develop an irregular pupil years after implantation of a silicone drainage device because the iris root may adhere to the tube (66). However, placing the intraocular portion of the silicone tube away from the cornea is more important to minimize corneal endothelial loss, because contact with the iris stromal root does not typically cause significant problems (66).

Figure 39.14 Slitlamp photograph. A: Massive suprachoroidal hemorrhage after glaucoma drainagedevice implantation. The tube with an intraluminal suture in place can be seen in the anterior chamber. B: Slit-beam illumination reveals a flat anterior chamber. (From Azuara-Blanco A, Katz LJ. Prevention and management of complications of glaucoma surgery. In: Tasman W, Jaeger EA, eds. Duane's Clinica Ophthalmology. Vol 6. Lippincott Williams & Wilkins; 2007:chap 24.)

Globe perforation can occur while suturing the plate to the sclera, causing retinal detachment or vitreous hemorrhage. The risk is greater in buphthalmic or highly myopic eyes with thin sclera. Implantation under the scleral buckle may be complicated by scleral perforation at the site of severe ectasia underlying the previous buckle (152).

Retinal complications with glaucoma drainage devices include retinal detachment, suprachoroidal hemorrhage, choroidal effusions, and vitreous hemorrhages. The most common risk factors for suprachoroidal hemorrhage (Fig. 39.14) are older age, postoperative choroidal effusions, low IOP immediately after the tube opened, hypertension, or atherosclerosis. Complete ligation of the proximal part of open-tube design with a 7-0 Vicryl suture, testing for watertightness before placing the tube in the anterior chamber, may decrease the rate of retinal complications (64). In one study with Baerveldt devices, the median onset of a postoperative retinal complication was 12.5 days, with 10 patients (83%) experiencing complications within 35 days. Serous choroidal effusions usually resolve spontaneously. Serious retinal complications were distributed evenly among patients with Krupin eye valves with discs and Molteno and Baerveldt devices (156).

OUTCOMES AND INDICATIONS Long-Term Outcomes

Outcome studies have been reported for the most commonly used glaucoma drainage devices. The following data were derived from long-term follow-ups (usually a mean of 12 months or more) of overall study populations in which success was typically defined as a low-end cutoff of 5 to 6 mm Hg and a high-end cutoff of 21 to 22 mm Hg with or without medication use. In trials with Molteno implants, the success rates were 73% to 74% with a mean or minimum follow-up of 18 months and 57% with a mean follow-up of 43 to 44 months

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(157, 158, 159 and 160). A success rate of 76% was reported in eyes with uveitic glaucoma and a follow-up of 5 to 10 years (161). A study of 82 black patients treated with Molteno implants and followed up for a mean of 30 months reported a similar success rate of 72% (162). Survival analysis in a retrospective study showed that failure was most common in the first postoperative year, and variables associated with a significantly increased risk for failure were pseudophakia and neovascular glaucoma. Postoperative IOP tended to be lower after doubleplate than after single-plate implantation. Outcomes with Molteno drainage devices did not significantly differ on the basis of age, sex, race, previous PKP, or previous conjunctival surgery (159).

With Schocket-type drainage devices, reported success rates were 91% with a mean follow-up of 10 months and 81% with a 17.5-month mean follow-up (35, 163) but fell to 30% at 36 months in one study using life tables (164).

Reported success with Baerveldt implants was 93% and 88% for 350-mm2 and 500-mm2 drainage devices, respectively, after 18 months (19), although other studies reported 71% to 72% success with a minimum of 6 months, a mean of 13.6 months, and 2 years of follow-up (165, 166 and 167).

Studies involving the Krupin eye valve and disc revealed 6-month and 12-month success rates of 84% and 66%, respectively (168), whereas another group found an 80% success rate with a mean follow-up of 25 months (44). Studies of the Ahmed drainage device revealed success rates of 77% to 87% at 1- year follow-up and 75% success rate at 2-year follow-up (9, 40, 91). The visual acuity improved or remained within one Snellen line of the preoperative value in 62% to 78% of the various studies, which is undoubtedly influenced by the relative proportion of glaucoma types in each study.

