You are in: eMedicine Specialties > Ophthalmology > INTRAOCULAR PRESSURE Glaucoma, Drainage DevicesArticle Last Updated: Oct 31, 2005AUTHOR AND EDITOR INFORMATIONSection 1 of 10
  Author: Ramesh S Ayyala, MD, FRCS, FRCOphth, Chief, Section of Ophthalmology, Charity Hospital of New Orleans; Director of Glaucoma Services, Assistant Professor, Department of Ophthalmology, Tulane University School of Medicine Ramesh S Ayyala is a member of the following medical societies: American Academy of Ophthalmology and American Medical Association Coauthor(s): Chian Hong, MD, Staff Physician, Department of Ophthalmology, Tulane University Medical Center; Jessica Laursen Duarte, BA, Tulane University Medical School Editors: Bradford Shingleton, MD, Assistant Clinical Professor of Ophthalmology, Harvard Medical School; Consulting Staff, Department of Ophthalmology, Massachusetts Eye and Ear Infirmary; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Louis E Probst, MD, Medical Director of Refractive Surgery, Chicago, Madison, Milwaukee, and Windsor Centers, TLC the Laser Eye Centers; Lance L Brown, OD, MD, Ophthalmologist, Affiliated With Freeman Hospital and St John's Hospital, Regional Eye Center, Joplin, Missouri; Hampton Roy Sr, MD, Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences Author and Editor Disclosure Synonyms and related keywords: glaucoma drainage devices, GDD, GDDs, GDD insertion, Molteno implant, Baerveldt implant, long tube implant, Ahmed glaucoma valve, AGV, Krupin implant, bleb, iridocorneal endothelial syndrome, ICE, neovascular glaucoma, penetrating keratoplasty, PKP INTRODUCTIONSection 2 of 10
  Glaucoma drainage devices (GDDs) create an alternate aqueous pathway by channeling aqueous from the anterior chamber (AC) through a long tube to an equatorial plate inserted under the conjunctiva that promotes bleb formation. GDDs are being used more frequently in the treatment of glaucoma that is not responding to medications and trabeculectomy operations. In certain conditions, such as neovascular glaucoma, iridocorneal endothelial (ICE) syndrome, penetrating keratoplasty (PKP) with glaucoma, and glaucoma following retinal detachment surgery, it is becoming the primary operation. This article outlines the current concepts involving different GDDs, surgical techniques, and management of complications following GDD insertion. History of the ProcedureThe earliest attempt to drain fluid out of the AC into the subconjunctival space at the limbus dates back to 1906 when Rollet and Moreau implanted a silk thread connecting the AC to the subconjunctival space. Since that time, additional unsuccessful attempts were made, including insertion of a polythene tube by Epstein in 1959 and a silicone tube by MacDonald and Pearce in 1965. These operations failed because of excessive scar formation near the limbus, seton migration, and conjunctival erosion. In 1969, Molteno introduced the concept that a large surface area was needed to disperse the aqueous beneath the conjunctiva. He inserted a short acrylic tube that was attached to a thin acrylic plate. The plate was sutured to the sclera close to the limbus. Most of the operations failed after the first 3-6 months because of plate exposure, tube erosion, and scar formation. In 1973, Molteno improved his device with the idea of draining the fluid away from the source to increase the success rate. He introduced the Molteno implant with a long silicone tube attached to a large end plate placed 9-10 mm posterior to the limbus (Molteno, 1976). All the currently available GDDs are based on this concept by Molteno. The Molteno implant and similar implants offer no resistance to the outflow, resulting in hypotony, flat ACs, and choroidal effusions. Since then, 2 major concepts have been introduced to modify the GDD. The first concept was that of a valve to offer resistance to the outflow, thereby reducing the incidence of postoperative hypotony. In 1976, Theodore Krupin developed a pressure-sensitive, unidirectional valve that provides resistance to the flow of aqueous and prevents early postoperative hypotony. This "slit valve" is designed to open at a pressure of 11 mm Hg and to close at a pressure of 9 mm Hg. In 1993, Mateen Ahmed introduced the Ahmed glaucoma valve (AGV), a pressure-sensitive, unidirectional valve that is designed to open when the intraocular pressure (IOP) is 8 mm Hg (Ayyala, 1998; Huang, 1999; Topouzis, 1999). The second major change has been the realization that by increasing the surface area of the end plate, the surface area of drainage could be increased, resulting in lower IOPs (Freedman, 1992; Lloyd et al, 1994; Smith et al, 1992). In 1981, Molteno introduced the double plate implant with a surface area of 270 mm2. In 1992, George Baerveldt introduced a nonvalved silicone tube attached to a large barium-impregnated silicone plate with a surface area of 250 mm2, 350 mm2, or 500 mm2 (Mills, 1996; Smith, 1993; Lloyd, 1994; Siegner, 1995; Nguyen, 1998). More recently, Optonol Ltd introduced the Ex-PRESS R50 glaucoma shunt in an attempt to simplify the GDD implantation. This device is a single-piece, stainless steel, translimbal implant that is placed using an inserter. Although its ease of implantation is greatly desired, its long-term efficacy and risk of complications have yet to be determined. Current glaucoma drainage devicesCurrent GDDs can be classified into those with no resistance, those with resistance, and those with variable resistance to aqueous outflow. GDDs with no resistance These GDDs consist of a silicone tube attached to an end plate that acts as a surface for bleb formation. Unless the operation is modified with a stent and ripcord technique, these implants are associated (in the early postoperative period) with a high incidence of overfiltration secondary to no aqueous outflow resistance. This can lead to hypotony, shallow-to-flat ACs, and choroidal effusions.
