Understanding drainage in glaucoma surgery

January 6, 2016

It is important for optometrists to be familiar with these devices and the rationale behind the device chosen. This article describes what each device is, how they work, complications, and postoperative care.

Glaucoma drainage devices are increasingly flowing in many glaucoma practices. You may be familiar with laser glaucoma procedures, including argon laser trabeculoplasty, selective laser trabeculoplasty, and micropulse  laser trabeculoplasty. Trabeculectomy is a commonly performed filtering surgery as well.

But, you may not know the differences among Baerveldt Glaucoma Implant (Abbott Medical Optics), Ahmed Glaucoma Valve (New World Medical, Inc), iStent (Glaukos), and ExPress Glaucoma Filtration Device (Alcon). It is important for optometrists to be familiar with these devices and the rationale behind the device chosen. This article describes what each device is, how they work, complications, and postoperative care.

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iStent

The iStent trabecular micro-bypass is a micro invasive glaucoma surgery (MIGS) tool.1 It is essentially a small snorkel comprised of Heparin (heparin sodium, Hospitra)-coated titanium. The iStent is usually implanted nasally into Schlemm’s canal during cataract surgery and is designed to improve the aqueous outflow and decrease intraocular pressure (IOP) by creating a permanent opening in the trabecular meshwork.

The procedure involves inserting the iStent through the phacoemulsification incision site past the pupillary margin. The angle is viewed with a gonioscopy lens, and an approach is made to the upper one third of the trabecular meshwork at an angle of 15 degrees. The trabecular meshwork is engaged, and the iStent is gently inserted into Schlemm’s canal. The bottom of the inserter is pushed to release the iStent. The button is released, and the side of the snorkel is gently tapped to ensure the device is properly seated. The inserter and viscoelastic are then removed.1

Because the procedure is minimally invasive, it spares tissue damage caused by traditional glaucoma surgery. It is the smallest FDA-approved device for mild to moderate glaucoma. The iStent Inject is being developed with multiple iStents in a preloaded injector system if the surgeon deems it necessary to use more than one.2

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Contraindications for iStent use include primary- or secondary-angle closure glaucoma, neovascular glaucoma, thyroid eye disease, Sturge-Weber syndrome, or any other condition that may cause elevated episcleral venous pressure. Gonioscopy should be performed before surgery to rule out peripheral anterior synechiae, rubeosis, and any angle abnormalities or conditions that would occlude sufficient visualization of the angle that could lead to improper placement of the stent.1 Complications can include corneal edema, posterior capsular haze, stent obstruction, early postoperative cells in the anterior chamber (AC), and early postoperative corneal abrasion.1

Postoperative care generally includes the usual cataract recovery drop schedule as well as the patient’s currently prescribed glaucoma medications. Commonly used postoperative drops include Besivance (besifloxacin, Bausch + Lomb) tid for one week; prednisolone tid for one week, then bid for one week, then qd for two weeks, and Ilevro (nepafenac ophthalmic suspension, Alcon) qd for four weeks. If the IOP remains the same as it was preoperatively, then usually the patient will continue with his glaucoma drop regimen. A trial discontinuation of the glaucoma drops may be used to see how well the IOP is maintained.3

Next: Baerveldt Glaucoma Implant

 

Baerveldt Glaucoma Implant

Baerveldt Glaucoma Implant is designed for patients with medically uncontrolled glaucoma or patients who have failed conventional surgery. It is available in three models: 250 mm, 350 mm, and 350 mm pars plana.4 The 250 mm is the most commonly used size. Its features include a large surface area plate, single quadrant insertion, a drainage tube, recessed knot capability, decreased bleb height, low edge height, and four fenestrations to promote fibrous adhesions to the sclera, which may reduce bleb height. A fenestrated Baerveldt may reduce bleb height by 50 percent. These advantages allow for long-term IOP control, easier implantation, decreased surgery time, less trauma, and faster healing.4

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A Vicryl suture is used to tie off the tube before implantation and is tested with balanced salt solution (BSS) to ensure it is occluded. Some surgeons also insert a ripcord into the tube to be released later if further IOP reduction is necessary. The superior temporal conjunctiva is dissected, creating a conjunctival flap between the superior and lateral rectus muscles. The plate is placed behind the muscles and is secured to the sclera. If superior temporal placement is not possible, it may be placed inferonasally. An incision is made parallel to the iris through the sclera for entry of the tube into the anterior chamber. The tube is cut to size before being inserted into the AC. The tube should be close to the surface of the iris without indenting it. The tube is then covered with a patch graft. Two to three fenestrations may be made into the tube as well. If a ripcord is used, it is placed in the inferior conjunctival space and the conjunctival flap is closed.