Success tends to be somewhat lower in pediatric populations. Ahmed glaucoma drainage-device surgery implantation in children was reported to have cumulative probabilities of success of 77.9% at 12 months

and 60.6% at 24 months (169), which is similar to those of other implants when used in a pediatric population (110). Another study showed that 6 months after glaucoma drainage-device surgery in the management of childhood glaucoma, the IOP was controlled in 72.2% with or without use of glaucoma medication, decreasing to 44.4% after 2 or more years (170). Although 38.9% remained within one line of preoperative vision or improved, 27.8% lost light perception. Most children required additional surgical procedures to control IOP or manage drainage device-related complications. The limited success rate in this study, the relatively high complication rate, and the need for frequent surgical intervention suggest caution regarding the prognosis of glaucoma drainage-device surgery in children with glaucoma.

Indications

Traditionally, glaucoma drainage-device surgery is reserved for patients in whom trabeculectomy with adjunctive antimetabolite therapy has either failed or is thought to have a very low chance of success, and in whom there is still a reasonable potential for vision. The Tube Versus Trabeculectomy study has shown an advantage with drainage-device implantation compared with repeated trabeculectomy. Some surgeons are exploring the possible role as a primary surgical procedure. Other traditional indications include young patients; individuals with neovascular glaucoma, glaucoma associated with uveitis, severe conjunctival scarring, refractory pediatric glaucoma, or glaucoma in aphakia or pseudophakia; and patients with other prior surgery, such as vitreoretinal surgery and PKP. Success rates vary with the different patient characteristics and underlying disorders.

Young Patients

As previously noted, glaucoma drainage-device surgery in the pediatric population (1 month to 13 years), as with any surgery for childhood glaucoma, is more problematic than in adults. Nevertheless, success rates of 55% to 95% have been reported, with no definite advantage among Molteno, Baerveldt, and Ahmed implants (107, 171, 172, 173 and 174).

Drainage-device implantation may be especially useful in children with juvenile rheumatoid arthritis and uveitic glaucoma and with glaucoma associated with the Sturge-Weber syndrome (61, 65, 175, 176). In the latter situation, an advantage of glaucoma drainage devices over trabeculectomy with antimetabolites is the reduced risk for expulsive hemorrhage associated with marked IOP reduction. Glaucoma drainage devices have also been shown to succeed in children after cycloablation (136). Complications of drainage-device implantation in children include tube malposition, flat anterior chamber, tube obstruction by iris or vitreous, cataract, corneatube touch, choroidal detachment, corneal edema, and corneal abrasion (65, 171).

Neovascular Glaucoma

Glaucoma drainage-device surgery has been successful in some eyes with neovascular glaucoma (177), although the success declines with time. In one study, the success rate with Molteno implants was 62.1% at 1 year, declining to 10.3% at 5 years (178). Reported success with the Baerveldt and Ahmed implants has been 60% to 80% with declining success over time and a generally lower success rate than with other forms of glaucoma (91, 179). Better outcomes in the eyes with neovascular glaucoma have been reported with glaucoma drainagedevice surgery than with noncontact cyclophotocoagulation (180, 181). Prospective comparison of Ahmed drainage implant and contact diode and endoscopic cyclophotocoagulation found no significant differences in the success rate at 24 months (182, 183). Uveitic Glaucoma

Ahmed drainage devices have been shown to be a safe alternative in high-risk patients with uncontrolled uveitic glaucoma who have had multiple previous ocular surgeries (184, 185). Success may be enhanced by preoperative and long-term postoperative immunotherapy. The most common complications are encapsulated bleb (Fig. 39.15), transient hypotony, and hyphema. Hypotony may occur less frequently in patients with uveitis with the use of valved versus nonvalved devices.

