Surgical Technique 3 (Ahmed Glaucoma Valve Drainage Implant)

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Surgical Technique 3 (Ahmed Glaucoma Valve Drainage Implant) JOHN W BOYLE IV, J RYAN McMANUS and PETER A NETLAND

Summary The Ahmed Glaucoma Valve is designed to drain aqueous humor from the anterior chamber through a silicone tube and across flow-resistant valve mechanism, and then onto a silicone or polypropylene plate located posterior to the limbus. The incorporation of a flow-resistant valve in the design of the Ahmed Glaucoma Valve distinguishes this implant from other open-tube designs, including the Baerveldt and Molteno implants. During the early postoperative period, the valve mechanism may minimize the incidence of hypotony and its associated complications, such as choroidal effusions, shallow or flat anterior chamber, and suprachoroidal hemorrhage. Visionthreatening complications are uncommon after Ahmed Glaucoma Valve implantation. The Ahmed Glaucoma Valve, like other glaucoma drainage implants, is effective for the treatment of patients who have a variety of refractory or intractable glaucomas, including failure to respond to trabeculectomy, extensive conjunctival scarring, or poor prognosis of trabeculectomy for primary surgery. The potential for broader use of the Ahmed Glaucoma Valve, including use for primary surgery, is under investigation.

Venturi-shaped chamber (Fig. 113-2). The elastic membranes of the valve are closed at pressures below 8–12 mmHg and open to allow flow when pressures are higher. In this way, the device is designed to reduce the problem of hypotony due to over-filtration. In vitro and in vivo studies have confirmed the ability of the Ahmed Glaucoma Valve to restrict flow by this valved mechanism.1–3 The end plate of the Ahmed Glaucoma Valve is available in several sizes and materials (Box 113-1). A firm polypropylene plate is used in the single-plate (S2 model) and the double-plate (B1 model). A more flexible silicone plate is used in the flexible single-plate (FP7 model) and the flexible double-plate (FX1 model). The double-plate Ahmed Glaucoma Valves allow for greater surface area for aqueous drainage, and may be implanted on either the right or left side of the eye. Both single-plated models (S2 and FP7) exist in smaller sizes (S3 and FP8) intended for pediatric patients, although many surgeons prefer to use adult-size implants in their pediatric patients.4

Indications Introduction Glaucoma drainage implants can be characterized as either resistance (valved) or non-resistance (non-valved) devices. The Molteno and Baerveldt implants are non-valved devices that drain aqueous from the anterior chamber through an open, unobstructed tube. The Ahmed Glaucoma Valve (New World Medical, Rancho Cucamonga, CA), introduced in 1993, was developed to address the problem of uncontrolled flow in nonresistance devices. It is the most frequently implanted resistance glaucoma drainage device. After placement of the Ahmed Glaucoma Valve, aqueous humor is directed out of the anterior chamber through a tube and across a flowrestricting valve before exiting onto a plate, which is implanted under the conjunctiva and Tenon’s capsule, posterior to the limbus.

Device The Ahmed Glaucoma Valve consists of a silicone tube attached to a valve mechanism on an end plate (Fig. 113-1). The valve is comprised of two thin silicone elastomer membranes (8 mm long × 7 mm wide) positioned in a

The indications for implantation of the Ahmed Glaucoma Valve are the same as other glaucoma drainage implants (Box 113-2). The indications include eyes which have previously failed or are at high risk of failing a trabeculectomy. Use of the implant for primary surgery can also be considered, though this is considered controversial by some.

HIGH RISK OF TRABECULECTOMY FAILURE Eyes that have previously failed trabeculectomy or have inadequate pressure control after trabeculectomy are considered higher risk for failure of a second trabeculectomy. In these eyes, drainage implants are a useful surgical option. Drainage implants should also be considered in eyes in which the conjunctival conditions confer a very high risk of trabeculectomy failure. These conditions may occur due to scarring from previous surgical procedures, severe ocular surface disease or injuries, or other conditions. Implantation of the Ahmed Glaucoma Valve may be performed even in the setting of extensive conjunctival scarring. In other instances, the patient’s underlying ocular pathology confers a high risk of trabeculectomy failure. This is the case with neovascular glaucoma, uveitic glaucoma, iridocorneal endothelial (ICE) syndrome, epithelial downgrowth, and pediatric glaucomas. In these settings, surgeons may choose to implant the Ahmed Glaucoma Valve rather than 1071

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Box 113-2  Indications for Ahmed Glaucoma Valve Failed trabeculectomy Likely failure of trabeculectomy, including: Extensive conjunctival scarring Neovascular glaucoma Uveitic glaucoma Glaucoma associated with penetrating keratoplasty ICE syndrome Epithelial downgrowth Refractory pediatric glaucoma Glaucoma following retinal detachment surgery Primary surgery* *Currently under investigation. Figure 113-1  Ahmed Glaucoma Valve, Model S-2. The arrow shows the direction of aqueous flow. (Modified from photograph provided by New World Medical, Inc., Rancho Cucamonga, CA.)

