Chapter 242 – Drainage Implants
• Surgical method for dealing with refractory glaucomas.
• Drainage plate attached to silicone tube.
• Varying plate size and number.
• Surgical method of insertion.
Drainage implants were developed before antifibrotic agents became available to enhance trabeculectomy surgery. These implants provided a good surgical option for eyes in which there was a high probability of trabeculectomy surgery failure because of extensive conjunctival scarring from previous procedures or the type of underlying glaucoma (neovascular, uveitic, iridocorneal endothelial [ICE] syndrome, etc). Today, many surgeons use drainage implants only when failure has occurred with one or more trabeculectomies in which antifibrotic agents were used. Probably a role exists for these implants at an earlier stage for some patients, particularly with the increased concern about postoperative late bleb leaks and risks of late endophthalmitis following the use of antimetabolites.
Early drainage devices, or setons, were made from a variety of materials and extended from the anterior chamber to the subconjunctival space.  As most devices were not “bleb spreading” in nature, their failure occurred as a result of fibrosis over the subconjunctival portion of the seton.
The most common drainage devices in use today are based on a design introduced by Molteno in 1969 and modified later in the 1970s. The initial Molteno implant consisted of an acrylic translimbal tube attached to and opening onto the surface of a curved episcleral plate, 8.5?mm in diameter. Aqueous drained into a potential space formed by the surface of the plate and the conjunctiva that overlay it. The fibrosis response to the aqueous caused the episcleral plate to become enclosed by a thin layer of connective tissue, which became distended with aqueous to form a large, unilocular bleb that freely communicated with the anterior chamber. The long-term tendency was for the bleb wall to become thinner and, although desirable for pressure control, the thinness of the wall occasionally led to perforation and/or exposure of anterior-placed implants. The redesigned implant
Figure 242-1 Double-plate, Molteno implant (left) and Baerveldt implant (right).
had an enlarged episcleral plate, which shifted the implant backward, and maintained connection to the anterior chamber by means of a fine-bore, elongated silicone tube. Further modification of the Molteno implant consisted of the addition of a second plate connected to the first by a second silicone tube. The dual-chamber implant developed later restricted drainage initially to a small area anteriorly placed on the surface of the plate and allowed aqueous to spread to the remainder of the plate at a later time.
The majority of modern implants follow the principle introduced by Molteno, namely a long tube that drains to an episcleral plate ( Fig. 242-1 ). Implants can be divided essentially into two groups, those with valves and those without valves. The nonvalved are the various types of Molteno implants, the Baerveldt implant, and the Schocket encircling tube. Valved implants include the Krupin disc, Ahmed valve, and White pump. All commonly used implants consist of a long tube through which aqueous drains from the anterior chamber to a posteriorly placed plate that acts as a bleb-spreading device.
PREOPERATIVE EVALUATION AND DIAGNOSTIC APPROACH
Drainage implants were designed for use in refractory glaucomas. This group includes eyes that have had one or more filtering procedures that have failed, aphakic and pseudophakic glaucomas, uveitic glaucoma, neovascular glaucoma, congenital glaucoma with iridocorneal dysgenesis, the ICE syndrome, and glaucoma that follows corneal transplantation. Scarring of the conjunctiva from causes other than previous filtering surgery may also warrant implant use if pressure control requires surgical intervention.
With the advent of antifibrotic agents, such as 5-fluorouracil and mitomycin, some eyes that previously would have required an implant today possibly may be treated using filtration, with
Figure 242-2 Silicone tube. Here it extends beyond the pupillary border in neovascular glaucoma. The tube is enveloped totally in fibrovascular tissue up to pupil margin and the cut end of the silicone tube beveled up to prevent occlusion by iris.
the addition of an antimetabolite. Nonetheless, conditions still exist for which an implant may be more useful; these include neovascular glaucoma, aphakic glaucoma, and conditions that produce extensive scarring of the angle of the eye and extensive anterior conjunctival scarring.
Filtering surgery is more likely to fail in neovascular glaucoma as a result of closure of the internal opening of the filter by neovascular fibrous tissue. This can be avoided if the tube of the draining implant is placed well into the anterior chamber, often as far as the pupil margin. Even with this type of tube placement, the whole base of the internal tube may become enveloped by neovascular fibrous tissue, which results in closure of a filtration site, despite antimetabolite treatment (which prevents external scarring only) ( Fig. 242-2 ). The ideal approach with neovascular glaucoma, seen in the acute stage, is total vitrectomy, endolaser photocoagulation of the fundus, and pars plana placement of the drainage implant tube.
