|Year : 2013 | Volume
| Issue : 2 | Page : 77-82
Glaucoma drainage devices
Parul Singh, Krishna Kuldeep, Manoj Tyagi, Parmeshwari D Sharma, Yogesh Kumar
Department of Ophthalmology, V. C. S. G. Government Medical Sciences and Research Institute, Srinagar Garhwal, Uttarakhand, India
|Date of Submission||17-Sep-2012|
|Date of Acceptance||10-Feb-2013|
|Date of Web Publication||20-May-2013|
Department of Ophthalmology, V. C. S. G. Government Medical Sciences and Research Institute, rinagar Garhwal, Uttarakhand
Source of Support: None, Conflict of Interest: None
Glaucoma drainage devices (GDD) occupy an important place in the surgical management of glaucoma that is not responding to medications and trabeculectomy operations. In certain conditions, such as neovascular glaucoma, pediatric glaucoma, iridocorneal endothelial syndrome, penetrating keratoplasty with glaucoma, glaucoma following retinal detachment surgery, it has become the preferred operation. GDD create an alternate aqueous pathway from anterior chamber by channeling aqueous out of the eye through a tube to subconjunctival space. Glaucoma drainage implants that have been used extensively include the non-restrictive and restrictive drainage devices. This article outlines history of implants, types of implant, surgical technique of implantation, various complications following GDD insertion and their management.
Keywords: Ahmed glaucoma valve, baerveldt glaucoma valve, drainage devices, glaucoma, surgery
|How to cite this article:|
Singh P, Kuldeep K, Tyagi M, Sharma PD, Kumar Y. Glaucoma drainage devices. J Clin Ophthalmol Res 2013;1:77-82
Glaucoma drainage devices (GDDs) work by creating an alternate pathway for aqueous outflow by channeling aqueous from anterior chamber (AC) through a tube of implant towards sub-conjunctival space. Trabeculectomy, the procedure of choice in conventional glaucoma filtration surgery, has remained essentially unchanged for over a quarter of a century. Local control over wound healing with anti-metabolites has improved the prognosis for cases with high risk of filtration failures; but flow control remains inexact despite the introduction of a variety of suture adjustment techniques. GDD occupy an important place for treatment of complicated and refractory glaucomas, both as primary surgical modality and as a secondary procedure where trabeculectomy with or without anti-metabolite treatment has either failed or is reported to have very low chances of success. ,,,,,, The latter group consists of pediatric glaucomas, , neo-vascular glaucomas,  uveitic glaucoma,  aphakic and pseudo-phakic glaucoma,  post-vitreoretinal surgery,  and post-penetrating keratoplasty surgery.  This article outlines the history of implants, types of implants, medication and contra-indication, surgical techniques of implantation, various complications following GDD insertion and their management.
| History|| |
The first attempt to implant a drainage device was made by Rollet and Moreau in 1907, when they performed a double paracentesis and used horse hair through the corneal punctures to treat patients with painful absolute glaucoma.  Later attempts include insertion of a polythene tube by Epstein in 1959, and silicon tube by MacDonald and Pearce in 1965. Molteno in 1969 scientifically explained the pathophysiology of bleb resistance and designed a tube.  Another significant development was in 1973 when Molteno improved his device with the idea of draining the fluid away from the limbus to increase the success rate. All of the currently available GDD are based on these fundamentals which were basis of Molteno implants.  The Molteno implants, however, offer no resistance to the outflow and post-operative complications like hypotony, flat ACs, and choroidal effusions were a regular phenomenon.  In 1976, Krupin developed a pressure sensitive, unidirectional valve that provides resistance to the flow of aqueous. In 1981, Molteno introduced the double plate implant with a surface area of 270 mm 2 .  In 1992, Baerveldt introduced a non-valved silicone tube attached to a large barium-impregnated silicone plate with surface area of 250 mm 2 , 350 mm 2 or 500 mm 2 . , In 1993, Ahmed introduced the Ahmed glaucoma valve (AGV), a pressure sensitive unidirectional valve. ,, Then there was development of Ex-Press R50-single piece, stainless steel translimbal implant that is placed with the help of an inserter.
| Types of implants|| |
- Non-valved/Non-restrictive implants: These GDDs consist of a silicone tube attached to an endplate that acts as a surface for the bleb formation.