A

B

Contraindications

C

Figure 113-2  Components of the Ahmed Glaucoma Valve. (A) The valve cover and upper part of the Venturi-style chamber. (B) Silicone tube and elastomer membrane. (C) The plate, containing the lower part of the Venturi-style chamber.

Box 113-1  Surface area of Ahmed Glaucoma Valve implants MATERIAL

MODEL

SIZE

Polypropylene

S2 B1 S3 FP7 FX1 FP8

184 mm2 364 mm2 96 mm2 184 mm2 364 mm2 96 mm2

Silicone

implantation with primary trabeculectomy. A randomized, prospective trial comparing trabeculectomy to the Ahmed Glaucoma Valve for primary surgery has been reported.5,6 In this trial, the trabeculectomy group had lower intraocular pressures during the first year, but the two groups had similar intraocular pressure control and success rates at an average follow-up of 31 months. Surgeons may also wish to extrapolate from the Tube Versus Trabeculectomy study, which found Baerveldt implantation to have a similar intraocular pressure, lower failure rates, and lower reop­ eration rates at 5 years when compared to trabeculectomy with MMC.7

perform trabeculectomy in order to improve the likelihood of long-term success.

PRIMARY SURGERY Generally, the Ahmed Glaucoma Valve is used for primary surgery when the surgeon judges a trabeculectomy likely to fail. However, several studies have compared primary

There are no absolute contraindications for implantation of the Ahmed Glaucoma Valve. Glaucoma drainage implants are relatively contraindicated in patients who are noncompliant with self-care in the postoperative period. The American Academy of Ophthalmology’s report on glaucoma drainage implants warns that the primary longterm complication of anterior chamber tubes is decompensation of the corneal endothelium,8 so care should be taken before implanting drainage implants in eyes with impaired endothelial function.

Surgical Technique Local anesthetic is administered, which may be retrobulbar, parabulbar, or peribulbar. A 6/0 silk or polyglactin traction suture on a spatulated needle is placed through the corneal stroma adjacent to the quadrant chosen for implantation and the eye is rotated to achieve maximal exposure (Video 113-1). The Ahmed Glaucoma Valve is most often placed in the superotemporal quadrant and the plate positioned approximately 8 mm posterior to the limbus. Care should be taken when implanting in the superonasal quadrant because of proximity of the plate to the optic nerve and risk of inducing a Brown’s syndrome.9,10 In the chosen quadrant, a fornix-based incision is made through the conjunctiva and Tenon’s capsule. Radial relaxing incisions on one or both sides of the conjunctival flap

113  •  Surgical Technique 3 (Ahmed Glaucoma Valve Drainage Implant)

are often added to improve surgical exposure. Blunt scissors are used to dissect between the episclera and Tenon’s capsule. Gentle blunt dissection continues posteriorly under Tenon’s capsule to create a pocket between the rectus muscles. Wet-field cautery is often used near the limbus to achieve hemostasis. Prior to implantation, the implant should be examined and primed (Fig. 113-3). The device’s sterilization process may cause the valve membranes to adhere to one another. Intraoperative priming of the valve with balanced salt solution though a 27- or 30-gauge cannula ensures the patency of the valve mechanism. The anterior edge of the plate is grasped manually or with non-toothed forceps and inserted into the pocket between the rectus muscles (Fig. 113-4). Care should be taken not to touch the valve mechanism with instruments during insertion, as this may damage the device.11 The valve is positioned 8–9 mm posterior to the limbus, and the plate is anchored to the sclera with 8/0 nylon, 9/0 nylon, or a similar permanent suture on a spatulated needle though the openings on the anterior edge of the plate.

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The drainage tube is extended over the cornea and then cut to a length which will allow the tube to extend 2–4 mm into the anterior chamber (Fig. 113-5). A 23-gauge needle is then used to make a track beginning approximately 0.5 mm posterior to the limbus and extending into the anterior chamber parallel to or angling slightly forward of the iris plane (Fig. 113-6). Some surgeons inject viscoelastic as the needle leaves the eye in order to lubricate this needle track. The 23-gauge track is an appropriate size to allow tube entry but minimize leakage around the tube. Entry into the anterior chamber posterior to Schwalbe’s line and anterior to the iris plane will minimize the risk of contact with the cornea or iris. The drainage tube is inserted into the anterior chamber through the needle track using nontoothed forceps or a specially designed tube inserter (New World Medical, Inc., Rancho Cucamonga, CA) (Fig. 113-7). The tube is then loosely secured to the sclera using a single

Figure 113-5  The tube is cut to the appropriate length, usually to extend 2–3 mm into the anterior chamber. For anterior chamber placement of the tube, the bevel of the cut tube is ‘up’ (anterior). Figure 113-3  Before implantation of the Ahmed Glaucoma Valve, the device is primed with balanced salt solution to ensure proper functioning of the valve mechanism.

