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

27 - Principles of Medical Therapy and Management Page 155 of 267

excimer laser allow an open communication between the anterior chamber and Schlemm canal. The minimal trauma to the eye of this procedure makes other types of glaucoma surgery possible if needed in the future (299).

Figure 38.13 Internal sclerostomy. A laser fiberoptic probe tip or automated trephine is inserted into the anterior chamber through a limbal stab incision and is used to create a full-thickness fistula beneath elevated conjunctiva 180 degrees from the entry site.

Despite the general interest and potential advantages of these approaches, they have not gained favor among glaucoma surgeons. This may largely be because most of these surgeries are full-thickness procedures, with the attendant risks of hypotony, shallow anterior chambers, and choroidal effusions. Other Internal Sclerostomy Techniques

Internal sclerostomies have also been successfully performed with an automated trephine, and bipolar cautery and diathermy probes (300, 301, 302 and 303). Other instruments and techniques will probably be evaluated in the future as this promising approach to glaucoma filtering surgery continues to evolve. Internal sclerostomy techniques have not been widely accepted to date and currently compete with trabeculectomy ab interno (Trabectome) and trabecular bypass shunts.

NONPENETRATING PROCEDURES

Krasnov (304) described a procedure called sinusotomy, in which a strip of sclera is excised to expose a portion of Schlemm canal. It is unclear whether the benefit of this operation is from relieving obstruction of the scleral outlet channels or from relieving the collapse of Schlemm canal (305, 306), or whether it is just another filtration technique.

A technique called nonpenetrating trabeculectomy carries the subscleral dissection of deep limbal tissue down to the Schlemm canal but leaves the trabecular meshwork intact (101). This was thought to be

especially advantageous in aphakic eyes and was reported to have fewer postoperative complications than a standard trabeculectomy did in the phakic eye (307). The technique was modified by using the Nd:YAG laser postoperatively to perforate the meshwork at the surgical site (308, 309). More recent reports have suggested that nonpenetrating surgery has advantages over conventional trabeculectomy by not entering the anterior chamber; avoiding iridectomy; and limiting early postoperative hypotony, shallow anterior chambers, hyphema, and choroidal effusions.

More recently described nonpenetrating surgery is currently divided into two techniques. The first, called deep sclerectomy, is based on the original description by Krasnov (304, 310) and was later modified by Kozlov (311). A Descemet window is created, which allows aqueous to escape the anterior chamber and drain subconjunctivally, forming a low-filtering bleb. The addition of a collagen implant in the scleral bed has been advocated to help maintain the scleral drainage (311, 312 and 313). The second technique, called viscocanalostomy, also requires deep scleral dissection and a filtering window. The outflow, however, appears to rely on the patency of aqueous exit channels, hypothetically achieved by identifying and dilating Schlemm canal by using high-density viscoelastic. The superficial scleral flap is sutured down tightly, minimizing subconjunctival aqueous outflow and bleb formation (314). However, subconjunctival drainage appears to be an important component of these procedures, in that blebs have been reported to be clearly visible after deep sclerectomy and in many cases of viscocanalostomy (315). The mechanism of action appears to be increasing permeability of the inner wall of Schlemm canal and the formation of an intrascleral lake (316, 317 and 318).

In a phase I study, a 193-nm photopolishing scanning excimer laser was used to achieve the deep dissection required to perform a “nonpenetrating la ser trabeculodissection” under a scleral flap throu gh the Schlemm canal and the juxtacanalicular trabecular meshwork. The scleral flap was closed loosely, and MMC was used intraoperatively. A good filtering bleb was achieved with substantial reduction in the IOP (277). Another study has also shown that an excimer laser may be an effective modification of nonpenetrating filtering surgery and may be easier to perform (319). Even though the nonpenetrating surgery may have fewer complications, it appears to be less effective in achieving low levels of IOP control when compared with conventional trabeculectomy. Randomized, controlled trials comparing viscocanalostomy and trabeculectomy have found no differences; however, to date studies have had only P.501