- Single plate Molteno implant is a silicone tube attached to 135 mm 2 polypropylene endplate.
- Double plate Molteno (DPM) is same as the single plate Molteno except that a second end plate is attached to the right or left of the original endplate, thus doubling its surface area.
- Baerveldt implant is a silicone tube attached to soft pliable, barium impregnated silicone endplate of various sizes (i.e., 250 mm 2 , 350 mm 2 or 500 mm 2 ).
- Schocket implant is a silastic tube, one end of which is inserted into the AC, and the other end is tucked beneath a No. 20 retinal encircling band.
- Ex-Press R50 implant is a single piece, stainless steel, translimbal implant that is placed with the help of an inserter.
- Valved/Restrictive implants:
- AGV is a silicone tube connected to a silicone sheet valve held in a polypropylene body. The endplate measures 185 mm 2
- (16 mm long × 13 mm wide × 1.9 mm thick). The valve consists of thin silicon elastomer membranes (18 mm long × 7 mm wide). The valve is designed to open when intra-ocular pressure (IOP) is 8 mmHg.
- Krupin slit valve consists of a silicone tube with a slit valve attached to a silicone oval endplate with a surface area of 180 mm 2 . The opening pressure of the slit valve is designed to be 11-14 mmHg and the closing pressure is designed to be 2 mmHg. 
- Others: Joseph, Optimed and White GDD.
- GDD with variable resistance:
- Molteno dual ridge device limits the initial drainage area by dividing the top portion of the plate into two separate spaces with a thin V-shaped ridge.
- Baerveldt bioseal is a flap that overhangs the silicone tube as it opens on the endplate.
- SOLX Goldshunt is an investigational device consisting of a flat, 24 carat gold implant (5.2 mm long and 3.2 mm wide) with numerous microtubular channels that bridge the AC and the suprachoroidal space.
Following implantation of GDD, a fibrous capsule forms around the endplate over a period of several weeks. A feature common to all glaucoma drainage implants is the construction of the plate from materials to which fibroblasts cannot adhere. Aqueous humor pools in the potential space between the endplate and surrounding non-adherent fibrous capsule when flow occurs through the AC tube. Aqueous then passes through the capsule by the process of passive diffusion and is absorbed by peri-ocular capillaries and lymphatics. It is the fibrous capsule around the end-plate that offers the major resistance to aqueous flow with drainage implants.
Glaucoma drainage device implantation is usually reserved for cases with refractory glaucoma, or those unlikely to respond successfully to a conventional filtration surgery. The indications for GDD implantation include the following:
- Neovascular glaucoma
- Penetrating keratoplasty with glaucoma
- Retinal detachment surgery with glaucoma
- Iridocorneal endothelial syndrome
- Traumatic glaucoma
- Uveitic glaucoma
- Open angle glaucoma with failed trabeculectomy
- Epithelial down growth
- Refractory infantile glaucoma
- Contact lens wearers who need glaucoma filtration surgery
- Sturge-Weber's syndrome.
- Eyes with severe scleral or sclera-limbal thinning
- Extensive fibrosis of conjunctiva
- Ciliary block glaucoma.
- Vitreous in AC
- Intra-ocular silicone oil-Implant if required is placed in inferio-temporal quadrant
| Surgical procedure|| |
The conjunctiva is undermined posteriorly by blunt dissect in superior-temporal quadrant. Adequate surgical exposure is done by placement of traction sutures and dissection of partial thickness scleral flap to cover the tube in case where preserved sclera/pericardium is not used. The AGV implant is irrigated with 2 ml of balanced saline solution (priming). The plate is secured to superficial sclera using two interrupted non-absorbable sutures 8 mm from limbus. The tube is cut to extend 1-3 mm beyond posterior surgical limbus. The AC is entered 0.5 mm posterior to the limbus by 23 gage needle directed parallel to and just anterior to iris plane. The tube is inserted with a smooth forceps through the needle tract ensuring that no iris or corneal touch was present. The tube is secured against sclera using figure of eight suture. Then, either scleral flap is approximated or donor graft is used to cover it. Conjunctival closure is then performed using 8-0 or 9-0 Nylon suture.
