Ординатура / Офтальмология / Английские материалы / Essentials in Ophthalmology Glaucoma_Grehn, Stamper_2008

60 7 Nonpenetrating Glaucoma Surgery

7

Fig. 7.1 Creation of a superficial scleral flap. A 5 × 5 mm superficial scleral flap is performed including one-third of the scleral thickness. In order to reach Descemet’s membrane later in the dissection, the superficial scleral flap has to be prolonged 1–2 mm anteriorly into the clear cornea

Fig. 7.2 Schematic representation of deep sclerectomy. Under the superficial scleral flap, a deep corneosclerotomy unroofing Schlemm’s canal is performed. Corneal tissue removal behind the anterior trabeculum and Descemet’s membrane is performed. When the anterior dissection is completed, the deep scleral flap is removed

7.2.2Deep Sclerectomy and Exposure of Trabeculo-Descemet’s Membrane

Deep sclerokeratectomy is performed by making a second deep 4 × 4 mm scleral flap (Fig. 7.2). The two lateral and the posterior deep scleral incisions are made using a No. 11 steel blade. The deep flap is smaller than the superficial

one, leaving a step in the sclera on the three sides, allowing for a tighter closure of the superficial flap in the case of an intraoperative perforation of trabeculo-Descemet’s membrane (TDM). The deep scleral flap is then dissected horizontally using the blade. The remaining scleral layer should be as thin as possible (50–100 mm). Deep sclerectomy is preferably started first in the posterior part of the deep scleral flap. On reaching the anterior part of the dissection, Schlemm’s canal is unroofed; it is located anterior to the scleral spur, where the scleral fibers are regularly oriented, parallel to the limbus. In patients with congenital glaucoma, localization of the canal is more difficult because it is often situated more posteriorly. Schlemm’s canal is opened and the sclerocorneal dissection is prolonged anteriorly for 1–2 mm in order to remove the sclerocorneal tissue behind the anterior trabeculum and Descemet’s membrane. This step of the surgery is quite challenging because there is a high risk of perforating the anterior chamber. To avoid a perforation, the anterior trabeculum and Descemet’s membrane can be gently detached using a sponge, a spatula or a blunt metallic blade. The best way to perform this last dissection is to make two radial corneal cuts without touching the anterior trabeculum or Descemet’s membrane. This is performed with a 15° diamond knife or preferably with a No. 11 steel blade with the bevel side up. When the anterior dissection between the corneal stroma and Descemet’s membrane is completed, the deep scleral flap is removed by cutting it anteriorly using microscissors. At this stage of the procedure, there should be evident percolation of aqueous through the remaining trabeculum. To peel away the thin Schlemm’s canal endothelium and juxtacanalicular trabeculum, it is crucial to dry the exposed inner wall of Schlemm’s canal, which can then be grabbed with a fine forceps and peeled away easily by pulling on it (Fig. 7.3). This additional procedure corresponds to ab-externo trabeculectomy [4, 9]. To keep the intrascleral space created patent, an implant may be used. The superficial scleral flap is then repositioned and sutured with 10/0 sutures (Fig. 7.4).

7.3Deep Sclerectomy Technique

■A superotemporal intracorneal suture is used to expose the surgical quadrant.

■Fornixor limbus-based conjuctival incision is performed.

■A 5 × 5 mm superficial scleral flap is dissected, extending 1–2 mm into clear cornea.

■A second 4 × 4 mm-deep scleral flap is created.

■Initiate the dissection flap by exposing the choroid and dissect slightly superficial to that.

Fig. 7.3 Schematic representation of ab-externo trabeculectomy. The juxtacanalicular trabeculum and Schlemm’s canal endothelium are removed. The inner wall of Schlemm’s canal can be grabbed with a blunt forceps and peeled away easily by pulling on it

Fig. 7.4 Use of implants. An implant may be used to keep the intrascleral space created patent. A collagen implant is secured in the scleral bed with a single 10/0 nylon suture. The superficial scleral flap is then repositioned and sutured with 10/0 sutures

■Gently press on the floor of Schlemm’s canal to detach Descemet’s membrane from the corneal stroma.

■Extend the deep scleral flap anteriorly by making two radial corneal cuts with a No. 11 stainless steel blade with the bevel side up.

■Dry the exposed inner wall of Schlemm’s canal before peeling away the thin endothelium of Schlemm’s canal and the juxtacanalicular trabeculum. Watch for

the percolation of aqueous humor through the TDM membrane and remove the deep scleral flap.

■A space-maintainer implant is placed in the scleral bed when nonpenetrating deep sclerectomy is performed. When viscocanalostomy is performed, high-viscosity hyaluronic acid is injected into the ostia of Schlemm’s canal.

