Efstratios Mendrinos,
Tarek Shaarawy
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Key Features: NPGS |
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HISTORICAL REVIEW
Nonpenetrating glaucoma surgery (NPGS) can probably trace its roots to 1962 with the first sinusotomy performed by Kraznov. This operation consisted of removing a band of the sclera, opening Schlemm's canal over 120° from 10 to 2 o'clock.[1-3] The inner wall of Schlemm's canal was left untouched and there was no scleral flap. Sinusotomy never gained wide popularity because it was a difficult operation; it needed a surgical microscope and Schlemm's canal had to be found which was not easy. In the late 1960s and for the next three decades, trabeculectomy, as described by Sugar[4] in 1961 and Cairns[5] in 1968, became the gold standard technique for filtering surgery. However, even with the numerous modifications proposed to the original trabeculectomy the lack of a reproducible postoperative intraocular pressure (IOP) reduction as well as the early postoperative complications, led several surgeons to consider other alternatives. Several techniques of NPGS have been described. Since the main aqueous outflow resistance is located at the juxtacanalicular trabeculum and the inner wall of Schlemm's canal,[6] these two anatomical structures were targeted. Ab-externo trabeculectomy was first proposed by Laage de Meux[7] in 1976 and later by Zimmerman et al[8,9] in 1984 and Arenas[10] in 1991. This procedure differs from sinusotomy by the removal of the inner wall of Schlemm's canal and of the juxtacanalicular trabecular meshwork as well as by the creation of a scleral flap. NPGS as practiced today, with removal of the corneal stoma behind the anterior trabeculum and Descemet's membrane has been described by Fyodorov et al[11] and Koslov et al[12] as deep sclerectomy and by Stegmann et al[13] as viscocanalostomy. These two last procedures are the most used and will be described in details.
PRINCIPLES OF NPGS AND MECHANISMS OF FILTRATION
The principal concept of nonpenetrating surgery is to create filtration through a naturally occurring membrane that acts as an outflow resistance site. This allows a progressive and relatively slow decrease in intraocular pressure, thus avoiding postoperative ocular hypotony. The whole procedure is performed without penetration into the anterior chamber. This membrane, the trabeculo-Descemet's membrane (TDM), consists of the anterior trabecular meshwork and the peripheral Descemet's membrane. To expose the membrane, a deep sclerokeratectomy should be performed, thereby also providing a postoperative intrascleral space (Fig. 221.1). This space may act as an aqueous reservoir and as a filtration site that may reduce the need for a large subconjunctival filtration bleb thus reducing the risk of late bleb-related complications. The main advantage of NPGS is the prevention of early complications associated with trabeculectomy; such as flat anterior chamber, hyphema and choroidal detachment. Furthermore, the postoperative period is relatively stable with rapid return to preoperative visual acuity levels. The main disadvantage of both deep sclerectomy and viscocanalostomy is the fact that they are associated with a long and demanding learning curve. Table 221.1 summarizes the advantages and disadvantages of NPGS and will be discussed further on.
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FIGURE 221.1 Schematic representation of deep sclerectomy. Under a superficial scleral flap, a deep corneosclerectomy unroofing Schlemm's canal is performed. Corneal tissues behind the anterior trabeculum and the Descemet's membrane are removed. Removing of the inner wall of the Sclemm's canal can also be performed, but is not represented on the figure. |
TABLE 221.1 -- Advantages and Disadvantages of NPGS
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Advantages |
Disadvantages |
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There are two sites of interest when the mechanisms of function of nonpenetrating surgeries are studied: the aqueous humor flow through the TDM and the aqueous resorption after its passage through the TDM.
FLOW THROUGH THE TDM
Vaudaux et al[14] studied the aqueous outflow through the TDM in an experimental model. The postoperative TDM resistance was found to be low enough to ensure a low postoperative IOP and yet sufficient enough to prevent collapse of the anterior chamber with its ensuing complications. It was also found that most of the outflow occurred through the anterior trabeculum and to a lesser degree through the posterior trabeculum and Descemet's membrane.
AQUEOUS HUMOR RESORPTION
After aqueous humor passage through the TDM, four hypothetical mechanisms of aqueous resorption may occur.
SUBCONJUNCTIVAL BLEB
As after trabeculectomy, almost all patients undergoing NPGS have a diffuse conjunctival bleb on the first postoperative day.[15] As demonstrated by ultrasound biomicroscopy studies (UBM), successful cases show a low profile and diffuse subconjunctival bleb even years after surgery.[16,17] 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.
INTRASCLERAL BLEB
In NPGS, a certain volume of sclera is removed, ranging from 5 to 8 mL. Provided the superficial scleral flap does not collapse, this scleral volume may be considered as an intrascleral bleb. The importance of intrascleral bleb has prompted research into ways to keep it patent. The idea of using a collagen implant was proposed by Kozlov et al.[12,18] The concept is simply to occupy this space during the period of maximal healing response leaving behind an aqueous lake after resorption of the implant. The intrascleral bleb was observed in more than 90% of patients who received a collagen implant and the mean volume of intrascleral bleb was 1.8 mL.[16] In the intrascleral bleb the aqueous may be resorbed by new aqueous drainage vessels, as demonstrated by Delarive et al (see Delarive T, Schnyder CC, Shaarawy T, Mermoud A: An aminal model for the study of non-penetrating glaucoma surgery. University of Lausanne, 2001, unpublished data).