DPM or Baerveldt implant insertion
To insert DPM, a fornix based conjunctival flap is made between medial and lateral rectus muscles. 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 8 mm from limbus in supra-temporal and supranasal quadrants with 9-0 suture. AC is entered with 23 gage needle, silicone tube trimmed and inserted into AC through needle tract. A 10-0 Nylon figure of eight suture tied around tube and donor scleral patch graft placed on the tube. The long end 4-0 Nylon stent is passed underneath lateral rectus or medial rectus muscle and tucked into the subconjunctival space inferiorly. The conjunctiva is then sutured.
The single plate Molteno implant and Baerveldt implant are inserted in similar fashion as AGV; however, with the Baerveldt implant, the endplate is tucked underneath the adjacent rectus muscles.
Ex-Press shunt implant insertion
The technique involves limbal peritomy and a 3 mm × 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 desired time followed by copious irrigation. Paracentesis is done, followed by an injection of high molecular weight visco-elastic. A 27 gage needle is used to create needle tract into AC under scleral flap. The express shunt is then placed into the AC through the needle tract. The scleral flap is secured with two interrupted 10-0 Nylon sutures. The conjunctiva is closed with 10-0 Vicryl.
Gold micro-shunt implantation
Gold shunt is typically inserted through a scleral incision 4 mm in length, 2.5 mm from limbus. The device enters AC through a scleral tunnel directly above scleral spur, with rear tabs placed in suprachoroidal space.
Modifications to prevent hypotony with non-valved implants:
- Two stage procedure: To prevent post-operative hypotony, a shunt procedure may be performed in two stages. In the first stage, the plate is attached to the globe and the tube is left in the subconjunctival space without entering the eye. Four to six weeks later, after a capsule has formed around the implant, the conjunctiva is opened and a tube is inserted into the AC to complete the procedure.
- Internal tube occlusion (stent): Aqueous drainage through a non-valved device can be regulated in the early post-operative period by passing a 4-0 or 5-0 prolene or nylon suture through the lumen of the implant. Once the fibrous capsule is formed around the implant, the stent suture is removed at slit lamp under local anesthesia.
- External tube occlusion (Ligature): The flow of aqueous humor through a non-valved device can also be restricted by placing a suture ligature around the external aspect of the tube. The external occlusion may be accomplished using a non-absorbable 7-0 suture with a releasable knot or a 7-0 or 8-0 absorbable vicryl suture tied around the tube. Alternatively, 9-0 nylon or 10-0 prolene suture may be used to ligate the tube inside the AC to allow for laser suture lysis with argon laser.
- Pars plana insertion: The tube of the glaucoma drainage implant is most commonly placed in the AC. However, the tube may also be placed in the sulcus in a pseudophakic eye or in pars plana in a vitrectomized eye.
Site of implantation
With the exception of the two plate implants, most glaucoma implants are placed in single quadrants. Whenever possible, single plate implants should be placed in the superior-temporal quadrant. This area provides the easiest access for the surgeon to implant the plate and is least likely to produce motility disturbances. In eyes containing silicon oil, the implant is placed in the inferior quadrant to minimize loss of oil, which is lighter than aqueous and floats up.