■The superficial scleral flap, Tenon’s capsule and the conjuctiva are then closed.

7.4 The Use of Implants

To avoid secondary collapse of the superficial flap, a space-maintainer implant is placed in the scleral bed. The first to be used was the Aquaflow collagen implant (Collagen Glaucoma Drainage Device, STAAR Surgical AG, Nidau, Switzerland) [10, 11], which is a highly purified porcine collagen dehydrated into a cylinder (4 mm × 1 mm × 1 mm). This device is placed radially in the center of the deep sclerectomy dissection, as far as possible anteriorly such that it is in contact with the remaining TDM membrane and secured in the scleral bed with a single 10/0 nylon suture (Fig. 7.4). It swells rapidly once exposed to the aqueous humor and is resorbed within 6–9 months after surgery [12]. Another device that has been proposed to maintain the scleral lake is the reticulated hyaluronic acid implant (SK-GEL, Corneal, Paris, France; an equilateral triangle 3.5 mm long and 500 mm thick or an isosceles triangle of size 4.5 mm × 3 mm with the same thickness) [13]. The advantages of this implant are that it occupies a large volume in the filtration area while allowing for sufficient circulation of the aqueous humor, and that it does not need to be sutured at the sclera. More recently, a nonabsorbable hydrophilic acrylic implant (T-flux implant, IOLTech Laboratories, La Rochelle, France) has been developed [14]. This is a T-shaped implant that creates an evacuating canal along the foot, and each arm of the T shape is inserted into one of the surgically created openings of Schlemm’s canal.

7.5 Viscocanalostomy

Stegmann et al. [8] described a variant of NPGS and termed it viscocanalostomy to emphasize the importance of injecting high-viscosity sodium hyaluronate (Healon GV) into Schlemm’s canal as a means of improving aqueous drainage by this route. It has been postulated that physiologic aqueous humor drainage may then be restored without the formation of a filtration bleb because the superficial scleral flap is tightly sutured, meaning that

62 7 Nonpenetrating Glaucoma Surgery

aqueous humor regressing through the TDM can only reach the two surgically created ostia of Schlemm’s canal, travel circumferentially within it, and enter the collector channel ostia and ultimately the aqueous veins. They

7also proposed an increased outflow mechanism for the procedure’s success; aqueous humor that passes through

the TDM window into the scleral bed can diffuse into the uveoscleral outflow system adjacent to it. The viscoelastic material is also placed in the scleral bed and may prevent fibrin crosslinking and early scarring. In vivo primate [15, 16] and human eye [15] studies reported that the injection of viscoelastic into Schlemm’s canal resulted in not only the dilatation of the canal and associated collector channels but also in focal disruptions of the inner wall endothelium of Schlemm’s canal and disorganization of the juxtacanalicular zone, resulting in direct communication of the juxtacanalicular zone’s extracellular spaces with the lumen of Schlemm’s canal. This may initially enhance conventional aqueous outflow [15], accounting for an approximately 30% increase in ouflow facility in nonhuman primates [16]. Disruption of the posterior wall of Schlemm’s canal may also provide direct communication between its lumen and the tissues of the ciliary body, thereby enhancing uveoscleral outflow [15].

7.6Mechanisms of Filtration

There are two sites of interest when studying the mechanisms involved in the efficiency and safety of nonpenetrating surgeries: (1) the flow of aqueous humor through the TDM, and (2) the resorption of aqueous after its passage through the TDM.

7.6.1Flow Through the TDM

The TDM offers resistance to aqueous humor outflow. This resistance appears to be low enough to ensure a low IOP and yet sufficiently high to maintain the anterior chamber depth and avoid postoperative complications in relation to hypotony. Vaudaux et al. studied the aqueous outflow through the TDM in an experimental model [17]. The mean rate of IOP decrease was 2.7 ± 0.6 mm Hg min−1. The ocular aqueous outflow resistance dropped from a mean of 5.34 ± 0.19 ml min−1 mm Hg−1 preoperatively to a mean of 0.41 ± 0.16 ml min−1 mm Hg−1 postoperatively. They also reported that the outflow facility increased from 0.19 ± 0.03 to 24.5 ± 12.6 ml min−1 mm Hg−1 after deep sclerectomy. The same study examined the surgical site histologically using ocular perfusion with ferritine, demonstrating that the main outflow through

the TDM occurred at the level of the anterior trabeculum [18]. There was, however, some degree of outflow through the posterior trabeculum and Descemet’s membrane.

7.6.2Aqueous Humor Resorption

After the passage of aqueous humor through the TDM, four hypothetical mechanisms of aqueous resorption may occur: a subconjunctival filtering bleb; an intrascleral filtering bleb; a suprachoroidal filtration; and an episcleral vein outflow via Schlemm’s canal.

