When IOP-lowering drugs aren't enough, these glaucoma surgeries can enable patients to maintain vision.
Derek Cunningham, O.D., F.A.A.O.,
With the increasing demand for ocular surgeries and a limited number of glaucoma surgeons, there has never been a better time for the availability of effective, efficient and safe procedures and skilled optometrists to comanage these patients.
Here, I describe the latest advances in glaucoma surgery, the best candidates for these procedures, their benefits and drawbacks and what you can expect post-surgery. In addition, I discuss glaucoma surgeries right around the corner.
Selective laser trabeculoplasty (SLT)
SLT is an innovation of the traditional argon laser trabeculoplasty (ALT). It uses a laser (Nd:Yag) that emits energy, which is thousands of times less than the argon laser. The lower energy application aggravates local pigment cells as opposed to killing all cells in the area, which ALT does. Thus, SLT preserves the local tissue and stimulates the body's repair mechanism to remodel the trabecular meshwork (TM), decreasing outflow resistance.
The best candidates for this procedure don't have secondary glaucomas (inflammatory, neovascular, angle closure), are using multiple glaucoma medications at once and/or aren't “ideal” candidates for glaucoma drops. Those candidates who aren't “ideal,” for glaucoma drops are defined as physically unable to instill drops and don't have a family member or friend who can do it for them; have contraindications to glaucoma drops, such as extreme sensitivity or allergies; and/or have erratic schedules or memory problems, which preclude them from taking the drops when prescribed.
The benefits of SLT: no incisions (which equates to less of a risk of postoperative complications), the procedure is mild and well-tolerated with minimal-tono postoperative restrictions, the typical IOP-lowering response is roughly 20% to 30% and should last for several years—reducing the patient's dependence on glaucoma medications postoperatively—and the procedure is repeatable.
The drawbacks: With regard to repeatability, it's important to note that while the procedure may be repeated with acceptable results, it can show decreased efficacy with repeat treatments, and the IOP-lowering effect may not be sufficient for some patients. If the patient presents postoperatively with a less favorable initial response than that described above (e.g. a 20%-to-30% decrease in IOP), this may indicate that the patient isn't a good retreatment subject, and incisional surgeries should be considered.
When comanaging SLT patients, keep in mind that the resulting inflammatory response (a mild amount of anterior chamber inflammation) is important to the long-term success of this procedure. This is because the body's inflammatory response brings macrophages into the TM. Once the macrophages get to work in the TM, a decrease in outflow resistance occurs, which leads to the subsequent lowering of IOP. The maximum IOPlowering effect may not be recognized for several weeks to months, and occasionally the IOP may slightly increase in the immediate postoperative period. Finally, routine follow-up is needed to adjust concurrent glaucoma medications, and patience should be stressed in slowresponding patients.
We've known for years that glaucoma is an outflow problem. Namely, the TM and more specifically the juxtacanalicular tissue is to blame. In knowing this, why not just get rid of the TM? The Trabectome (NeoMedix, Inc., Tustin, Calif.) is an elegant way of doing this.
Specifically, it is a 19-gauge probe inserted through a 1.7mm temporal clear corneal incision. Via direct gonioscopic visualization, the surgeon typically passes the probe across the anterior chamber toward the nasal angle. At the end of the probe is a triangular footplate, which is inserted through the TM into Schlemm's canal. This footplate is used to ablate the TM and inner wall of Schlemm's canal, while cauterizing the surrounding tissue for about two-to-four clock hours.
The best candidates for this procedure: Those patients who are able to temporarily come off of blood thinners to minimize complications related to anterior chamber bleeding.
Something to keep in mind: Trabectome has not gained wide acceptance as a stand-alone treatment in phakic patients due to cost-limited IOP benefit. It is more commonly performed concurrently with cataract surgery or in pseudophakic patients.
On combined cases, the Trabectome procedure typically adds approximately five-to-10 minutes to the usual cataract surgery. Surgeons make a similar self-sealing wound to that of cataract surgery and typically do not have to use sutures.
