Surgery: Ahmed Valve Implant in Congenital Glaucoma

This video shows an Ahmed valve implant surgery in a child with congenital glaucoma, where previous surgeries failed to control the IOP. The Ahmed valve was implanted using a limbal based conjunctival flap, the tube was inserted in a scleral flap and then covered with tutoplast.

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


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DR BRANDT: I just placed a traction suture so that we could get started here. This is a little girl with congenital glaucoma, in whom previous surgery has failed to control her pressures. And so we are going to place an Ahmed glaucoma valve in her right eye. It’s not much different — you know, the manufacturers who make the tubes use the same plastic as is used in the making for nasolacrimal duct surgery. For glaucoma drainage device surgery, many people do the surgery — most people do the surgery by making a large incision over here and then putting the tube in. I do things differently. I like to do the surgery in this way, in what is called a limbal-based conjunctival flap. The advantage of this approach is that the eyes are much more comfortable for the patients. And I’m in the superior temporal quadrant. And I will now clear this quadrant of adhesions. So this is a little clamp that I find very useful. This little forceps allows me to have my assistant hold very easily — I’ll take a curved Stevens tenotomy scissor. And now I’ll simply make room. It allows me — gives me plenty of room to place the Ahmed implant. There’s now no adhesions there. Now, there are two different kinds of glaucoma drainage implants. The non-valved implant, such as the Baerveldt implant, or the (inaudible) implant. The Ahmed implant is an implant that has a valve in it. The Ahmed implant is a little bit easier to implant, but several studies have suggested that in the long term, it may not work quite as well. But we don’t really know that for children. I find them about equal in children. So this is the device, as you can see. It consists of a silicone rubber plate, and there is a one-way valve built into this structure. And one of the very important things to do before you implant it is to make sure that the valve is working. So I’m going to put the cannula on here and flush the system. You will see the fluid go down the tube, and eventually — so right now I’m meeting resistance, but you can see that the leaflets of the valve usually stick during the manufacturing process. Now we have primed the valve so it is now working. Now, I’m going to secure the device using 8-0 nylon. Most people do not realize, but nylon is not a permanent suture. Nylon dissolves after about a year. But that is long enough for the implant to scar into place. And if you notice, when I showed you the entire plate, there are some holes in the plate posteriorly, and during the healing process, tissue grows through those holes, in order to essentially rivet the plate into place. So these sutures only have to hold the implant in for a few months. And the implant will no longer move. Now, the advantage of a valved implant is that it lowers the pressure immediately. There’s very little risk of a shallow or flat anterior chamber. I just want this not to move during the first few weeks. Children tend to rub their eyes. So I want it to be nice and secure, until it has scarred into place. Tuck the tube out of the way, so it doesn’t bother anything. And now we will focus on bringing our dissection forward. So I’m opening things to give myself some exposure to the limbus. So what I’m doing now is figuring out what route I’m gonna take to bring the tube forward. This is a little Axenfeld loop, which is a nerve loop that comes up with some blood vessels, and I’d like to avoid doing any suturing or dissecting around that. That can be quite painful for the patient and cause chronic irritation. So I’m gonna avoid that. I will cauterize it, but I’m not going to do any dissection right near it. Just peeling off episclera here. Just want to have nice bare sclera if I can. So what I’m gonna do is create a shelf, a little flap like this. That’s probably about 4 millimeters from where I wanna be, from the limbus. Now I’m gonna create a tunnel from back here. Go all the way forward to meet up with the opening that I made near the limbus. So in this way, the tube can be covered with the patient’s own tissue. I’m just gonna make a side port so that I have access to the anterior chamber. You always want to have control of the anterior chamber, so I am going to position this laterally or temporally, as the case may be. I always put the side port incision in a position where I can both put in Healon to deepen the chamber, but also I would be able to reach in across with the Sinskey or some similar device. This tube will go in — in an angle sort of like that. So sometimes — this child has a big eye and slightly thin sclera. So I do have a little bit of concern about erosion. So I will go ahead and use Tutoplast to reinforce over the tube. And this just has to hold it in place for a few days, while it scars into place. I like to close the Tenon’s and conjunctiva in two separate layers. In the tube versus trabeculectomy study, in which we compared tubes to trabeculectomies, the short-term complications of a trabeculectomy were more common than complications with tubes. And the long-term complications were the same. In theory, the valve lowers the pressure to about 10 millimeters of mercury, but doesn’t let it go any lower. So usually on the first day after surgery, the pressure is between about 8 and 15. So I like to close in a double layer, like this, because I think it is is more watertight and less likely to break down. As you can see, once we rotate the eye back into its normal position, you’ll see that the limbus is very smooth and comfortable for the patient. So the patients, after doing the surgery in this way, are usually much more comfortable than in eyes in which the limbus was taken down. I also think it’s important to do it this way in children or adults with aniridia, because in aniridia, they have lost the ability to make — their stem cells are very thick at the limbus. Just want to make sure that the pressure comes down a little bit.

June 15, 2017

Last Updated: October 31, 2022

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