GDDs with set resistance Even though manufacturers claim that these devices contain true valves, independent examinations of the flow characteristics for these devices suggest a wide divergence between observed function and the manufacturers' claims. The valves appear not to close after initial opening in perfusion tests at physiological flow rates. Of the 2 valved devices that are used commonly, the AGV has the lowest incidence of hypotony of all GDDs. The AGV is a silicone tube connected to a silicone sheet valve held in a polypropylene body. The end plate measures 185 mm2 (16 mm long X 13 mm wide X 1.9 mm thick). The valve consists of thin silicone elastomer membranes (8 mm long X 7 mm wide) and creates a venturi-shaped chamber. The inlet cross-section of the chamber is wider than the outlet (Bernoulli principle), with a resultant pressure differential between the AC and the bleb. The valve is designed to open when the IOP is 8 mm Hg. The Krupin slit valve consists of a silicone tube with a slit valve attached to a silicone oval end plate. The surface area of the end plate is 180 mm2. The opening pressure of the slit valve is designed to be 11-14 mm Hg, and the closing pressure is designed to be 2 mm Hg. Unfortunately, these opening and closing pressures may vary significantly. GDDs with variable resistance These devices are modifications of the original Molteno implant and the Baerveldt implant. They attempt to incorporate a resistance mechanism dependent on tissue apposition to limit flow. Because the force of tissue apposition is variable, these devices do not function as true valves, and IOP levels remain unpredictable. The Molteno dual ridge device (Molteno with a pressure ridge) attempts to limit the initial drainage area by dividing the top portion of the plate into 2 separate spaces with the help of a thin V-shaped ridge. Aqueous must overcome the overlying conjunctival resistance to flow across the ridge. The resistance offered by the overlying conjunctiva presumably prevents overfiltration and hypotony. In the authors' experience, these complications are not prevented by the pressure ridge mechanism, so the authors still recommend a stent with ripcord modification. The Baerveldt bioseal is a flap that overhangs the silicone tube as it opens on the end plate. Apposition of the bioseal element to the sclera with absorbable sutures is supposed to provide early flow resistance, limiting initial aqueous escape from beneath the device. However, early clinical trials failed to prove this concept, and this modification was discontinued. INDICATIONSSection 3 of 10
The indications for GDD implantation include the following:
CONTRAINDICATIONSSection 4 of 10
Contraindications are discussed in relevant sections. TREATMENTSection 5 of 10
Surgical therapyThe surgical technique for GDD implantation is discussed in this section. Preoperative detailsRetrobulbar anesthesia or modified topical anesthesia is administered. Valium, 10 mg by mouth, is given 1 hour prior to surgery, followed by intravenous midazolam, 2 grams, and fentanyl, 100 mcg, at the time of surgery, followed by lidocaine gel insertion into the inferior fornix. Following Betadine prep and limbal stay suture placement, a sub-Tenon injection of preservative-free 1% lidocaine mixed with 1 in 10,000 epinephrine is administered through limbal peritomy in the quadrant of the operation. In patients who are sensitive to anesthesia, the lidocaine mixture can be injected into the muscle cone via the sub-Tenon space. Intraoperative detailsInsertion of Ahmed glaucoma valveThe AGV is inserted using a fornix-based conjunctival flap method. First, a traction suture is placed through a clear cornea close to the 12-o'clock position so the eye can be easily rotated and stabilized inferiorly by securing the suture to the drape with a hemostat. With the eye properly placed, a limbal peritomy is made at the 12-o'clock position. The incision is extended to the superiotemporal or superionasal quadrant to ultimately cover 3-4 clock hours. A 27-gauge cannula is used to inject preservative-free 1% lidocaine mixed with 1 in 10,000 epinephrine as far posteriorly as possible to create a sub-Tenon pocket. This technique provides the necessary anesthesia while preventing excessive bleeding. It also helps in dissecting the sub-Tenon tissue in a nontraumatic fashion before the Westcott scissors are inserted to lyse adhesions and to continue the dissection. At this point in the procedure, bleeding can first be encountered. A dry Weck-cel sponge is inserted as far posteriorly as possible to provide hemostasis and to allow further dissection of the sub-Tenon pocket. Bleeding control is accomplished by light cautery used in conjunction with topical 1% lidocaine mixed with epinephrine drops. Warning