7.6.2.1 Subconjunctival Bleb

Just like after trabeculectomy, almost all patients that undergo nonpenetrating filtering surgeries have a diffuse, conjunctival bleb on the first postoperative day. As demonstrated by UBM studies, successful cases show a low and diffuse subconjunctival filtering bleb even years after surgery [19]. However, this bleb tends to be shallower and more diffuse than the one seen after trabeculectomy. It occurs more commonly with deep sclerectomy than with viscocanalostomy.

Controversy exists regarding the issue of conjuctival blebs following viscocanalostomy. Negri-Aranguren [20] did not find filtering blebs except in one out of 23 eyes 7–9 months after viscocanalostomy, thus suggesting a mechanism of filtration other than the subconjuctival one. O’Brart et al. [21] reported evidence of subconjuctival blebs in all patients, with successful drainage and disappearance of the blebs in patients with drainage failure after viscocanalostomy, suggesting the significance of subconjuctival fibrosis. Drüsedau et al. [22] observed subconjuctival drainage in more than half of their patients at one year despite attempts to make the scleral flap watertight and to resuture leaks in the early postoperative period. In another study [23], conjuctival blebs were present in all eyes with successful IOP control, which may indicate that at least some of the drainage takes place after VCS by the subconjuctival route.

7.6.2.2 Intrascleral Bleb

During deep sclerectomy, a certain volume of sclera ranging between 5 and 8 mm3 is removed. Provided the superficial scleral flap does not collapse, this scleral volume may be transformed into an intrascleral filtering bleb. The use of implants is aimed at keeping this intrascleral space patent. In a study of deep sclerectomy with collagen implants by Kazakova et al. [24], an intrascleral bleb was observed in more than 90% of patients who

received a collagen implant, and the mean volume of the intrascleral bleb was 1.8 mm3. In the intrascleral filtering bleb, the aqueous resorption mechanism may be different to the one that occurs in the subconjunctival space. The aqueous is probably resorbed by new aqueous drainage vessels, as has been demonstrated by Delarive et al. [25] This study showed that in the scleral space created after deep sclerectomy, regardless whether or not a collagen implant was used, new aqueous humor drainage vessels grew and resorbed the aqueous flow through the TDM.

7.6.2.3 Suprachoroidal Space

Aqueous humor outflow into the suprachoroidal space may occur upon thinning the sclera by 90%; in fact, on UBM, it is possible to observe a hyporeflective suprachoroidal area, and this may represent the accumulation of fluid in the suprauveal space through the thin deep scleral wall [26]. However, this could also indicate a chronic localized ciliary body detachment with a subsequent reduction in aqueous production. Chiou et al. [12] found this UBM sign in 23 (51%) out of 45 cases of DSCI, and stated that its presence was associated with lower IOP that was statistically significant at two and three months postoperatively. Roters et al. [27] detected a suprachoroidal hyporeflective area in six (40%) out of 15 eyes one year after viscocanalostomy, but its presence was not associated with surgical success. Negri-Aranguren et al. [20] performed a similar study, but observed this area in only two of 23 eyes that underwent viscocanalostomy, and so they considered that this did not support a major role for the uveal pathway. It is not yet known how much aqueous is reabsorbed by this route, and further studies are needed to elucidate it.

7.6.2.4 Schlemm’s Canal

When performing deep sclerectomy dissection, Schlemm’s canal is opened and unroofed. On either side of the deep sclerectomy, the two surgically created ostia of Schlemm’s canal may drain the aqueous humor into the episcleral veins. This mechanism is probably more important after viscocanalostomy, during which the ostia and Schlemm’s canal are dilated with high-viscosity hyaluronic acid. This mechanism is supported by the observation that it produces a periodic appearance of the viscoelastic substance in the aqueous veins as blood is displaced [8]. It is probably also important with HEMA implants, because the two arms of the T-shaped implant are inserted into the two ostia of Schlemm’s canal, thereby preventing their collapse. Research is still needed to establish the importance of this mechanism.

Summary for the Clinician

■The principal common concept in nonpenetrating glaucoma surgery is to create filtration through a naturally occurring membrane, the TDM, that acts as an outflow resistance site, allowing a progressive drop in IOP and avoiding postoperative ocular hypotony.

■The TDM consists of the trabeculum and the peripheral Descemet’s membrane.

■To expose the TDM, a deep sclerokeratectomy should be performed, thereby also providing a postoperative intrascleral space.

■The intrascleral space may act as an aqueous reservoir and filtration site, which may prevent the need for a large subconjunctival filtration bleb. The use of implants is aimed at keeping this space patent.