small sample sizes, leaving the general applicability of this result in question (320, 321). Canaloplasty, a modification of earlier nonpenetrating surgeries, has recently been advocated. In this

procedure, Schlemm canal is exposed and vasodilation is performed similar to those described earlier. A microcatheter is used to cannulate Schlemm canal throughout its circumference. A nonabsorbable tensioning suture is placed within the Schlemm canal, stretching the canal and improving aqueous egress through the episcleral venous system. Initial results are promising. A multicenter trial reported reductions in IOP from a baseline of 23.6 mm Hg to 16.3 mm Hg in patients having canaloplasty alone (322).

PREVENTION AND MANAGEMENT OF COMPLICATIONS

The following complications may occur with any filtering procedure, although some operations and techniques appear to provide certain advantages over others. We first consider the complications in general and then compare the merits of the various filtering procedures. It is helpful to think of these complications in three phases: intraoperative, early postoperative, and late postoperative. Intraoperative Complications

Tearing or Buttonholing the Conjunctival Flap

The conjunctiva may be inadvertently torn or cut during preparation or closure of the flap. A buttonhole was reported in 3% of fornix-based conjunctival flaps in one series (323). This complication can be minimized by gentle handling of the tissues as outlined earlier in this chapter. When it does occur, it may be possible to close the Tenon conjunctival defect by using 10-0 nylon mattress suture on a round, tapered, noncutting needle (324, 325). When 10-0 polyglycolic acid or polyglactin sutures are used, they have the advantage of being absorbable. With small holes, the tissue can be puckered together with a

figure-of-8 or mattress suture, whereas a large tear may require a running suture. Tissue adhesive and light bipolar cautery may also be used to close small holes (326), but these methods are less reliable than suturing. Small leaks may close spontaneously or with the application of a large bandage contact lens. Hemorrhage

Episcleral bleeding is particularly common in patients who have been on long-term antiglaucoma medications. It can be managed with irrigation or light cautery and should be under control before the anterior chamber is entered. Once inside the eye, inadvertent cutting of the ciliary body may cause brisk bleeding. Cauterization is difficult in these cases, although the intraocular, bipolar units at a low setting are usually effective. Alternative management involves gentle, sustained pressure over the fistula with a sponge or a large air bubble in the anterior chamber. A choroidal or expulsive hemorrhage is a particularly devastating complication that usually results from sudden reduction in the IOP with rupture of a large choroidal vessel. Risk factors for intraoperative suprachoroidal hemorrhage include high preoperative pressure, generalized atherosclerosis, and elevated intraoperative pulse (327, 328). The most important step in the management of these cases is immediate closure of the fistula. Some surgeons make a scleral incision in the inferior-temporal quadrant to allow the blood to drain from this site until it stops spontaneously, although the value of this approach has not been substantiated.

Choroidal Effusion

This complication may occur intraoperatively during glaucoma filtering surgery, especially in eyes with prominent episcleral vessels, as in patients with Sturge-Weber syndrome (329), nanophthalmos, or any condition associated with elevated episcleral venous pressure. The suprachoroidal fluid in patients with Sturge-Weber syndrome contains little protein (18% of plasma concentration), suggesting that a pressure differential drives fluid and small molecules from choroidal capillaries into extravascular spaces (330). This complication is usually recognized by a sudden shallowing of the anterior chamber during the operation or by the rotation of ciliary processes through the iridectomy and into the surgical fistula. If severe, it can be managed by making a scleral incision 3 to 5 mm posterior to the limbus to release the suprachoroidal fluid (329). Placement of posterior sclerotomies before or after trabeculectomy should be considered for surgical patients in whom this complication is likely to occur, such as those with nanophthalmos or SturgeWeber syndrome.

