Drainage devices for glaucoma
Last reviewed: 23.04.2024
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Drainage devices for glaucoma - fluid or tubular shunts - are used to reduce intraocular pressure in patients with uncontrolled glaucoma, in whom a fistulizing operation using antimetabolites has already been unsuccessful or has little chance of success. The instruments that shunt the fluid consist of an epiccleral explant located behind the back, providing the formation of a filtration pad, and a connected silicone tube that is injected into the eye, usually into the anterior chamber (sometimes through the pars plana). The posterior filtration pad is formed around the episcleral explant. The moisture passes passively through the wall of the capsule and is reabsorbed by the venous and lymphatic capillaries.
Currently, there are several types of drainage devices that differ in the presence or absence of an element limiting the outflow, as well as the design of the episcleral plate or plates. Non-limiting devices [i.e. One- or two-chamber Molteno (Molteno), Baerfeldt (Baerveldt)] provide free flow of fluid from the inner tube opening into the anterior chamber to the episcleral explant. Limiting devices (Krupina, Joseph, White, Optimed, one- or two-plate Ahmed) contain an element (valve, membrane or resistant metric) limiting the fluid flow in the end of the tube to prevent postoperative hypotension.
[Description of draining devices for glaucoma
Implantation of draining devices in glaucoma is usually performed under retrobulbar, peribulbar or subtenon anesthesia. The preferred place of implantation is the upper-temporal quadrant. To ensure good visibility of the operating field, a seam is applied to the upper rectus muscle, or the corneal or scleral traction joint.
A conjunctival flap can be either a base to the limbus or a base to the arch. For single-layer implants, a conjunctival incision of 90-110 ° is sufficient. The drainage layer is placed episclerally between the adjacent rectus muscles so that its anterior margin is at least 8 mm posterior to the limbus. Non-absorbable threads (nylon 6-0-8-0) are made through fixation holes in the drainage body, the plate is sewed to the sclera. The optimal length of the tube is determined by laying the tube across the cornea. Then the tube is cut with a bevel upwards so that it enters the front chamber 2-3 mm. Perform a corneal paracentesis. To create limbal-scleral access to the anterior chamber at an oblique angle parallel to the plane of the iris, a needle of caliber 23G is inserted approximately 1-2 mm behind the corneoscleral limb. Then, through this access, an anatomic tweezers are inserted into the anterior chamber.
Proper placement of the tube in the anterior chamber is very important.
Make sure that the tube does not touch the iris, lens or cornea. The tube can be fixed to the sclera by stitches with nylon 10-0 or with a seal. The front seam is tightly wrapped around the tube to prevent it from moving inside or out of the front chamber. In order to avoid postoperative erosion of the conjunctiva over the tube, a donor sclera, a wide fascia, a solid medulla or pericardium can be used to cover its limbal part. The site of such a fabric is sewn in the necessary place with single nylon seams with nylon 10-0, a cut or a vikril.
The tube can also be inserted through the pars plana if its introduction into the anterior chamber is complicated or contraindicated (corneal graft, very small anterior chamber at the site of the iridocorneal joint, etc.) In this case it is necessary to perform vitrectomy through the pars plana with careful removal of the anterior border membrane of the vitreous body at the site of injection of the tube.
To prevent postoperative hypotension with the introduction of non-limiting devices, an additional method is necessary. Before sewing the plate to the episclerus, the tube is ligated with a resilient vikrilic filament from 6-0 to 8-0, causing its temporary occlusion.
Since the tube is completely bandaged, several cutting incisions with an acute blade can be made in the anterior extrasclural segment to maintain some outflow of fluid in the early postoperative period. The amount of expiring moisture can be measured with a 27G cannula on a syringe with saline solution, which is injected into the end of the tube. The ligation of the resorbable tube can be further modified by introducing a nylon thread 4-0 or 5-0 (Latina seam) into the tube from the side of the reservoir. The remaining length of the thread should be enough to place its other end under the conjunctiva in the lower quadrant. If the level of intraocular pressure does not lend itself to drug control before resorption of the ligature, cauterization of the vichril thread with an argon laser can open the shunt. If Latina's seam was applied, then a small incision at the bottom of the conjunctiva away from the reservoir allows you to remove the nylon thread from the tube lumen, which makes the shunt functional. The Latina seam has the advantage of: it does not require the use of an argon laser when early shunt opening is necessary. Hermetic suturing of the conjunctiva completes the procedure for establishing drainage devices for glaucoma.
Post-operative care
Postoperative treatment includes local administration of antibacterial and sometimes cycloplegic drugs for 2-4 weeks, as well as topical use of glucocorticoids within 2-3 months after the operation. Simultaneously, non-steroidal anti-inflammatory drops can be used.
Complications of drainage devices for glaucoma
The introduction of shunting tubes is associated with a significant risk of postoperative complications. The early postoperative complications include hypotension and associated makulopathy, a small anterior chamber, a choroidal detachment, a suprachoroidal hemorrhage, an abnormal fluid flow, a hyphema, and an increased intraocular pressure. Hypotension - one of the most frequent complications, usually occurs as a result of excess outflow of watery moisture. It can lead to the shredding of the anterior chamber and the choroid detachment. The stability of the shallow anterior chamber may require additional ligation of the tube. Restrictive or valve implants are less likely to cause complications in the form of hypotension than non-limiting devices, but there has been no prospective comparative study.
The increase in intraocular pressure may be due to the occlusion of the tube with fibrin, a blood clot, an iris or a vitreous body. Fibrin and blood clots can dissolve on their own. Intracameral injection of a tissue plasminogen activator may contribute to resorption of the thrombus within a few hours, but there is a danger in this case of severe bleeding. If the tube lumen is occluded by the iris, its patency can be restored with neodymium AIG laser iridotomy or argon laser iridoplasty. Infringement of the vitreous humor can be successfully eliminated by neodymium AIG laser, but to prevent relapses it is necessary to perform anterior vitrectomy.
Late postoperative complications include increased intraocular pressure, hypotension, implant migration, conjunctival erosion, corneal edema or decompensation, cataracts, diplopia and endophthalmitis. Later, increased intraocular pressure is usually due to excessive fibrosis around the implant body. Decompensation of the cornea can be the result of direct contact between the tube and the cornea. If the tube touches the cornea, then reposition the tube, especially if there is a risk of damage to the endothelium (cases of focal edema of the cornea or after penetrating keratoplasty). Diplopia can be caused by a mechanical contraction of the extraocular muscles. If diplopia is long and not corrected by prismatic lenses, you must remove or move the shunt.