Complications can include a choroidal hemorrhage, hyphema, choroidal effusion, hypotony, flat AC, phthisis bulbi, retinal detachment, endophthalmitis, tube erosion, tube touch to cornea, tube block by iris or vitreous, bullous keratopathy, uveitis, and diplopia.5 Corneal patch grafts are used to prevent tube erosion. The tube is initially restricted with a suture to prevent early hypotony. Some surgeons make fenestrations in the tube to control pressure early in the postop period. Tube touch to cornea can be avoided by placing the tube in the sulcus in pseudophakic patients.3

Regarding postoperative care, if an elevation in the IOP occurs early in the postop period and the suture has not broken, breaking the suture is an option. Using a ripcord suture gives the surgeon an additional choice. Glaucoma drops are continued during the initial postop period until the suture dissolves or is broken. Prednisolone drops are prescribed qid for approximately two weeks then tapered and Polytrim (trimethoprim/polymyxin B, Allergan) qid for 10 days. Routinely, patients are seen at one day, one week, three weeks, and five weeks until IOP is stabilized.3

Next: Ahmed Glaucoma Valve

 

Ahmed Glaucoma Valve

Although there are several models of this device, the original S2 is commonly used. The body plate is made of polypropylene, and the valve is made of polypropylene with a silicone elastomer membrane to control IOP. The Ahmed features immediate reduction of IOP and a valve system to prevent excessive drainage and AC collapse. There is no need for drainage tube ligature sutures, ripcord sutures, and occluding sutures. Other models include a pediatric or small globe S3, FP7, pediatric F8, PC7, pediatric PC8, and FX1 (with a bi-plate design). The latest model is M4 It is comprised of a porous polyethylene which allows soft tissue growth into the pores, promoting integration with surrounding tissue and vascularization.2

The procedure is performed almost the same as the Baerveldt Implant; however, no ripcord or tube occlusion is needed because it is a valved device. The valve needs to be primed with BSS. A patch graft is also used to prevent erosion in this procedure. Patch grafts can be corneal, pericardial or scleral. Our glaucoma specialist, Tyler Kirk, MD, prefers a corneal patch graft.3

Complications with an Ahmed Valve are similar to those of the Baerveldt and can include hypotony. However, it is usually transient and often spontaneously resolves.

Postop care includes discontinuation of all glaucoma drops, prednisolone qid for two weeks, and Polytrim qid for 10 days. Patients are seen at one day, one week, and three and five weeks until IOP stabilizes and the eye has healed.3

Next: ExPress Glaucoma Filtration Device

 

ExPress Glaucoma Filtration Device

ExPress Glaucoma Filtration Device is a 3-mm long non-valved device that, like a trabeculectomy, diverts aqueous humor flow from the AC to a bleb in the subconjunctival space. The initial procedure is similar to that of a trabeculectomy as well. ExPress is preloaded in an injector with a metal rod fitted through the lumen, which is attached to the end of the injector. The shunt is then placed under a scleral flap into the AC through the incision made with a 25-gauge needle. The shunt is inserted all the way into the wound so the plate is flush with the scleral bed. Like a punctal plug, the shaft of the injector is depressed, retracting the metal rod and releasing the shunt. The scleral flap and the conjunctiva are sutured. The flow is tested by inflating the AC with BSS through the temporal paracentesis. A fluorescein strip is used to check for wound leak.

Complications with ExPress Glaucoma Filtration Device include hypotony, although a study by Maris et al6 show a 32 percent hypotony rate with trabeculectomy and a four percent rate with the ExPress device. It is thought that this lower rate of hypotony is attributed to the resistance to flow due to the 50 µm lumen of the shunt.7

Postoperative care consists of discontinuation of all glaucoma drops, prednisolone four to six times per day for approximately four weeks, and Polytrim qid for 10 days. If the device is combined with cataract extraction, it is common to add Ilevro qd. Patients are seen at one day and every week after for several weeks. Suture lysis may occur at three weeks as needed. Prednisolone drops are generally tapered at four weeks.

Next: Choosing a device

 

Choosing a device

Selection of the device depends on numerous factors, such as patient’s age, glaucoma subtype, and treatment goals.8 There can be considerable pressure volatility in the early postoperative period with the Baerveldt Implant. However, lower long-term pressure control is often achieved. The Baerveldt tube is occluded during the first four to six weeks after surgery while the bleb forms around the plate. Flow begins when tube occlusion dissolves or is removed. This often causes a quick pressure drop and may cause hypotony-related complications. The Ahmed device has a built-in valve that allows for immediate flow postoperatively and thus prevents hypotony. However, glaucoma medications may be required long term. There are many other tube shunt devices such as the Molteno 3 and the Krupin.8