Other Intraoperative Complications

Vitreous loss may occur during creation of the fistula or iridectomy because of rupture of the lens zonules and hyaloid membrane, which usually results from excessive manipulation. The vitreous should be carefully removed from the surgical site with sponges and scissors or, where visualization permits, a vitrectomy instrument. Lens injury may remain limited to the surgical site if it is small, whereas larger injuries may cause gradual widespread extension or acute cataract formation, occasionally with severe inflammation (331). Stripping of Descemet membrane during glaucoma surgery, with subsequent corneal edema, has also been reported (332). The scleral flap may be inadvertently torn from its limbal hinge, in which case it can be reattached with 10-0 nylon mattress sutures or, if the flap is too thin, replaced with donor sclera or a pericardial (Tutoplast) graft (333, 334). Alternatively, a new site for the scleral flap may be chosen.

Early Postoperative Complications

During the first few days or weeks after a filtering procedure, the most common complications are IOPs that are too low (hypotony) or too high. In either case, the anterior chamber may be shallow to flat or deep. Physicians should know the mechanisms that can lead to the resulting four categories of complications and how these complications can be managed.

P.502

Figure 38.14 Slitlamp appearance of shallow anterior chamber in early postoperative period following a trabeculectomy showing iridocorneal touch with separation between cornea and lens.

Hypotony and Flat Anterior Chamber

A low, often nonrecordable IOP is not uncommon during the early postoperative period and is typically associated with a shallow anterior chamber. The anterior chamber is usually shallowest on postoperative day 2 or 3 and gradually deepens over the next 2 weeks (335). It is important to distinguish between a shallow anterior chamber with iridocorneal touch and a flat anterior chamber with cornea-lens touch, because the management and prognosis differ significantly (336). In the former situation, the cornea is typically clear and the iris stroma has not been flattened by the gentle touch with the cornea (Fig. 38.14). In most of these eyes, the anterior chamber deepens spontaneously with time and requires no special management beyond the usual postoperative care. The prolonged shallow anterior chamber may be associated with a reduced corneal endothelial cell count (337) and peripheral anterior synechia formation (338). However, these sequelae do not usually influence the long-term outcome and must be weighed against the risk of interfering with the bleb function by premature intervention. If the shallow chamber persists beyond the first week or two, measures to reform the anterior chamber are usually indicated. With a truly flat anterior chamber, in which the cornea is swollen, usually as a result of direct lens-cornea contact, and the iris stroma is flattened, immediate postoperative management is required to avoid a poor result.

As in all cases, the best way to deal with a potential complication is to take steps to avoid it. Careful closure of scleral flap to reduce the likelihood of postoperative overfiltration and meticulous conjunctival closure (as discussed earlier) are two such steps to avoid a flat anterior chamber. Other measures (also discussed earlier) are the injection of a viscoelastic into the anterior chamber (45, 46 and

47, 339) or use of a combination of a long-acting gas and a viscoelastic material (340). Most studies have shown that these measures do not reduce the incidence of flat anterior chambers when injected at the end of the filtering procedure (37, 38), although deepening the anterior chamber with sodium hyaluronate at the beginning of the operation and maintaining the chamber depth throughout the procedure may result in deeper chambers postoperatively (40, 41).

When hypotony and a flat anterior chamber do occur, the first step is to determine the cause and then take the appropriate corrective steps. These causes and their management are considered here. Conjunctival Defect

If there is an obvious hole in the conjunctival flap or a leak at the wound edge, it may be possible to achieve spontaneous closure with a pressure patch (Fig. 38.15). A fusiform-shaped cotton ball can be placed over the lid in the area of the fistula and held in place with the gauze pads to act as a tamponade. If this type of pressure dressing is used, the patient should be directed to look straight ahead, because the Bell phenomenon of sleep may place the tamponade over the center of the cornea. Examination 1 to 2 hours later (the pressure patch is usually left on from morning until evening) often reveals closure of the defect and reformation of the anterior chamber. If the leaking defect persists, however, a large-diameter (17 to 22 mm) therapeutic soft contact lens can be effective. If patching with a contact lens is not successful, repairing the leak with cyanoacrylate tissue adhesive or autologous fibrin glue has been described (341, 342, 343 and 344). If the leak is small, temporarily tapering topical corticosteroids to allow increased fibrosis can be effective. Other cases may require suturing of the defect or, when the defect is large, constructing a new conjunctival flap from tissue posterior to the defect or free conjunctival autografts. Injections of autologous fibrinogen concentrate inside a bleb have been used to treat persistent hypotony after MMC-augmented trabeculectomy, with improvement of macular edema and visual acuity and preservation of a functioning trabeculectomy (345).