SUPRACHOROIDAL SPACE
Since the remaining layer of sclera over the ciliary body and peripheral choroid after deep sclerectomy is very thin, there may be drainage of aqueous humor into the suprachoroidal space; in fact using UBM, it is possible to observe fluid between the ciliary body and the remaining sclera in 45% of the patients studied years after the deep sclerectomy.[16] Aqueous in the choroidal space may reach the uveoscleral outflow and increase this outflow pathway. It could also induce a chronic ciliary body detachment and reduce the aqueous production.[19]
SCHLEMM'S CANAL
When performing deep sclerectomy, Schlemm's canal is opened and unroofed. On either side of the deep sclerectomy, the two ostia of Schlemm's canal may drain the aqueous humor into the episcleral veins. This mechanism may be more important after viscocanalostomy since the canal is dilated with high viscosity hyaluronic acid during surgery.
INDICATIONS AND CONTRAINDICATIONS FOR NPGS
INDICATIONS
Most published trials have evaluated efficacy of NPGS in primary and secondary open angle glaucoma; in cases where the angle is grossly distorted or closed, NPGS should be avoided.
Open Angle Glaucoma
NPGS has been advocated as a safer option to trabeculectomy in open angle glaucoma.[20] Instead of excising a portion of peripheral cornea and trabecular meshwork, NPGS targets the presumed site of pathology, namely the Schlemm's canal and the juxtacanalicular meshwork.
Glaucoma Patients with High Myopia
Conventional glaucoma surgery in patients with high myopia carries a higher risk of complications. One study reported on the results of NPGS in highly myopic glaucoma patients: 2 out of 21 patients developed choroidal detachments, one of which was secondary to blunt trauma to the operated eye.[21] This low rate of complications is attributed to the gradual intraoperative reduction of the IOP with NPGS.
Pigmentary Glaucoma
NPGS is a potential therapy for pigmentary glaucoma. It targets the site of pathology, namely the pigment-loaded trabecular meshwork, which can be reconditioned to reestablish filtration.
Pseudoexfoliative Glaucoma
NPGS is an option in this type of glaucoma. One study reported 2-year acceptable IOP control rates and a low incidence of complications in patients with pseudoexfoliative glaucoma[22] that was maintained over 4 years.[23]
Aphakic Glaucoma
In aphakic glaucoma, iridectomy is not desirable because the vitreous moves forward through the iridectomy and blocks the filtration site. NPGS does not require iridectomy and thus may be indicated. The only drawback of NPGS in aphakic glaucoma is the status of the trabeculum which in long-standing cases is often collapsed and scarred; restoration of its function depends on its status and the surgeon's experience. In many instances, the conjunctiva and the limbus are severely scarred by previous surgeries. The appropriate site for NPGS in aphakic glaucoma should be free of previous surgical scars.
Congenital Glaucoma
Tixier et al[24] were the first to report on results of NPGS in congenital glaucoma. They concluded that NPGS is at least as effective as trabeculectomy in congenital glaucoma with fewer complications. Noureddin et al[25] also reported on the efficacy and the safety of visconalostomy in patients with primary congenital glaucoma of the isolated trabecular dysgenesis category and found it equally effective compared to trabeculotomy ab-externo. One study[26] examined primary viscocanalostomy in medically uncontrolled juvenile open-angle glaucoma cases and found it to efficiently and safely reduce IOP with an overall success rate of 80%. The degree of success is function of the angle structure malformation and the surgeon's experience. This also concerns glaucoma associated with aniridia and anterior segment dysgenesis syndromes.
Glaucoma Associated with Sturge-Weber Syndrome
Glaucoma associated with this congenital hemangiomatous disease is often resistant to medical treatment. It has been advocated that filtering operations bypassing the episcleral veins represent the most effective surgical treatment. Trabeculectomy has been reported to have good short-term results but carries the risk of massive choroidal effusion or expulsive hemorrhage[27] which is already increased in these patients. NPGS offers a safer and effective[28] alternative to trabeculectomy when it is technically possible.
Glaucoma Secondary to Uveitis
When elevated IOP persists after uveitis has been under control, glaucoma surgery is indicated. NPGS is indicated in these cases because it explores the site of resistance to aqueous outflow and the trabeculum can be reconditioned to improve filtration with a high success rate in postoperative IOP reduction[29-31] and associated fewer complications than trabeculectomy.[32] However, in cases in which multiple peripheral anterior synechia have occurred, NPGS may not offer an efficient solution.