Role of anti-fibrosis agents
Using anti-metabolites with improved success in trabeculectomy led to considerable interest in using these agents with GDD. One early study indicated that patients receiving mitomycin-c at the time of glaucoma implant surgery has lower final IOP, required fewer post-operative medications and has less pronounced hypertensive phase. However, the duration of the post-operative hypotensive phase was prolonged and was associated with an increase in choroidal effusions, flat AC and other post-operative complications.  But, subsequent studies have failed to show effectiveness of these agents. Two retrospective studies reported no benefit of intra-operative use of mitomycin-c with Baerveldt implants. , Two post-operative randomized trials studied the effectiveness of intra-operative use of mitomycin-c with Molteno and AGV implants. Neither of the trials demonstrated higher success rates in terms of final IOP, visual acuity and number of anti-glaucoma medications required post-operatively. ,
Following GDD surgery, the patient is examined on post-operative day one and attention is paid to the tube position and wound architecture. Topical antibiotic and steroids are started 4 times daily and continued for 5-6 weeks. Initial follow-up is at one week and further frequency of visits depends on the clinical status of the eye. For valved implants, pre-operative glaucoma medications are discontinued to prevent hypotony. For non-valved implants, the glaucoma medications are usually continued until a fibrous capsule forms around the plate.
Implantation of GDDs may be followed by all or one of the following phases:
From day 1-3-4 weeks following the operation, clinical examination during this phase reveals a diffuse and thick walled bleb with minimally engorged blood vessels. The IOP is low, i.e., from 2-3 mmHg to 10-12 mmHg.
Starts 3-6 weeks after the operation and lasts from 4 to 6 months. It is more commonly seen with the AGV. On examination, an inflamed and dome shaped bleb is seen and increased IOP, at times greater than 30 mmHg may be noted. During the hypertensive phase, when the IOP is too high (usually >21 mmHg), anti-glaucoma medications may be initiated, along with digital massage. In case the patient doesn't respond needling may be indicated. A subconjunctival injection of 5-FU(5-fluorouracil) in opposite quadrant may also be given.
This phase follows the hypertensive phase and is characterized by stabilization of IOP usually in early teens.
Post-operative complications and management:
- Hypotony/choroidal detachment: Low IOP (<5 mmHg) with a shallow AC in the immediate post-operative period may be due to-overfiltration, wound leaks, or choroidal effusions. Hypotony due to overfiltration is seen in 20-30% of the cases with non-valved implants. Modifications like placement of a suture in the lumen of the tube (Ripcord technique) have been devised to lower its incidence.
- Management: Hypotony from overfiltration generally does not require treatment unless flat AC develops with lens cornea touch. AC may be reformed with visco-elastic. In persistent cases GDD may be revised. If persistent wound leaks, repair is done with sutures. Choroidal effusions may be treated with topical and oral steroids. However, if choroidal effusions are kissing or involving the macula, they must be drained surgically.
- Tube obstruction: Obstruction of tube may be caused by blood, fibrin, vitreous or iris plug or it may be related to tight external ligature around the tube. Tube obstruction because of the kinking of the tube has been reported after pars plana AGV insertion.  It manifests as IOP rise associated with deep AC.
- Management: Blood or fibrin clot-Intracameral injection of 5-10 mg of tissue plasminogen activator in 0.1 ml of balanced salt solution. Vitreous incarceration-Neodymium-yttrium aluminum garnet (Nd-YAG) laser is used to dissipate the vitreous strands.  Iris incarceration-peripheral argon laser iridoplasty applied to the base of the plug. Tight external ligature can be cut with argon laser.
- Elevated IOP: Early operative IOP elevation may be due to obstruction of tube by fibrin, blood, iris tissue or vitreous. Management for these conditions is described under tube obstruction heading. Late IOP elevation is usually due to excessively thick fibrous capsule. This can be dealt by removing a portion of capsule beneath the conjunctival flap.
- Overhanging bleb: If the patch graft is too thick or the plate is too anterior, an overhanging bleb may be created resulting in chronic dellen formation and ocular irritation. This complication is best prevented by appropriate plate and patch graft placement during surgery.
- Bleb encapsulation: Failure to control IOP after GDD implant surgery may occur secondary to encapsulation of the bleb around the plate. This complication is analogous to encapsulated bleb that develops after trabeculectomy and is treated in similar fashion with anti-glaucoma medication.
- Tube exposure/migration/extrusion: The incidence of tube exposure varies from 0-15%. Management: To prevent tube exposure, prophylactically use for donor sclera, adequate anchorage to scleral bed by sutures and superficial flap must be evenly dissected. Treatment of this complication may be initially by rotating an adjacent partial thickness flap to cover the tube but ultimately a fresh site may be needed.
