Hello I’m Dr. David Richardson. I’m a cataract and glaucoma surgeon here in sunny Southern California, which you can see today is not. So, I actually elected not to drive-and-video today because here in California, drivers don’t know how to drive in the rain. Now, say what you will about Boston drivers but when I was back there for medical school they knew how to drive in the rain.

Gonioscopy-Assisted Transluminal Trabeculotomy and Kahook Dual Blade Goniotomy

So anyway, today, I would like to talk about something that’s getting a lot of traction in the ophthalmic community. And so I would expect patients with glaucoma to be offered a minimally invasive glaucoma surgery that goes by the name of either goniotomy or trabeculotomy. Now, there are two that are getting quite a bit of interest right now. One is Gonioscopy-Assisted Transluminal Trabeculotomy or GATT for short and the other one is Kahook Dual Blade Goniotomy. Now, what these both have in common is that a small incision is made in the cornea, through which either an instrument, the Kahook dual blade is used to tear open the trabecular meshwork, or a suture or catheter is threaded into the Schlemm’s canal and then torn through the trabecular meshwork. So they both are trabecular meshwork destructive. They’re both quick, they reimburse well, and so as you know, we’ll talk about whether they work and some of the issues involved.

Same Thing That Was Done 40-Plus Years Ago

Now the interesting thing is that these procedures are actually based on trabeculotomy goniotomy procedures that have been around for 40 plus years.

Now, the question of course comes up, “well, if they’ve been around for this long why is this kind of a new interest?” Well, they’ve been used in pediatrics for  this whole time with a fair amount of success but in adults, after some initial excitement 40-plus years ago, it kind of fell out of favor (in adults) because the effect did not seem to last.  And the thought was that, where the suture pulled through or the instrument pulled through the trabecular meshwork, which is the drainage grate in the eye (that’s generally how it’s thought of) that it left little leaflets, that could kind of scar down over time. So the effect of a goniotomy or trabeculotomy in adults did not work well, long term. In kids, there’s actually a membrane that is torn through and that membrane does not seem to grow back so that’s why it seems to work in kids whereas it doesn’t work so well in adults.

Now a few years ago —actually in 2005, Dr. Baerveldt and colleagues patented a device called the Trabectome. And the purpose of the Trabectome was to essentially remove the trabecular meshwork without there being any residual leaflet. So it prevented the opening from scarring down allowing fluid to get directly into the drainage canal which is called schlemm’s canal and then out through what are called the collector channels into the the blood stream. Now the problem was that the Trabectome was a very expensive interesting instrument. I never priced one but I heard they were around $50,000 and there weren’t too many physicians or surgery centers that were interested in paying that upfront cost. And then they the handpiece itself was a had to be paid for every single time so Trabectome for that reason as well as some others such as it just didn’t seem to work all that well. I mean, it would bring the pressures on average into the high teen which is okay for somebody who has mild to moderate glaucoma but it’s not really of benefit to anyone with a more severe glaucoma. So that fell out of favor then recently the Kahook blade came out which is essentially a single-use version Trabectome so there’s no upfront investment and it removes the trabecular meshwork without leaving any leaflets so that has gained quite a bit of traction as well.

The most interesting thing I find, in terms of the recent interest in Goniotomy- Trabeculotomy,  is Gonioscopy-Assisted Transluminal Trabeculotomy. This is essentially same thing that was done 40-plus years ago. So why is there this excitement? Now it involves creating a small incision of the cornea, threading a suture through the trabecular meshwork into the canal and then ripping it through the canal. Very similar to what was done before. There are a couple of reasons why, I think that there’s interest in it. MIGS (minimally invasive glaucoma surgery)—surgery in the angle through small incision, is really exciting right now in the glaucoma treatment community. And pretty much anything that you can do in the angle under a gonio prism and the microscope is of interest. So, it is easier to perform this procedure using this Gonioscopic approach than it used to be from the outside of the eye (from the sclera). So that’s part of it. It’s a quick surgery, it reimburses really well when you break it down by the number of minutes it takes and the ease of doing it and the, you know, limited post-operative risk and complications. And early on, it does seem to work. So the early results look pretty good but of course they look pretty good 40-plus years ago, so it’s probably not going to last that long… we’ll see. But there’s still the issue of those leaflets sealing down.so it’s interesting to me that we’ve gotten in ophthalmology,  at least along ophthalmic surgeonsm has this collective amnesia of this procedure not working well in adults 40-plus years ago but we’re all seemed to be interested in doing it again now for the reasons I just  mentioned.

So one might say well so what if you can get a year so of benefit from a simple, easy procedure that’s reimbursed by most insurances so that’s also important from the patient’s perspective, why not do it why not just rip through the trabecular meshwork. Well for the same reasons that that the Trabectome was developed and the Kahook dual blade there’s a couple but there’s actually something more involved.