CONTRAINDICATIONS
There are no published reports on NPGS in primary angle closure glaucoma. This is not surprising considering the principles of function of NPGS. Likewise, secondary angle closure etiological entities are a relative contraindication. The decision, though, depends on the degree of angle closure. Neovascular glaucoma is an absolute contraindication because new blood vessels invade the iridocorneal angle and the trabeculum loses its filtering function because of the neovascularization, providing little chance of surgical success.
SURGICAL TECHNIQUE
NPGS is a very challenging technique and involves a long learning curve.
ANESTHESIA
Topical anesthesia with 5% cocaine eye drops is sufficient with most patients. If patients cannot tolerate topical anesthesia, adding subonjunctival injection intraoperatively is always possible.
CONJUNCTIVAL AND SUPERFICIAL SCLERAL FLAPS
A superotemporal intracorneal suture is used to expose the upper nasal or superotemporal surgical quadrant. The conjunctiva is opened either in the limbus or in the fornix. The sclera is exposed and moderate hemostasis is performed. A superficial scleral flap measuring 5 × 5 mm is dissected aiming at one-third of the scleral thickness. The initial incision is made with a number 11 stainless steel blade and the horizontal dissection with a crescent blade. In order to be able to dissect the corneal stroma down to Descemet's membrane later, the scleral flap is dissected 1-1.5 mm into clear cornea (Fig. 221.2). In high-risk patients, mitomycin or 5-fluorouracil may be used.
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FIGURE 221.2 The superficial scleral flap is one-third of the scleral thickness and is prolonged 1-1.5 mm into clear cornea. |
DEEP SCLERECTOMY AND EXPOSURE OF THE TRABECULODESCEMETIC MEMBRANE
Deep sclerokeratectomy is performed by making a second deep scleral flap 4 × 4 mm (Fig. 221.3). The two lateral and the posterior deep scleral incisions are made using a 15° diamond blade. The deep flap is smaller than the superficial one, leaving a step of sclera on the three sides allowing for a tighter closure of the superficial flap in case of an intraoperative perforation of the TDM membrane. The remaining scleral layer should be as thin as possible (50-100 ?m). 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. Schlemm's canal is opened and the sclerocorneal dissection is prolonged anteriorly for 1-1.5 mm in order to remove the 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 perforation of 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 (Fig. 221.4). The best way to perform this last dissection is to do two radial corneal cuts without touching the anterior trabeculum or Descemet's membrane. This is performed preferably with the number 11 steel blade with the bevel side up. When the anterior dissection between the corneal stroma and the Descemet's membrane is completed, the deep scleral flap is removed using a microscissor (Fig. 221.5). At this stage of the procedure, there should be evident percolation of aqueous through the remaining trabeculum. The juxtacanalicular trabeculum and Schlemm's endothelium are then removed using a small blunt forceps (Fig. 221.6). This additional procedure has been called abexterno trabeculectomy. To peel the thin Schlemm's canal endothelium and juxtacanalicular trabeculum membrane, it is crucial to dry the exposed inner wall of Schlemm's canal which can then be grabbed with the forceps and peeled easily by pulling it. A space maintainer implant is placed in the scleral bed and the superficial scleral flap is then closed and secured with two loose 10/0 nylon sutures. The conjunctiva and Tenon's capsule are closed with running 8/0 vicryl sutures. Thus the procedure has in fact evolved into a combination of deep sclerectomy and ab-externo trabeculectomy.
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FIGURE 221.3 The deep sclerectomy is delineated with a diamond blade. The deep sclerectomy measures 4 × 4 mm and the sclera is dissected leaving ?5% of sclera over the choroid and ciliary body. |
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FIGURE 221.4 Detachment of the anterior trabeculum and Descemet's membrane using a sponge, a spatula or a blunt metallic blade. |
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FIGURE 221.5 The deep scleral flap is removed using Gallan scissors. |
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FIGURE 221.6 The inner wall of the Sclemm's canal and the juxtacanalicular trabeculum is peeled off using fine forceps. It is a fact that major obstruction to aqueous outflow is, in primary and secondary open-angle glaucoma, the inner wall of the Schlemm's canal and the juxtacanalicular trabeculum, and proper peeling of this portion is the key to success. |
POSTOPERATIVE TREATMENT
Routine medications used during the first 2-3 weeks after surgery include a topical regimen of corticosteroids and antibiotics. Drops are given every 4 h during waking hours for at least 2 weeks and tapered over the next 2-4 weeks, then topical steroids are replaced by nonsteroidal antiinflammatory agents and continued for 6-12 weeks.