■The injection of viscoelastic material into Schlemm’s canal during viscocanalostomy results in dilatation of the canal and in the direct communication of the juxtacanalicular space with the lumen of Schlemm’s canal. Enhanced aqueous outflow through Schlemm’s canal may occur following viscocanalostomy.

■Aqueous humor outflow into the suprachoroidal space may also occur and partially account for filtration after nonpenetrating glaucoma surgery.

7.7Nd:Yag Goniopuncture

When filtration through the TDM is considered to be insufficient because of elevated IOP, Nd:Yag goniopuncture can be performed. An insufficient surgical dissection can be the reason for elevated IOP in the first postoperative period or fibrosis of the TDM if it is required later than approximately nine months, which may lead to a flattened bleb. Using a gonioscopic contact lens, the aiming beam is focused into the semitransparent TDM. Using the free-running and Q-switched mode, with a power of 5–10 mJ, 2–15 shots are applied, resulting in the formation of microscopic holes through the TDM and allowing the direct passage of aqueous from the anterior chamber to the intrascleral space. In their studies on the results of deep sclerectomy, Shaarawy et al. performed goniopuncture in 42–46% of their patients who had undergone deep sclerectomy without implant, and in 46–51% of those who had undergone DSCI [28–30]. The immediate success rate was 91.6% [30]. In their study on the results of viscocanalostomy [31], 37% of their patients needed

64 7 Nonpenetrating Glaucoma Surgery

goniopuncture postoperatively to control raised IOP. The mean time between surgery and goniopuncture was 9.4 months, with an immediate reduction in mean IOP of 39.5%.

7

7.8Technique

■Topical anesthesia with oxybuprocaine eyedrops 0.5%

■Using a gonioscopic contact lens, focus the aiming beam of the laser into the semitransparent TDM

■Settings: free-running and Q-switched mode, power 5–10mJ

■2–15 laser shots are applied

7.9Indications for Nonpenetrating Glaucoma Surgery

7.9.1Primary Open Angle Glaucoma

NPGS targets the presumed site of pathology in primary open-angle glaucoma (POAG), namely the trabecular meshwork [32]. The site of aqueous outflow resistance is presumed to be the juxtacanalicular trabeculum, the inner wall of Schlemm’s canal, and the endothelial lining. Scraping, thinning out and peeling the posterior trabeculum improve filtration. In NPGS, deep sclerectomy and ab-externo trabeculectomy are both necessary to obtain an optimal decrease in outflow resistance. Nonpenetrating glaucoma surgery has the advantage of being less cataractogenic than trabeculectomy and ideally should be considered as a safer option in phakic patients with POAG. It is an efficient surgery in medically uncontrolled POAG [33].

7.9.2Glaucoma in High Myopia

Conventional glaucoma surgery in patients with high myopia carries an especially high risk of complications because of the abnormal globe dimensions. NPGS appears to offer glaucoma patients with high myopia a safer outcome because of the gradual intraoperative IOP reduction.

Hamel et al. studied NPGS in 21 highly myopic glaucoma patients with medically uncontrolled primary or secondary open-angle glaucoma [30]. Complete (IOP < 21 mm Hg) and qualified success rates were 38 and 81%, respectively, at four years following surgery. In their series, only two patients developed choroidal detachment.

7.9.3Pseudoexfoliation and Pigmentary Glaucoma

NPGS is a safe and valuable option in patients with PEXG and seems especially appropriate in these patients, given the increased permeability of the blood–aqueous barrier as well as the higher risk of complications with intraocular surgery, such as trabeculectomy in pseudoexfoliation syndrome eyes [34]. In a prospective study, Droslum [35] compared the results of deep sclerectomy with implant in pseudoexfoliative glaucoma (PEXG) with those in POAG and found higher complete success rates (IOP < 19mm Hg without medical therapy) in the PEXG group after a mean follow-up of 18 months, with complete success seen in 60.7 and 37.9%, respectively. The difference was maintained after a longer mean follow-up of 3.5 years (50% in the PEXG group compared with 33% in the POAG group) [36].

NPGS is also a potential therapy for pigmentary glaucoma. It targets the site of pathology, namely the pig- ment-loaded trabecular meshwork, which can be reconditioned to establish filtration. To our knowledge there are no reported results in the literature for a large series of patients with pigmentary glaucoma. Existing data refer to a small number of patients with pigmentary glaucoma included in large series of patients with POAG.

7.9.4Uveitic Glaucoma

Glaucoma secondary to uveitis presents a management challenge. When medical treatment fails to control IOP, surgery is indicated, although conventional techniques are at high risk of failure due to marked postoperative inflammation and scarring. Although the use of antimetabolites can improve the success rate of glaucoma surgery, it also increases the severity of well-known complications [37]. NPGS is indicated in these cases because it explores the site of resistance to aqueous outflow and is associated with less postoperative inflammation [38].

