Past decade shows a surgical renaissance in glaucoma management

Thomas W. Samuelson, MD, discusses the latest techniques and technologies in glaucoma surgical management.

John A. Hovanesian

John A. Hovanesian, MD, FACS: Today I’m interviewing Thomas W. Samuelson, MD, the Glaucoma Section Editor of Ocular Surgery News, an attending surgeon at Minnesota Eye Consultants and a clinical associate professor of the University of Minnesota. Tom, thanks for joining us.

Thomas W. Samuelson, MD: Good to be here, John.

Dr. Hovanesian: Tell us about the status of glaucoma surgery.

Dr. Samuelson: I’m fond of saying that if the late 1990s were a pharmaceutical renaissance in glaucoma management, the first decade of the 21st century has been a surgical renaissance. There are several reasons for this. We are doing our traditional trabeculectomies a bit differently so that they are better and safer, the Tube Versus Trabeculectomy Study has suggested that tubes might have an important role earlier in the disease process, and we have several new technologies entering this space, so a lot is going on in glaucoma.

Dr. Hovanesian: Can you put all that in perspective for clinicians?

Thomas W. Samuelson

Dr. Samuelson: Sure. I guess I would divide what is going on into two broad classifications. There are some trends that are evolutionary; they slightly change what we are already doing. And then there are several things that are revolutionary, completely revamping the surgical strategies. With regard to the “evolutionary” things, what we are seeing lately is a lot of people modifying their trabeculectomies to get more favorable bleb morphology. We want to see diffuse, broad blebs that direct the flow of aqueous posterior to try to avoid bleb-related conditions such as blebitis or bleb-related endophthalmitis or just a painful bleb from dellen formation.

Another modification is that a lot of surgeons have gone to very broad mitomycin exposure. There is a growing concern that fornix-based flaps appear to be more amenable to a better bleb morphology than the traditional limbus-based flaps.

And then there are some new devices that are adjuncts to guarded filtration surgery trabeculectomy, most notably the Ex-PRESS device (Optonol), which has had a fairly rapid adaptation worldwide and now in the U.S. as well, a trend that I think is likely to continue.

Dr. Hovanesian: Tell us how the Ex-PRESS device works.

Dr. Samuelson: It is a stainless steel device that standardizes the sclerostomy. You still have to apply very sound trabeculectomy principles. It is still important to suture the scleral flap to the appropriate tension to avoid hypotony. The device itself does not prevent hypotony. But it does standardize a very important part of the procedure, and I think it makes it easier and probably safer. Moreover, it is less invasive because it is placed through a 25-gauge needle tract; thus, the anterior chamber remains formed. There is no chance for iris prolapse or inadvertent incision into the scleral spur or ciliary body, as might occur with a descemetic punch.

Dr. Hovanesian: Originally this device was intended to be implanted under the conjunctiva, but now it is being implanted primarily under a scleral flap. Is that right?

Dr. Samuelson: That is correct, and frankly, I have reversed my opinion of the device now that the surgical strategy has changed to a guarded procedure. When I first learned of the original iteration, I was a big naysayer. In fact, I was opposed to the unguarded strategy. I got trained on it, but never did one case when it was underneath the conjunctiva without a scleral flap. I knew it would cause hypotony, and frankly, I often called it glaucoma roulette from the podium, which made me unpopular with the manufacturers. And I think that is an accurate description of the device when used in that fashion. However, under the scleral flap, I think it is actually a very reasonable adjunct to trabeculectomy, and I use it often.

Dr. Hovanesian: Can you describe how it differs from a Baerveldt or Ahmed shunt?

Dr. Samuelson: It has been likened to those devices, but it is completely different. The traditional aqueous drainage devices — the Baerveldt (Abbott Medical Optics), the Ahmed (New World Medical), the Molteno (Molteno Ophthalmic), the Krupin (Eagle Vision) — are designed to deliver the aqueous to the equatorial region of the globe. This does not do that. This delivers aqueous a few millimeters posterior to the limbus, much like the trabeculectomy. But it does deliver the aqueous a bit more posterior than a trabeculectomy would. And I think it helps with that concept of creating a more posterior bleb.

Dr. Hovanesian: And what about other new devices?

Dr. Samuelson: There are some relatively new technologies that are available for use now and are approved by the U.S. Food and Drug Administration One would be the Trabectome (NeoMedix), which is basically a combination ab interno trabeculectomy/trabeculotomy using a corneal incision and removing 120° or so of the inner wall of the canal of Schlemm, which would then, of course, include the trabecular meshwork. The concept is that if the resistance to outflow is at the juxtacanalicular meshwork, you can eliminate that site of resistance and then tap into the natural drainage system. Obviously, the inherent resistance to the episcleral venous system may limit the reduction in pressure, as would any resistance in the collector channels. So we don’t know the final word on that technology or really any of the Schlemm’s canal-based technologies. They are very exciting, but we will need to see some long-term data.

We are starting to accumulate such data. I was part of the canaloplasty study that led to FDA approval of that technology, and we are seeing good long-term pressure reduction, so efficacy, I think, has been fairly well established with canaloplasty. What has limited its adaptation is the technical difficulty of the procedure. I have been doing it for 2.5 to 3 years, and it is evident to me that the learning curve is steep initially, but once you have done many cases, it becomes much easier and much more efficient.