Figure 113-4  The device is inserted in a quadrant, taking care to avoid damaging the valve mechanism. During insertion, avoid grasping the valve mechanism with forceps.

Figure 113-6  A 23-gauge needle is used to prepare a needle track for tube insertion. Larger openings allow aqueous leakage around the tube, whereas tube insertion is difficult or not possible through smaller openings.

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procedure to reform the anterior chamber with balanced salt solution, if necessary. Subconjunctival steroids and antibiotics are injected in a quadrant, preferably 180° away from the plate. Depending on the type of anesthesia used, an ointment containing antibiotic and steroid is applied to the eye, and it is lightly patched and shielded until postoperative day one.

MODIFICATIONS

Figure 113-7  The silicone tube is inserted into the anterior chamber through the needle track.

Figure 113-8  The tube is covered with pericardium, sclera, or other suitable patch material, which is anchored with two or more interrupted sutures.

9/0 or 10/0 nylon suture with care taken to avoid compression. To prevent erosion of the tube through the conjunctiva near the limbus, a patch graft is sutured over the tube (Fig. 113-8). Processed pericardium (Tutoplast; New World Medical, Inc., Rancho Cucamonga, CA; or IOP, Inc., Costa Mesa, CA) is the most commonly used patch graft, but other materials, including preserved donor sclera or cornea, fascia lata, or dura may be used. Both corners of the conjunctival flap are then reapproximated to the limbus. The anterior edge of the conjunctiva may also need to be sutured to the limbus anterior to the patch graft. For conjunctival closure, monofilament 9/0 polyglactin suture is preferred over braided 8/0 polyglactin because it has a smaller diameter but a higher tensile strength. Relaxing incisions are also closed using the same suture in a continuous or interrupted manner. A temporal clear corneal paracentesis should be considered to allow for postoperative reformation of the anterior chamber, if needed. This can also be used at the end of the

The Ahmed Glaucoma Valve is most commonly implanted in the superotemporal quadrant (Videos 113-2 and 113-3). However, some surgeons have implanted them inferiorly, due to individual preference or specific patientrelated factors. Placement of the plate in an inferior quadrant is recommended in eyes with silicone oil in order to minimize the loss of oil through the tube during the postoperative period.14 Inferior placement is considered more technically difficult. In a prospective cohort study, superior and inferior implantation had similar reduction in intraocular pressure and success rates at 1 year, but inferior placement had a higher rate of complications (25%), which included exposure, cosmetically unappealing appearance, and endophthalmitis, compared to superior placement (5%).12 In a retrospective study, inferior placement had a similar reduction in intraocular pressure but a statistically significant higher rate of wound dehiscence and transient diplopia.13 Viscoelastic is not required for routine cases. However, if a patient is thought to be high risk for hypotony or shallowing of the anterior chamber, the surgeon may make a temporal paracentesis and inject viscoelastic into the anterior chamber. Alternatively, viscoelastic may be injected into the anterior chamber through the 23-gauge needle as the tube tract is being created. In eyes that contain silicone oil, viscoelastic may avoid intraoperative loss of oil through the tube.14 The viscoelastic may either be left in the eye or removed at the end of the case. As an alternative to creating a needle tract through the full-thickness of the sclera, a limbal-based scleral flap can be made. The needle track is then created and the tube inserted into the anterior chamber under the flap, which is then closed with 10/0 nylon. This may protect the tube from conjunctival erosion in lieu of a patch graft. In certain patients who are pseudophakic or aphakic and who have had a vitrectomy performed previously, it may be preferable to place the tube into the vitreous cavity rather than the anterior chamber. A pars plana clip (Model PC, New World Medical, Rancho Cucamonga, CA) is available to allow for the tube to curve toward the pars plana without kinking.15 The tube can also be inserted posterior to the iris in the anterior chamber in pseudophakic or aphakic patients, especially those with closed or scarred anterior chamber angles. These maneuvers may reduce the risk of corneal endothelial damage. The use of antifibrotic agents in conjunction with Ahmed Glaucoma Valve implantation has been reported. However, a randomized, prospective, multicenter trial showed no benefit of intraoperative mitomycin C compared with controls for the postoperative intraocular pressure, number of postoperative medications, or postoperative success rates.16 The American Academy of Ophthalmology has