patients that they may expect some degree of discomfort during the cautery phase is important. After priming the AGV with balanced salt solution (BSS), using a 30-gauge cannula, the end plate is gently tucked into the sub-Tenon pocket with the tips of a nontoothed forceps held perpendicular to the plate or by holding the islet of the end plate. The plate and the valve are very delicate and should not be touched with the forceps. The smallest dents may attract fibroblasts and promote scar tissue formation, thus occluding the valve and causing a failure. The plate is secured 7-8 mm from the limbus using 10-0 nonabsorbable sutures. At this time, the hemostat holding traction is released and the eye is returned to its natural position. The silicone tube is cut with the Westcott scissors 1-1.25 mm anterior to the limbus. Then, the AC is entered 0.5 mm posterior to the limbus by a 23-gauge butterfly needle directed parallel to and just anterior to the iris plane. The entry point should be posterior to the Schwalbe line and anterior to the iris plane. This will minimize the risk of corneal decompensation. Easy insertion of the tube is accomplished by grasping the anterior lip with 0.12 mm forceps as the needle is withdrawn and by grasping the silicone tube close to the tip with angled smooth forceps. Problems during the tube insertion can be avoided by holding the tube in the same direction as the needle tract. In some cases, injecting viscoelastic substance into the AC and into the needle tract can facilitate the insertion of the tube by pushing the iris away from the tube. Before the human donor patch graft is placed, the silicone tube is secured to the underlying sclera with a figure-of-eight 10-0 nylon suture. The graft is placed with one end along the limbus and secured to the underlying sclera with 2 interrupted 10-0 nylon sutures. Then, the graft is shaped using the Stevens scissors. Further securing of the graft is done with 2 posterior sutures, which also prevents the bleb from migrating anteriorly. A conjunctival closure is performed using 10-0 Vicryl suture on a spatulated needle. The conjunctiva on each side of the peritomy is secured to the underlying sclera to prevent leaks. The middle portion is secured to the cornea with a horizontal mattress suture. Insertion of double-plated Molteno or Baerveldt implantTo insert a DPM, a fornix-based conjunctival flap involving the superior half is created between the medial and lateral rectus muscles. The rectus muscles are identified. The DPM is irrigated with saline solution to verify patency. A 4-0 nylon stent is inserted into the silicone tube. The end plates are secured to the sclera 7-8 mm from the limbus in the supratemporal and supranasal quadrants with a 9-0 suture. The authors do not attempt to insert the connecting silicone tube underneath the superior rectus. The AC is entered 0.25 mm posterior to the corneoscleral limbus with a 23-gauge needle; the needle tract is anterior and parallel to the iris plane. The silicone tube is trimmed, so the bevel faces the corneal endothelial surface, flush with the nylon stent, and then is inserted into the AC through the needle tract. A human donor scleral patch graft is placed on the tube with the anterior edge adjacent to the limbus, and it is sutured to the sclera with a 10-0 nylon suture. A 10-0 nylon figure-of-eight suture is tied around the tube and anchored to the episclera between the end plate and the posterior edge of the scleral patch graft. This suture can be lasered in the postoperative period if the IOP is considered to be high. The long end of the 4-0 nylon stent is passed underneath either the lateral rectus muscle or the medial rectus muscle, depending upon the side, and is tucked into the subconjunctival space inferiorly. The conjunctiva is secured to the limbus with interrupted 10-0 nylon sutures. The technique of ripcord suture with a 4-0 nylon stent can be used with all nonvalved implants, such as Baerveldt and Molteno. Some surgeons prefer to tie the tube tightly with a Vicryl suture and to create a slit vent anterior to it with a sharp blade. This technique allows some fluid to escape from the vent, maintaining a low IOP and, at the same time, allowing time for the bleb to form around the end plate. The other modification of this technique is to combine the ripcord with an orphan trabeculectomy to control the IOP in the first 6 weeks. Topical steroids and antibiotics, along with cycloplegic agents, are used for at least 2 months after the operation. Several studies have shown that no significant difference exists in complications or in the success of the operation with the use of mitomycin-C at the time of the operation (Kurnaz et al, 2005). In fact, it may lead to conjunctival melts and leaks. The