- Tube retraction: Retraction of the tube from AC may be managed by placing an extender sleeve with larger inner diameter over the existing tube.
- Corneal endothelial touch: It is usually seen when the tube has not been placed accurately or the bevel has not been cut in the proximal orifice. The other reason for this complication is shallow AC. Corneal endothelial touch lead to corneal decompensation, which is cause of long term visual outcome.
- Ocular motility disturbance: Exotropia, hypertropia or limitation of ocular rotation usually occurs with larger plates, e.g., Baerveldt and Krupin implant, but can also occur with smaller plates. Diplopia was noted to be significantly higher with Baerveldt implant than with AGV or Molteno implant. This extra-ocular muscle imbalance with diplopia results from mass effect of plate and surrounding bleb on adjacent extra-ocular muscle. Other possible causes include Faden effect, entrapment of superior oblique muscle, fat fibrosis syndrome , or pseudo-brown syndrome. ,
- Suprachoroidal hemorrhage: Sudden excruciating pain with increased IOP in the operated eye during the operation or in the post-operative period might indicate a suprachoroidal hemorrhage. Clinical signs include a shallow AC, increased IOP, and choroidal elevations. B-scan is helpful in diagnosing this condition. Management: Includes supportive therapy, followed by topical and oral steroids, glaucoma medications, cycloplegic agents and painkillers.
- Indications for drainage: Involvement of the macula by the hemorrhage kissing choroids, corneo-lenticular touch and severe pain.
- Corneal graft failure: GDD surgery appears to be associated with high incidences of graft failure in patients with glaucoma. The presence of chronic inflammation, extensive peripheral synechiae and multiple previous surgeries may compromise the graft.
- Endophthalmitis: Endophthalmitis following GDD operation is very rare, and is more common through thin walled blebs or areas of aqueous leakage, in children and following needling of the bleb. 
- Loss of vision: This may occur due to hypotonous maculopathy, progression of cataract, glaucoma, corneal decompensation, suprachoroidal hemorrhage, and endophthalmitis.
Comparison of glaucoma drainage devices
A meta-analysis of various studies published between 1966 and 2002 were carried out by Hong et al.  A total of 147 articles were reviewed and 54 articles were included in final analysis (29 with Molteno, single and double plate with some form of intra-operative modification to prevent hypotony, 6 with single plate Molteno without any form of surgical modification to prevent hypotony, 9 with Baerveldt, 8 with AGV and 2 with Krupin). The overall surgical success rate averaged between 72% and 79% among the five devices with no statistically significant difference at the last follow-up. All five implants significantly lowered IOP (P < 0.001).
There was no statistically significant difference between in either the percentage change in IOP or the overall surgical success rate at the last follow-up among the five devices or within the sub-division of the Molteno group or the size of the endplate.
Diplopia was seen more frequently with the use of Baerveldt implant (P = 0.01).  Plate size of various implants has been investigated to determine its influence on the final IOP. Heuer et al. reported improved IOP control the Molteno double plate when compared with the single plate in a prospective study assessing outcomes in aphakic and pseudophakic glaucoma.  In a retrospective study, the DPM demonstrated lower mean IOP when compared with a single plate AGV, 13.3 ± 5.1 mmHg versus 19 ± 5.8 mmHg (P = 0.009) respectively at 24 months.  In a prospective study comparing 350 mm square and 500 mm square Baerveldt implants, Llyod et al. reported statistically comparable results with respect to IOP control, visual acuity and complications. 
The Ahmed Baerveldt Comparison Study is a multi-center randomized, prospective clinical trial. Two hundred seventy six subjects with uncontrolled glaucoma received either an AGV (model FP7) or a Baerveldt implant (model 350 mm square). The majority of subjects had either primary open angle glaucoma or neo-vascular glaucoma. Forty two percent of the subjects had previously failed trabeculectomy. The mean baseline IOP was 30 mmHg. Failure was defined as IOP greater than 21 mmHg and less than 6 mmHg, less than 20% of IOP reduction from baseline, repeat surgery or loss of light perception. At one year, the mean IOP was 15.4 ± 5.5 mmHg in the Ahmed group and 13.2 ± 6.8 mmHg in Baerveldt group (P = 0.007). The cumulative probability of failure was 16.4% and 12.3% in AGV and Baerveldt groups respectively. The Baerveldt group required more surgical interventions post-operatively. 