Deep sclerectomy and viscocanalostomy has been found to be a safe and effective surgical alternative in eyes with uncontrolled uveitic glaucoma [39, 40]. However, in cases in which multiple peripheral anterior synechiae have occurred, NPGS may not offer an efficient solution. Larger studies are needed to fully assess the role of NPGS in the management of uveitic glaucoma.

7.9.5Congenital and Juvenile Glaucoma

The desire to reduce complications and fulfill the need for a good success rate that is comparable with those of current surgical standards has led to an evaluation of

NPGS in congenital glaucoma. Tixier et al. [41] were the first to report on results of deep sclerectomy in 12 eyes with congenital glaucoma. No intraor immediate postoperative complications were observed, and success was achieved in 75% of eyes (IOP < 16 mm Hg under general anesthesia at final examination). They concluded that deep sclerectomy is at least as effective as trabeculectomy in congenital glaucoma, with fewer complications due to the absence of anterior chamber penetration. Other authors have reported similar results with deep sclerectomy and viscocanalostomy on congenital and juvenile glaucoma [42–44]. When NPGS is insufficient because there is weak percolation through the TDM or it is technically demanding, it is always possible to combine it with other ab-externo procedures or to convert to penetrating glaucoma surgery, particularly in cases where the anatomy of the angle is severely distorted.

7.9.6Glaucoma Associated with Sturge–Weber Syndrome

Sturge–Weber syndrome (SWS) is a rare congenital disease characterized by a facial angioma, an ipsilateral leptomeningeal hemangioma and ocular manifestations, including hemangiomas of the conjuctiva, episclera, uvea and retina. Glaucoma is the most common ophthalmic complication of SWS, occurring in 30–70% of patients [45]. Trabeculectomy has been reported to have good short-term results but carries the risk of massive choroidal effusion or expulsive hemorrhage, which is already increased in these patients [46, 47]. A few reports exist on the effect of NPGS on SWS [48, 49]. We consider NPGS a valuable therapeutic option that can be associated with medical and/or laser treatment, offering a safer and efficient alternative to trabeculectomy when it is technically possible. Further studies of NPGS for the treatment of glaucoma associated with SWS are warranted.

7.9.7Glaucoma in Aphakia

The surgical management of uncontrolled IOP in aphakia remains one of the most difficult problems encountered in patients with glaucoma [50]. It is also a serious, sightthreatening complication in children who remain aphakic following congenital cataract surgery, with an incidence varying from 15 to 45% [51]. Zimmerman et al. [52] performed nonpenetrating trabeculectomy on 28 aphakic eyes, consisting of a first group of 18 eyes with chronic open-angle glaucoma and a second group of ten eyes with secondary and/or complicated glaucoma. Results were better in the first group with the IOP controlled (£ 24 mm

Hg) with or without medication in 77–92% of eyes at each follow-up vs. 30–50% of eyes in the second group. At one year after surgery, 89 and 37.5% of eyes were controlled in the first and second group, respectively, with no major complications. The authors, however, did not perform peeling of Schlemm’s canal endothelium during surgery. NPGS may be valuable as an initial procedure in aphakic patients who require surgery, at least in POAG.

Summary for the Clinician

■NPGS is an efficient surgery in medically uncontrolled POAG. It should be considered a safer option than trabeculectomy in phakic patients with POAG.

■NPGS appears to offer glaucoma patients with high myopia a safe filtering procedure.

■NPGS is a safe and valuable option in patients with pseudoexfoliative glaucoma, and seems especially appropriate in these patients given the increased permeability of the blood–aqueous barrier as well as the higher risk of complications with intraocular surgery.

■NPGS is also a potential therapy for pigmentary glaucoma. It targets the site of pathology, namely the pigment-loaded trabecular meshwork, which can be reconditioned to establish filtration.

■NPGS is indicated in uveitic glaucoma cases because it explores the site of resistance to aqueous outflow and is associated with less postoperative inflammation.

■NPGS may be indicated in some cases of congenital, juvenile glaucoma and aphakic glaucoma when the iridocorneal angle is not severely distorted. If not sufficient, it can be associated with other ab-externo procedures and/or with laser or medical treatment. Converting to penetrating surgery may be necessary in refractory cases.

7.10Contraindications for Nonpenetrating Glaucoma Surgery

7.10.1Relative Contraindications

The relative contraindications for NPGS are inherent to the status of the trabeculum because this surgery relies on the integrity of this structure for its outcomes.