113  •  Surgical Technique 3 (Ahmed Glaucoma Valve Drainage Implant) 40 30 IOP (mmHg)

reported that there is no advantage to the use of antifibrotic agents with any currently available glaucoma drainage implants.8 The use of anti-VEGF agents has been advocated as an adjunct to Ahmed Glaucoma Valve placement. These agents have been used in the perioperative period for neovascular and primary open-angle glaucoma by both intravitreal and subconjunctival injection, but no conclusive benefit has been demonstrated.17,18

Outcomes Since the introduction of the device, multiple studies have reported outcomes with the Ahmed Glaucoma Valve implant in refractory glaucoma. In these studies, success was typically characterized as an intraocular pressure less than 21 or 22 mmHg and greater than 4 or 5 mmHg with or without medicines and without further glaucoma surgery or loss of light perception. These studies tend to report outcomes as probability of success. The majority of the studies are not randomized, prospective trials but retrospective, noncomparative case series.

OVERALL EXPERIENCE IN REFRACTORY GLAUCOMA The mean postoperative intraocular pressure after Ahmed Glaucoma Valve implantation typically ranges in the mid to low teens in most studies (Fig. 113-9).22–25 The average number of postoperative glaucoma medications required is usually around one.16,22–24 The cumulative probability of success reported in different studies ranges from 76% to 87% at 1 year and 68% to 77% at 2 years (Fig. 113-10).22–25 One study with long-term follow-up found probabilities of success at 4 years of 76%.23

20 10 0

POSTOPERATIVE COURSE

0

1d

2w

1m

3m

6m

12m

24m

36m

Time Figure 113-9  Mean intraocular pressure after Ahmed Glaucoma Valve implantation. In this study, the preoperative intraocular pressure of 32.7 mmHg was decreased to 11.7 mmHg at 1 day, 14.8 mmHg at 1 year, and 13.3 mmHg at 2 years after surgery. (Data from Huang MC, Netland PA, Coleman AL, et al. Intermediate-term clinical experience with the Ahmed Glaucoma Valve implant. Am J Ophthalmol 1999;127: 27–33.)

100 80 Percent success

Topical steroid and antibiotic drops are used after surgery. The antibiotic is usually stopped after 2–3 weeks, and the steroid is tapered over weeks to months. Frequent follow-up is required in order to monitor for complications, though interventions are rare after surgery. In a retrospective study, the adjunctive use of topical ketorolac in addition to steroid and antibiotic after implantation of the Ahmed Glaucoma Valve was reported to be associated with lower intraocular pressure at 6 months.19 A prospective, randomized controlled trial compared topical ketorolac to topical dexamethasone postoperatively and found that the ketorolac group had significantly lower intraocular pressures at 4 weeks with a trend toward lower pressures at all time points and a lower risk of a hypertensive phase. However, the ketorolac group had significantly more cases of conjunctival retraction and a trend toward more wound leaks.20 Digital ocular massage has also been described as an effective adjunct for patients whose intraocular pressures are not at target in the postoperative period. In one series, massage reduced IOP by an average of 19% at one hour, and 50% of participants were able to maintain a 20% reduction in intraocular pressure at 2 weeks, 6 weeks, and 6 months by continuing a massage regimen.21

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60 40 20 0

0

6

12

18

24

30

36

Time (months) Figure 113-10  Cumulative probability of success following Ahmed Glaucoma Valve implantation (Kaplan–Meier analysis). The success rates were 87% at 1 year and 75% at 2 years. In this study, prior to treatment with Ahmed Glaucoma Valve, patients were not responsive to medical treatment, laser treatment, or previous glaucoma surgery. (Data from Huang MC, Netland PA, Coleman AL, et al. Intermediate-term clinical experience with the Ahmed Glaucoma Valve implant. Am J Ophthalmol 1999;127:27–33.)

PEDIATRIC GLAUCOMA Multiple studies have found success rates in these patients of 69% to 93% at year 1 and 46% to 86% at year 2.26–30 The majority of patients in these studies had either primary congenital or aphakic glaucoma. Patients with aphakic glaucoma had higher success rates than those with congenital glaucoma. An additional study in patients with primary congenital glaucoma reported a success rate of 33% at five years. In this study, patients who required a second Ahmed Glaucoma Valve had success rates of 86% at one year and 69% at five years after second implant.31 The hypertensive phase is thought to be less common in children than in adults.26 Children need to be carefully monitored due to their vigorous healing response and the

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risk of formation of cataracts after implantation. It appears children are more likely to have tube-positioning problems. One study found a 26% rate of tube malpositioning requiring intervention.32 Implantation of the Ahmed Glaucoma Valve in pediatric patients usually only requires general anesthesia for the initial surgery. Unlike open-tube implants, two-stage pro­ cedures and techniques to restrict flow are usually not necessary. However, in pediatric patients at high risk for complications, such as those with advanced buphthalmos or Sturge–Weber syndrome associated with glaucoma, surgeons may choose to implant the Ahmed Glaucoma Valve in two stages over a 4–6-week period. This approach allows capsule formation around the plate, thereby providing additional protection against postoperative hypotony and its associated complications.