Excessive Filtration

In other cases, there may be no apparent conjunctival defect or wound leak, but overfiltration may occur as a result of loose scleral flap closure or an exceptionally large filtering bleb. It is in this regard that trabeculectomies offer a significant advantage over full-thickness filtering procedures, since the protective scleral flap reduces the likelihood of excessive filtration. However, with the advent of antimetabolite adjunctive therapy, there is a tendency for increased flow of aqueous around the scleral flap and through the conjunctival bleb, and overfiltration has become a more common early postoperative complication. Antimetabolites in and of themselves do not cause hypotony but allow it to persist by inhibiting the natural fibrotic response, thus reducing aqueous outflow resistance to a level insufficient to produce a more physiologic IOP. To minimize this risk, some surgeons choose to increase the protective aspect of a trabeculectomy by using multiple nylon sutures to create a tighter closure of the scleral flap. Sutures can be selectively cut postoperatively with a laser if filtration is inadequate. Other surgeons prefer to secure the scleral flap with releasable sutures, which can be removed postoperatively as needed (75, 76, 77 and 78, 346).

If the early postoperative period is complicated by excessive filtration associated with a quiet bleb, a flat anterior chamber, and corneal decompensation, the first step is to decrease the frequency of postoperative topical corticosteroid administration. Firm patching of the eye with a bandage contact lens or

P.503

other tamponading device may be used. If the chamber depth cannot be maintained after several days, and especially if corneal decompensation is present, surgical intervention is usually indicated. It is generally necessary to deepen the anterior chamber with a viscoelastic substance. Air, perfluoropropane, and sulfur hexafluoride have also been used (347, 348). However, the air and gases are more toxic than balanced salt solution or viscoelastics and can cause cataract formation (348, 349 and 350). A study with rabbits, however, suggests that 15% perfluoropropane or 50% sulfur hexafluoride is no more toxic than air and may be beneficial and relatively safe in reforming persistently flat anterior chambers (350).

Figure 38.15 Pressure patch technique for eye with flat anterior chamber due to excessive filtration in early postoperative period. A: Fusiform-shaped cotton ball placed over upper lid in location corresponding to surgical fistula. B: Folded eye pad placed just below brow. C: Second, open eye pad positioned. D: Multiple strips of tape applied with moderate tension.

Serous Choroidal Detachments

Anterior chamber deepening alone may not be sufficient if large choroidal detachments are also present. Fluid commonly collects in the suprachoroidal space in hypotonus eyes. Hypotony is generally thought to contribute to the mechanism of choroidal detachments, although additional factors, such as inflammation and venous congestion, also appear to be important (351). The fluid in the detachments is high in protein (67% of plasma concentration), suggesting that a pressure differential causes fluid with smalland medium-sized protein molecules to pass from choroidal capillaries to extravascular spaces (330, 352). The choroidal detachment apparently prolongs the hypotony by reducing aqueous production and possibly by increasing uveoscleral outflow.

Most serous choroidal detachments resolve spontaneously when the IOP rises during the first few postoperative days or weeks. Typically, choroidal effusions resolve after IOP rises above 7 to 9 mm Hg. If limited in size and duration, they do not interfere with the long-term outcome of trabeculectomy surgery, and it is usually only necessary to drain them when they are associated with a persistent flat anterior chamber or when a choroidal hemorrhage is suspected. The technique involves draining the suprachoroidal fluid through one or more sclerotomies in the inferior quadrants and deepening the anterior chamber with a balanced salt solution or viscoelastic.