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Key Features: Surgical Technique |
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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 collagen Aquaflow implant,[12] a highly purified porcine collagen dehydrated into a cylinder and secured in the scleral bed with a single 10/0 nylon suture (Fig. 221.7). It swells rapidly once exposed to the aqueous humor and is resorbed within 6-9 months after surgery. Another device that has been proposed to maintain the scleral lake is the reticulated hyaluronic acid implant[33] which resorbs in ?3 months and more recently a T-shaped hydrophilic acrylic implant which is nonabsorbable.[34] The role of implants is still controversial but studies comparing deep sclerectomy with implant versus without it, seem to show higher success rate with the use of an implant.[35]
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FIGURE 221.7 A collagen implant is sutured in the scleral bed. This implant will serve as a space maintainer to create an intrascleral space for aqueous humor to filter. |
VISCOCANALOSTOMY
Stegmann et al[13] described a variant of NPGS and termed it viscocanalostomy to emphasize the importance of injecting high viscosity hyaluronic acid 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 formation of a filtration bleb because the superficial scleral flap is tightly sutured so that aqueous humor regressing through the TDM has the only possibility to reach the two surgically created ostia of Schlemm's canal. The viscoelastic material is also placed in the scleral bed and may prevent fibrin cross-linking. It is resorbed in 4-5 days. In vivo primate[36,37] and human eye[36] studies reported that injection of viscoelastic in Schlemm's canal resulted not only in dilatation of the canal and associated collectors 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 juxtacanalicular zone extracellular spaces with the lumen of Schlemm's canal. The continuous presence of sodium hyaluronate might prevent repair of these defects.
ND-YAG GONIOPUNCTURE AFTER DEEP SCLERECTOMY
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 of elevated IOP in the first postoperative period or fibrosis of the TDM if it is required later than ? 9 months. Using a gonioscopy contact lens, the aiming beam is focused in the semitransparent TDM. With a power of 4-5 mJ, 2-15 shots are applied resulting in the formation of microscopic holes through the TDM and allowing a direct passage of aqueous from the anterior chamber to the subconjunctival space. It may be needed in up to 51% of NPGS over a period of 8 years and is successful in lowering postoperative IOP (mean IOP before goniopuncture was 20 mm Hg, dropping to 11 mm Hg after goniopuncture).[38] The success depends mainly on the thickness of the TDM, hence the importance of sufficiently deep intraoperative dissection. By opening the TDM, goniopuncture converts a nonperforating filtration procedure into a perforating one. Nevertheless, the combined complications rates of deep sclerectomy and goniopuncture is significantly lower than the complication rates associated with trabeculectomy.[39]
COMPLICATIONS
Although there is almost unanimous agreement that NPGS is associated with significantly less complications than conventional penetrating surgery,[15,40] it is not totally devoid of complications which may occur intraoperatively or during the early or late postoperative period.
INTRAOPERATIVE COMPLICATIONS
The commonest intraoperative complication is perforation of the TDM. It is acceptable to have a perforation rate of 30% during the first 10-20 cases. After the initial learning phase surgeons can expect perforations in less than 5% of cases.
Management: The factors that determine the management of a TDM perforation are the size of it, the depth of the anterior chamber (AC) and the presence of iris prolapse. Small holes with no iris prolapse or loss of AC depth should be ignored and the surgery continued. Perforations with shallow or flat AC and no iris prolapse should be dealt with in order to prevent iris prolapse or peripheral anterior synechia formation; viscoelastic material should be injected through a parencentesis into the AC under the TDM window to reform the AC and reposition the iris. In addition an implant can be placed on the perforation site to tamponade the hole. Iris prolapse accompanying larger holes or tears must lead to converting NPGS to trabeculectomy.
EARLY POSTOPERATIVE COMPLICATIONS
Inflammation
The low incidence of inflammation is one major advantage of NPGS over penetrating filtering surgeries. The very nature of NPGS being an "extraocular" intervention without the need for an iridectomy explains why anterior chamber inflammation is mild in the initial postoperative phase and practically nonexistent thereafter.[41] Inflammation is treated with topical steroids for 6 weeks.
Hyphema
Hyphema is a complication with a low incidence after NPGS.[15,42] 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.
Hypotony
Early postoperative hypotony (?5 mmHg) is a good indicator of proper surgical dissection and a prognostic factor for long-term IOP reduction.[43] IOP usually increases over the first postoperative days with topical steroids. To best of our knowledge there is no reported case of flat anterior chamber after NPGS in the literature. Choroidal detachment is a rare complication; contrary to trabeculectomy with an almost 20% incidence,[41] available literature[9,12,13,15] reports an incidence rate of 2-5% after NPGS. Prolonged hypotony in trabeculectomy eyes has been identified as the main risk factor for suprachoroidal hemorrhage.[44] There is one published report in the literature of this complication occurring after deep sclerectomy.[45] Therefore, hypotony after NPGS is common during the first postoperative week, but associated complications are significantly less than with conventional trabeculectomy.
Postoperative Increase In IOP
Increased IOP can have different origins and should be treated accordingly: (1) Insufficient surgical dissection. In such cases the operative site can be revised but many opt for a re-operation in a different site. (2) Hemorrhage in the scleral bed. This usually spontaneously resolves without treatment within a few days. (3) Excess viscoelastic remaining into the anterior chamber after combined surgery or anterior chamber reformation with a microperforation. This also resolves in a few days. (4) Postoperative rupture of the TDM membrane with iris prolapse, secondary to increased IOP from eye rubbing, Valsava's maneuver etc. This should be managed with miotics and Yag laser to the prolapsed iris. If this doesn't work surgical iridectomy is indicated. (5) Peripheral anterior synechia formation at the site of the filtering window, often secondary to intraoperatively microperforation. (6) Steroid induced IOP increase within the first postoperative weeks.
