Laser Treatments for Glaucoma – Laser Trabeculoplasty

Part 5 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

Currently Available Laser Treatments (Laser Trabeculoplasty)

Let’s move on to the Surgical Treatments. You’re going to start with the FDA-approved surgical treatments— laser and incisional is what’s available here. In terms of laser treatments, we’ve got Iridotomy, Iridoplasty, Trabeculoplasty, and Cyclodestructive Procedures.

Iridotomy

Iridotomy, I’m not going to spend a lot of time on that – we poke a hole on the Iris, allows fluid through and out the natural drainage system.

Iridoplasty

Iridoplasty – It’s Plasty. So instead of making a hole you’re basically shrinking the Iris. This is used in plateau iris and what you see here in this picture is here’s the Iridotomy. When Iridotomy doesn’t work in plateau iris you then do a Iridoplasty. So you do is you make a whole bunch of little spots here that pull the iris away from the angle.

Glaucoma Surgery Categories

But what I really want to talk about here is the Open Angle Glaucoma treatments because narrow angle is pretty straightforward. So not that interesting—there’s not that much going on right now. Whereas with Open Angle Glaucoma there’s a lot.

We can split Open Angle Glaucoma surgeries into categories: the non-invasive laser, the minimally invasive, which is the most exciting and then the penetrating which is, for the most part, the older style of surgery.

Now, we can also think about glaucoma surgical treatments in terms of how they work. They can SHUNT, they can ENHANCE–So they can shunt fluid out of the eye. They can enhance the natural outflow, or they can ABLATE – they can basically destroy tissues. So mostly when we’re talking about destroying tissue we’re talking about destroying the ciliary body. So I like to think of this in terms of mnemonics as SEA. Let’s look at Enhancing here.

Laser Trabeculoplasty

Laser Trabeculoplasty – you can split this up into Argon, Selective and Micropulse.

Argon Laser Trabeculoplasty (ALT)

The Argon Laser Trabeculoplasty or ALT has been around for a very, very long time.

Quick aside—of interest, I always love to hear the stories about how scientific discoveries are made. In the case of Laser Trabeculoplasty, this was actually an accident. They were studying monkeys, when those laser treatment came about and they thought well let’s poke little holes in the trabecular meshwork so that fluid can get through the trabecular meshwork, which tends to be the primary location of restriction of flow and shunt it directly into Schlemm’s canal. So they did it. But the problem with the monkeys is that they scarred down. So then they thought, “ah we can use this laser instead to create a monkey model of glaucoma”. So instead of poking holes we’ll just use a lower energy, will shrink or scar down the trabecular meshwork and now we’ll have these monkeys that we can study glaucoma treatments on because we will essentially have created glaucoma in these monkeys. Well, lo and behold, after the monkeys healed up from the initial inflammation, what happened?! Their pressures went down. So that’s how ALT was discovered. Then it was used in humans to essentially create small micro burns in the trabecular meshwork and the thinking was that in between the burns you stretch open the trabecular meshwork. Nobody really knows. It can only be used in open angle glaucoma, performed in one or two sessions, may result in microscopic scars — you are actually coagulating tissue, and it may limit future surgical options, in particular some of the newer options that are becoming available. So for that reason it’s not the best choice.

Selective Laser Trabeculoplasty (SLT)

Selective laser trabeculoplasty is becoming more commonly recommended primarily because it doesn’t destroy tissue. And because it’s now becoming affordable. When this first came out it was $70,000 to buy the laser, who other than glaucoma specialist are going to be able to do that but lately the laser cost has come down into the 20,000-40,000 range. This uses a Q-switched frequency-doubled Nd:YAG laser (not that anybody need to know that). It can be performed on its own or even after ALT. It’s less traumatic because it doesn’t coagulate tissue, less damage, it’s quick and it’s usually painless. And interestingly enough, it can be performed either using a gonio mirror (as with the Alt) or a recent study that was just published showed that you can actually do this Transscleraly. So you can just sit the patient at the slit lamp, aim the beam at the limbus and place 100 spots around the limbus and it works. Perhaps not as well — we don’t know—but it does work. So there it is. There’s a laser spot and it’s lasering. Fascinating.

Micropulse® Laser Trabeculoplasty (MLT)

Micropulse® Laser Trabeculoplasty (MLT) – This basically uses micropulses—really, really, really short pulses. And the idea is if you separate the pulses into tiny little pulses followed by a little pause and then another little pulse and then a little pause what happens is you get what’s called “thermal relaxation”. So the tissue heats up and then cools off and then heats up and cools off and you do not get coagulative damage when you do this. Basically this is a newer version of SLT. It’s a cheaper version of SLT, seems to work as well as SLT and so there’s some benefits to having this.

NEXT → Continuous Wave and Micropulse® Cyclophotocoagulation