Much less commonly, a serous retinal detachment may occur after glaucoma filtering surgery, presumably by a mechanism similar to that for choroidal detachments (353). In most cases, these also resolve spontaneously, although the patient may not regain full preoperative visual acuity.

Hypotony and Deep Anterior Chamber

A lower-than-normal IOP in the first week or two after trabeculectomy usually does not constitute a complication, as long as there are no related problems, such as wound leak, excessive

P.504

inflammation, flat anterior chamber, or posterior pole abnormality. If the hypotony persists, however, it can lead to one of the more serious complications, referred to as hypotony maculopathy. The typical fundus findings include fine macular striae radiating from the fovea, often with more extensive choroidal folds and tortuous retinal vessels and occasional disc swelling, but no evidence of vascular leakage. The visual acuity can be markedly reduced. The maculopathy does not develop in all patients with subnormal IOP; risk factors for this complication include young age, myopia, and the preoperative use of carbonic anhydrase inhibitors (354, 355). The hypotony can occur with any filtering surgery technique, although the risk is increased with the use of adjunctive antimetabolites.

The best approach is prevention by minimizing the use of antimetabolites and using tight wound closure. When the complication does occur, it is difficult to treat. Standard measures, such as pressure patching or the application of trichloroacetic acid or cryotherapy to the bleb, are rarely effective, especially when antimetabolites have been used. Oversized bandage contact lenses have been helpful in the management of early hypotony (356). Some success has been reported with the injection of autologous blood into the bleb or around the bleb, or a combination of autologous blood injection and bleb compression sutures (Fig. 38.16) (357, 358, 359, 360, 361, 362, 363, 364 and 365). However, some studies have not found the results of autologous blood injection to be favorable (366, 367), and reported complications have included a markedly raised IOP, corneal blood staining, loss of vision, delayed hyphema, and intravitreal blood (368, 369, 370, 371 and 372).

When these measures are not successful in managing hypotony maculopathy, surgical revision is indicated. Surgical approaches include conjunctival compression sutures, resuturing the scleral flap, and patch grafting with donor sclera or preserved pericardium (373, 374, 375, 376 and 377). Another effective technique is to excise the filtering bleb, undermine adjacent conjunctiva, and pull it down to the limbus to create a new filtering bleb (179). More recently, an approach involving placement of transconjunctival sutures through the scleral flap has been described (378). It is unclear how long an eye can tolerate hypotony maculopathy before the visual loss is irreversible, but return of good vision has been reported when the overfiltration was reversed within 6 months of the onset of the complication (375).

Figure 38.16 The injection of autologous blood to manage a leaking or overfiltering bleb. Blood is withdrawn from a vein in the patient's arm; after replacing the needle with a 30-in. gauge, the needle is passed beneath the conjunctiva, adjacent to the bleb, then into the bleb, and the bleb is filled with the blood, as shown in A and B. One complication of the procedure is the extension of the blood into the anterior chamber, which can be minimized by injecting viscoelastic into the anterior chamber. Elevated Intraocular Pressure and Flat Anterior Chamber

An elevated IOP with a flat anterior chamber in the early postoperative course suggests one of three mechanisms: (a) aqueous misdirection syndrome (also known as malignant [ciliary block] glaucoma),

(b) an incomplete iridectomy with pupillary block, or (c) a delayed suprachoroidal hemorrhage. Although the diagnosis and management of these conditions are discussed in Chapter 26, here are a few additional details regarding the delayed hemorrhage.

