Glaucoma Drainage Devices Treatment & Management

The surgical technique for glaucoma drainage device (GDD) implantation is discussed in this section.

Retrobulbar anesthesia or modified topical anesthesia is administered. Systemic anesthesia may include Valium, 10 mg by mouth, 1 hour prior to surgery, followed by intravenous midazolam, 2 grams, and fentanyl, 100 mcg, at the time of surgery. Lidocaine gel insertion or frequent topical anesthetic may be placed 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.

Insertion of Ahmed glaucoma valve

The Ahmed glaucoma valve (AGV) is inserted using a fornix-based conjunctival flap method. A traction suture may be placed through a clear cornea or in the limbal sclera 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 superotemporal or superonasal 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. 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 valve is very delicate and should not be touched with the forceps. The plate is secured 7-8 mm from the limbus using 8-0 or 9-0 nonabsorbable suture.

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 anterior chamber is entered 0.5 mm posterior to the limbus by a 23-gauge 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 tying forceps or specially designed tube 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 anterior chamber 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 may be secured to the underlying sclera with 2 interrupted 10-0 nylon sutures. Some authors have used tissue glue to attach the patch graft and limbal closure.

A conjunctival closure is performed using an 8-0 Vicryl suture or a 9-0 nylon 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 implant

To insert a double-plate Molteno (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 anterior chamber 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 anterior chamber 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 7-0 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 6-8 weeks 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.^[16] 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.

The image below depicts the insertion of a Molteno implant.

Ex-PRESS shunt implantation

Ex-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 anterior chamber. This injection is administered to prevent postoperative hypotony from overfiltration. A 27-gauge needle is used to create a needle tract into the anterior chamber, under the scleral flap, at the limbus. The Ex-PRESS shunt is then placed into the anterior chamber 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.

A study by Seibold et al determined that the Ex-PRESS device moves in the presence of high magnetic fields.^[17] However, the clinical significance of this finding is unclear. Further studies are needed to assess how patients may be affected postimplantation and how they should be counselled in regards to MRI safety.

Gold Micro-shunt implantation

A surgical guide published by the manufacturer indicates that the gold shunt is typically inserted through a scleral incision 4 mm in length, approximately 2.5 mm from the limbus. The device enters the anterior chamber through a scleral tunnel directly above the scleral spur, with the rear tabs placed into the suprachoroidal space.

Difficult conjunctiva

Difficult 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 (eg, 64 blade) can be used to dissect the conjunctiva and the Tenon capsule along with any superficial sclera beyond the scar tissue. Spreading and gently releasing the adhesions of the sclera to the scarred episclera with frequent snips of a Westcott scissors is a safer method of dissection in an eye that has undergone prior surgery. 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.

Hypotensive phase

This 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). See image below.

Hypertensive phase

This 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 phase

Following 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. See image below.

For 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).

Gedde and associates provide the first multicenter, controlled clinical trial examining the efficacy and the outcomes of nonvalved GDDs versus trabeculectomy with mitomycin-C in similar patient populations with previous ocular surgery.^{[14, 15]} They reported a surprising equivalence of intraoperative complications in the two groups. A higher incidence of postoperative complications was encountered in the trabeculectomy group; however, serious complications causing reduced vision and/or the need for reoperation were comparable between the two groups. Gedde and associates also found that the presence of intraoperative or postoperative complications did not increase the risk of treatment failure. This is in contrast to what was found previously by the Advanced Glaucoma Intervention Study (AGIS) study.^[18] The rate of postoperative complications in the tube group was less than has been previously reported.

The most common complications in GDD surgeries are discussed below.

Hypotony

Low IOP (< 5 mm Hg) with a shallow anterior chamber 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, the DPM may 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 anterior chamber develops with lens-cornea touch. In this case, the anterior chamber 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 obstruction

Tube obstruction presents with elevated IOP and deep anterior chamber. 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 retraction

Tube retraction from the anterior chamber 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 anterior chamber.

Hypertensive phase and its management

The 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).^[2] 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.^{[19, 20]}

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.

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.

Diplopia

Diplopia, as a complication, was first noted in detail with the early models of the Baerveldt implant.^{[9, 6, 10]} 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 by a 30-gauge needling procedure followed by digital massage.

Corneal decompensation

The 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 anterior chamber leading to endothelial damage. If tube-corneal touch is noticed, the tube should be repositioned.

Graft failure

GDD 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 anterior chamber 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 exposure

In cases with end plate exposure, a conjunctival autograft can be performed to close the defect, usually with temporary Vicryl ligation of the tube. 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 hemorrhage

Sudden 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 anterior chamber, 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 failure

For 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.

Endophthalmitis

Endophthalmitis following a GDD operation is very rare. Estimates of less than 2% have been reported.^[21] 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.^[22] It has also been reported that the incidence of endophthalmitis is higher in children and following needling of the bleb.^[21]

Loss of vision

Loss 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.

Overall, both the success rates and the complication rates following any glaucoma drainage device (GDD) implantation are similar (see Table below). The choice of the GDD in the treatment of recalcitrant glaucoma depends upon the patient and the surgeon.

Currently, 5 GDDs are available. The Ahmed glaucoma valve (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. No peer-reviewed publications concerning the SOLX shunt are available at this time.

Table. Meta-Analysis of the Glaucoma Drainage Devices* (Open Table in a new window)

Advantages of the valved implants

The 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. On the other hand, GDDs with larger surface areas, such as the double-plate Molteno (DPM) implant and the Baerveldt implant, appear to exhibit a lower incidence of the hypertensive phase and may achieve slightly lower IOP.

Recommendations

The 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. See image below.

The Baerveldt implant and the DPM implant require more extensive dissection, additional operative time, and the use of a stent to avoid postoperative hypotony and a shallow anterior chamber. The larger surface area of the end plate results in larger blebs and lower IOPs.