Year : 1998 | Volume
: 46 | Issue : 1 | Page : 41--46
The role of artificial drainage devices in glaucoma surgery
R Thomas, A Braganza, G Chandrasekhar, S Honavar, AK Mandal, R Ramakrishnan, BS Rao, R Sihota, NN Sood, B Shantha, L Vijaya
Christian Medical College, Vellore, Chennai, India
Christian Medical College, Vellore, Chennai
The use of artificial drainage devices (ADDs) or «DQ»setons«DQ» in glaucoma surgery is generally restricted to patients with refractory glaucoma at high risk for failure from conventional filtration surgery. ADDs, both valved and nonvalved are currently available in this country. Recently, some of these devices have been propogated as primary treatment even for primary glaucomas. This article examines the role of ADDs in the modern management of the glaucomas. Specific indications for ADDs and methods to reduce the complication of overfiltration are discussed. The use of antimitotics, such as 5-fluorouracil or mitomycin, with traditional filtration has decreased the indications for ADDs. The literature and our experience confirm that currently there is no role for use of ADDs as a primary procedure in most glaucomas.
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Thomas R, Braganza A, Chandrasekhar G, Honavar S, Mandal A K, Ramakrishnan R, Rao B S, Sihota R, Sood N N, Shantha B, Vijaya L. The role of artificial drainage devices in glaucoma surgery.Indian J Ophthalmol 1998;46:41-46
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Thomas R, Braganza A, Chandrasekhar G, Honavar S, Mandal A K, Ramakrishnan R, Rao B S, Sihota R, Sood N N, Shantha B, Vijaya L. The role of artificial drainage devices in glaucoma surgery. Indian J Ophthalmol [serial online] 1998 [cited 2023 Mar 22 ];46:41-46
Available from: https://journals.lww.com/ijo/pages/default.aspx/text.asp?1998/46/1/41/14978
Although modern techniques of trabeculectomy can successfully lower the intraocular pressure (IOP) in many patients with glaucoma, some have a poor prognosis for successful filtration. These include patients with juvenile glaucoma, neovascular glaucoma, secondary glaucoma, glaucoma in aphakia and pseudophakia, post-keratoplasty glaucoma, and in those with previously failed filtration surgery.
In order to facilitate filtration in these high-risk patients, surgeons have used a wide variety of foreign materials to provide a shunt for aqueous. These include horse hair, gold, tantalum, platinum, glass, autologous lacrimal canaliculus, polyethylene, teflon, gelatin film, and cartilage. The first person to use an acrylic plate implant was Qadeer. These early implants were associated with high complication rates, poor results, and extensive intraocular inflammation.
In the late 1960s with Molteno's description of his acrylic drainage device, implants began to show promise for successful filtration in select glaucoma patients., Subsequently a number of other artificial drainage devices (ADDs) have become available.
A recent innovation has been the incorporation of a valve to try and prevent overfiltration, the most common complication of ADDs. An impression is being created in the minds of the lay public as well as the medical profession, that such devices are a total cure for all kinds of glaucoma and safe to use as a primary procedure. It is in this context that we examine the role of ADDs in current glaucoma management.
Description of Artificial Drainage Devices
The Molteno implant consists of a silicone tube (outer diameter 0.6 mm and inner diameter 0.3 mm) that opens onto the upper surface of a circular, acrylic plate 13 mm in diameter. The conjunctival bleb that forms over the implant cannot contract to a size smaller than the acrylic plate.
The surface area of the single-plate model is 134 mm. The edge of the plate has a thickened rim 0.7 mm high that is perforated to permit suturing to the sclera thus preventing plate migration. To increase the potential space available for aqueous absorption, Molteno designed a double-plate model. The double-plate implant consists of two 13 mm plates (surface area of 268 mm). They are connected to each other by a 10 mm silicone tube entering 90-away from the primary, intracameral tube. The plates are sutured to adjacent quadrants with the connecting tube placed either above or below the appropriate rectus muscle. The implantation of a double-plate involves more dissection and therefore is more demanding than the single-plate implant. The two plates in effect double the amount of potential surface area through which aqueous can be absorbed. Molteno found that two plates provided better drainage than one, but four plates were not better than two. It has been observed that children initially controlled with double-plate implants may, over a period of years, require another double-plate implantation for adequate control of IOP. Molteno noted that the single-plates have higher success rates in pseudophakic/aphakic glaucoma, while double-plate implants had better success rate in neovascular glaucoma.