The benefits of Trabectome: Should the procedure be combined with cataract surgery, the patient experiences just one trip to the operating room. In addition, patients who undergo this procedure experience improved vision from the cataract surgery and reduction of IOP (typically 20% to 30%), which decreases the patient's dependence on glaucoma medications. Further, as neither the conjunctiva nor sclera is damaged, the surgeon can perform a filtering glaucoma surgery (i.e. trabeculectomy or tube shunt procedure) at a latter point, if needed. Finally, the procedure results in a significantly easier postoperative course compared with filtering glaucoma surgeries, as no bleb is created. No postoperative bleb, or permanent communicating space to the anterior chamber, greatly decreases the severity of postoperative complications, such as blebitis. Further, symptoms of dry eye have been associated with having a bleb and using glaucoma drops.
The drawbacks of the procedure: mild-to-moderate hyphema, initial IOP spike, and Trabecutome is expensive in the short-term to the healthcare system when compared with glaucoma medications.
When comanaging patients who undergo this procedure, keep in mind that the one-day postoperatively often does not look as clean as a typical one-day cataract surgery postoperatively. This is because, as mentioned above, mild-to-moderate hyphema is common. Typically this just needs to be monitored and will resolve with time. In addition, in roughly 20% of the cases, a one-day postoperative IOP spike was noted. But in most cases, this is self-resolving as well. If combined with cataract surgery, all normal postoperative procedures typically hold true, and additional follow-up appointments are rare.
This procedure is the disco party of glaucoma surgery. Specifically, it involves the circumferential viscodilation and tensioning of Schlemm's canal using a flexible microcatheter that has a flashing LED light on the end. The surgeon dissects the sclera to expose Schlemm's canal. Then, he inserts the flexible microcatheter to dilate the full circumference of the canal by injecting sodium hyaluronate (Healon) during catheterization. (I've had the pleasure of observing this procedure, and I can tell you that you can actually see the flashing catheter circumnavigate its way 360° around Schlemm's canal.) Finally, the surgeon places a suture loop in the canal to permanently tension it.
The best candidates for canaloplasty: Patients using multiple glaucoma medications who would benefit from a modest IOP drop.
The benefits of a canaloplasty: As with the Trabectome, this procedure is typically combined with cataract surgery, providing patient convenience (e.g. one trip to the operating room). Further, the IOP decrease is typically 30% to 40%, allowing for less patient dependence on glaucoma drops. Also, this surgery is not a penetrating surgery. As a result, it enables the conversion to a trabeculectomy at a latter point, if warranted. In addition, no bleb is created, greatly reducing postoperative complications. Finally, with the lack of a bleb, the patient isn't likely to experience dryness upon using glaucoma drops.
The drawbacks: The procedure is likely not useful for inflammatory glaucoma due to the likelihood of scarring local drainage tissue. Also, while canaloplasty isn't considered a fullpenetrating surgery, because the inner wall of Schlemm's canal is left intact and no bleb is created, the surgeon does significantly dissect the conjunctiva and create a scleral flap, and this could result in postoperative scarring, limiting options for subsequent glaucoma surgeries.
When comanaging these patients, keep in mind that canaloplasty is not considered a fullpenetrating surgery because the inner wall of Schlemm's canal is left intact. As a result, postoperatively, you will see some sutures and incisions on the sclera adjacent to the limbus. But, you should not see a formed bleb. Typical postoperative management after a combined cataract procedure again is not much different from the stand-alone cataract protocols. Close inspection of the wound for infection or poor wound closure are the major additional steps. (See “When All Else Fails,” below.)
Around the corner
A couple of investigational glaucoma surgeries are close to FDA approval. One technique involves placing a 1mm-in-length stent through the TM and directly into Schlemm's canal with the purpose of providing a direct channel of flow into Schlemm's canal. Proper placement of such a device would be critical, as this is the smallest device ever to be implanted in the human body. On the other hand, with such little tissue disruptions, complications are likely minimal. Trials are under way to assess whether multiple stents will have an appreciable effect. This surgery is also being studied with concurrent cataract surgery.