The Importance of the Trabecular Meshwork

It turns out that the Trabecular meshwork, what we traditionally think of is just kind of a drainage grate, through which fluid motion is restricted… and it is known that that in the mid or there’s strong, strong evidence that the majority of patients with open-angle glaucoma, that is where the restriction flow is in the trabecular meshwork. So it makes sense to remove the Trabecular Meshwork. Remove that restriction to flow. The problem is is that we’re discovering that the trabecular meshwork is not just a simple grate. The work of Dr. Murray Johnstone has shown elegantly through videos that you can see on YouTube. There’s actually a pulsatile flow of the trabecular meshwork that is in sync with the cardiac cycle. So you can actually see the Trabecular Meshwork pushing fluid out of the Schlemm’s canal. The trabecular meshwork is a pump so if you rip the trabecular meshwork out you’ve lost that pumping mechanism and now you’re   hoping that just through passive flow that you’ll get the same kind of flow out of the system. So that that’s an assumption that needs to be looked into a bit further. You know,  will you still—long term after ripping out this pump mechanism—still get long term flow? And again, the early studies done decades ago…so just probably not, after goniotomy or trabeculotomy. But there’s more. There are other studies that have shown that in and around the trabecular meshwork and schlemm’s canal there are actually mechanosensory  regulators or sensors. So there are microscopic, at the molecular level proteins, that act as strain and stress gauges and then can have a feedback. So when they detect certain types of strain or stress, they up or down regulate the flow out of the canal and through the Trabecular meshwork.

I prefer trabecular meshwork-sparing procedures such as canaloplasty

So if you don’t have trabecular Meshwork and you just have an open system there’d be no strainers test, nothing to detect, nothing to up or down regulate…so we’re losing that when we destroy the trabecular meshwork. But then there’s also something that’s quite practical: regardless of what the laboratory studies show in terms of the function of the trabecular meshwork, there is now a new class of medications the rock inhibitors of the rock net inhibitors one of which was just approved by the FDA which is Rophressa®. The generic name is Netarsudil and that works at the trabecular meshwork. So if you’ve destroyed or ripped or torn out the trabecular meshwork there’s nothing for this class of medications to work on and Rophressa® is just the first of what will likely be a half a dozen medications that use this or similar mechanisms. So, from my perspective, I don’t see any reason to remove or destroy the trabecular meshwork when I may need to use that in prescribing a class of medications for my patients. So although I understand why other surgeons are excited about Goniotomy/Trabeculotomy in the form of Kahook dual blade or GATT, I personally don’t recommend these surgical treatments early on. I prefer trabecular meshwork sparing procedures such as canaloplasty, either the Ab-externo approach from the outside of the eye or the AB interno approach which is called ABIC using…I generally use iTrack micro catheter because it has a lit tip that really allows you to see where it’s going very elegantly. in any case I will prefer canaloplasty or say a hydrous shunt to actually shunt fluid into the canal before I would consider removing or destroying the canal.

When Might GATT or Kahook Dual Blade Trabeculotomy Be a Reasonable Surgical Option?

That being said there are times when that procedure does make sense because the trabecular meshwork sparing procedures have failed and that the next procedure we might be looking at would be trabeculectomy or glaucoma drainage device and those have quite a few potential risks and side effects which I’ve described elsewhere on my websites and I may make a video about that at some point in the future as well. So in any way I know any case whether this is a long video and a nice rainy day so I got here to the office early had some extra time hopefully this has been as with all my videos useful to you and have a great day

References:

  1. Luntz MH, Livingston DG. Trabeculotomy ab externo and trabeculectomy in congenital and adult-onset glaucoma. Am J Ophthalmol.1977;83:174-179.
  2. Amari Y, Hamanaka T, Futa R. Pathologic investigation failure of trabeculotomy. J Glaucoma. 2015 Apr-May;24(4):316-22.
  3. Lutjen-Drecoll E. Functional morphology of the trabecular meshwork in primate eyes. Prog Retin Eye Res 1999;18:91-119. 
  4. Johnstone M, Martin E, Jamil A. Pulsatile flow into the aqueous veins: manifestations in normal and glaucomatous eyes. Exp Eye Res. 2011;92:318-327.
  5. WuDunn D. Mechanobiology of trabecular meshwork cells. Exp Eye Res. 2009;88:718-723.
  6. Lin CW, Sherman B, Moore LA, et. al. Discovery and Preclinical Development of Netarsudil, a Novel Ocular Hypotensive Agent for the Treatment of Glaucoma. Journal of Ocular Pharmacology and Therapeutics. Volume: 34 Issue 1-2: March 2018.
  7. Trabectome Animation via TrabectomeChannel https://youtu.be/uxMVgHHmJFs
  8. Performing Goniotomy with Kahook Dual Blade via New World Medical https://youtu.be/Zp3IdE_biW8
  9. GATT with 5-0 Prolene Suture via Davinder Grover, MD, MPH https://youtu.be/1laohyDLi2A
  10. Animation: Glaucoma via National Eye Institute, NIH https://youtu.be/hASPt3hksbA
  11. Trabecular Meshwork Pulse-induced Motion Video via Murray Johnstone https://youtu.be/51MheK88170
David Richardson, MD

David Richardson, MD

Medical Director, San Marino Eye

David Richardson, M.D. is recognized as one of the top cataract and glaucoma surgeons in the US and is among an elite group of glaucoma surgeons in the country performing the highly specialized canaloplasty procedure. Morever, Dr. Richardson is one of only a few surgeons in the greater Los Angeles area that performs MicroPulse P3™ "Cyclophotocoagulation" (MP3) glaucoma laser surgery. Dr. Richardson graduated Magna Cum Laude from the University of Southern California and earned his Medical Degree from Harvard Medical School. He completed his ophthalmology residency at the LAC+USC Medical Center/ Doheny Eye Institute. Dr. David Richardson is also an Adjunct Assistant Professor of Clinical Ophthalmology at the Keck School of Medicine of USC. Twice weekly, he treats veterans at the VA Greater Los Angeles Veterans Healthcare System.

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