Other variations of the Molteno implant include a pediatric size plate for use in eyes with short axial lengths, and the V-chamber plate. The V-chamber modification is designed to decrease postoperative hypotony from over-filtration. The V-chamber implant contains a thin V-shaped rim of polypropylene on the plate surface below the tube's entry, occupying one-eighth of the plate's area. Since this V-shaped ridge is the same height as the circumferential rim of the plate, the weight of the overlying, hydrated Tenon's tissue will in theory collapse and form a temporary roof for the smaller V-chamber, thus limiting the extent of the bleb and filtration. The clinical effectiveness of this design has not yet been established.
Most of the other devices available are made of similar materials and have a similar silicone tube for shunting aqueous or draining aqueous from the anterior chamber. Other non-valved ADDs include the Baerveldt implant and the Joseph Hitchings tube. Recently introduced valved implants include the Krupin valve, the Ahmed implant, and the Optimed device. The more commonly available devices and some of their characteristics are listed in the Table. We will concentrate on the implants most commonly used in this country, namely the Molteno implant and the recently introduced Ahmed valve. The discussion however is equally applicable to the other devices.
Indications for Use
ADDs are associated with serious intraoperative and postoperative complications. Because of these complications, they are usually reserved only for high-risk glaucoma patients where the prognosis for traditional filtration surgery is poor, or where previous surgical attempts have failed to control the intraocular pressure.
Patients who require ADDs typically have few options other than cyclodestruction. Recently published results of traditional filtration with antimitotics, such as 5-fluorouracil and mitomycin, are encouraging, and will further decrease the need for seton surgery.
ADDs are indicated in patients with elevated IOP or progressive disc damage or field loss despite maximally tolerated medical therapy and prior failure with conventional filtration surgery preferably with the use of antimitotics. ADDs are used in such eyes with primary open-angle, closed-angle, and congenital glaucomas, in secondary glaucomas including uveitic, neovascular glaucoma, glaucoma in aphakia and pseudophakia, and glaucoma following penetrating keratoplasty. Patients with aphakia who need a contact lens may require an ADD. Additionally, patients with glaucoma associated with the irido-corneal-endothelial (ICE) syndrome may benefit from an ADD. Epithelial ingrowth, badly traumatized eyes with conjunctival or scleral injury that precludes conventional filtration, and bad surface disease such as pempihgus are also reasonable indications for an ADD.
In most cases trabeculectomy with an antimitotic, such as 5-fluorouracil or mitomycin, should probably be attempted before an ADD is used. If the visual potential is poor, cyclodestructive procedures would probably be preferable.
The surgical technique is similar for most implants. A fornix-based conjunctival flap is created with two relaxing incisions. A large rectangular, half-thickness limbus-based scleral flap is then prepared in order to cover as much of the tube as possible. The episcleral draining part of the implant is placed in Tenon's space and the anterior portion sutured to the sclera approximately 7 mm posterior to the limbus in the selected quadrant.
The silicone tube is placed radially across the scleral flap and excess tube is trimmed to allow it to overlap the limbus by 2 mm. The anterior chamber is entered parallel to the iris plane preferably with a 22 or 23 gauge needle, and the tube is inserted into the anterior chamber. The scleral flap is sutured. Tenon's tissue and conjunctiva are drawn forward and sutured to the limbus.
Most surgeons modify this technique by omitting the scleral flap, and covering the tube at the limbus with a scleral patch graft (either preserved in glycerin or from a fresh donor eye). When a scleral patch graft is used, the entire procedure is essentially extraocular, except for the insertion of the needle into the anterior chamber for the insertion of the tube. An additional advantage of the scleral flap is that this technique creates forces which help keep the tube away from the corneal endothelium.