Aphakic glaucoma requires extensive vitrectomy for a simple filter to function. A less extensive vitrectomy allows the tube of the implant to be placed laterally on the iris, well away from the vitreous. A more recently applied treatment is the insertion of a drainage implant with the tube occluded by a releasable suture, accompanied by nonpenetrating glaucoma surgery. The glaucoma implant remains as a backup and can be activated should the filter fail. Placement of the tube via the pars plana is an alternative approach requiring total or almost total vitrectomy.
Extensive Scarring of the Angle of the Eye
Conditions that produce extensive scarring of the angle of the eye, such as uveitis, the iridocorneal dysgenesis syndromes, and congenital glaucoma with iridocorneal dysgenesis, are subject to closure of the internal opening of the drainage fistula, and better results are obtained with the use of a draining implant.
Extensive Anterior Conjunctival Scarring
Extensive anterior conjunctival scarring, such as occurs after multiple previous surgeries or in rheumatoid arthritis, sometimes precludes successful filtration even with the use of
Figure 242-3 Traction suture beneath the superior rectus muscle. With a connecting silicone tube that passes above the superior rectus muscle (arrow) and 4-0 silk marker sutures in the free edge of
antimetabolites and may require a drainage implant, with the tube inserted via the pars plana, associated with total vitrectomy.
The alternatives to drainage implant surgery include trabeculectomy surgery with use of adjunctive antimetabolites (see Chapters 239 and 240 ) or, especially for eyes that already have poor vision, a cyclodestructive procedure (see Chapter 237 ).
Drainage implant surgery involves traction on the recti muscles and a retrobulbar injection anesthetic is generally recommended. If discomfort occurs later in the procedure, additional anesthesia with lidocaine (lignocaine) using a soft cannula directly into the cone between the muscles is easily performed, as this site is already dissected for placement of the drainage implant.
All draining implants, except for encircling tube devices, are fixed in a similar manner; namely, the silicone tube is inserted into the eye and the plate or plates fixed to the sclera in a posterior position. The insertion of a double-plate Molteno implant is described here as an example, but variations in technique exist.
A fornix-based conjunctival flap is fashioned by elevation of the conjunctiva from the underlying sclera using balanced salt solution injected through a 30-gauge needle inserted at the limbus of the cornea. The conjunctiva is dissected from the limbus from the 10 o’clock to the 2 o’clock positions. A relaxing incision of about 7?mm length is then made by the insertion of one blade of a Westcott scissors posteriorly, parallel to the upper borders of the lateral and medial rectus muscles. The two free corners of the conjunctiva thus formed are marked with a suture to ensure accurate replacement at the end of the procedure ( Fig. 242-3 ). By blunt dissection, the conjunctiva is elevated off the underlying sclera for a distance of 7?mm.
Further posterior dissection of the conjunctiva is carried out by inserting a cellulose sponge posteriorly into the superotemporal and superonasal quadrants ( Fig. 242-4 ). This blunt dissection with the sponge is relatively atraumatic and creates a pocket for both medial and laterally placed plates. A muscle hook is placed beneath the superior rectus muscle, which is freed from the overlying conjunctiva by blunt dissection, with dissection close to the conjunctiva rather than the muscle, and entry into the muscle sheath
Figure 242-4 Cellular sponge dissection pocket for the plate of a Molteno implant.
is avoided. A 4-0 bridle suture is then passed beneath the superior rectus muscle and is used as a traction suture (see Fig. 242-3 ). If previous surgery has resulted in scarring of the conjunctiva in the anterior aspect of the bleb, the fornix-based flap can be fashioned from as far back as 3–4?mm from the limbus. More extensive scarring than this may require insertion of the tube through the pars plana, a procedure that requires the addition of an extensive vitrectomy. The implant may also be placed inferiorly, but this can be done only where binocular vision is not present or of poor enough quality to avoid diplopia, as inferior implant placements may result in some restriction of ocular motility and result in diplopia.
