Monday, November 20, 2006

Section 8-C: Glaucoma Drainage Devices (Glaucoma Tube or Seton Implant)

A glaucoma drainage device (GDD) or tube is usually implanted when glaucoma is uncontrolled with medications, laser, or trabeculectomy. It is also used when there is not enough healthy tissue to proceed with trabeculectomy or in cases where trabeculectomy would likely fail. The goal of GDD is to allow aqueous fluid to leave the eye so that IOP will be lowered and halt the progression of glaucomatous visual loss.

Several models of GDD exist. The implants are typically made of silicone or polypropylene. Ahmed (figure 8-9. New World Medical, Inc., Rancho Cucamonga, CA), Krupin (Hood Laboratories, Pembroke, MA), Baerveldt (figure 8-10. Advanced Medical Optics, Inc., Santa Ana, CA), and Molteno (IOP Inc., Costa Mesa, CA) implants are the most common implants available. The GDDs are tubes, which are attached to a plate, and allow aqueous fluid to drain from the inside to outside of the eye. Both the tube and plate are covered by donor tissue and by patient’s own conjunctiva. A GDD can be with or without a valve. The tubes with a valve (Ahmed and Krupin) are made so that a set pressure is required before the tube opens and begins to drain aqueous fluid. They are usually implanted in cases where an immediate lowering of IOP is desired. The tubes without a valve (Baerveldt and Molteno) have no resistance to outflow of aqueous fluid, which may result in too low of an IOP (hypotony) initially. Severe or prolonged hypotony may lead to decreased vision or hemorrhage. To avoid these complications, the non-valved tube is often tied off with a dissolvable suture. The suture dissolves in approximately 6 weeks. During this time period, scar tissue develops over the tube plate which causes the required resistance to outflow that is necessary to avoid hypotony. Patients with non-valved GDDs are forewarned that the vision may suddenly become blurry with floaters about 6 weeks after surgery when the tube opens. The symptoms typically resolve over time.



Figure 8-9. Ahmed FP7 implant.Figure 8-10. Baerveldt 350 implant.

Indication for Tube Surgery
Drainage implant surgery is used in patients who may have failed other filtering surgeries and need a lower IOP. It is also useful in patients at higher risk of failure from trabeculectomy, due to previous scarring or inflammation of conjunctival tissue. Such conditions include neovascular glaucoma, uveitic (inflammatory) glaucoma, and conjunctival scarring from previous ocular surgeries. In these cases, GDD surgery may be more successful in controlling glaucoma.

The Tube Surgery
Prior to surgery, patients may be asked to stop any medication that “thins” the blood (e.g. aspirin, ibuprofen, warfarin, (Coumadin), clopidogrel (Plavix), or ticlopidine (Ticlid)). Usually, this is coordinated with the primary care physician who is managing these medications. The surgery is typically performed under local anesthesia. Either a periocular injection of anesthetic is given, and/or topical medications to provide adequate pain control.
The conjunctiva in the designated quadrant of the eye is opened so that the eye muscles may be identified. The plate of the tube is placed between or underneath the eye muscles of the eye. It is fastened to the underlying sclera with permanent sutures. The tube is then cut to appropriate length and inserted into the anterior chamber. A small piece of donor tissue (sclera, cornea, pericardium, or dura) is then placed over the tube so that it does not erode through the overlying conjunctiva. The conjunctiva is placed back into place over the plate to cover the tube. In non-valved tube, a dissolvable suture may be used to tie off the tube. The surgery is typically performed under local anesthesia, in an outpatient setting.

Post-operative care
Patients who receive a valved implant are asked to discontinue their glaucoma medications after surgery, since the tube is expected to lower IOP immediately. During the postoperative course, glaucoma medications may be re-instituted based upon the level of IOP. Since non-valved implants do not work until approximately 6 weeks after surgery when the suture dissolves, patients are often asked to continue their glaucoma medications until this occurs. Once the tube opens and the IOP decreases, medications are discontinued as tolerated. In both types of implants, patients are treated with topical steroids and antibiotics post-operatively. Occasionally pupil-dilating drops (cycloplegics) are used to keep the eye comfortable and to keep the anterior chamber well-formed.
Patients are asked to avoid heavy lifting, bending their head down below the waist, and getting dirty water in the eye. A shield is often used at night for eye protection initially. The postoperative visits are important since medication adjustments will be made after the IOP is checked. It is important not to dwell too much on the IOP in the early postoperative period since it can fluctuate significantly. It is not uncommon to have significant fluctuation in IOP during the first several weeks after glaucoma surgery.

Success Rates
In general, the success rate of GDD is approximately 75% after 1-2 years. This varies slightly according to the type of GDD used and type of glaucoma being treated. Another 10-15% are successful with the addition of glaucoma medications (partial success). Failure to control IOP occurs in approximately 10%. These patients will need further surgical intervention to control their glaucoma.

Any ocular surgery including the GDD has the potential complication of bleeding, infection, and discomfort. After GDD surgery, vision loss may occur from bleeding, infection, retinal detachment, swelling of the cornea or retina, hastening of cataract formation, or too low an eye pressure (hypotony). Additional glaucoma medications or surgery may be needed if the IOP remains higher than desired. The implant may also migrate or become exposed by eroding through the conjunctival tissue. Sometimes, the eyelid may become droopy (ptosis) after surgery or double vision (diplopia) may occur. These complications can be treated medically or surgically. Serious, vision-threatening complications are uncommon. If they occur, additional medication or surgery may be needed.


Anonymous Marcia Cox said...

I received information about A Patient's Guide to Glaucoma on the web site from Dr. Kwon. He performed the Seton implant procedure July 17, 2007, on my mother. Although, Dr. Kwon explained the procedure, the section referring to the procedure helped me to more fully understand how the implant works. The book is very well written and easily understood.
I appreciate the care my mother, Dorothy Ferguson, received during pre-op and post-op at the hospital. I especially appreciate the care provided by Dr. Kwon and his surgical team.

Thank you,

Marcia Cox

8:21 PM  
Blogger Julie said...

Seems like it would be more valuable to know the GDD success rate after 8-10 years, versus just 1-2 years. It's hard to tell from reading this article whether GDD can be considered a life-time treatment for glaucoma, suitable for maintaining lowered IOP for decades. The idea of having repeat surgeries every few years is not appealing, obviously.

11:36 AM  

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