single-plate Molteno implant, Krupin valve, and Baerveldt implant are inserted in a similar fashion to the AGV; however, with the Baerveldt implant, the end plate is tucked underneath the adjacent rectal muscles. Ex-PRESS shunt implantationEx-PRESS shunt insertion via the subconjunctival dissection is associated with a high failure rate secondary to subconjunctival fibrosis and complications, such as hypotony and conjunctival erosion with the risk of endophthalmitis. In select patients, using the Ex-PRESS shunt under the scleral flap appears to result in good IOP control while avoiding complications. The technique involves limbal peritomy and a 3 X 3-mm partial thickness scleral flap. Sponge pieces soaked in the desired concentration of mitomycin-C should be placed under the scleral flap and the conjunctiva for the desired time, followed by copious irrigation similar to a trabeculectomy operation. Paracentesis is performed in the temporal quadrant followed by an injection of a high molecular weight viscoelastic substance into the AC. This injection is administered to prevent postoperative hypotony from overfiltration. A 27-gauge needle is used to create a needle tract into the AC, under the scleral flap, at the limbus. The Ex-PRESS shunt is then placed into the AC through the needle tract, with the rim being flush with the scleral bed. The scleral flap is secured to the surrounding sclera with 2 interrupted 10-0 nylon sutures (moderately tight). The conjunctiva is secured to the limbus with interrupted 10-0 Vicryl sutures. This technique has the advantages of preventing complications related to overfiltration and conjunctival erosion and, at the same time, providing good postoperative IOP control. Difficult conjunctivaDifficult conjunctiva is one of the major problems facing the surgeon during glaucoma surgery. The conjunctiva may be scarred, tight, and/or button holed. Prevention is always best, so performing primary ocular surgery away from the 12-o'clock limbal position is important in patients with a history of glaucoma, as this can cause scarring at the location of future trabeculectomy or GDD surgeries. In GDD cases with extensive conjunctival scar tissue extending several millimeters from the limbus, a dull blade, such as a 64 blade, can be used to dissect the conjunctiva and the Tenon capsule along with any superficial sclera beyond the scar tissue. At this point, further dissection can commence as usual at the sub-Tenon plane. If the conjunctiva is too tight, securing the conjunctiva to the limbus after inserting the end plate of the GDD may be difficult. Several techniques can be used to overcome this problem. If minimal shortening (1-2 mm) is present, the limbal peritomy can be extended by 2 mm into a quadrant with loose conjunctiva and then pulled back and secured. If more length is needed (3-5 mm), partial-thickness, relaxing incisions may be made close to the fornix. This is accomplished using a 64 blade on taut conjunctiva. Staying in the superficial conjunctiva and not extending into the Tenon tissue is important. Two or three of these incisions may safely be performed. In the worst cases, the conjunctiva may be anchored directly to the scleral patch covering the GDD end plate as close to the sclera as possible. The conjunctiva will grow over the scleral graft in 3-6 weeks. Button holes are an unfortunate consequence that can occur during any glaucoma surgery. Even careful handling and diligent dissection cannot prevent button holes from occurring in delicate conjunctiva. Small holes can be closed with 10-0 sutures on a BV needle. If the conjunctiva is extremely delicate allowing holes at suture sites, a double folding technique may be used. The conjunctiva posterior to the leak is anchored to the limbus and adjacent cornea with a mattress suture. This double fold covers the suture leak and heals nicely. A large hole can be anchored to the scleral patch itself and the conjunctiva will grow over the exposed graft in 3-6 weeks. Postoperative detailsHypotensive phaseThis phase lasts from day 1 to 3-4 weeks following the operation. During this phase, the bleb appears to be diffuse and thick-walled with minimally engorged blood vessels. The IOP is low (ie, from 2-3 mm Hg to 10-12 mm Hg). Hypertensive phaseThis phase begins 3-6 weeks after the operation and lasts for 4-6 months. The bleb becomes visibly inflamed and dome shaped and, in some cases, is associated with increased IOP to greater than 30 mm Hg. The incidence of the hypertensive phase appears to be increased with the AGV as compared to the Baerveldt implant or the DPM. This increased incidence could be explained because of the larger surface area of the Baerveldt implant and the DPM or because of different biomaterials being used in the different implants. Stable phaseFollowing the hypertensive phase, this phase is characterized by stabilization of the IOP in the mid-to-high teens. At this time, the blebs are supposed to maintain IOP for the rest of the patient's lifetime; however, in reality, more than 50% of blebs fail by the end of 5 years. The bleb appears as a thick-walled, dome-shaped, elevated area overlying the end plate with no associated inflammation. Follow-upFor excellent patient education resources, visit eMedicine's Glaucoma Center and Eye and Vision Center. Also, see eMedicine's patient education articles Glaucoma FAQs and Subconjunctival Hemorrhage (Bleeding in Eye). COMPLICATIONSSection 6 of 10