7.10.1.1 Narrow-Angle Glaucoma

There are no available studies in the literature on NPGS in narrow-angle glaucoma, but most authors consider this condition a relative contraindication [30]. Laser iridotomy

66 7 Nonpenetrating Glaucoma Surgery

or surgical iridectomy is mostly a temporary therapeutic option in narrow-angle glaucoma. Cataract extraction or removal of a clear crystalline lens deepens the anterior chamber and opens the angle of the eye. When narrow-

7angle glaucoma has persisted for a certain length of time, glaucoma surgery is indicated in combination with lens

extraction. For these combined procedures, NPGS may be attempted, even though the iris root is very close to the trabeculum and effective filtration may not occur immediately.

7.10.1.2 Status Post Laser Trabeculoplasty

during surgery. NPGS can be then converted to classical trabeculectomy.

7.10.1.3 Post-Traumatic Angle-Recession Glaucoma

In angle-recession glaucoma, the trabeculum loses its function because of scarification processes and NPGS may not be possible. An attempt at NPGS can be made, as the damage to the trabeculum is not always complete and its function may be restored by scraping and peeling its posterior surface.

7.10.2 Absolute Contraindications

NPGS is contraindicated in neovascular glaucoma, where new blood vessels invade the angle. NPGS will fail in these cases because the iridocorneal angle is invaded by blood vessels. The trabeculum loses its filtering function because of the presence of the neovascularization. This type of glaucoma is the most difficult to treat and until now only the implantation of drainage devices has yielded favorable results [53].

Summary for the Clinician

■Secondary angle closure etiologic entities are a relative contraindication. The decision, though, depends on the degree of angle closure.

■Neovascular glaucoma is an absolute contraindication.

7.11Complications of Nonpenetrating Glaucoma Surgery

There is an agreement among published reports that nonpenetrating surgery offers a lower rate of complications when compared to conventional trabeculectomy, with

or without antimetabolites. This is largely due to the fact that the eye is not fully penetrated as in trabeculectomy, and that the aqueous is percolated through the remaining TDM, thus preventing a sudden intraand postoperative hypotony. Moreover, visual acuity is generally preserved after NPGS and returns to the preoperative level within the first postoperative week [54]. This is because postoperative cycloplegic medication is not used as well as due to low inflammation after surgery. Table 7.1 summarizes the advantages and disadvantages of NPGS.

Complications of nonpenetrating glaucoma surgery can be intraoperative, early postoperative or late postoperative. These complications are listed in Table 7.2 and are discussed here.

7.11.1 Intraoperative Complications

Probably the most common intraoperative complication of nonpenetrating surgery is perforation of the TDM. It is acceptable to have a perforation rate of about 30% in the first 10–20 cases. After the initial learning phase, the surgeon should expect a perforation in about 2–3% of cases. Karlen et al. [55] report a perforation in three out of the first ten surgeries (30%). With increased surgical experience, this complication was rare, occurring in three of the subsequent 96 deep sclerectomies (3.1%). Different types of perforations include transverse tears and TDM holes.

7.11.1.1 Transverse Tears

Occur at the junction of the anterior trabeculum and Descemet’s membrane, probably the weakest point of the TDM, and corresponds to Schwalbe’s line on gonioscopy. A perforation at this level will usually lead to the formation of a long tear, followed by immediate iris prolapse.

7.11.1.2 TDM Holes

Holes may occur in the TDM during the anterior deep dissection. Holes may be small with no loss of depth of the anterior chamber or large and accompanied by a shallow or flat anterior chamber and/or iris prolapse.

The two factors that determine the management of a TDM perforation are the size of it, the depth of the anterior chamber, as well as the presence of an iris prolapse [56]. Small holes with no iris prolapse or loss of anterior chamber depth can be ignored and the surgery continued normally. Small or large perforations with a shallow or flat anterior chamber and no iris prolapse should be dealt with in order to prevent subsequent iris prolapse or peripheral anterior synechia formation. Viscoelastic material should be injected, through a paracentesis, into

Low rate of postoperative complications

Shorter ambulatory care

Rapid visual acuity recovery

Limited postoperative inflammation Significantly less cataract formation More diffuse and shallow filtering blebs

Limited risk for endophthalmitis Safe surgery for end-stage glaucoma Easy postoperative follow-up Closed globe surgery

More difficult surgery

Long learning curve

Prolonged surgery time

May need Nd-Yag goniopuncture

Increased cost (implant or viscoelastics)

Not applicable in neovascular glaucoma and relatively contraindicated in closed-angle glaucoma

the anterior chamber under the TDM window to reform it and reposition the iris. The smallest possible amount of viscoelastic material of low molecular weight (Healon®) should be used to avoid a postoperative ocular pressure spike. In addition, an implant resting on the perforation site may be used to tamponade the hole. The superficial scleral flap should also be tightly sutured with 6–8 10/0 nylon sutures. Iris prolapse accompanying a long tear or large hole must lead to converting NPGS to trabeculectomy with a peripheral iridectomy; the superficial flap should again be tightly closed and viscoelastic material should be injected into the surgically created scleral space to increase the outflow resistance.