The circular plates of a Molteno implant are 13.5?mm in diameter but fit adequately into the pockets created by the blunt dissection of conjunctiva from underlying sclera formed by the cellulose sponges, as described previously. The double-plate Molteno implants are designated right or left and, if used, as such result in the plate with the silicone tube for the anterior chamber being implanted in the superomedial quadrant of the eye. However, it is more convenient to place this plate laterally, where more room exists, and, therefore, it is preferable to use a left-sided implant for right eyes and vice versa. The plates have four holes for sutures, but only the anterior two are used. Prior to insertion of the plates, two 8-0 silk sutures are preplaced using curved needles (Alcon c5; Fig. 242-5 ). The medial plate is inserted and sutured to the sclera, approximately 8?mm behind the limbus. This rather anterior placement of the anterior edge of the plate ensures accessibility of the bleb at a later stage if needling is required. Insertion of the plate 12–15?mm posteriorly, as generally advocated, often does not allow any view of the bleb postoperatively, which precludes its assessment of viability or nonviability except by ultrasonography. Once the medial plate has been fixed between superior and lateral rectus muscles, the interconnecting silicone tube is passed over the belly of the superior rectus muscles (see Fig. 242-3 ). In this way, the silicone plate does not have to pass beneath the muscle, a relatively traumatic procedure to the superior rectus muscle.
The lateral plate can now be sutured to the sclera 8–10?mm behind the limbus, using the preplaced 8-0 silk sutures. Prior to insertion of the plate posteriorly, a 3-0 Supramid suture is passed
Figure 242-5 8-0 silk sutures preplaced in the plate. Prior to insertion and fixation of the plate. A 3-0 Supramid suture (arrow) is in the lumen of the silicone tube.
Figure 242-6 Scleral patch graft (arrow) with preplaced 10-0 nylon sutures fixed on one side and rotated laterally to allow access to the tube. Paracentesis is made using a microsharp blade.
into the lumen of the silicone tube. The excess 3-0 suture that emerges from the surface of the plate is left long (see Fig. 242-5 ). To prevent postoperative hypotony, the tube is occluded totally using a 7-0 polyglactin (Vicryl) suture, which is placed around the tube at its junction with the plate and constricts the tube on to the obturating 3-0 Supramid suture. Slits, with the use of a microsharp blade, are placed in the silicone tube in front of the 3-0 Supramid suture to act as a temporary valve and prevent excessive buildup of pressure in the early postoperative period.
The silicone tube is then covered by a patch graft of either glycerin-preserved sclera or rehydrated preserved pericardium. The patch is fixed to sclera with four separate 10-0 nylon sutures, inserted at the four corners of the patch. The two lateral sutures are tied and the two medial sutures are left untied so that the patch can be rotated laterally to leave the tube exposed for further handling ( Fig. 242-6 ). The silicone
Figure 242-7 Silicone tube is inserted through 22- or 23-gauge needle opening at limbus. Note distal end of Supramid suture that protrudes forward beneath anterior cut edge of the conjunctiva and the tube of the previously placed implant.
Figure 242-8 Two single-plate Molteno implants in one eye. Supramid suture (arrow) emerges from the conjunctiva at the limbus with the conclusion of the insertion of the second implant.
tube is then cut to size, which varies according to the requirements of the individual surgeon. The insertion of the tube into the anterior chamber is accomplished by the manufacture of a tract from the limbus into the eye using a 22 or 23 gauge needle inserted parallel to the iris plane (see Fig. 242-7 ). Prior to insertion of the tube, a paracentesis opening is made near the limbus using a microsharp blade to allow access for assistance in tube placement if the need arises (see Fig. 242-6 ). The end of the tube is cut in a manner that allows the opening to be beveled upward and so prevent occlusion by the iris (see Fig. 242-2 ). The tube is fixed to the sclera with a single 10-0 nylon suture beneath the scleral patch (see Fig. 242-6 ). The scleral patch is secured by tying the previously placed two 10-0 sutures that were left untied.
The conjunctiva is then brought forward and, using the two marker sutures, is sutured back to the limbus at the extreme ends of the incision using 7-0 Vicryl sutures. The relaxing incisions are closed with a continuous 7-0 Vicryl mattress suture. The 3-0 Supramid suture that protrudes from the posterior lumen of the silicone tube is brought forward beneath the conjunctiva so that it emerges at the limbus. The suture is trimmed so that its free edge just protrudes from the free limbal edge of the conjunctiva ( Fig. 242-8 ), which allows free access to the suture postoperatively. The suture is not exposed as postoperative edema of the conjunctiva just covers its free edge. No conjunctival incisions are needed to remove the suture when this becomes necessary, which is usually 2–3 weeks postoperatively, by which time a capsule has formed over the plate and prevents the occurrence of hypotony.