HypotonyLow IOP ( <5 mm Hg) with a shallow AC in the immediate postoperative phase may be related to overfiltration, wound leak, and/or choroidal effusions. The incidence of hypotony, mainly from overfiltration, is 20-30% higher with nonvalved implants in the absence of the ripcord technique or stent insertion. The incidence of hypotony is much less with the AGV (9%) than with any other GDD. However, in the authors' experience, the DPM can also achieve similar results, providing the operation is performed with a stent and a 10-0 nylon stay suture around the tube. Hypotony from overfiltration generally does not require any treatment unless a flat AC develops with lens-cornea touch. In this case, the AC has to be reformed with a viscoelastic agent. In persistent cases, the GDD may have to be revised. Persistent wound leak, especially at the limbus, caused by conjunctival retraction should be treated by securing the conjunctiva to the limbus with interrupted sutures. Choroidal effusions may be treated with topical and/or oral prednisone. However, if the choroidal effusions are kissing and/or involving the macula, they must be drained surgically. Tube obstructionTube obstruction presents with elevated IOP and deep AC. The obstruction may be caused by blood, fibrin, vitreous, or iris plug, or it could be related to a tight external ligature around the tube. In the case of blood or fibrin clot, intracameral injection of 5-10 mg of tissue plasminogen activator (TPA) in 0.1 mL of BSS can be injected. Watch for recurrent hemorrhage after TPA injection. Vitreous incarceration can be severed with Nd:YAG laser. Iris incarceration into the tube can be reversed by peripheral argon laser iridoplasty (applied to the base of the plug). A tight external ligature can be cut with argon laser. Tube retractionTube retraction from the AC should be confirmed by gonioscopy and can be corrected by attaching an extender sleeve tube with a larger diameter over the preexisting tube to lengthen it. If the anterior portion of the tube is found to be too short at the time of surgery, the end plate should be moved more anteriorly to the limbus to allow enough of the tube in the AC. Hypertensive phase and its managementThe incidence of the hypertensive phase is higher with the AGV as compared to the DPM or the Baerveldt implants. This may be related to the larger surface area of the DPM (270 mm2) and the Baerveldt implant (350 mm2 or 500 mm2) as compared to the AGV (185 mm2) (Ayyala, 1998). The higher incidence of the hypertensive phase with the AGV may also be related to the biomaterial and the shape and consistency of the end plate (Ayyala et al, Arch Ophthalmol, 2000; Ayyala, Surv Ophthalmol, 2000). Even though the DPM and the AGV are made of the same biomaterial (polypropylene), the shape and consistency of the end plates are very different. For example, the AGV end plate is extremely rigid; therefore, it may exhibit more micromotion in the postoperative period, resulting in more inflammation and increased IOP. On the other hand, the ridged, disc-shaped end plates of the DPM are more flexible and may be more stable on the scleral surface. Also, the ridge may prevent the fibrous capsule from growing directly on the implant. The smooth surface of the AGV end plate seems to attract white cells and collagen to grow on its surface, which can lead to a failed bleb. During the hypertensive phase, when the IOP is considered by the physician to be too high (usually >21 mm Hg), antiglaucoma medications, along with digital massage, are indicated. In those patients who do not respond, needling of the bleb is indicated. Needling of the bleb is performed in an outpatient clinic, as follows:
Frequently, a change in the appearance of the bleb is seen during or soon after needling, with the size increasing and the bleb becoming less tense. When 5-fluorouracil is injected (5 mg in 0.1 cc), it is administered into the subconjunctival space in the inferior fornix, away from the site of the bleb. A slit lamp examination with Seidel test is performed 30-60 minutes later. Patients are instructed to use topical antibiotics with steroid drops and usually are seen again in 3-5 days. Some eyes need repeat needling for recurrence of fibrosis. As many as 3-5 separate needlings can be completed over a period of 3-4 months (Ayyala, 1998). In patients with the DPM or the Baerveldt with the stent who are not responding to topical medications, the 10-0 nylon ripcord suture can be lasered and/or the 4-0 nylon stent pulled by making a small incision of the overlying conjunctiva in the inferior fornix. This usually results in a dramatic decrease in IOP, especially in the first 2-4 weeks after the operation. DiplopiaThis complication was first noted in detail with the early models of the Baerveldt implant (Smith, 1993; Lloyd, 1994; Siegner, 1995). The occurrence of diplopia and strabismus was significantly higher (18%) with the Baerveldt implant than with the AGV or the Molteno implant (3% and 2%, respectively). This difference is attributed to the unique design of the Baerveldt implant, because of the placement of the reservoir plate beneath the 2 adjacent rectus muscles. The resulting bleb incorporates the overlying rectus muscles and muscle sheath, leading to extraocular muscle imbalance and diplopia. Modifications of the Baerveldt end plate with fenestrations have minimized these results. Persistent diplopia might require the removal of the implant. Other implants may also cause diplopia if the height of the reservoir pushes down the eye. This height could be reduced with the needling procedure followed by digital massage. Recently, the authors were successful with this technique in one patient who developed diplopia following insertion of an AGV. Corneal decompensationThe incidence of corneal decompensation appears to be similar following all GDDs (10-20%), but the etiology remains unknown. Corneal decompensation could be related to tube-corneal touch and chronic low-grade inflammation from the presence of the silicone tube in the AC leading to endothelial damage. If tube-corneal touch is noticed, the tube should be repositioned. Graft failureGDD surgery appears to be associated with a high incidence of graft failure (10-51%; average, 36.2%) in patients with corneal graft associated with glaucoma. The cause for this failure is multifactorial. The presence of underlying chronic inflammation, extensive peripheral synechiae, and multiple previous surgeries may compromise the graft. The timing of GDD surgery is another factor. A trend toward a higher incidence of graft failure exists when seton surgery is performed after PKP. This may simply reflect the poor graft prognosis associated with any intraocular surgery. The introduction of a GDD into the AC may also be associated with increased inflammation and may compromise the graft. In these cases, topical steroids should be used for prolonged periods to prevent graft rejection. Tube and end plate exposureIn cases with end plate exposure, conjunctival autograft can be performed to close the defect. A pericardial patch graft sutured to the Tenon capsule can be used in some cases. If the tube is exposed, a scleral or pericardial patch graft may be used to cover the tube, followed by a conjunctival autograft. In some cases, the area of the conjunctival melt is too large or the autograft fails. The GDD may have to be removed at this time. Suprachoroidal hemorrhageSudden excruciating pain with increased IOP in the operated eye either during the operation or in the postoperative period might indicate a suprachoroidal hemorrhage. Clinical signs include a shallow AC, increased IOP, and choroidal elevations that appear darker than choroidal effusions. B-mode ultrasonography is helpful in making this diagnosis. The incidence of suprachoroidal hemorrhage among the different GDDs is similar. Management of suprachoroidal hemorrhage includes supportive therapy, followed by topical and oral steroids, glaucoma medications, cycloplegic agents, and pain medications. Indications for drainage include intractable pain, involvement of the macula by the hemorrhage, kissing choroids, and cornea-lens touch. Late failureFor most GDDs, the Kaplan-Meier estimated probability of success is 70-80% at 12 months following surgery and is 40-50% at 36-48 months following surgery. Multiple reasons for late failure exist, including chronic low-grade inflammation leading to fibrosis of the bleb, fibrosis of the valve or the outlet of the nonvalved implants, extrusion of the end plate or the tube from conjunctival melt, or infection. The fibrosis of the bleb could be triggered by another operation, such as cataract surgery. It also may be related to the biomaterial of the end plate, micromotion of the end plate with ocular movements, and blinking. EndophthalmitisEndophthalmitis following a GDD operation is very