Surgery: Ahmed Valve Implant

This video demonstrates a routine Ahmed Valve Implant surgery through a fornix based peritomy. Dr. Brandt created a scleral tunnel for the tube to travel from the plate to the anterior chamber.

Surgeon: Dr. James Brandt, University of California, Davis


DR BRANDT: This is a gentleman in whom we’re going to place an Ahmed glaucoma valve implant. The first step in any of these glaucoma surgeries is to place a traction suture, and I do so generally through the peripheral cornea. With the traction suture, you want to be careful not to penetrate the cornea, because you want to keep the eye relatively firm. Many surgeons prefer to do a large limbal incision. In other words, a fornix-based conjunctival flap, to implant these devices. I was taught many years ago to perform these using a limbal-based incision. In other words, make the incision in the deep fornix. And I find that this is easier to close watertight and is more comfortable for the patient. So once I make this incision, I can use a conjunctival clamp, and we’re now exposing the upper temporal quadrant, and going to use blunt dissection to spread the muscles here and clear all adhesions. Here’s the edge of the superior rectus muscle. So I moved a little bit more superiorly than I want, so I’m gonna adjust things a little bit here and get over more temporally. Now, we’re using an Ahmed glaucoma valve FP7 implant. This is the flexible silicone-based implant. The way this device works is: The tube, which will end up in the anterior chamber or in the posterior chamber, in the case of a vitrectomized eye, and there’s a valve system here that consists of two leaflets of silicone rubber. These leaflets in the valve tend to stick during manufacturing, so it’s very crucial that during the surgeries to implant these devices — is that you must flush them. And here you can see that I’m pushing pretty hard right now, to push fluid through the system. And once the leaflets unstick, you see fluid flow through the system, and you know that the valve is unstuck. If you do not do this, and just implant the device without flushing the valve system, if the leaflets are stuck together, there would be nowhere for the fluid to go, and the implant would fail immediately, because the valve system is blocked. All right. The next thing we need is 9-0 nylon. I generally use 9-0 or 8-0 nylon. It’s important to realize that nylon is not a permanent suture, but it doesn’t need to be. It maintains its tensile strength for about 6 months to 9 months. But by then, there should be adequate scarring around the implant and through the various fixation holes that will keep the tube from moving. Placing these sutures is among the hardest parts of the procedure, because you’re working in the bottom of a hole. And I’m now gonna tuck the tube out of the way so it doesn’t get in my way as I do the more anterior dissection. And, again, what I just did was, in some people’s hands, the most difficult and challenging part of the procedure. I do like to bury these sutures so that they don’t poke out and bother the patient. I rotate it so that the knot is inside the fixation hole, and we now have plenty of length on the tube. So I’m releasing some traction. He has a lot of fibrosis here. So I’m going to do my anterior dissection using mostly blunt dissection. Pushing everything forward, just under the limbus. I think we’re anterior enough to place the implant. It’s safer to use blunt dissection, rather than sharp dissection, because the last thing you want to do is to create a buttonhole through the conjunctiva. So now, before we enter the eye or do any dissection to enter the eye, I’m gonna create a paracentesis through the peripheral cornea. This ensures that I have access to the anterior chamber, if I should need it. Now I’m gonna take the crescent blade and make essentially a shelf or pocket through which I’ll enter the eye. Creating a tunnel to get there, through which the tube will travel, and what I’m essentially doing is creating two tunnels that intersect. I will trim the tube to the appropriate length. I trimmed the tube with a forward-facing bevel. And that makes it easier to get in through the needle tract. And you can see the needle going through here, through the apex of this long tunnel, into the anterior chamber. I usually use a 23-gauge disposable needle. In younger patients, especially children, I will use a 25-gauge disposable needle. The sclera is usually flexible enough that one can push the tube through a 25-gauge needle tract. It’s important not to make the tube too long, although it’s useful to make them a little bit longer in children, to accommodate for growth of the eye. Again, it’s important, if you’re starting off doing this surgery, to do this primarily in pseudophakic or aphakic eyes, before you run the risk of hitting a crystalline lens. If there’s a lot of angle closure or PAS, peripheral anterior synechiae, in the eye, you can do a small surgical iridectomy through the clear cornea, overlying where you’re going to end up inserting the tube, so that you can be sure that you’re well away from the cornea. Insertion of the tube is one of the most challenging parts of the procedure. It’s important that the tube not be too far anterior, because the tube rubbing against the cornea will eventually cause the cornea to fail. And in many of these eyes, the endothelial function is less than perfect. So now we can see the tube. Happy about its position. Now, the only question at this point is whether or not to put a graft on top of these. But at this point, I’m not sure it’s actually necessary. We often place pericardial or corneal grafts, but this tube is nicely covered with the patient’s own sclera, so I don’t think it’s necessary here. Okay. I think we can start closing with 9-0 vicryl suture. I’m gonna start closing, and I can show you my closure. I like to close in two layers. I close the Tenon’s capsule in a running, locking manner. And I do this in order to support the overlying conjunctival layer. So the Tenon’s closure with the running, locked suture supports everything, and helps make it as watertight as possible. So now, using the same suture, I come out onto the surface of the conjunctiva, and then do a simple running closure, and that previous underlying Tenon’s locked suture reinforces and takes tension off the conjunctiva. So now you can see the tube is in a really nice position, and he has a very smooth surface that should heal down very nicely over the next few weeks. And this should be very comfortable for the patient. They typically feel a little bit of achiness around the eye and discomfort on eye movement, because we’ve been pulling on the muscles, and there’s some new hardware in this quadrant. But the discomfort for the patient usually is gone within a few days. I generally place a subconjunctival injection of a steroid and antibiotic, and put them on topical antibiotics for about a week, and then have them continue steroids for at least a month or two, before beginning to taper off of the steroids.

3D Version

July 11, 2017

Last Updated: October 31, 2022

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