A combination corticosteroid antibiotic drop and topical atropine are used for 3 weeks postoperatively. After this, topical corticosteroids alone are used for a further 6 weeks. After 4–6 weeks, the IOP often becomes elevated as a result of excessive fibrous tissue in the bleb capsule. This IOP rise needs to be treated or it results in further fibrous tissue deposition and failure of the procedure. The use of a topical carbonic anhydrase inhibitor together with a topical ß-blocker is often adequate to control this IOP rise. If these measures prove to be inadequate, aspiration of the bleb and removal of aqueous result in a temporarily lower IOP, which continues for 1–2 weeks. This procedure can be repeated until IOP control is achieved.
Complications may be subdivided into intraoperative, early postoperative, and late postoperative.
Intraoperative complications are uncommon but include bleeding, misdirection of silicone tube, and loss of anterior chamber. Bleeding occurs particularly in neovascular glaucoma, and large hyphemas must be evacuated as they can block the tube. Misdirection of the silicone tube into the posterior chamber may occur in the presence of peripheral anterior synechiae. The tube must be removed and reintroduced more anteriorly. This can be assisted by the insertion of a thin iris repositor through a previously prepared paracentesis opening and placement of the repositor beneath the tube as it enters the anterior chamber, which prevents the tube from following the old tract to the posterior chamber. Loss of anterior chamber may be remedied by the introduction of saline or viscoelastic solution through a previously placed paracentesis opening.
Early Postoperative Complications
The most common early postoperative complication is hypotony, with or without associated choroidal effusions. Hemorrhagic effusions are often associated with pain, even though the eye remains hypotonic. Small choroidal effusions may be left to resolve spontaneously. Large effusions that result in “kissing choroidals” may have to be evacuated, which may need to be combined with gas injection into the vitreous cavity to prevent rapid recurrence. Overfiltration may also need to be addressed by occlusion of the anterior silicone tube. Choroidal effusions may occur even with tubal occlusion, particularly in diabetic patients. Hypotony is best treated by prevention, either by the use of valved implants or by occlusion of the silicone tube with a stent and/or a constricting ligature, as described earlier. Neither method is fail-safe, but tubal occlusion is more likely to prevent hypotony. When using a double-plate Molteno implant, an additional safeguard against hypotony may include an absorbable ligature placed around the silicone tube that connects the two plates.
Increased IOP may occur as an early postoperative complication, usually because of blockage of the silicone tube. The opening of the tube may be obstructed by iris, which may actually enter the lumen of the tube. This can be treated by ablation of the iris tissue with the yttrium-aluminum-garnet laser. When an internal obturator is used for the silicone tube, postoperative hypertension can be prevented by the placement of venting slits in the tube. Also, hypotensive agents may be used in the early postoperative period to treat elevations in IOP, which allows the stent to remain in position until an adequate capsule has developed around the plate, usually at about 14 days. This capsule prevents the occurrence of extensive hypotony when the stent is removed. The use of a 22-gauge needle by some surgeons to introduce the silicone tube into the eye usually results in some
minimal leakage around the tube, which prevents extreme elevations in IOP.
Tube-corneal contact may occur and is best treated by prevention, which consists of accurate placement intraoperatively away from the endothelium and parallel to the iris. Total tube corneal touch requires the tube to be repositioned.
Occlusion of the tube by vitreous may occur in aphakic eyes. This is prevented by placement of the tube on the iris and away from the pupil and where necessary by the combination of this with an adequate anterior vitrectomy. Vitreous in the tube is best treated using vitrectomy.
The most significant late complication is the development of a thick capsule around the plate(s), which results in an elevation of IOP. Often, a hypertensive phase may be seen 4–6 weeks postoperatively because of the development of a fibrous capsule. Thinning of the capsule may occur subsequently, but for this to happen the IOP must be normalized. The IOP may be controlled using hypotensive agents, exclusive of cholinomimetics. If this proves inadequate, the bleb may be aspirated, a procedure that lowers IOP and may be repeated on a weekly basis until thinning of the bleb occurs.
