Part 1 of 14 of “Adjusting the Faucet or Opening the Drain – Currently Available Methods to Treat the Plumbing Problem of Open Angle Glaucoma” | A San Gabriel Valley Optometric Society (SGVOS) Continuing Education Dinner Event – 2 hours CE | Featured Speaker: Dr. David Richardson, MD | April 12, 2017
Adjusting the Faucet or Opening the Drain- Currently Available Methods to Treat the Plumbing Problem of Open Angle Glaucoma
Tonight we’ve got two hours of CE, I understand. And I’m not going to talk for the whole two hours, I want to leave some time for Question and Answer. But this is a big topic tonight and the topic is, “Adjusting the Faucet or Opening the Drain.” Basically, what are the current and near future methods of treating glaucoma.
So by the end of this presentation, besides having a really nice dinner, you should be familiar with the currently available and soon to be available (we hope) methods of treating glaucoma and how they work. So you should be aware of them all and have a pretty good idea of the mechanism.
What is Glaucoma?
Now this brings up something that’s rather interesting. In order to figure out how to treat it and to talk about mechanisms we first have to discuss, well what is glaucoma? Now, we all have an idea of what it is. It’s got something to do with the optic nerve, it’s a progressive optic neuropathy, and it involves cupping and typical visual field or retinal nerve fiber layer loss. Now, it’s also got something to do with pressure. We know all of those things.
It’s not so simple
But we’re finding out that it’s not so simple. It’s the idea that high pressure is glaucoma so we have to lower it, we figured that out a while ago that it wasn’t that simple (normal tension glaucoma, patients with ocular hypertension but not glaucoma). So clearly there’s something else going on. And what we’re discovering is that blood supply is important, oxidative damage may be important, and there may be some other issues involved such as inflammation. So a lot of the laboratory research that’s being done is actually focusing on those three things, not pressure. But that’s pretty far into the future. Nothing that is involving non-IOP lowering therapy is anywhere near clinical usefulness.
So we pretty much have to view glaucoma as a problem of plumbing. Even though we know glaucoma is far more complex than flow issues, this is all we’ve got. This is what we have to work with. And so given that, what tools do we have available to us? And just like a good plumber if you don’t have the right tools or you don’t know how to use the right tools for the right job you’re not going to be able to fix the faucet.
Adjusting the Faucet
So we can think about fixing glaucoma or treating glaucoma as fixing the sink. So you’ve got a backed-up sink, what can you do? Well you could potentially just the faucet. So if the water is flowing and the sink is overflowing one thing you can do is simply turn off the faucet. But with glaucoma of course you don’t want to turn off the faucet because if you don’t have any flow then you end up with hypotony and with hypotony you can end up with maculopathy, phthisis—things that you generally don’t want. So we can adjust the flow but we can’t turn it off. Well the problem is that if the drain is stopped up even turning down the flow might not be enough.
Fixing the Drain
So of course then we can look at fixing the drain and if we’re going to fix the drain we have to think about, in terms of glaucoma, the outflow pathways. And there are physiologic pathways—the pathways that are used by everyone’s eye that doesn’t have glaucoma. And then there are the non-physiologic, so basically those that we create.
Physiologic pathways (Outflow Pathways)
Now, in terms of the physiologic pathways there’s the trabecular meshwork. Trabecular Meshwork – we can think of is basically the drainage grate here. So that’s the first level at which fluid can come into a resistance.
Behind the grate is the Schlemm’s canal. So this is the canal that encircles the angle, sitting just behind trabecular meshwork as you all know and this can be thought of roughly as the drain that the you drain or whatever in again I’m not a plumber I use the metaphor here of it I don’t know anything beyond that grate when it comes to the sink of my house. Alright, so but Schlemm’s canal we know is basically a tube. And there are ways that we can interact with Schlemm’s canal.
Then there’s the Collector Channel System. The collector channel system is rather mysterious we don’t have a way of testing it at this point but we know that it’s really important in terms of drainage. If the collector channel system, which takes fluid from Schlemm’s canal to the Venus collector system, does not work then many of the treatments I will be discussing today simply won’t work.
So that brings us to the next one which is the Uveal-Scleral Pathway, which is a pathway that was little known prior to the advent of prostaglandin analogs. Now this pathway does not use the classical or the usual pathway of the trabecular meshwork, Schlemm’s canal and collector channel system. It actually goes through the uvea here and we’ll talk about that because it’s a very interesting option to take advantage of.
In terms of the non-physiologic pathways, we can shunt fluid. So whenever we’re using a non-physiologic pathway we’re essentially creating a shunt. So a pathway, which wasn’t there before and the standard pathway that’s been used surgically since 1968 was Trabeculectomy—essentially poking a hole in the eye and shunting fluid from the anterior chamber into the subconjunctival space and creating a bleb.
Now, the other thing we can do now (and we’ll get to this) is shunt fluid into what’s called the supraciliary or suprachoroidal space which is below the sclera. So we’ve got above the sclera and below the sclera options that are non-physiologic shunts.
Currently Available Glaucoma Treatments
So what I’d like to do is review the currently available glaucoma treatments because although you’ve been aware of many of them there are a couple of FDA-approved treatments that are relatively new And it’s helpful to put it in perspective of—put them in perspective in relationship to what’s been available in the past. In terms of the currently available: medical treatments (you’re going to break these up into) medical, laser, and surgical. Although, (technically) laser is surgery it’s not incisional. You know most patients they take more kindly to laser than they do incisional surgery.
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Currently Available Methods to Treat Open Angle Glaucoma Series:
- Currently Available Methods to Treat Open Angle Glaucoma
- Beta-blockers, Selective Alpha Adrenergic Agonist, CAIs
- Prostaglandin Analogs, Cholinergic Receptors Agonists, Fixed Combination Agents
- Carbonic Anhydrase Inhibitors (CAIs)
- Laser Trabeculoplasty
- Continuous Wave and Micropulse® Cyclophotocoagulation
- Trabeculectomy and Glaucoma Drainage Devices
- Ab-Externo Canaloplasty
- Ab-Interno Canaloplasty
- IStent®, Cypass® Microstent, Xen® 45 Gel Stent, Cataract Surgery
- Next-Generation Glaucoma Medications and Surgeries
- iStent Supra®, Hydrus™ Microstent, and InnFocus MicroShunt®
- Canaloplasty with Stegmann Canal Expander