Other postoperative aids may include fibrin glue. Fibrin glue is a biological tissue adhesive that mimics the final stages of the coagulation cascade. Fibrin glue incorporates a fibrinogen and a thrombin component, both prepared by processing plasma. Fibrin glue forms a smooth seal along the wound and helps reduce hypotony and increase patient comfort. The glue is used in conjunction with sutures.9 If IOP is extremely low early in the postoperative period, atropine can be administered bid to deepen the AC and raise IOP. Additionally, a large diameter contact lens can be applied to tamponade the flow.3

The Centers for Medicare and Medicaid Services (CMS) announced in September 2015 that it will bundle and revalue tube shunt and patch graft surgeries.10 Surgeons have been placing patch grafts over tubes for years to reduce the incidence of tube erosion through the underlying conjunctiva. Therefore, a patchless technique is now appearing. Dr. Rafael Bohorquez recorded a video to demonstrate a 6-mm scleral tunnel used in lieu of a patch graft to cover the tube on its way into the AC.11 He recommends inserting a 22-gauge needle parallel to the iris to create the tunnel. He closes the back of the tunnel with a Vicryl suture to reduce the chance of filtration around the tube.12

Next: Looking ahead

 

Looking ahead

There are continually new procedures and devices on the horizon. InnFocus Micro Shunt is currently in Phase I FDA trials at 11 U.S. centers and is being implanted either alone or in combination with cataract surgery in clinical trials outside the U.S. The company reports that patients are experiencing a “stable reduction in mean IOP to below 14 mm Hg.” The report states that 70 to 80 percent of patients are requiring few medications or no medications at all.13

Other procedures include endocyclophotocoagulation, which reduces aqueous inflow by selective ablation of the ciliary body. This procedure can be done in conjunction with outflow procedures as well.13

Canaloplasty decreases IOP by creating a Descemet window and dilation and tensioning of the trabecular meshwork. This is performed using an iTrack micro catheter, developed by iScience Interventional, and a suture placement in Schlemm’s canal.13

Trabectome by NeoMedix uses bipolar cautery on a disposable handpiece to ablate a certain number of clock hours of the trabecular meshwork in an effort to increase outflow. It is approved for mild to moderate glaucoma and can be combined with cataract surgery.13

CyPass Micro-Stent by Transcend Medical is inserted via a clear corneal incision and placed in the supraciliary space. Its design is to increase uveoscleral outflow and it can be combined with cataract surgery.13

The ability of these many options allows the glaucoma specialist to customize procedures based on the physiological needs of each diseased eye and meet each patient’s individualized needs.

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References

1. Glaukos Corporation website. Available at: http://www.glaukos.com/istent. Accessed 12/22/15.

2. New World Medical, Inc. website. Available at: http://www.ahmedvalve.com. Accessed 12/22/15.

3. Kirk, Tyler. Personal interview. 16 Jan 2015.

4. Abbott Medical Optics website. Available at:

http://www.abbottmedicaloptics.com/products/cataract/glaucoma-implants/baerveldt-bg-101-350-glaucoma-implant. Accessed 12/22/15.

5. Sarkisian SR. Going with the flow: Managing tube shunts. Rev Ophthalmology. Available at: http://www.reviewofophthalmology.com/content/d/glaucoma_management/i/1210/c/22807/. Accessed 12/28/15.

6. Maris PJ Jr, Ishida K, Netland PA. Comparison of trabeculectomy with Ex-PRESS miniature glaucoma device implanted under scleral flap. J Glaucoma. 2007 Jan;16:14-9

7. Sarkisian SR. The ExPress mini glaucoma shunt: technique and experience. Middle East Afr J Ophthalmol. 2009 Jul-Sep;16(3): 134-137.

8. Ahmed IK, Christakis PG. Ahmed, Baerveldt, or something else? Rev Ophthalmology. Available at: http://www.reviewofophthalmology.com/content/t/glaucoma/c/41000/. Accessed 12/28/15.

9. Panda A, Kumar S, Kumar A, Bansal R, Bhartiya S. Fibrin glue in ophthalmology. Indian J Ophthalmol. 2009 Sep-Oct; 57(5): 371–379.

10. Corcoran S. Glaucoma coding: 2015 brings changes. Ophthalmol Management. Available at:

http://www.ophthalmologymanagement.com/articleviewer.aspx?articleID=112312

11. Eyetube.net: Available at: www.eyetube.net/video/non-extrusion-b-drainage-device-technique/. Accessed 12/28/15.

12. Myers JS. Tube coverage: Another approach. Glaucoma Today. Available at: http://glaucomatoday.com/2014/12/tube-coverage-another-approach/. Accessed 12/28/15.

13. Noecker RJ. Update on new glaucoma surgical devices. EyetubeOD. Available at: http://eyetubeod.com/2011/12/update-on-new-glaucoma-surgical-devices. Accessed 12/28/15.