Overall, this complication should not occur if the membrane dissection has been performed correctly.
Malignant Glaucoma
Predisposing factors resulting in malignant glaucoma are (intra)ocular surgery (e.g., trabeculectomy and cataract surgery) and anterior segment laser procedures. Due to the property of NPGS to be extraocular, this complication is quite rare. Chiou et al reported one case who developed malignant glaucoma after deep sclerectomy.[46]
LATE POSTOPERATIVE COMPLICATIONS
Late Rupture of the TDM
The thin remaining TDM can rupture at any time after surgery but this risk decreases with time due to increased postmembrane outflow resistance. Clinically, often an accompanying iris prolapse with a decentralized pupil and darkening of the subconjunctival space can be seen. If the IOP remains under control, no further treatment is required. If IOP rises, medical or surgical therapy, including Yag laser or surgical iridectomy and anterior chamber formation, should be performed.
Descemet's Membrane Detachment
This is an unusual complication after NPGS, occurring in ?1 out of 250-300 operated cases.[47] It can occur after deep sclerectomy when aqueous humor is forced from the scleral space to the sub-Descemet's space, secondary to increased intrableb pressure from trauma, encysted bleb, and vigorous ocular massage. In viscocanalostomy the pathogenesis can be attributed to a misdirection of viscoelastic material. This is generally a self-resolving complication but in severe cases descemetopexy can be tried with injection of a viscoelastic or air to put the detached scroll back into place.
Peripheral Anterior Synechia (PAS)
This may occur in the site of filtration with or without an iris prolapse after rupture (Valsava or trauma), intraoperative microperforations of the TDM, or iris entrapment after goniopuncture.[48] PAS can inhibit aqueous flow and cause an associated IOP increase. Nd-Yag laser synechiolysis should be attempted to detach the iris from the osteum. If this fails, medical or surgical treatment should be considered.
Scleral Ectasia
There is a single reported case in the literature of scleral ectasia following deep sclerectomy in a 12-year old girl with chronic juvenile oligoarticular arthritis and glaucoma secondary to chronic uveitis.[49]Since the scleral flap is weaker than in trabeculectomy and the deep scleral flap creates a zone of weakness, a thinner than usual sclera - as seen in patients with high myopia, associated rheumatoid or juvenile arthritis, or chronic uveitis- can lead to this condition. Due to anatomical vulnerability, the use of antimetabolites in these patients may increase the risk of this complication and requires careful consideration.
Cataract Progression
It was reported that cataract progression is not influenced by deep sclerectomy contrary to trabeculectomy.[50] Shaarawy et al followed 104 patients for up to 48 months and showed progression of existing senile cataract in 21% of eyes.[35]
Bleb Fibrosis and Encapsulated Bleb
It is due to conjunctival or episcleral fibrosis and is slightly more frequent after NPGS than after trabeculectomy. Signs of an early bleb fibrosis are an elevated IOP, diffuse conjunctival injection and the presence of large vessels. In case 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. They occur more often when antimetabolites are used and their incidence after NPGS is comparable to 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.
RESULTS
Prospective and retrospective clinical trials of deep sclerectomy and viscocanalostomy provide evidence that these procedures reduce IOP. Results with nonpenetrating deep sclerectomy reported from retrospective studies vary from a complete success rate (IOP <21 mmHg without antiglaucomatous medication) of 36-92%.[42,51-55] Prospective studies of deep sclerectomy with collagen implant report complete success rates of 45-69%[15,20,35,38,56] with qualified success rates (IOP <21 mmHg with medication) being much more higher. In addition, the use of a collagen implant enhances the success rates and lowers the need for postoperative medications.[35,56,57]
In 1999 Stegmann et al reported an 83% viscocanalostomy success rate in a black African population.[13] Several studies have been published since then, reporting viscocanalostomy results; Sunaric-Mégevand et al[58] reported a 68% complete success rate at 1 year, 60% at 2 and 59% at 3 years. In 2003, Carassa et al[59] reported a 76% success rate in a 2-year randomized controlled clinical trial, and Shaarawy et al[60] a complete success rate of 60% at 5 years. Kobayashi et al[61] and O'Brart et al[62] found a similar 64% complete success rate at 1 year. In 2004 Yalvac et al reported in a 3-year prospective randomized trial a complete success rate of 52.9% at 6 months in the viscocanalostomy group and of 35% at 3 years.[63] Lüke et al reported a complete success rate of 30%[64] and 40%[65] at 1 year in patients having viscocanalostomy and Drüsedau et al[66] found a complete success rate of 36% at 1 year and a qualified success rate of 79%. It is often difficult to compare intermediate and long-term follow-up studies because the success criteria are not uniform but overall indicate that NPGS has the potential to reduce IOP.