Delayed Suprachoroidal Hemorrhages

Patients with delayed suprachoroidal hemorrhages after filtering surgery typically present during the first few postoperative days with severe pain, occasional nausea, and a marked reduction in vision. The IOP is usually elevated, the anterior chamber is shallow or flat, and large choroidal detachments, often with central apposition, are present. On the basis of retrospective studies, the complication is uncommon, occurrin in approximately 2% of most large series (379, 380, 381, 382 and 383). However, in a prospective study involving ultrasonographic evaluation of 158 patients after filtering surgery, delayed suprachoroidal hemorrhage was detected in 11 patients (7%), suggesting that most cases go clinically unrecognized (384). One large retrospective study showed a slightly higher incidence (2.9%) of delayed suprachoroidal hemorrhages with all filtering procedures, but the relative incidence varied depending on the type of procedure (385). In one study, delayed suprachoroidal hemorrhage occurred in 1.5% of trabeculectomies without antimetabolite, 2.4% of trabeculectomies with antimetabolite, 2.8% of implantations of valved glaucoma drainage devices, and 7.1% of implantations of nonvalved glaucoma drainage devices (385). In addition, the incidence goes up considerably with certain risk factors, especially in the presence of aphakia

P.505

or previous vitrectomy (379, 380, 381 and 382, 384). In one series of 305 filtering procedures, the overall incidence of delayed suprachoroidal hemorrhage was 1.6%, but this rose to 13% in aphakic eyes and to 33% of aphakic, vitrectomized eyes (381).

High-frequency ultrasonography in eyes with suprachoroidal hemorrhage may show high reflectivity in the inner space of a choroidal detachment, with the ciliary processes and iris anteriorly displaced due to the ciliary detachment and forward pressure of the anterior vitreous (386). Not all cases require surgical correction, and in those that do, it is best to wait until the clotted blood has lysed. In one series monitored by echography, the mean time for clot lysis was 14 days, and the mean duration of central retinal apposition was 15 days (387). The visual outcome of patients with delayed suprachoroidal hemorrhages is poor and is worse with associated retinal detachment and 360-degree suprachoroidal hemorrhage (385). The latter findings constitute indications for surgical intervention, along with kissing choroidal detachments, vitreous incarceration, and vitreoretinal adhesions (388, 389 and 390). Surgical intervention is usually limited to drainage of the hemorrhage through anterior sclerostomies, with vitrectomy reserved for vitreous incarceration or vitreoretinal adhesions (389, 390). In most cases, drainage of choroidal blood must wait 7 to 10 days for the clot to liquify.

Delayed suprachoroidal hemorrhage after viscocanalostomy has also been reported, suggesting that the risk of suprachoroidal hemorrhage may not be completely eliminated even with nonpenetrating glaucoma procedures (391).

Elevated Intraocular Pressure and Deep Anterior Chamber

An elevated IOP with a deep anterior chamber indicates inadequate filtration, most often due to a tight scleral flap or obstruction of the fistula by iris, ciliary processes, lens, blood, or vitreous. A tight flap is treated by laser suture lysis. Creating an adequate fistula and iridectomy can prevent the most common causes of obstruction. When faced with a high pressure and deep anterior chamber, the possibility of obstruction of the fistula should first be evaluated by gonioscopy. If iris or ciliary processes are obstructing the fistula, it may be possible to retract the tissue with the application of low-energy argon laser therapy or by Nd:YAG laser disruption. If the internal obstruction cannot be eliminated with laser therapy, it is usually necessary to revise the filter.

When the fistula is thought to be obstructed by scar tissue along the margins of the scleral flap but a filtering bleb is still present, internal bleb revision may be useful. In the operating room, an incision is made through peripheral cornea 90 to 180 degrees from the fistula. Viscoelastic may be injected to maintain a deep anterior chamber. A cyclodialysis spatula is passed through the incision and into the fistula to elevate the scleral flap and break adhesions along the margins with a sweeping action of the spatula. 5-FU should probably be used postoperatively to reduce subsequent scarring of the fistula. If fistula obstruction is not found, attention must then be given to bleb failure, which (as discussed earlier) is the most common cause of failure in glaucoma filtering surgery (107). Distinction must be made

Figure 38.17 Typical appearance of a failing filtering bleb, characterized by a low-to-flat, heavily vascularized conjunctiva.