7.11.2Early Postoperative Complications

7.11.2.1 Inflammation

The degree of inflammatory reaction following the surgical trauma is considerably less in nonpenetrating surgery compared to trabeculectomy. Chiou et al. [38], in a study of postoperative inflammation after deep sclerectomy with collagen implant and standard trabeculectomy, found significantly lower postoperative flare measurements in the first group, with the preoperative level reached within one week. In contrast, following trabeculectomy, the inflammation in the anterior chamber was much more intense and persisted for one month before getting down to the preoperative level. This may be due to the lack of iridectomy, irrigation, and penetration of the anterior chamber. Eyes at increased risk of postoperative inflammation, such as those with pseudoexfoliative glaucoma and particularly those with uveitic or traumatic glaucoma, may benefit from this procedure.

7.11.2.2 Hypotony and Associated Complications

The mean IOP after nonpenetrating filtering surgeries has been reported to be 5 mm Hg on the first postoperative day [8, 57]. Thus, about 50% of the patients present with an early ocular hypotony for some days. If short-lived and not associated with any secondary complication, ocular hypotony should not be regarded as a worrying complication. On the contrary, early hypotony without any perforation is an excellent indicator of good surgical dissection and a positive prognostic factor for long-term IOP reduction [28]. Moreover, the risk of longstanding hypotonia is minimal [8, 57], but when present can be complicated by hypotonic maculopathy [58]. Sanchez et al. [11] reported two cases of hypotonic maculopathy out of 168 eyes (1.2%) that underwent deep sclerectomy.

Choroidal detachment is a rare complication. The available literature [8, 56, 59] reports an incidence rate of up to 5% after NPGS, whereas it can be observed in 20% of cases following trabeculectomy [60]. Prolonged hypotony in trabeculectomy eyes has been identified as the main risk factor for suprachoroidal hemorrhage [61], which has been rarely reported to occur after deep sclerectomy [62] or viscocanalostomy [63]. Therefore, hypotony after NPGS is common during the first postoperative week, but associated complications are significantly less than with conventional trabeculectomy.

To date no case of completely flat anterior chamber has been reported after NPGS. This is due to the lack of an abrupt IOP decrease during nonperforating procedures [54]. A shallow anterior chamber can occasionally be observed. An overfiltrating bleb may be prominent and result in dellen formation near the corneal limbus.

68 7 Nonpenetrating Glaucoma Surgery

Table 7.2 List of complications that have been reported after nonpenetrating glaucoma surgery

one out of 250–300 operated eyes [54]. The pathogenesis depends on the type of surgery. With viscocanalostomy, detachment is related to the viscoelastic injection into the artificial ostia of Schlemm’s canal, the canula probably being slightly misdirected [64]. After deep sclerectomy, this complication may be explained by the passage of aqueous humor from the scleral space to the subDescemet space at the anterior edge of Descemet’s window, secondary to an increased intrableb pressure as may occur after trauma, encysted bleb, and vigorous ocular massage. This is generally a self-resolving complication, but in severe cases descemetopexy can be tried with the injection of a viscoelastic or air into the anterior chamber to put the detached scroll back into place.

7.11.2.4 Hyphema

Hyphema is a complication with a low incidence after NPGS [56, 65]. It usually originates from a rupture of small iris vessels, ciliary processes, or from leakage of red blood cells through the TDM. No particular treatment is required.

7.11.2.5 Wound and Bleb Leaks

Wound leaks or positive Seidel tests occur with the same frequency after trabeculectomy and NPGS, and are often due to inadequate conjunctival wound closure [56, 66]. In most cases, the leaking stops after one week and the discontinuation of steroid therapy. On rare occasions surgical intervention is necessary to repair the wound leak. In a two-year prospective study on the bleb characteristics of 125 eyes that underwent mitomycin C augmented glaucoma surgery, bleb leaks were more frequently observed in the trabeculectomy group than in the deep sclerectomy group (24.6% vs. 3.1%, respectively) [67].

7.11.2.6 Infectious Complications

Blebitis is a well-known and potentially dangerous infection after trabeculectomy that can lead to endophthalmitis [68]. In NPGS, the TDM offers a barrier against the intraocular spread of bacteria. Out of a total of more than 2000 NPGS procedures, Roy and Mermoud [56] observed only one case of blebitis. No case of endophthalmitis has been reported to date. Infectious keratitis is a rare complication; there is a single case report of fungal keratitis occurring one week after viscocanalostomy in a

63year-old patient [69].