Randomized controlled trials comparing NPGS to trabeculectomy[39,59,61-63,67,68] have a consensus on the superior safety profile of NPGS but are not in agreement when it comes to efficacy, where we find conflicting results about how low NPGS renders IOP compared to trabeculectomy. This is attributed to a number of factors including the fundamental differences between NPGS and penetrating filtering techniques, the long learning curve of NPGS and the need to use goniopuncture to achieve target IOPs.
CONCLUSIONS
NPGS is a viable option for glaucoma patients requiring surgery. Its superior safety profile makes it a first choice in many cases. In young patients NPGS has a definite advantage. NPGS with its lower cataract formation compared to trabeculectomy, provides an interesting option. This is also the case in patients where complications cannot be tolerated like single eye patients, patients with high myopia and patients with tubular visual fields. The fact that the anterior chamber is not entered makes it a potential surgery of choice for uveitic glaucoma cases. It is important, at least for tertiary care centers to have the means and the skills needed to perform this surgery when indicated.
The controversy between IOP-lowering effect of trabeculectomy versus NPGS will remain as long as surgical trials continue to be designed and reported independently without any clear guidelines that would allow surgical studies to be readily comparable so that conclusions can be made.
The impact of NPGS on glaucoma surgery is quite evident from the generated interest in developing new surgical methods that would offer better safety and efficacy than the gold standard, which had reined king for the last four decades.
REFERENCES
1. Krasnov MM: Sinusotomy in glaucoma. Vestn Oftalmol 1964; 77:37-41.
2. Krasnov MM: Externalization of Schlemm's canal (sinusotomy) in glaucoma. Br J Ophthalmol 1968; 52:157-161.
3. Krasnov MM: Symposium: microsurgery of the outflow channels. Sinusotomy. Foundations, results, prospects. Trans Am Acad Ophthalmol Otolaryngol 1972; 76:368-374.
4. Sugar HS: Experimental trabeculectomy in glaucoma. Am J Ophthalmol 1961; 51:623-627.
5. Cairns JE: Trabeculectomy. Preliminary report of a new method. Am J Ophthalmol 1968; 66:673-679.
6. Grant WM: Experimental aqueous perfusion in enucleated human eyes. Arch Ophthalmol 1963; 69:783-801.
7. De Laage de Meux: Kantelip B Surgical anatomy of corneoscleral limbs. Arch Ophthalmol 1976; 36:39-50.
8. Zimmerman TJ, Kooner KS, Ford VJ, et al: Effectiveness of nonpenetrating trabeculectomy in aphakic patients with glaucoma. Ophthalmic Surg 1984; 15:44-50.
9. Zimmerman TJ, Kooner KS, Ford VJ, et al: Trabeculectomy vs. nonpenetrating trabeculectomy: a retrospective study of two procedures in phakic patients with glaucoma. Ophthalmic Surg 1984; 15:734-740.
10. Arenas E: Trabectulectomy ab externo. Highlights Ophthalmol 1991; 19:59-66.
11. Fyodorov SN, Koslov IV, Timoshkina NT, et al: Non penetrating deep sclerectomy in open angle glaucoma. Eye Microsurgery 1989; 1:52-55.
12. Koslov VI, Bagrov SN, Anisimova M, et al: Deep sclerectomy with collagen. Eye Microsurgery 1990; 3:44-46.
13. Stegmann R, Pienaar A, Miller D: Viscocanalostomy for open-angle glaucoma in black African patients. J Cataract Refract Surg 1999; 25:316-322.
14. Vaudaux J, Uffer S, Mermoud A: Aqueous dynamics after deep sclerectomy : in vitro study. Ophthalmic Pract 1999; 16:204-209.
15. Karlen ME, Sanchez E, Schnyder CC, et al: Deep sclerectomy with collagen implant: medium term results. Br J Ophthalmol 1999; 83:6-11.
16. Kazakova D, Roters S, Schnyder CC, et al: Ultrasound biomicroscopy images: long-term results after deep sclerectomy with collagen implant. Graefes Arch Clin Exp Ophthalmol 2002; 240:918-923.
17. Marchini G, Marraffa M, Brunelli C, et al: Ultrasound biomicroscopy and intraocular-pressure-lowering mechanisms of deep sclerectomy with reticulated hyaluronic acid implant. J Cataract Refract Surg 2001; 27:507-517.
18. Koslov VI, Bagrov SN, Anisimova SY, et al: Nonpenetrating deep sclerectomy with collagen. Eye Microsurgery 1990; 3:157-162.
19. Mermoud A: Sinusotomy and deep sclerectomy. Eye 2000; 14:531-535.
20. Mermoud A, Schnyder CC, Sickenberg M, et al: Comparison of deep sclerectomy with collagen implant and trabeculectomy in open-angle glaucoma. J Cataract Refract Surg 1999; 25:323-331.
21. Hamel M, Shaarawy T, Mermoud A: Deep sclerectomy with collagen implant in patients with glaucoma and high myopia. J Cataract Refract Surg 2001; 27:1410-1417.
