Developer of viscocanalostomy still seeking lower pressures

The South African surgeon who was an early investigator of Healon is looking to get glaucoma patients routinely down to 9 mm Hg.

Issue: July 15, 2001

Robert Stegmann, MD, received the Albert von Graefe award for innovation at this year’s German Ophthalmic Surgeons meeting (Deutschen Ophthamochirurgen) in Nuremberg, Germany. Dr. Stegmann is well-known in ophthalmology for his work in the development of sodium hyaluronate viscoelastics and for his introduction of the glaucoma procedure he termed viscocanalostomy.

After his von Graefe Lecture, Dr. Stegmann spoke to Ocular Surgery News about the particular demands of his practice in Pretoria, South Africa, and his vision of the present and future of glaucoma surgery.

Ocular Surgery News: You said in your von Graefe presentation that you “work with what nature has provided.” Can you describe the nature of glaucoma in your typical patient?

Robert Stegmann, MD: The incidence of glaucoma in South Africa, or the whole of Africa, is much higher than in the United States or Europe, probably twice as high per decade of life. The onset is much earlier as well. I may have youngsters 15 or 20 years of age with manifestations of glaucoma far more serious than a 40-year-old Caucasian. So it’s a much more severe disease. The onset is much earlier, and the pressures are higher, much higher. In the series that I have operated to date, which is very carefully followed, the mean preoperative in traocular pressure (IOP) is 49 mm Hg. Now, when you compare that with your colleagues in Europe and America, their mean pressure is around 24 mm Hg or 25 mm Hg.

The severity of the problem related to the pressure alone is not one-dimensional, because when the pressure in the eye gets to 50 mm Hg or more, a lot of things go wrong in there, a lot of the delicate tissues.

---Robert Stegmann, MD, receives the von Graefe award from E. Haefliger, MD, at this year’s German Ophthalmic Surgeons meeting. The title of Dr. Stegmann’s Albrecht von Graefe Innovators Lecture was “Necessity + Serendipity + Obsession = Innovation.”

The cells inside the canal of Schlemm, these juxtacanalicular epithelial cells are changed as well, and it becomes a vicious circle. They are no longer capable of playing their role in transporting aqueous actively into the canal so it can leave by the collector channels. And then the canal of Schlemm in these patients is narrowed even further.

OSN: Why did you develop the technique of viscocanalostomy?

Dr. Stegmann: Because I just could not treat African glaucoma successfully with normal filtration surgery. For one, the complication rate is too high – for me, unacceptably high — and two, the failure rate is very, very high.

Being in the operating theater 5 days a week, my hands are full. I can’t afford to have too many patients coming back to be reoperated and handle all the problems related to so-called traditional filtration surgery: blebs that don’t work, blebs that don’t do well, endophthalmitis, choroidal detachments. We can’t afford to have these things, and this was the reason I went away from the classic operation.

OSN: Necessity was the mother of invention?

Dr. Stegmann: Absolutely, in this instance.

OSN: You have developed for your patients what appears to be an efficient surgical remedy to the problems you face in treating glaucoma.

Dr. Stegmann: It’s not the ultimate yet; I want to refine it. My goal is to be able to take any patient and tailor-make his or her pressure down to 9 mm Hg. And 9 mm Hg is to me the Holy Grail, because below that you would run into problems with disturbing the hemodynamics of the circulation. Nine millimeters is the neutral point, because if the pressure in the anterior chamber is 9 mm Hg, that is equal to the episcleral venous pressure. So, in other words, you have no more gradient.

OSN: What average postop pressure are you getting?

Dr. Stegmann: About 16.8 mm Hg. It’s not good enough yet. Well, in Africans, that’s another thing; if you drop a patient from 55 mm Hg down to 18, that’s phenomenal, and if he or she is not losing any more field, then as far as I am concerned, this is an unqualified success.

There is another phenomenon I can’t explain. Many of my patients will drop another 3 to 5 mm Hg after 1 year. I don’t know why. It’s been observed by Clive Peckar in the U.K. as well.

OSN: You said in your von Graefe lecture that you think you “can beat this disease.” What is needed to do this?

Dr. Stegmann: You know the Chinese say that even a blind cat will ultimately stumble across a dead rat. I’m just looking for that dead rat now. Because if I can get 8% of all the patients I operate to achieve an IOP of 9 mm Hg, regardless of how high their pressure was, I’m talking about dropping a patient from 48 or 62 mm Hg down to 9, I did something right.

What did I do right? I’ve got to determine yet what I did right; Why did those 8%, that was like 21 cases out of 216, achieve 9 mm Hg constant pressure? I have yet to fully understand why.