NEOVASCULAR GLAUCOMA Neovascular glaucoma is a refractory glaucoma with a high surgical failure rate. The Ahmed Glaucoma Valve has been used with some success for this refractory condition. In a retrospective study, the Ahmed Glaucoma Valve had similar success rates to trabeculectomy with MMC at 3 and 6 months. The two groups had similar visual acuity and intraocular pressures.33 A retrospective study compared the Ahmed Glaucoma Valve in neovascular and nonneovascular glaucoma patients. Success rates were significantly lower in the neovascular group at 1 year (73%), 2 years (62%), and 5 years (21%). The neovascular group was also more likely to lose vision, though this was attributed to the associated retinopathy.34

UVEITIC GLAUCOMA Ahmed Glaucoma Valve implantation has been shown to be an effective means to lower intraocular pressure (IOP) in uncontrolled uveitic glaucoma. In a study of 21 eyes with average follow-up of 24.5 months, the average postoperative IOP was 11.6 mmHg compared to 35.1 mmHg preoperatively, with an overall success rate of 94% at 4 years.35 An average reduction of 2.9 antiglaucoma medications per eye was observed, and no patient lost Snellen visual acuity. In this study, patients were treated with intensive antiuveitis therapy, including aggressive use of immunomodulatory drugs, which probably influenced the results. In a study of 19 eyes, success rates were 94% at 1 year and 60% at 2 years, with occlusion of the tube cited as the most common complication leading to surgical failure.36 In a study using standard corticosteroid-based uveitis therapy for patients, the success rate at 14 months after Ahmed Glaucoma Valve implantation was 57% with an intraocular pressure reduction from a mean of 32.6 mmHg on 2.8 medicines preoperatively to 17.6 mmHg on 0.7 medicines postoperatively.37 In this study, the most common complications were encapsulated bleb, hypotony, and hyphema. In patients with uveitis and uncontrolled glaucoma, the success rates are usually improved in patients treated with intensive antiuveitis therapy, including the use of immunomodulatory medications, which also occurs in studies of trabeculectomy.38

GLAUCOMA AND PENETRATING KERATOPLASTY Eyes that undergo corneal transplantation frequently develop elevated intraocular pressure, and conventional filtration surgery may have an increased likelihood for failure.39,40 In 31 eyes that had undergone penetrating keratoplasty (PK) and treated with the Ahmed Glaucoma Valve, the success rate was 75% at 12 months and 52% at 20 months.41 Eyes with a history of infectious keratitis or keratouveitis had 5.8 times the risk of graft failure after placement of the Ahmed Glaucoma Valve (see also Chapter 119). In another study, the cumulative probabilities of success of intraocular pressure control were 92% and 86% at 1 and 3 years, respectively, while corneal graft success was 92% and 50% at 1 and 3 years, respectively.42 In some instances, the risk of graft failure may be increased after glaucoma drainage device implantation due to mechanical endothelial trauma intra- and postoperatively or inflammation associated with multiple surgeries. These studies of graft failure after Ahmed Glaucoma Valve implantation are noncomparative studies. In a comparative study, the risk of graft failure was not higher after glaucoma drainage implant surgery, compared with trabeculectomy or cyclodestructive procedures.43 Also, other glaucoma procedures, such as trabeculectomy, have been associated with graft failure. Moreover, the risk of graft failure in patients with uncontrolled intraocular pressure without surgical glaucoma therapy is high.43

PLATE MATERIAL AND DOUBLE-PLATE MODELS The Ahmed Glaucoma Valve is available with a flexible silicone plate (Model FP7) or a rigid polypropylene plate (Model S2). These models have the same surface area. The silicone plate (Model FP7) has low-profile ridges intended to stabilize the plate. The flexible silicone model is generally considered easier to implant and is much more popular than the polypropylene plate in current clinical practice. In a prospective, randomized clinical trial, there was a slight, but statistically significant, increase in success rate after implantation of the silicone plate compared with the polypropylene plate.44 There was a higher incidence of Tenon’s cyst formation in the polypropylene group compared to the silicone group, but no difference in postoperative hypotony. Both silicone and polypropylene valves are available in a double-plate model. The second plate attaches to the primary plate on either side and is intended to increase the surface area of the drainage implant. As in single-plate models, all aqueous flow is directed through the primary valve; there is no valve on the second plate. In a noncomparative series of 50 eyes treated with the double-plate Ahmed Glaucoma Valve, surgical success rates, mean intraocular pressure, mean number of medicines, and incidence of hypotony were comparable to previous studies reported after implantation of the single-plate Ahmed Glaucoma Valve.45 However, the eyes treated with the double-plate Ahmed Glaucoma Valve included a high proportion of eyes with increased risk of failure of drainage implant surgery.

