Surgery: Pediatric Ahmed Valve Implant

This is an Ahmed Valve Implant surgery in a 10-year-old boy with an advanced glaucoma in left eye. The glaucoma was caused by steroid use due to uveitis, caused probably by juvenile idiopathic arthritis. The tube was placed through a scleral flap and it was covered with a donor pericardium.

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


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DR BRANDT: This is a 10-year-old little boy with a very advanced glaucoma in his left eye. His glaucoma is believed to be due to a mixture of steroid use along with his uveitis. Probably juvenile idiopathic arthritis, also called JIA. He presented with a very high pressure. We measured the pressure at 52 millimeters of mercury when we saw him yesterday. And we’ve decided to go ahead and implant an Ahmed glaucoma valve in his eye. This is a more typical implantation of an Ahmed valve implant, and I’m going to put it in superotemporally, which is the usual position. The choice of putting an Ahmed implant in him, instead of a different kind of implant, or doing a trabeculectomy, is in part because he does have a cataract, which is the result of his uveitis and steroids, and the thought behind putting an Ahmed glaucoma valve in is twofold: First of all, he’s definitely going to need cataract surgery at some point. And at least in uveitis patients, regular trabeculectomies will usually fail after cataract surgery, because of the significant amount of inflammation in the eye. The other reason I chose an Ahmed implant in this patient is that in patients with uveitis and particularly those with juvenile idiopathic arthritis, they tend to have periods where they have inflammation. They hyposecrete or stop making aqueous, and their pressure drops almost to zero, because the Ahmed valve implant has a valve — or at least a flow restrictor — they are less likely to develop a flat chamber when there are episodes of inflammation and hyposecretion. Here you can see that I’m flushing the tube to make sure that it works. These devices have a valve system made of two leaflets of silicone rubber. And they tend to stick during manufacturing. So it’s very important to prime these tubes, as the two leaflets can stick together. And we need to remove any obstruction inside the tube, to ensure that the valve is working and there is smooth flow of fluids through the system. I’m picking up the implant. Go ahead and give me the calipers. This is set at 10 millimeters — probably a bit further than that. I’d like it to be about 12 millimeters back from the limbus. So this is good. I’ll take the 8-0 nylon. So I’m fixating this device about 10 to 12 millimeters back with nylon. It’s important to know that nylon is not a permanent suture, but it lasts long enough for scars to develop through the various fixation holes, in such a way that the implant will not move. So you can see how much easier it is to do this right side up. I’m going to rotate these knots. I generally rotate them into the holes. This is to make sure that nothing will bother the patient with sutures poking out through the conjunctiva or irritating. And now I’ll tuck the tube out of the way, so that it’s not in my way, as I do the rest of the dissection, and don’t do anything inadvertently that cuts the tube or disrupts it. I’m gonna be very careful not to create a buttonhole, so I mostly do blunt dissection, once I get into the correct tissue plane. I’ll take the crescent blade now, and use this to create a long tunnel. Over the last year or so, I’ve started making scleral flaps, especially in children, because I want them to have as much natural tissue as possible over the tube implant. Answer to the question when you do the scleral tunnel: You’ve been dividing it into two or three segments, correct? That’s what I’m doing right now, but I guess you can make one long tunnel. But it’s a little hard at the very end to make the needle entry at the eye, so this is the compromise I’ve come up with. So let’s figure out how long this tube is going to be. I will trim the tube to the appropriate length. I trim the tube with a forward-facing bevel, and that makes it easier to get in through the 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. The tube is inserted through the scleral flap. Now I’m going to make a paracentesis incision. This ensures that I have access to the anterior chamber if I should need it. The anterior chamber is entered using generally a 23-gauge disposable needle. I usually use a 23-gauge disposable needle. In younger patients, especially children, I will use a 25-gauge disposable needle, as the tissue is more flexible. The tube is inserted into the anterior chamber, using the needle tract. 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. I’d encourage — if you’re gonna try to start doing tube implants, it’s important to, in my opinion, to start off with pseudophakic patients where, as you pass the needle into the eye, you’re less likely to hit the crystalline lens. Sometimes I’ll do a small peripheral iridectomy, particularly in patients with angle closure, where the iris is drawn up forward in the anterior chamber angle. And then point the tube through the iridectomy, so that the tube is nicely posterior. So now we’ll take a piece of donor pericardium. I position it so that the rough surface is on the bottom, and I like to trim it, making a slight curve like this, so it matches up with the limbus. It’s much easier to cut the pericardium when it’s dry. It’s very difficult to cut and trim to an appropriate shape once it becomes soft. But once it’s in position, I make the pericardium wet, and it sticks down very nicely. I then suture the pericardium to the sclera, securing the implant. Other materials can be used to cover the implant, including donor sclera or cornea. Many places in the United States use corneas that are not of transplant quality, but cornea itself is quite thick, so one needs to cut it about half thickness to have it not create problems on the ocular surface. So at this point I will start closing. In answer to the question: No need to fix the tube to the sclera with stay sutures. I’ve started doing this recently. It’s a little bit faster. At home, I use a slightly different smaller crescent blade that’s only 1.25 millimeters in size, and I find this is a very nice way to make a small and narrow tunnel. The tube doesn’t tend to move, and it is embedded within living tissue, so that it doesn’t erode as easily. There’s a nice vascularized tissue. It forms a nice scar over the tube, and prevents it from moving. On the first postoperative day, I expect to see a formed anterior chamber, but it might be shallow. I would not expect it to be flat, but it might be shallow, just because he’s uveitic, and he might undersecrete aqueous. This is common for uveitic patients, to have shallow chambers, because they’ll often develop choroidal effusions more easily. The other reason for the shallow chamber in him might be because he started at a very high pressure of over 50 millimeters, and whenever you drop the pressure that much, you’re much more likely to develop a choroidal effusion. The other reason I chose an Ahmed implant in this patient is that in patients with uveitis, and particularly those with juvenile idiopathic arthritis, they tend to have periods where they have inflammation. They hyposecrete or stop making aqueous, and their pressure drops almost to zero. Because the Ahmed valve implant has a valve or at least a flow restrictor, they are less likely to develop a flat chamber when there are episodes of inflammation and hyposecretion. My experience with children and young adults with JIA is that they go back and forth with periods of inflammation and very low pressures, and then on to very high pressures, occasionally. These children sometimes do very well with some of the steroid-sparing agents like Remicade and methotrexate. So it will be important for this young man to be followed by a rheumatologist, who can manage those medications and reduce his need for systemic or even ocular steroids. And when he has his cataract removed, it’ll be important for his ophthalmologist to hit him very hard with lots of steroids for the perioperative care. As you can see, he has a little blood in the anterior chamber, so he will almost certainly have a small hyphema on the first postoperative day. And I expect the pressure to be between about 8 and 15 on his first postop day. I generally place subconjunctival injection of a steroid and antibiotic.

July 12, 2017

Last Updated: October 31, 2022

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