22. Drolsum L: Deep sclerectomy in patients with capsular glaucoma. Acta Ophthalmol Scand 2003; 81:567-572.
23. Drolsum L: Longterm follow-up after deep sclerectomy in patients with pseudoexfoliative glaucoma. Acta Ophthalmol Scand 2006; 84:502-506.
24. Tixier J, Dureau P, Becquet F, Dufier JL: Deep sclerectomy in congenital glaucoma. Preliminary results. J Fr Ophtalmol 1999; 22:545-548.
25. Noureddin BN, El-Haibi CP, Cheikha A, Bashshur ZF: Viscocanalostomy versus trabeculotomy ab externo in primary congenital glaucoma: 1-year follow-up of a prospective controlled pilot study. Br J Ophthalmol 2006; 90:1281-1285.
26. Stangos AN, Whatham AR, Sunaric-Megevand G: Primary viscocanalostomy for juvenile open-angle glaucoma. Am J Ophthalmol 2005; 140:490-496.
27. Iwach AG, Hoskins HD Jr, Hetherington J Jr, Shaffer RN: Analysis of surgical and medical management of glaucoma in Sturge-Weber syndrome. Ophthalmology 1990; 97:904-909.
28. Audren F, Abitbol O, Dureau P, et al: Non-penetrating deep sclerectomy for glaucoma associated with Sturge-Weber syndrome. Acta Ophthalmol Scand 2006; 84:656-660.
29. Miserocchi E, Carassa RG, Bettin P, Brancato R: Viscocanalostomy in patients with glaucoma secondary to uveitis: preliminary report. J Cataract Refract Surg 2004; 30:566-570.
30. Auer C, Mermoud A, Herbort CP: Deep sclerectomy for the management of uncontrolled uveitic glaucoma: preliminary data. Klin Monatsbl Augenheilkd 2004; 221:339-342.
31. Souissi K, El Afrit MA, Trojet S, Kraiem A: Deep sclerectomy for the management of uveitic glaucoma. J Fr Ophtalmol 2006; 29:265-268.
32. Souissi K, El Afrit MA, Trojet S, Kraiem A: Trabeculectomy for the management of uveitic glaucoma. J Fr Ophtalmol 2006; 29:153-156.
33. Sourdille P, Santiago PY, Villain F, et al: Reticulated hyaluronic acid implant in nonperforating trabecular surgery. J Cataract Refract Surg 1999; 25:332-339.
34. Ates H, Uretmen O, Andac K, Azarsiz SS: Deep sclerectomy with a nonabsorbable implant (T-Flux): preliminary results. Can J Ophthalmol 2003; 38:482-488.
35. Shaarawy T, Nguyen C, Schnyder C, Mermoud A: Comparative study between deep sclerectomy with and without collagen implant: long term follow up. Br J Ophthalmol 2004; 88:95-98.
36. Smit BA, Johnstone MA: Effects of viscoelastic injection into Schlemm's canal in primate and human eyes: potential relevance to viscocanalostomy. Ophthalmology 2002; 109:786-792.
37. Tamm ER, Carassa RG, Albert DM, et al: Viscocanalostomy in rhesus monkeys. Arch Ophthalmol 2004; 122:1826-1838.
38. Shaarawy T, Mansouri K, Schnyder C, et al: Long-term results of deep sclerectomy with collagen implant. J Cataract Refract Surg 2004; 30:1225-1231.
39. Ganfoldi S, Quaranta L, Cimino L, Bettelli S: Deep sclerectomy versus trabeculectomy. Prospective randomised clinical trial. 4 year interim analysis. Proceedings of the Second Intrenational Congress on Glaucoma Surgery. Luxor, Egypt; 2003.
40. Watson PG, Jakeman C, Ozturk M, et al: The complications of trabeculectomy (a 20-year follow-up). Eye 1990; 4(Pt 3):425-438.
41. Chiou AG, Mermoud A, Jewelewicz DA: Post-operative inflammation following deep sclerectomy with collagen implant versus standard trabeculectomy. Graefes Arch Clin Exp Ophthalmol 1998; 236:593-596.
42. Lachkar Y, Neverauskiene J, Jeanteur-Lunel MN, et al: Nonpenetrating deep sclerectomy: a 6-year retrospective study. Eur J Ophthalmol 2004; 14:26-36.
43. Shaarawy T, Flammer J, Smits G, Mermoud A: Low first postoperative day intraocular pressure as a positive prognostic indicator in deep sclerectomy. Br J Ophthalmol 2004; 88:658-661.
44. Tuli SS, WuDunn D, Ciulla TA, Cantor LB: Delayed suprachoroidal hemorrhage after glaucoma filtration procedures. Ophthalmology 2001; 108:1808-1811.
45. Neudorfer M, Sadetzki S, Anisimova S, Geyer O: Nonpenetrating deep sclerectomy with the use of adjunctive mitomycin C. Ophthalmic Surg Lasers Imaging 2004; 35:6-12.
46. Chiou AG, Mermoud A, Hediguer SE: Malignant ciliary block glaucoma after deep sclerotomy - ultrasound biomicroscopy imaging. Klin Monatsbl Augenheilkd 1996; 208:279-281.