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Figure 39.15 Bleb encapsulation of a glaucoma drainage device, producing elevated IOP in the late postoperative period. (From Junk AK, Katz LJ. Tube shunts for refractory glaucomas. In: Tasman W, Jaeger EA, eds. Duane's Clinical Ophthalmology. Vol 6. Lippincott Williams & Wilkins; 2007:chap 17.) Severe Conjunctival Scarring and Previous Ocular Surgery

A failed trabeculectomy, especially when the conjunctiva is scarred down in both superior quadrants, could be an indication for a glaucoma drainage-device procedure. In addition, other types of ocular surgery may cause such conjunctival scarring that an implant will have a better chance than a trabeculectomy. Both Molteno and Baerveldt drainage devices have been effective for glaucomas associated with aphakia or pseudophakia (186, 187). The Molteno device has also been used with some success in eyes with epithelial downgrowth (188). Molteno and Schocket devices have been used in association with pars plana vitrectomy in eyes with vitreoretinal disorders and in eyes following PKP (189, 190 and 191). The Molteno device and the Ahmed device have also been used with success in eyes with prior cyclodestructive therapy (136, 192).

Aniridia

Medical and surgical therapy may not always be efficient in controlling IOP in aniridia. Molteno drainage devices and the Ahmed drainage device have been used in these patients (193, 194). In a retrospective review, implantation of a glaucoma drainage device in patients with aniridia had a success rate of 88% after 1 year (195), reducing the IOP from 35 to 15 mm Hg, with most of the eyes having improved or unchanged visual acuity.

Comparison with Alternative Procedures

In patients with glaucomas associated with a high risk for surgical failure, the surgeon usually must choose among a filtering operation with adjunctive antimetabolites, a glaucoma drainage-device procedure, or a cyclodestructive operation. Aside from the Tube Versus Trabeculectomy study, similar results have been reported with implantation of a single-plate Molteno device and trabeculectomy without use of an adjunctive antimetabolite (196), or trabeculectomy with postoperative 5-fluorouracil (197), whereas trabeculectomy with intraoperative mitomycin C provided significantly greater IOP reduction (198). In each of these studies, the types of complications differed between the two procedures (as previously discussed), but they tended to be more frequent with the glaucoma drainage-device operations. However, a randomized comparison of Ahmed drainage devices and trabeculectomy with

mitomycin C found no difference in the rate of complications, although the IOP was better controlled in the trabeculectomy group during the first year (199). After 3 years, the results were similar in both groups (200).

Glaucoma drainage devices provide better IOP control in eyes with advanced uncontrolled glaucoma than cyclophotocoagulation, but they more often require repeated surgery and have a higher rate of complications, including vision loss (201). The two procedures were similar in one series of eyes with PKP, although a trend toward more graft failure, hypotony, and visual loss occurred with the laser surgery (202). As mentioned previously, in eyes with neovascular glaucoma, Ahmed drainage devices provide IOP control at 12 to 24 months similar to that achieved with contact or endoscopic cyclophotocoagulation.

KEY POINTS

Glaucoma drainage devices have been successful in controlling IOP since the development of tubes that drain into subconjunctival reservoirs created by external plates.

Implant designs differ according to the size and the shape of the external plate and whether the tube is open (Molteno, Schocket, and Baerveldt) or valved (Krupin and Ahmed).

The basic surgical technique involves implantation of one end of the tube in the anterior chamber, with the other attached to the plate near the equator. A fibrous capsule develops around the plate, which regulates the aqueous flow.

Complications include hypotony, elevated IOP, ocular motility disturbance, and loss of visual acuity.

Indications for glaucoma drainage-device surgery include previous failed filters, young age, neovascular glaucoma, glaucoma associated with uveitis, and glaucomas after cataract extraction or other types of ocular surgery.

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