Medical expert of the article
New publications
Drainage devices for glaucoma
Last reviewed: 06.07.2025
All iLive content is medically reviewed or fact checked to ensure as much factual accuracy as possible.
We have strict sourcing guidelines and only link to reputable media sites, academic research institutions and, whenever possible, medically peer reviewed studies. Note that the numbers in parentheses ([1], [2], etc.) are clickable links to these studies.
If you feel that any of our content is inaccurate, out-of-date, or otherwise questionable, please select it and press Ctrl + Enter.
Glaucoma drainage devices, either fluid or tubular shunts, are used to reduce intraocular pressure in patients with uncontrolled glaucoma in whom fistulizing surgery with antimetabolites has failed or has little chance of success. Fluid shunting devices consist of a posteriorly positioned episcleral explant, which forms a filtration pad, and an attached silicone tube that is inserted into the eye, usually into the anterior chamber (sometimes through the pars plana). A posterior filtration pad is formed around the episcleral explant. Aqueous fluid passes passively through the capsular wall and is reabsorbed by venous and lymphatic capillaries.
Currently, there are several types of drainage devices that differ in the presence or absence of an outflow-limiting element, as well as in the design of the episcleral plate or plates. Non-restrictive devices [i.e., single- or dual-chamber Molteno, Baerveldt] provide free outflow of fluid from the inner opening of the tube into the anterior chamber to the episcleral explant. Restrictive devices (Krupin, Joseph, White, Optimed, single- or dual-plate Ahmed) contain an element (valve, membrane, or resistant metrics) at the end of the tube that limits the flow of fluid to prevent postoperative hypotony.
Description of drainage devices for glaucoma
Implantation of drainage devices for glaucoma is usually performed under retrobulbar, peribulbar, or sub-Tenon anesthesia. The preferred site of implantation is the superior temporal quadrant. To ensure good visibility of the surgical field, a suture is placed on the superior rectus muscle, or a corneal or scleral traction suture.
The conjunctival flap can be either a limbal or fornix-based flap. For single-plate implants, a 90-110° conjunctival incision is sufficient. The drainage sheet is placed episclerally between the adjacent rectus muscles so that its anterior edge is at least 8 mm posterior to the limbus. Non-absorbable sutures (nylon 6-0-8-0) are passed through the fixation holes in the drainage body, and the plate is sutured to the sclera. The optimal length of the tube is determined by laying the tube across the cornea. Then the tube is cut with an upward bevel so that it enters the anterior chamber by 2-3 mm. Corneal paracentesis is performed. To create limbal-scleral access, a 23G needle is inserted into the anterior chamber at an oblique angle parallel to the plane of the iris approximately 1-2 mm posterior to the corneoscleral limbus. Then, through this access, using anatomical tweezers, a tube is inserted into the anterior chamber.
Correct positioning of the tube in the anterior chamber is very important.
Care must be taken to ensure that the tube does not touch the iris, lens, or cornea. The tube can be secured to the sclera with 10-0 nylon or prolene sutures. The anterior suture is wrapped tightly around the tube to prevent movement in or out of the anterior chamber. To avoid postoperative conjunctival erosion above the tube, donor sclera, fascia lata, dura mater, or pericardium can be used to cover the limbal portion of the tube. This tissue is sutured in place with single interrupted 10-0 nylon, prolene, or vicryl sutures.
The tube can also be inserted through the pars plana if its insertion into the anterior chamber is complicated or contraindicated (corneal transplant, very shallow anterior chamber at the iridocorneal junction, etc.). In this case, it is necessary to perform a vitrectomy through the pars plana with careful removal of the anterior limiting membrane of the vitreous body at the site of tube insertion.
To prevent postoperative hypotension when introducing non-restrictive devices, an additional procedure is necessary. Before suturing the plate to the episclera, the tube is ligated with an absorbable vicryl thread from 6-0 to 8-0, causing its temporary occlusion.
Since the tube is completely ligated, several release incisions can be made in the anterior extrascleral segment with a sharp blade to maintain some drainage in the early postoperative period. The amount of aqueous drainage can be measured with a 27-gauge cannula on a saline syringe inserted into the end of the tube. The absorbable tube ligation can be further modified by inserting a 4-0 or 5-0 nylon suture (Latina suture) into the reservoir side of the tube. The remaining suture should be long enough to place the other end under the conjunctiva in the inferior quadrant. If intraocular pressure is not controlled medically before the ligature is absorbed, cauterization of the vicryl suture with an argon laser may open the shunt. If a Latin suture has been placed, a small incision in the lower part of the conjunctiva away from the reservoir allows the nylon thread to be removed from the lumen of the tube, making the shunt functional. The Latin suture has the advantage of not requiring the use of an argon laser if early opening of the shunt is necessary. Hermetic suturing of the conjunctiva completes the procedure for installing drainage devices in glaucoma.
[ 4 ], [ 5 ], [ 6 ], [ 7 ], [ 8 ]
Post-operative care
The postoperative regimen includes local administration of antibacterial and sometimes cycloplegic drugs for 2-4 weeks, as well as local application of glucocorticoids for 2-3 months after surgery. Nonsteroidal anti-inflammatory drops can be used simultaneously.
Complications of drainage devices in glaucoma
The insertion of shunt tubes is associated with a significant risk of postoperative complications. Early postoperative complications include hypotony and associated maculopathy, a shallow anterior chamber, choroidal detachment, suprachoroidal hemorrhage, abnormal aqueous flow, hyphema, and increased intraocular pressure. Hypotony is one of the most common complications and usually results from excess aqueous outflow. It may lead to a shallow anterior chamber and choroidal detachment. A persistent shallow anterior chamber may require additional ligation of the tube. Restrictive or valved implants are less likely to cause hypotony complications than nonrestrictive devices, but no prospective comparative study has been conducted.
Increased intraocular pressure may be due to occlusion of the tube by fibrin, a blood clot, the iris, or the vitreous. Fibrin and blood clots may resolve spontaneously. Intracameral injection of tissue plasminogen activator may promote resolution of the clot within a few hours, but there is a risk of severe bleeding. If the lumen of the tube is occluded by the iris, its patency can be restored by neodymium-YAG laser iridotomy or argon laser iridoplasty. Vitreous incarceration can be successfully treated with a neodymium-YAG laser, but anterior vitrectomy is necessary to prevent recurrence.
Late postoperative complications include increased intraocular pressure, hypotony, implant migration, conjunctival erosion, corneal edema or decompensation, cataract, diplopia, and endophthalmitis. Late increases in intraocular pressure are usually due to excessive fibrosis around the implant body. Corneal decompensation may result from direct contact between the tube and the cornea. If the tube touches the cornea, the tube should be repositioned, especially if there is a risk of endothelial damage (cases of focal corneal edema or after penetrating keratoplasty). Diplopia may be caused by mechanical contraction of the extraocular muscles. If diplopia is prolonged and not corrected by prismatic lenses, the shunt should be removed or relocated.