47. Ravinet E, Tritten JJ, Roy S, et al: Descemet membrane detachment after nonpenetrating filtering surgery. J Glaucoma 2002; 11:244-252.
48. Kim CY, Hong YJ, Seong GJ, et al: Iris synechia after laser goniopuncture in a patient having deep sclerectomy with a collagen implant. J Cataract Refract Surg 2002; 28:900-902.
49. Milazzo S, Turut P, Malthieu D, Leviel MA: Scleral ectasia as a complication of deep sclerectomy. J Cataract Refract Surg 2000; 26:785-787.
50. Henchoz L, Nguyen C, Schnyder C, et al: Surgery induced cataract and catarct progression following deep sclerectomy with collagen implant compared to trabeculectomy. Ophthalmology 2000; 107:205.
51. Detry-Morel M, Pourjavan S, Detry MB: Comparative safety profile between 'modern' trabeculectomy and non-penetrationg deep sclerectomy. Bull Soc Belge Ophtalmol 2006; 300:43-54.
52. Demailly P, Lavat P, Kretz G, Jeanteur-Lunel MN: Non-penetrating deep sclerectomy (NPDS) with or without collagen device (CD) in primary open-angle glaucoma: middle-term retrospective study. Int Ophthalmol 1996; 20:131-140.
53. Massy J, Gruber D, Muraine M, Brasseur G: Non-penetrating deep sclerectomy in the surgical treatment of chronic open-angle glaucoma. Mid-term results. J Fr Ophthalmol 1999; 22:292-298.
54. Hamard P, Plaza L, Kopel J, et al: Deep nonpenetrating sclerectomy and open angle glaucoma. Intermediate results from the first operated patients. J Fr Ophthalmol 1999; 22:25-31.
55. Bas JM, Goethals MJ: Non-penetrating deep sclerectomy preliminary results. Bull Soc Belge Ophtalmol 1999; 272:55-59.
56. Shaarawy T, Mermoud A: Deep sclerectomy in one eye vs deep sclerectomy with collagen implant in the contralateral eye of the same patient: long-term follow-up. Eye 2005; 19:298-302.
57. Sanchez E, Schnyder CC, Sickenberg M, et al: Deep sclerectomy: results with and without collagen implant. Int Ophthalmol 1996; 20:157-162.
58. Sunaric-Mégevand G, Leuenberger PM: Results of viscocanalostomy for primary open-angle glaucoma. Am J Ophthalmol 2001; 132:221-228.
59. Carassa RG, Bettin P, Fiori M, Brancato R: Viscocanalostomy versus trabeculectomy in white adults affected by open-angle glaucoma: a 2-year randomized, controlled trial. Ophthalmology 2003; 110:882-887.
60. Shaarawy T, Nguyen C, Schnyder C, Mermoud A: Five year results of viscocanalostomy. Br J Ophthalmol 2003; 87:441-445.
61. Kobayashi H, Kobayashi K, Okinami S: A comparison of the intraocular pressure-lowering effect and safety of viscocanalostomy and trabeculectomy with mitomycin C in bilateral open-angle glaucoma. Graefes Arch Clin Exp Ophthalmol 2003; 241:359-366.
62. O'Brart DP, Rowlands E, Islam N, Noury AM: A randomised, prospective study comparing trabeculectomy augmented with antimetabolites with a viscocanalostomy technique for the management of open angle glaucoma uncontrolled by medical therapy. Br J Ophthalmol 2002; 86:748-754.
63. Yalvac IS, Sahin M, Eksioglu U, et al: Primary viscocanalostomy versus trabeculectomy for primary open-angle glaucoma: three-year prospective randomized clinical trial. J Cataract Refract Surg 2004; 30:2050-2057.
64. Luke C, Dietlein TS, Jacobi PC, et al: A prospective randomized trial of viscocanalostomy versus trabeculectomy in open-angle glaucoma: a 1-year follow-up study. J Glaucoma 2002; 11:294-299.
65. Luke C, Dietlein TS, Jacobi PC, et al: A prospective randomised trial of viscocanalostomy with and without implantation of a reticulated hyaluronic acid implant (SKGEL) in open angle glaucoma. Br J Ophthalmol 2003; 87:599-603.
66. Drusedau MU, von Wolff K, Bull H, von Barsewisch B: Viscocanalostomy for primary open-angle glaucoma: the Gross Pankow experience. J Cataract Refract Surg 2000; 26:1367-1373.
67. El Sayyad F, Helal M, El-Kholify H, et al: Nonpenetrating deep sclerectomy versus trabeculectomy in bilateral primary open-angle glaucoma. Ophthalmology 2000; 107:1671-1674.
68. O'Brart DP, Shiew M, Edmunds B: A randomised, prospective study comparing trabeculectomy with viscocanalostomy with adjunctive antimetabolite usage for the management of open angle glaucoma uncontrolled by medical therapy. Br J Ophthalmol 2004; 88:1012-1017.