Management of the Failing Bleb

The filtering bleb in these cases is typically low to flat and heavily vascularized with no microcysts (Fig. 38.17). The risk for failure is high unless immediate, aggressive steps are taken. Corticosteroid therapy should be increased, typically consisting of prednisolone acetate, 1%, every 1 to 2 hours, occasionally with the addition of subconjunctival steroids. Scleral flap sutures should be lysed or removed in the case of releasable sutures. Tissue plasminogen activator may be injected subconjunctivally or in the anterior chamber when blood or fibrin is present in the aqueous outflow pathway (392, 393). As previously noted, subconjunctival 5-FU may also be effective even if started several days after the surgery (150). Anti-VEGF therapy may prove to be beneficial but is investigational at the time of this publication. Intermittent application of digital pressure can be used to expand the subconjunctival space by forcing aqueous into it. This may be performed by applying steady pressure with the index finger to the inferior sclera through the lower lid for approximately 15 seconds. Applying pressure with the index finger or a Q-tip through the upper lid behind the bleb, with the patient looking down, allows visualization of the bleb during the procedure. If the digital pressure lowers the tension and expands the bleb, certain reliable patients may be instructed to perform the digital pressure through the lower lid at home several times each day. A modification of digital pressure, after trabeculectomy, involves pressing an anestheticmoistened applicator beside the edge of the scleral flap (394). If the IOP cannot be lowered by digital pressure, the next step is usually laser suture lysis or removal of a releasable suture (395, 396, 397, 398, 399 and 400). Laser suture lysis or removal, by acutely lowering the IOP, may be associated with complications common to glaucoma surgery, including hypotony, flat anterior chamber, external aqueous leak, malignant glaucoma, iris incarceration, and excessive filtering blebs (72, 401). Most of these complications resolve with appropriate management (discussed previously) (72).

The argon laser is the most commonly used procedure for suture lysis, with typical settings of 50 µ m,

0.1-second duration, and 250 to 1000 mW of power. Other lasers may also be effective, including krypton and diode, and a laser lens holder

P.506

has been developed for performing diode laser suture lysis in children under anesthesia (397, 402). Suture lysis is performed through the conjunctiva, which is compressed with a corner of a four-mirror goniolens or with a specially designed Hoskins lens or Ritch lens to improve visualization of scleral flap sutures. After one suture had been lysed, the status of the eye should be reassessed and IOP remeasured with and without digital pressure. If the bleb has reformed and the IOP has decreased, the patient can be examined the next day. If no effect is seen within 1 hour, a second suture lysis or removal may be considered. Longer time from surgery to laser suture lysis is associated with decreased IOP-lowering effect. In general, laser suture lysis is best performed within the first 3 weeks of surgery; beyond that time, responses are often inadequate.

If suture lysis or release is ineffective, or if a blood or fibrin clot appears to be obstructing the fistula, intracameral tissue plasminogen activator may be beneficial (392). The recommended intracameral dose is 6 to 12.5 µg. A subconjunctival dose of tissue p lasminogen activator can be used to free a scleral flap closed by blood and fibrin in the early postoperative period (403).

When these measures fail, use of glaucoma drug should be resumed. Revision of a flat, vascularized bleb has a low chance of success but can be tried. In most cases, a repeated filtering procedure with adjunctive MMC or 5-FU or implantation of a glaucoma drainage device will eventually be required. Encapsulated Filtering Bleb

These blebs, which have also been called Tenon capsule cysts and high bleb phase, are characterized by a highly elevated, smooth-domed bleb with large vessels but intervening avascular spaces and no microcysts (Fig. 38.18). It is typical to see a patent sclerostomy on gonioscopy. Movement of the conjunctiva reveals a second, stationary set of vessels beneath the conjunctiva, which is in the layer of fibrous tissue that lines the bleb. It is important to distinguish this type of bleb from the typical failing bleb, as previously discussed. Both are associated with an elevated IOP and deep anterior chamber in the early postoperative period, but the prognosis and management differ considerably.