A major complication of ADDs is a flat anterior chamber resulting from over-filtration. Attempts to reduce this complication include ligatures around the external portion of the tube or suture occlusion of the internal lumen., The latter method originally involved a chromic suture that was temporarily threaded inside the lumen of the tube to occlude it. The other end was brought out of the conjunctiva, enabling the suture to be removed in a rip-cord fashion approximately one week after surgery. This technique was associated with sterile hypopyon following the removal of the suture due to autolysis of the suture material. In order to prevent this complication, a non-absorbable suture can be used instead.
In an attempt to allow bleb formation without the inflammatory stimulus of aqueous a two-stage procedure may be used. In the first stage, the plate is secured to the episclera, but the tube is not inserted into the anterior chamber. Six to eight weeks later, the tube is connected intracamerally and aqueous is allowed to drain into the preformed bleb, thereby preventing the free-flow of aqueous that would lead to hypotony and a flat anterior chamber.
Molteno described a complicated regimen of anti-inflammatory drugs to be used after the second stage,but this is not used by any of the authors. A major disadvantage of two-stage implantation is that the IOP remains uncontrolled until the second stage is performed. While this can be avoided by performing a "temporary" trabeculectomy during the first stage, most surgeons prefer to use a one-stage operation. Theoretically, a two-stage procedure or ligature is not necessary for a valved implant.
Most authors report success rates for IOP control between 67-96%.,,,,,, Due to the heterogenous patient groups, and differing definitions of success exact comparison of these studies is difficult. A significant number of successful cases require additional antiglaucoma medications to control the IOP.
The success rate depends on the type of glaucoma. The highest success rates occur in eyes with open or closed angle glaucoma that have a history of prior failure after filtration surgery. Success rates are poorer in eyes with neovascular and other types of secondary glaucoma, and in the pediatric patient., In neovascular glaucoma a success rate of 10% after 5 years has been reported, the main advantage being that pain was relieved and enucleation avoided. In uveitic glaucoma the success rate is similar to trabeculectomy with mitomycin and ADDs have only been recommended where marked postoperative inflammation is expected. The experience of one of the authors (AKM; presented at All India Ophthalmological Society Annual Meeting, Mumbai, 1995) suggests that trabeculectomy with mitomycin-C may be preferable to ADDs as primary treatment in post penetrating keratoplasty glaucoma. Patients with glaucoma following congenital cataract surgery seem to have a better result than other pediatric patients.
Experimental studies on rabbit eyes and clinical studies suggest that use of ADDs with adjunctive intraoperative mitomycin-C may be able to achieve target pressure in high-risk glaucomas.
Most authors emphasize the need for intensive postsurgical management. This is a major reason why, even in remote areas, ADDs should not be considered a primary procedure.
ADD surgery is associated with a high rate of complications. This is in part due to the severity of glaucoma and poor prognosis that these patients have to begin with.
Intraoperative complications can include perforation and exposure of uveal tissue during fixation of the implant to the sclera or during dissection of the scleral flap, especially in eyes that have been operated on several times previously. Complications during the insertion of the tube include ciliary body bleeding and vitreous loss. With a large entry incision, there can be leakage around the tube with creation of a limbal bleb. If the needle track is not parallel to the plane of the iris, kinking of the tube with subsequent tube-cornea or tube-iris contact may occur.
Other potential intraoperative complications include hyphema, suprachoroidal hemorrhage or expulsion, and vitreous hemorrhage.