Dr. Hovanesian: What about other techniques for trabecular shunts or other devices that are coming out?

Dr. Samuelson: There are several in the works. Glaukos is well under way with its FDA trial and has now submitted its data for FDA review. It involves another ab interno approach to the canal performed through clear corneal incision, a very elegant approach. And Glaukos is also working hard toward the development of a suprachoroidal drainage system, as is Transcend Medical, as well as SOLX, so there are several companies that are working hard to improve glaucoma surgery.

Dr. Hovanesian: What effect do you anticipate the new understanding of cataract surgery’s pressure-lowering properties will have on our future treatment of glaucoma?

Dr. Samuelson: I think that we have learned quite a bit about the IOP-lowering effect of cataract surgery. In the past, when asked what effect cataract surgery has on IOP, I would generally say 1 mm Hg to 2 mm Hg of pressure reduction. And the literature supports that answer. However, if you really look at the data, that number comes from an average of all patients undergoing cataract surgery, including those who have normal IOP prior to cataract removal.

For example, if your starting pressure is 12 mm Hg, the postoperative pressure may actually go up a little bit because a normal physiological outflow system is not changed that much by cataract surgery. In fact, it might go up or down a few points within the normal physiological range. But a diseased system seems to be favorably influenced by removing the cataract, such that if you have a starting pressure of 24 mm Hg or 26 mm Hg or 28 mm Hg, implying some pathology within the system, removing the cataract, favorably affects the IOP so that those patients may get a 6 mm Hg or 8 mm Hg reduction. But when populations are studied without regard to preop IOP, the more pronounced IOP-lowering effect that occurs in those with high preop pressures is diluted out by those who have normal physiology whose pressure may go up or down or remain unchanged. So when you average out the entire population in a study, you may get 1 mm Hg or 2 mm Hg, but when you stratify them based on their pre-treatment pressure, you learn that the pressure actually went down quite a bit within those who had high pre-treatment pressures.

Dr. Hovanesian: Why do we think this change happens among diseased, glaucomatous eyes?

Dr. Samuelson: While much remains to be studied in terms of mechanisms, I am starting to believe that most adult acquired, phakic glaucoma has a phacomorphic component. Now that is different than what we are used to thinking. We are used to thinking that phacomorphic glaucoma means the iris is mechanically impeding access of aqueous to the meshwork. But phacomorphic glaucoma in this new sense could involve simple compression of the meshwork from a posterior vantage point. The iris could anatomically be well away from the meshwork, but there could be a phacomorphic component in that this enlarging mass, the aging lens, is immediately behind the iris, and the iris root is attached to the scleral spur which is attached to the meshwork. And as the iris is pushed forward, it might rotate the scleral spur and change the tone within the meshwork, therefore reducing outflow, such that relieving that compression by taking out that enlarging mass (cataract) and replacing it with a thin-profile IOL just might allow the scleral body to rotate back, improving the facility of outflow within the trabecular meshwork.

Dr. Hovanesian: So we think it is probably mostly a mechanical mechanism. Is that right?

Dr. Samuelson: I believe so. Of course, that is conjecture. We do not have a good way to study that. There may be some chemopharmacologic effect due to release of chemical mediators such as interleukins and macrophage activity within the meshwork as well. We don’t know for certain, but I think just the mechanical effect of removing the cataract does seem to lower pressure, especially if the system is abnormal to start with and you have a high starting pressure.

Dr. Hovanesian: Finally, all the changes in our thinking on glaucoma and all the devices that are soon to be available — what implications do they have for the general ophthalmologist in practice?

Dr. Samuelson: For now, I would say in the majority of patients with both cataract and glaucoma, I think it is very reasonable to simply take the cataract out — for patients with controlled glaucoma certainly, and even patients with a modestly uncontrolled glaucoma. Now the exceptions to that would be those with far advanced disease — I tend to do more combined procedures on those patients — and patients on maximum medical therapy who are uncontrolled. In such patients, you do not have a rescue if they have a pressure crisis postoperatively. But in general, I am doing far fewer combineds than I used to, and I am a little bit reluctant to give up the meshwork. That is, I am a little bit reluctant to create a bleb and basically kiss the meshwork goodbye forever because once you bypass it with a bleb or a tube, you are not going to go back. And so with some of these new technologies that are coming out, I may be using medicines a bit more aggressively and taking cataracts out without filtering procedures, knowing that there may be some procedures in the future that I could offer patients that may be safer and further enhance physiologic outflow.

Dr. Hovanesian: Dr. Samuelson, thank you so much for joining us.

• John A. Hovanesian, MD, FACS, can be reached at Harvard Eye Associates, 24401 Calle De La Louisa, Suite 300, Laguna Hills, CA 92653; 949-951-2020; fax: 949-380-7856; e-mail: drhovanesian@harvardeye.com.
• Thomas W. Samuelson, MD, can be reached at Minnesota Eye Consultants, 701 E. 24th St., Suite 100, Minneapolis, MN 55404; 612-813-3628; fax: 612-813-3656; e-mail: twsamuelson@mneye.com. Dr. Samuelson is a consultant for iScience, AMO, Alcon Surgical, Glaukos, AqueSys, Ivantis, Pfizer, Santen and Allergan.