113  •  Surgical Technique 3 (Ahmed Glaucoma Valve Drainage Implant)

AFRICAN-AMERICAN AND CAUCASIAN PATIENTS Multiple studies have shown that African-American race is a risk factor for surgical failure of trabeculectomy with adjunctive MMC, presumably due to vigorous wound healing. In a retrospective, comparative study, AfricanAmerican race was also shown to be a risk factor for failure of Ahmed Glaucoma Valve implantation.46 Success for white patients and African-American patients was 100% and 91% at 1 year and 96% and 79% at 3 years, respectively. Visual outcomes and complications were similar between the two groups.

GLAUCOMA ASSOCIATED WITH SEVERE OCULAR SURFACE DISEASE A keratoprosthesis is an option for patients with a failed cornea and poor prognosis for corneal transplant. Such patients with severe corneal disease may have open-angle or closed-angle glaucoma before surgery, and those without glaucoma often develop elevated intraocular pressure after keratoprosthesis surgery. In a study of 55 eyes with severe ocular surface disease treated with keratoprostheses, there was an incidence of glaucoma of 64%.47 These patients then underwent Ahmed Glaucoma Valve (AGV) implantation at the same time as the keratoprosthesis if they were previously diagnosed with glaucoma (20 of 35 eyes) or underwent AGV implantation at a later time if a diagnosis of postkeratoprosthesis glaucoma was made (15 of 35 eyes). Intraocular pressure was controlled in 81% of patients, with 25% requiring additional medications. Vision was improved in 63%, worse in 20%, and unchanged in 17% of eyes. The most common complications were blocked tube and choroidal effusions.

GLAUCOMA FOLLOWING RETINAL DETACHMENT Elevated intraocular pressure can occur after vitrectomy and placement of silicone oil for complicated retinal detachment (see also Chapter 118). Most of these cases can be managed with antiglaucoma medicines. Trabeculectomy has a poor prognosis in this clinical situation due to significant conjunctival scarring, possible blockage of sclerostomy by silicone oil, and other adverse effects. In a study of such eyes that had failed medical therapy, elevated intraocular pressure was managed with the Ahmed Glaucoma Valve.14 Viscoelastic was used in the anterior chamber and the implants were placed in an inferior quadrant to prevent loss of silicone oil. The intraocular pressure was reduced from a mean of 44 mmHg preoperatively to 14 mmHg postoperatively, with a reduction of antiglaucoma medicines from 3.5 to 1.2. A multicenter, retrospective trial compared the Ahmed Glaucoma Valve in patients with and without silicone oil with an average of two years of follow-up. No significant difference was found between mean IOP, number of medications, or complications. However, the success rate was higher in the eyes without silicone oil and silicone oil was found to be a risk factor for surgical failure.48 A need for prolonged steroid therapy in eyes containing silicone oil was observed in both studies. Silicone oil did not

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cause obstruction or loss of function of the tubes, but migration of silicone oil through the Ahmed Glaucoma Valve into the subconjunctival space and orbit has been reported.49

Complications Adverse events may occur after any type of glaucoma drainage implant surgery. Early postoperative hypotony, choroidal effusions, and suprachoroidal hemorrhage are less common after Ahmed Glaucoma Valve than with open-tube glaucoma drainage implant implantation (Box 113-3).

HYPOTONY Hypotony and complications associated with hypotony may occur during the immediate postoperative period of any full-thickness glaucoma surgery, but they are less common after Ahmed Glaucoma Valve. In a study of eyes treated with the Baerveldt implant, hypotony and choroidal effusions occurred in 32% and 20% of eyes, respectively.50 Similarly, hypotony-induced choroidal detachments and shallow anterior chamber occurred in 20% of eyes after placement of the Molteno implant.51 Hypotony has been reported to occur in less than 10% of eyes on the first postoperative day after implantation of Ahmed Glaucoma Valve.22,24 Younger age, myopia, and lack of previous intraocular surgeries have been identified as risk factors for postoperative shallow anterior chambers in these pateints.52 Hypotony and choroidal effusions usually resolve without surgical treatment. However, flat chamber and lens–corneal touch may be ameliorated by injection of viscoelastic into the anterior chamber, either at the slit lamp or under an operating microscope. Choroidal effusions may be treated with topical corticosteroid and cycloplegic medications, while large or persistent choroidal effusions may be drained surgically. Removal of the tube can be considered in severe cases.