7.11.2.7Postoperative Increase in IOP

Descemet’s membrane detachment is a rare complication after nonpenetrating filtering surgery, occurring in about

Postoperative increase in IOP, secondary to the superficial scleral flap being too tightly closed, is regularly observed

after trabeculectomy, and needs either laser suture lysis and/or ocular massage unless releasable sutures have been used. Because the main site of postoperative aqueous humor outflow resistance after nonpenetrating filtering surgery is located at the TDM level, this complication should not occur if the dissection of the membrane has been done properly. Early postoperative IOP spikes can be due to:

1.Insufficient surgical dissection—most common after nonpenetrating filtering surgeries by inexperienced surgeons.

2.Hemorrhage in the scleral bed, which usually spontaneously resorbs within a few days.

3.Excess viscoelastic remaining in the anterior chamber, which mainly occurs after combined surgeries or anterior chamber reformation following perforation of the TDM. This also resolves in a few days.

4.Malignant glaucoma. Shaarawy et al. also reported one out of 105 eyes that developed malignant glaucoma on the first postoperative day following DSCI, which was successfully treated with cycloplegics [57].

5.Postoperative rupture of the TDM with iris prolapse [70], secondary to increased IOP from eye rubbing, Valsalva’s maneuver, etc. This should be managed with miotics and Nd:Yag laser to the prolapsed iris. If this doesn’t work, surgical iridectomy is indicated.

6.Peripheral anterior synechia formation at the site of the filtering window, often secondary to an intraoperative microperforation [70].

7.Steroid induction within the first few postoperative weeks.

Overall, IOP spikes are rare postoperative complications and should be treated according to each specific cause.

7.11.3 Late Postoperative Complications

Unlike immediate postoperative complications, late postoperative complications occur with the same frequency in penetrating and nonpenetrating filtering surgeries. This may be explained by the fact that late complications are often related to excessive scarring of the operated tissues and that the surgical procedure as such does not influence this process.

7.11.3.1 Late Rupture of the TDM

The risk of membrane rupture decreases with time, because the post-membrane outflow resistance slowly builds up for several weeks after surgery. However, rupture can happen after severe ocular trauma. Often there is a concomitant iris prolapse with a distorted pupil and darkening of the subconjunctival area. If the IOP remains

under control, no further treatment is needed. However, if the iris prolapse blocks the aqueous humor outflow and the IOP rises, medical, laser or surgical therapy should be considered.

7.11.3.2Peripheral Anterior Synechiae and Iris Prolapse

The iris may adhere to the TDM window and form peripheral anterior synechiae (PAS) after the following situations: intraoperative microperforation of the TDM, or iris entrapment into a goniopuncture hole [70], which usually occurs rapidly after laser treatment, and rupture of the TDM (e.g., blunt trauma, eye rubbing, coughing) with subsequent iris prolapse. There may be an associated increase in IOP if there is insufficient aqueous humor flow through the membrane. A laser synechiolysis may be attempted to reposition the iris back; if this fails, a medical or secondary surgical treatment should be considered.

7.11.3.3 Cataract Progression

It was reported that cataract progression is not influenced by deep sclerectomy, contrary to trabeculectomy. The Advanced Glaucoma Intervention Trial estimated that the rate of cataract formation after the first trabeculectomy is 78% at five years. The risk of cataract is doubled if there is a significant postoperative inflammation or a flat anterior chamber [71]. Shaarawy et al. [28] followed 105 patients for a mean of 64 months and showed progression of existing age-related cataract in 25% of eyes, but no surgery-induced cataracts.

7.11.3.4 Bleb Fibrosis and Encapsulated Bleb

Bleb fibrosis is due to conjunctival or episcleral fibrosis and is slightly more frequent after NPGS than after trabeculectomy [54]. In cases of increasing IOP, subconjunctival injections of an antimetabolite are required to stop the scarring process. An encapsulated bleb or Tenon’s cyst develops through a fibroblastic overgrowth that results in a tight-appearing opalescent bleb with a thick wall and vessels on the surface that entraps the aqueous humor in the subconjunctival space. These occur more often when antimetabolites are used, and their incidence after NPGS is comparable to that for trabeculectomy. If the IOP becomes uncontrolled, needling with or without antimetabolites and subconjunctival injections should be done. In cases of recurrence, excision of the cysts can be attempted. Shaarawy et al. [28] performed subconjuctival injections of 5-FU in 25 out of the 105 patients (23%) who underwent DSCI.