The most common postoperative complication is excess flow through the drainage device. This occurs early postoperatively, before encapsulation around the exoplant has occurred. The excess flow can result in a flat anterior chamber, prolonged hypotony and choroidal detachment. Drainage of the choroidals and reformation of the anterior chamber is particularly indicated if there is lenticulo-corneal touch. This complication should theoretically be seen less frequently with valved devices or where temporary occlusion of the tube lumen has been effected. However, in our experience over-filtration does occur even with the Ahmed valve. Of the three cases in which this valve was used in one center, two shallowed and one flattened; two required surgical intervention. Another of the authors has had similar experience in 11 cases. The implant had to be removed in one eye in that series. This lack of valvular function is because the characteristics of the valve described by the manufacturer have been determined in air which is not analogous to the clinical situation in aqueous. Also, studies have shown that the valve functions at flow rates considerably in excess of normal aqueous inflow, and fails to perform its function in vitro when wet with balanced salt solution or plasma. These results would seem to negate any claim that the valved implants are in any way superior to the non-valved devices with regard to the potential for postoperative hypotony. This has been borne out by a recent multicentric study evaluating the results of Ahmed valve implantation. The authors reported a success rate at 12 months (78%) comparable to other similar devices, valved or non-valved. Complications reported included early hypotony and shallow anterior chamber in 16.7%, choroidal effusions in 22%, cumulative complication rate of 72%, resurgery rate of 25% for valve related complications, and a mean number of 14 patient visits in 9 months. The fact that 32% of the eyes in the study were primary unoperated glaucomas, indicates that the argument that complications occur because ADDs are used only as a late modality in management is not entirely true.
The intracameral portion of the tube can touch the corneal endothelium and cause localized corneal edema or corneal decompensation. If it is away from the optical axis it usually does not affect the visual acuity. However, in some patients, diffuse corneal edema and bullous keratopathy have developed. This tube-corneal touch is decreased by using ha scleral patch graft instead of a scleral flap, and also by having a longer corneal intralamellar track through which the tube is placed. Tube-lens touch may be associated with cataract and tube-intraocular lens (IOL) touch associated with dislocation of IOL.
Postoperative intraocular inflammation is frequently intense in these patients necessitating frequent topical steroids. Occasionally, systemic steroids are required.
The open end of the anterior chamber tube can be blocked with fibrin, blood, vitreous, or iris tissue. The Argon or Nd:YAG laser can be used to free the opening of debris or tissue or retract the iris from the tube opening.,
Posterior migration of the tube out of the anterior chamber can result from inadequate anchoring of the tube to the episclera. In a child, growth of the eye can also lead to retraction of the tube out of the anterior chamber. Late erosion of the either the tube or the episcleral exoplant can occur. Melting of the scleral flap or the scleral patch graft results in the tube being covered only with the conjunctiva. The episcleral exoplant can erode either externally through the conjunctiva or internally through the sclera.
Epithelial ingrowth may result from the insertion of the anterior chamber tube through a corneal wound. Endophthalmitis of the bleb can occur as a late complication.
Other late complications include choroidal effusion, choroidal hemorrhage, pupillary-block glaucoma, malignant glaucoma, infection, endophthalmitis, retinal detachment, and phthisis bulbi.
Motility disorders may occur following ADD implantation and result in diplopia., These are caused by restrictions or "faden" effects on the extraocular muscles. In children, motility disorders may result in amblyopia and must be looked for and treated appropriately. Diplopia is likely to be more of a problem if ADDs are used as primary therapy for glacucomatous eyes with good visual acuity.
It has been suggested that in order to prevent strabismus in patients with binocular vision, implantation of a large implant in the nasal quadrant is better avoided. A recent case report highlighted another potential danger of a large sized implant in the nasal quadrant. Examination of an enucleated eye revealed an implanted Ahmed implant to be within 1mm of the optic nerve. This potential for contact with the optic nerve was confirmed in a donor eye. The authors suggest that placement of the Ahmed implant in the superonasal quadrant is better avoided.
The high potential for complications and the need for close follow up of eyes with ADDs has prompted the Food and Drug Administration in the USA to classify these devices as Category III, presenting potential unreasonable risk requiring the highest level of regulation.
Artificial drainage devices expand the range of therapeutic options in difficult glaucomas. However, they should be reserved only for eyes refractory to or with high risk of failure for conventional filtering surgery (with pharmacological modulation), or where such surgery may not be technically possible. The potential for complications and need for intensive, often aggressive postoperative care rules out any role for ADDs in previously unoperated primary glaucomas, especially in remote areas of developing countries.
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