Deflation of the bleb is designed to allow compressed channels in the wall of the bleb to expand and reestablish drainage.  Because the encysted blebs contain a relatively large amount of aqueous, as much as 1?cm3 of aqueous may be withdrawn to deflate the bleb with no loss of the anterior chamber. Also, because these blebs are relatively avascular, to needle them is less traumatic than an anterior chamber paracentesis, which risks damage to intraocular structures, particularly in phakic patients. The needling is done with a 27- or 30-gauge needle, the tracks of which are self-healing and are not associated with hemorrhage or infection.  The application of an antimetabolite, such as mitomycin C, to the eye at the site of plate implantation intraoperatively has been reported with moderate success. Molteno and colleagues  suggested the use of fibrosis suppression medication, which consists of a nonsteroidal anti-inflammatory agent, systemic corticosteroids, colchicine, topical corticosteroids, and topical epinephrine (adrenaline). A modified regimen that consists of diclofenac 75?mg daily, prednisone 40?mg daily, and topical corticosteroids has also had some success. This systemic regimen needs to be given no later than 14 days postoperatively to be of any use and should be continued for at least 6 weeks. Removal of preexisting implants is inadvisable and failure as a result of bleb fibrosis is best treated by the insertion of another drainage implant.
Erosion of the silicone tube through the sclera or scleral patch and conjunctiva can occur ( Fig. 242-9 ). More rarely, the plate may erode through the conjunctiva; this is most likely if the
Figure 242-9 Totally exposed silicone tube. It has eroded through the sclera and conjunctiva.
original conjunctival incision for plate implantation is made over or close to the plate. Fornix-based conjunctival flaps are most likely to prevent the occurrence of plate erosion.
Plate migration is extremely rare, even if the anchoring sutures become loose, as the enclosing capsule, once it has formed, keeps the plate in position.
Limitation of eye movement may occur because of the size of the blebs that overlie the plate or plates. The movement most commonly affected is upgaze, but this usually has little effect on the patient clinically. Placement of the implants in the lower quadrants restricts downgaze, with associated diplopia where vision is good in both eyes, and, therefore, plate implantation into the lower quadrants is to be avoided in an eye that has vision adequate enough to produce diplopia. Certain implants may produce more motility problems than others, even when placed in the superior quadrants. Retinal detachment has been described as a complication, albeit rare, of implant use. Sterile hypopyon has been reported to occur with Molteno implants and may be related to the presence of an obstructing ligature. The occurrence however, is, very rare.
Most reported results indicate fairly favorable outcomes in the short term with the use of glaucoma implants.     This is true especially when dealing with neovascular glaucoma. Mermoud et al. reported 62.1% success at 1 year and 10.3% success at 5 years. Success rates reported with shunt procedures have been based on relatively high end IOP as the criterion for success. Most published reports use an end IOP of 21?mmHg (2.8?kPa) or lower as a successful IOP level, which is not acceptable for cases of advanced glaucoma that have severe optic nerve damage.    It is important to note that shunt procedures in general do not give very low end IOPs, irrespective of the size of the plates used. Nonetheless, it is reported that the greater the surface area of the plates, the lower the end IOPs. Neovascular glaucoma is the one condition most likely to be treated with a glaucoma implant. Rates reported for neovascular glaucoma using different implants are given in Table 242-1 and provide a
TABLE 242-1 — RESULTS WITH DRAINING DEVICES IN NEOVASCULAR GLAUCOMA
Percentage Success [<21?mmHg (<2.8?kPa)]
Molteno (black patients only)
TABLE 242-2 — RESULTS WITH DRAINING DEVICES IN REFRACTORY GLAUCOMA
Percent Success Aphakic/Pseudophakic (Number)
Percent Success Glaucoma <13 Years (Number)
Percent Failed Filter (Number)
good perspective on the efficacy of these devices in the management of this condition. Results obtained in other types of refractory glaucoma are given in Table 242-2 . The Ahmed valve implant has been reported to achieve a 78% probability of success at 12 months in patients who have refractory glaucoma. The Krupin disc implant has been reported to achieve 83% success in patients who have refractory glaucomas. Molteno et al. recently reported long-term results of uveitis with secondary glaucoma drained by Molteno implants. Insertion of a Molteno implant was effective in controlling the IOP at 21?mmHg or less in 76% of cases over a mean follow-up period of 7.1 years.
Glaucoma implants have found a place in the management of refractory glaucomas. With the development of new implants and methods to overcome postoperative hypotony and with the ongoing research to achieve thinning capsules over the plates and thus lower IOPs, a future may exist for the use of implants as a primary surgical procedure for glaucomas that are not refractory. With careful patient and implant selection, many eyes that might have been lost may be retrievable.
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