Tube Versus Trabeculectomy (TVT) study
Tube shunt surgery had a higher success rate compared to trabeculectomy with MMC during 5 years of follow-up in the TVT Study. Both procedures were associated with similar IOP reduction and use of supplemental medical therapy at 5 years. A total of 212 eyes of 212 patients were enrolled, including 107 in the tube group and 105 in the trabeculectomy group. At 5 years, IOP (mean ± SD) was 14.4 ± 6.9 mmHg in the tube group and 12.6 ± 5.9 mmHg in the trabeculectomy group (P = 0.12). The number of glaucoma medications (mean ± SD) was 1.4 ± 1.3 in the tube group and 1.2 ± 1.5 in the trabeculectomy group (P = 0.23). The cumulative probability of failure during 5 years of follow-up was 29.8% in the tube group and 46.9% in the trabeculectomy group (P = 0.002; hazard ratio = 2.15; 95% confidence interval = 1.30-3.56). The rate of reoperation for glaucoma was 9% in the tube group and 29% in the trabeculectomy group (P = 0.025). 
Newer glaucoma drainage devices
MIDI Arrow: It is made from proprietary material called poly styrene-block-isobutylene-block-styrene (SIBS). It has been demonstrated in over 60 rabbit studies that ophthalmic implants made from SIBS are significantly less irritating, less inflammatory, less capsule forming and non-occluding as compared to similarly shaped silicon rubber controls.  Human clinical studies are also demonstrating encouraging performance but results are yet to be published.
The iStent is a very small titanium tube, approximately 1 mm in length. It is surgically placed into the eye through an incision in the cornea and inserted through the filtering tissue meshwork. This creates an opening between the eyes AC and Schlemm's canal that bypasses the damaged drainage system and directs aqueous fluid into deeper tissues potentially decreasing IOP. The Food and Drug administration (FDA) reviewed effectiveness data from a study on total of 240 eyes for 239 participants. The FDA also reviewed the safety data for these and an additional fifty participants. At 1 year following procedure, 68% of the participants with iStent had target pressure of 21 mmHg or lower without the use of eye pressure lowering medication, compared to 50% of participants who underwent cataract surgery alone. The iStent may be considered as a new option in treatment of open angle glaucoma patients needing cataract extraction.
The Hydrus stent is one of several promising mini-drainage devices now in clinical trials in the United States and other countries. If future trials confirm micro-stents' effectiveness, they could someday help protect millions of glaucoma patients from vision loss or blindness. In this particular study of 69 patients suffering from mild to moderate open-angle glaucoma, IOP was reduced to acceptable levels in 100% of participants after they received minimally invasive stent implant surgery. In 40 patients the stent was placed during cataract surgery, a procedure that also reduces IOP. Twenty-nine patients had the Hydrus stent placed without cataract surgery to assess whether the stent would be effective on its own. No significant complications occurred in either patient group. At the 6-month follow-up, 85% of combined surgery and 70% of stent-only patients no longer needed eye drop medications to control their IOP. Reductions in IOP were consistent among all patients and remained stable at the one year follow-up.
| Conclusion|| |
GDD have been successful in controlling IOP in eyes with previously failed trabeculotomy and for cases with refractory glaucoma. Since their introduction, numerous modifications in design and improvements in surgical technique have enhanced clinical outcomes and minimized complications. These devices are available in different sizes, materials, and designs. The decision to choose a particular type of drainage device depends on a patient's underlying characteristic in terms of pre-operative IOP and optic nerve status, desired long-term IOP control and the surgeon's comfort and preference. Careful pre-operative screening and planning along with meticulous surgical technique help minimize post-operative complications.
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