Many glaucoma experts (and I’m not a glaucoma expert, I just do a lot of glaucoma work) want a magical number, very low. And I think it varies from patient population to patient population. I think my patient population, with a mean preop IOP of 49 mm Hg, and a mean postop IOP of say 17 mm Hg, 17.5 mm Hg, is pretty good.

But I can understand in the Caucasian population where a lower pressure is needed.

OSN: You are often working at unusually high magnification. Why?

Dr. Stegmann: I remember in those earlier days watching some of the real gurus of glaucoma surgery operating with loupes. When I went away from the loupe, as a resident, to an operating microscope, the first thing I realized was all the mistakes I was making. So now I operate at very high magnification.

I like to operate at 253 magnification, and many surgeons don’t like that. Your proprioception has to be re-established to operate at that high magnification. It’s not necessary, but you know again, what I observe at that magnification is phenomenal. I’ve developed some of my own optical modifications in the operating microscope that will give me currently up to 843 magnification, and this is really exciting. What you see at 843 magnification – you see a lot of things you are missing.

Now I’m not sure that everything will translate into making the operation better, but it might, because the canal of Schlemm is such a delicate structure. People think from the textbooks it’s much bigger. In my population, it may be as narrow as 35 µm, in Caucasians, 50 µm. That’s a little thicker than a human hair. Operating at between 243 and 483 magnification, you can have an appreciation of just how delicate this structure really is. And almost how almost intimate the contact point or the space is between the outer wall of the canal and the trabecular meshwork itself with the juxtacanalicular epithelial cells.

There is so little room in there that any inappropriate instrument tension does tremendous damage. I mean those little collector channels, there are hundreds and hundreds and hundreds of them. If you look at any electron scanning microscopy, you see how delicate they are. You don’t push big instruments in and around there. You do more damage. It’s like a giant walking in a potato field. This is important.

OSN: What do you mean by “stretching the canal of Schlemm?”

Dr. Stegmann: If you stretch the canal of Schlemm from its normal 35 µm to 50 µm, up to 240 µm with a high-viscosity sodium hyaluronate, it will not stay 240 µm, no, but will probably shrink back down to 100 µm or 150 µm. But what’s important is, by Bernoulli’s Law, by Parsons’ law, the resistance to outflow is decreased by a factor of 16 (the fourth root of the radius of the diameter), so if you go from 50 µm to 100 µm in the canal of Schlemm, you reduce resistance to outflow by a factor of 16, which is wonderful. So we currently stretch the canal to 250 µm.

OSN: Can the procedure be improved by adjunctive implants?

Dr. Stegmann: I’ve had an interest in implants into the canal of Schlemm that started many years ago. This is possibly a promising way to go, and I am very encouraged. Viscocanalostomy, as far I’m concerned, is merely the beginning.

What has happened is, there are a lot of good surgeons out there with good ideas. Regarding implants, this reminds me of the late 1970s with IOLs, and now look where we are today. So I believe we are going to refine surgery for glaucoma.

OSN: Is high magnification allowing you to observe the physiology in unique ways previously unobserved?

Dr. Stegmann: With this type of observation and follow-up, you can actually determine the aqueous pathway by allowing reflux of blood, when you press on the gonio lens, to come into the chamber, and then you release the gonio lens and the flow is reversed and you can see the blood going back into the canal and being washed out by aqueous and transported to the collector channels.

And that’s why when many of my colleagues doubt that the pathway is really through the canal of Schlemm, it’s just because they have not observed this. And now it’s interesting to see when I show this, because I only brought this work to bear since the 2001 ASCRS; I haven’t shown it before. Now a lot of skeptics are sort of saying, “Hey, I think you are right, it does flow into the canal of Schlemm.”

It’s amazing, the myths and dogma. I remember when I got into IOLs in the mid-1970s. I mean, if you were into IOLs then, you were seen as a heretic to be burned at the stake.

Colleagues have said: “Aqueous doesn’t go through the canal of Schlemm. In the canal, there is no circumferential flow.” Now I’ve shown today that almost individual erythrocytes can be seen moving clockwise or counterclockwise through the canal. That has made people sit up and say, “Wow, maybe it’s possible,” and that’s nice.

I think in the future we will be able to do intracanalicular surgery so atraumatically that we will be able to almost customize a patient’s pressure. I believe that, absolutely.

And if I don’t get there myself, there will be someone else following up.

For Your Information:
Robert Stegmann, MD, can be reached at the Medical University of South Africa, 188 Copse Lane, 2A Lynnwood Glen, 0181 Pretoria, South Africa; (27) 12-5293118; fax: (27) 12-476038