Box 113-3  Complications Less common with Ahmed Glaucoma Valve compared with open-tube implants Hypotony Choroidal effusion Associated with Ahmed Glaucoma Valve* Valve malfunction (rare) Associated with all glaucoma drainage implants, including the Ahmed Glaucoma Valve Obstruction of tube by fibrin, blood, iris, vitreous Tube retraction and erosion Tube kink Motility disturbance Corneal decompensation and graft failure Endophthalmitis Retinal detachment *Although not usually considered a ‘complication,’ a hypertensive phase may occur after Ahmed Glaucoma Valve implantation.

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HYPERTENSIVE PHASE After Ahmed Glaucoma Valve implantation, satisfactory intraocular pressure control in the early postoperative period may be followed, in some instances, by a rise of intraocular pressure, typically at 3–6 weeks after surgery (Video 113-4). When the increased intraocular pressure is transient, improving after nonsurgical therapy, it has been described as a ‘hypertensive phase.’ The hypertensive phase is presumably due to formation of a thickened capsule around the plate of the implant. An encapsulated bleb or Tenon’s cyst presents as a smooth, high, dome-shaped bleb that causes increased resistance to aqueous flow. In one study, ‘encapsulated’ blebs were observed in 23% of patients, occurring at a median of 32 days after surgery with a mean intraocular pressure of 34.4 mmHg.46 Methods to lower IOP include medical therapy, digital ocular compression, needling with or without 5-fluorouracil (5-FU) injection, or surgical excision of the bleb. The incidence of the hypertensive phase has varied in different reports, occurring in 30–82% of patients following polypropylene (Model S2) Ahmed Glaucoma Valve implantation.24,25,44,46,53 The incidence of the hypertensive phase may be lower after silicone plate (Model FP7) than after polypropylene plate (Model S2) implantation.44 A hypertensive phase has not been commonly observed after treatment with the Baerveldt implant.24,25,54

ELEVATED INTRAOCULAR PRESSURE DUE TO OTHER CAUSES Failure to prime the valve with balanced salt solution intraoperatively can lead to increased intraocular pressure postoperatively. Fibrosis of the valve is rare but has been reported.9 Fibrovascular ingrowth into the Ahmed Glaucoma Valve is uncommon, but has been documented as a cause of late failure in adult and pediatric patients. Fibrovascular ingrowth may occur at the posterior junction between the valve chamber and the plate and may be due to improper handling of the valve during implantation.55 The aggressive healing reaction in children may explain their higher incidence of fibrovascular ingrowth. Other causes of increased intraocular pressure are similar to those found after implantation of other glaucoma drainage devices. Elevated intraocular pressure may be caused by obstruction of the tube by fibrin, blood, iris, vitreous, or other substances. This was found in 11% of patients in one study, most frequently by blood in patients with neovascular glaucoma.24 Intracameral injection of tissue plasminogen activator (0.1–0.2 mL of 5–20 µg) may dissolve a fibrin or blood clot. Neodymium:yttrium-aluminum-garnet (Nd:YAG) laser can be used to ablate iris tissue or the posterior capsule occluding the tube. A vitrectomy may be required for vitreous in the tube.

MOTILITY DISTURBANCES AND DIPLOPIA Motility disorders may result from mechanical displacement (mass effect) by the implant and bleb, fat adherence syndrome, or posterior fixation suture (Faden) effect associated with scarring under the rectus muscles. Diplopia has

been reported in 3–5% of patients following Ahmed Glaucoma Valve insertion.24 This complication has been reported more frequently following Baerveldt or doubleplate Molteno implants. Two cases of acquired Brown’s syndrome secondary to Ahmed valve implanted in the superior nasal quadrant have been reported.10

TUBE RETRACTION AND EROSION Tube retraction and erosion can occur after any type of glaucoma drainage implant surgery. Erosion of the tube through the cornea was reported in one pediatric patient after implantation of the Ahmed Glaucoma Valve.56 Having more previous ocular surgeries prior to implantation of the Ahmed Glaucoma Valve has been identified as a risk factor for implant exposure.57 If tube retraction occurs and the tube is too short to reposition, a new valve can be inserted, the tube can be reinserted in the pars plana, or a tube extender can be utilized to lengthen the tube.58

GRAFT FAILURE AND CORNEAL DECOMPENSATION In eyes with penetrating keratoplasty, the reported incidence of graft failure following Ahmed Glaucoma Valve implantation is 25–35%.41 Conversely, in eyes with Ahmed Glaucoma Valves that subsequently had penetrating keratoplasty, the graft failure rate has been reported at 59% at three years.59 The cause for this failure is likely multifactorial, including the presence of underlying chronic inflammation, extensive peripheral synechiae, and multiple previous surgeries. Focal or generalized corneal decompensation may occur after placement of any type of glaucoma drainage implant. In a prospective study, specular microscopy was used to follow corneal endothelial density after placement of Ahmed Glaucoma Valve. The endothelial cell count was reduced by 18.6% at 24 months after surgery, and this was statistically significant when compared against baseline and fellow eye measurements. The corneal quadrant nearest the tube implant showed the greatest cell loss (22.6%), while the central cornea showed the least.60 The long-term clinical significance of these findings is not known. Shortening the tube, placing the tube more posteriorly in the anterior chamber, or placing the tube in the pars plana or posterior to the iris may reduce this complication.