The other procedure being studied is a little more radical. Specifically, it involves shunts that travel all the way into the suprachoroidal space. Because of the distance traveled, these devices must be larger than the aforementioned stunts and require more invasive techniques for placement. Thus far, typical postoperative complications have included anterior chamber inflammation, hypotony, hyphema and blurred vision. Most of these adverse events appear mild and transient with no trends of serious complications being seen yet.
Given the availability of safer/less invasive procedures now rivaling medication management, it's more important than ever to develop a close relationship with glaucoma specialists. This way, you can ensure you remain part of the patient management team and retain the patient post-surgery. OM
|When All Else Fails|
|When the aforementioned surgeries and IOP-lowering drugs do not keep the thief of sight at bay, placing the patient in the advanced or high-risk glaucoma category, it's time to refer him for filtering microsurgery. The two most commonly performed filtering glaucoma surgeries are the trabeculectomy (trab) and the filtering tube shunt (tubes).
During a trab, the surgeon excises a small portion of the trabecular tissue lying between the anterior chamber of the eye and Schlemm's canal. The procedure leaves a bleb just adjacent to the limbus. The bleb is usually in the superior temporal quadrant of the eye and is a permanent communicating cavity to the anterior chamber. The trab has been considered the gold standard first line of surgery for uncontrolled glaucoma for the past 30 years.
The benefits: The procedure creates a modified outflow system to enable aqueous humor drainage.
The drawbacks: In the immediate postoperative period, the procedure can result in a choroidal hemorrhage, elevated IOP (due to tight sutures, blocked internal ostium, hyphema or retained viscoelastic ); a flat anterior chamber with elevated IOP (due to papillary block, choroidal hemorrhage, annular choroidal detachment and aqueous misdirection); decreased IOP with a flat anterior chamber (due to over filtration, bleb leaks or choroidal effusions) and blebitis and possible endophthalmitis. The longterm concerns of the procedure: a scarred failing bleb, an over-filtering bleb with hypotony, bleb dyesthesia (ocular surface discomfort due to highly elevated blebs); cataract development and the lifelong increased risk of blebitis/endophthalmitis — keep in mind that infection has a direct path inside the eye now.
When comanaging these patients, stay vigilant regarding all the aforementioned complications, and closely monitor blebs. It's important to note, however, that advances have occurred in the technique of bleb creation and subsequent wound healing that have greatly improved long-term outcomes such that filtration surgery is much safer. For instance, the use of antimetabolites at the time of surgery, including 5-flurouracil and mitomycin-c, have helped in the reduction of scarring. In addition, the method of creating a much wider bleb surface area with a larger scleral flap has dramatically reduced ischemic, cystic blebs and long-term endophthalmitis rates. Much of the credit for these advancements goes to Professor PT Khaw from Moorfields Eye Hospital in London.
Tubes have traditionally been reserved for complex cases, such as trab failures, inflammatory glaucomas, angle obstructions, etc. Similar to a trab in its purpose, the surgeon places a prosthetic tube in the anterior chamber to allow aqueous in the anterior chamber to bypass the TM to a filtering plate that is placed underneath the conjunctiva, thus lowering IOP.
Many surgeons have begun to use tubes as first-line glaucoma surgery. The reason: These surgeons have noted a higher frequency of complications and a higher variability in the postoperative period with trabs vs. tubes. To test the efficacy and complication rates of these two procedures, the Primary Tube vs. Trabeculectomy Study began in April 2008. The estimated study completion date in April 2016. (See http://clinicaltrials.gov/ct2/ show/NCT00666237.)
|Dr. Cunningham is director of optometry at Dell Laser Consultants, Austin, Texas, where he has comanaged several glaucoma patients. E-mail him at email@example.com, or send comments to firstname.lastname@example.org.
Optometric Management, Issue: October 2011