rare. Estimates of less than 2% have been reported (Al-Torbak et al, 2005). Early bleb-associated endophthalmitis is typically caused by host flora, whereas late bleb-associated infection may be caused by transconjunctival migration of bacteria, especially through thin-walled blebs or areas of aqueous leakage (Gedde et al, 2001). It has also been reported that the incidence of endophthalmitis is higher in children and following needling of the bleb (Al-Torbak et al, 2005). Loss of visionLoss of vision by 2 or more lines can occur in 20-40% of patients following GDD surgery. This may be related to the various complications listed above, such as suprachoroidal hemorrhage, corneal edema, and endophthalmitis. It may also be secondary to the formation of cataracts, the progression of glaucoma, band keratopathy, and cystoid macular edema. OUTCOME AND PROGNOSISSection 7 of 10
Overall, both the success rates and the complication rates following any GDD implantation are similar (see Table). The choice of the GDD in the treatment of recalcitrant glaucoma depends upon the patient and the surgeon. Currently, 5 GDDs are available. The AGV and the Krupin implant offer resistance to the outflow in the form of a sheet valve and a slit valve, respectively. The Molteno implant and the Baerveldt implant offer no resistance to the outflow and may lead to hypotony; however, the problem can be overcome using the ripcord technique. Long-term success and complications associated with the Ex-PRESS shunt have yet to be demonstrated. Meta-Analysis of the Glaucoma Drainage Devices*
*Values are based on the weighted mean of the published studies in the respective GDD group. For mean percentages, standard deviations are shown in parentheses. NR = not recorded Advantages of the valved implantsThe advantages of the valved implants, especially of the AGV, appear to be easy insertion following 1-quadrant dissection and low incidence of hypotony in the immediate postoperative phase. However, it is associated with a high incidence of the hypertensive phase (as much as 80%) that occurs 1-3 months after the operation and may require needling with 5-fluorouracil injections. On the other hand, GDDs with larger surface areas, such as the DPM implant and the Baerveldt implant, appear to exhibit a lower incidence of the hypertensive phase and may achieve slightly lower IOP. Overall, the success rate and complications, including corneal decompensation, appear to be similar in all GDDs. The authors prefer the AGV in cases with mild-to-moderate glaucomatous optic nerve damage. Cases with more advanced optic nerve damage need more significant pressure reduction. Therefore, larger surface area implants, such as the DPM implant and the Baerveldt implant, are preferred. The surgeon should take intraoperative precautions to decrease the incidence of postoperative hypotony and shallow ACs. Topical steroids should be used liberally and for prolonged periods of time following the operation. RecommendationsThe AGV is easy to insert, has 1-quadrant dissection, requires less operative time as compared to other GDD operations, and has a low incidence of hypotony in the postoperative period. The AGV has a higher incidence of the hypertensive phase postoperatively that might require additional glaucoma medications or needling of the bleb. This implant is ideal for patients with diseases presenting with high IOP and minimal damage to the optic nerve, such as neovascular glaucoma, PKP with glaucoma, glaucoma following retinal detachment surgery, and uveitic glaucoma. The DPM implant requires a more extensive dissection, additional operative time, and the use of a stent to avoid postoperative hypotony and a shallow AC. The larger surface area of the end plate results in larger blebs and lower IOPs. The DPM implant is reserved for patients with advanced glaucomatous optic nerve damage. FUTURE AND CONTROVERSIESSection 8 of 10
The ideal GDD has yet to be developed. The design should include the following:
The end plate should be made of a totally inert biomaterial and should not attract fibroblast or protein deposits, which could lead to cytokine release with chronic low-grade inflammation and bleb failure. Soft and flexible end plates attract less inflammation compared to rigid end plates based on laboratory studies. The rigid end plates potentially can exhibit another factor, namely micromotion, which could stimulate chronic low-grade inflammation and contribute to bleb failure in the long term. Future research should be directed toward minimizing the fibrous reaction around the bleb with new drugs that target the inflammatory factors (Ayyala, 2001; Ayyala, 2000; Lim, 1998). MULTIMEDIASection 9 of 10
REFERENCESSection 10 of 10
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