VISION-THREATENING COMPLICATIONS Complications that threaten vision are not common after Ahmed Glaucoma Valve implantation. Suprachoroidal hemorrhage, choroidal effusions, and retinal detachments can potentially occur. They have been reported in up to 2–5% of patients.24,25 Endophthalmitis is a rare complication of glaucoma drainage implant surgery that can be associated with any intraocular surgery. The incidence in one study, which examined 542 eyes, was 1.7%. Haemophilus influenzae and Streptococcus were the most commonly identified organisms.61 The majority of cases of endophthalmitis occurred at least 6 weeks after implantation. Conjunctival erosion overlying the Ahmed glaucoma tube was found to be the most important risk factor.

113  •  Surgical Technique 3 (Ahmed Glaucoma Valve Drainage Implant)

Comparison with Other Techniques Because of its valved mechanism, the Ahmed Glaucoma Valve is thought to be more protective against hypotony than non-valved tube implants and trabeculectomy. The plate has a narrow profile, intended to fit between the rectus muscles during implantation. Clinical results with the Ahmed Glaucoma Valve plate have been compared with alternative plate designs.

AHMED GLAUCOMA VALVE VERSUS BAERVELDT IMPLANT The Ahmed–Baerveldt Comparison study randomized 276 patients with intraocular pressure of 18 mmHg or more in whom a drainage implant was planned to receive either Ahmed or Baerveldt implants at multiple sites. There was no difference in intraoperative complications. The Ahmed group had lower initial pressures, probably due to early flow-restricting techniques used in the Baerveldt implants. The Ahmed Glaucoma Valve had significantly higher intraocular pressure at one year (15.4 mmHg vs. 13.2 mmHg) (Fig. 113-11). There was no significant difference in failure rates or number of glaucoma medicines used. The Baerveldt group had a significantly higher postoperative complication rate and a significantly higher rate of serious complications resulting in reoperation or loss of visual acuity.62 At 3 years there was a lower risk of reoperation for glaucoma in the Baerveldt group.63 In the Ahmed Versus Baerveldt study, 238 patients with refractory glaucoma who had failed medical, laser, and incisional surgery were randomized to receive Ahmed or Baerveldt implants at multiple sites. The two groups had a similar rate of intraoperative complications. At one year, the Ahmed Glaucoma Valve group had a significantly higher failure rate (43% vs. 28%), significantly higher intraocular pressure (16.5 mmHg vs. 13.6 mmHg), and required significantly more glaucoma medicines (1.6 vs. 1.2). The Baerveldt group required significantly more 35 Ahmed

30

Baerveldt

IOP (mmHg)

25 20 15 10 5 0

Baseline

1 day

1 week

1 month 3 months 6 months

1 year

Figure 113-11  One-year results of the Ahmed Baerveldt Comparison Study. The Ahmed study had lower initial pressures, but the Baerveldt study had lower pressures at one year. IOP = intraocular pressure. (Data from Budenz DL, Barton K, Freuer WJ, et al. Treatment outcomes in the Ahmed Baerveldt Comparison Study after 1 year of follow-up. Ophthalmol 2011;118:443-52.)

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interventions in the first year (42% vs. 26%),64 although at 3 years this did not reach statistical significance.65 There was no significant difference between visual acuity or complications between the two groups.64

AHMED GLAUCOMA VALVE VERSUS MOLTENO IMPLANT In a prospective, randomized comparison in patients with refractory glaucoma, the single-plate Molteno showed significantly more lowering of intraocular pressure at 24 months after surgery than the Ahmed Glaucoma Valve (–49.7% change vs. –41.9% change). There was no significant difference in rate of failure, visual acuity, visual field preservation, use of glaucoma medicines, or intraoperative or postoperative complicatons.66

AHMED GLAUCOMA VALVE VERSUS TRABECULECTOMY In a randomized, controlled clinical trial, the cumulative probabilities of success were 84% for the trabeculectomy group and 88% for the Ahmed Glaucoma Valve group (p = 0.43).5 The trabeculectomy group had a statistically significant lower IOP through months 11–13. In months 20–24 through 52 months, the intraocular pressure was similar in both groups.6 Although long-term bleb-related complications are a concern, the number of complications was similar in both groups during the period of the study.

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