Many different types of devices have been developed to aid filtration by shunting aqueous to a site away from limbus, such as the equatorial subconjuntival space.
Aqueous shunts, or glaucoma drainage devices, generally have a tube placed into the anterior chamber, in the ciliary sulcus, or to the pars plana into the vitreous cavity (1).
Early over-filtration in an eye with the shunt in anterior chamber results in a flat chamber and shunt-cornea touch. Flat Anterior Chamber (AC) and hypotony caused by over-filtration are uncommon complications of these surgeries. Untreated hypotony and flat AC may lead to vision-threatening complications, including Peripheral Anterior Synechia (PAS) formation, cataract, corneal decompensation, choroidal effusion, suprachoroidal hemorrhage, endophthalmitis, and hypotony maculopathy.
Hypotony and flat AC can be avoided by the use of valve device, an occlusion technique, or viscoelastic agents. However in some cases, flat AC is related to valve malfunction (2).
We present a 65-year-old woman with repeated episodes of flat AC immediately at the postoperative period after Ahmed Glaucoma valve implantation for neo-vascular glaucoma. The eye had previously undergone deep vitrectomy. The patient underwent an uncomplicated Ahmed valve surgery in her left eye and the tube was covered with scleral patch graft, and the conjunctiva and tenon water-tightly sutured at the end of operation. AC was formed and there was no leakage around the conjunctiva. On the examination at the first postoperative day, flat AC was observed without any leakage from the incisions or conjunctival wound, and the Intraocular Pressure (IOP) was low.
The patient was returned to the operation room and AC was filled with a large air bubble, and then closure of the incisions was ascertained. A few hours later, AC was spontaneously flattened again. At this time, AC was formed with a viscoelastic agent. On the examination at the first postoperative day, AC was flattened again. With the diagnosis of valve malfunction, the patient returned to operating room for the third time. We decided to obliterate the Ahmed tube with a removable suture. Therefore, we made a stab incision at the limbus and inserted 5-0 Nylon suture through the stab incision into the Ahmed tube and fixed the other end of the suture to the subconjunctiva and covered it with conjunctiva (figure 1).
The conjunctiva was sutured with 10-0 Nylon. After this procedure, AC was formed on the first postoperative day. Two weeks after the surgery, AC was found to be formed and IOP was 10mmHg. Thus, we removed the 5-0 releasable sutures without any complication. Anterior chamber remained deep. At the last follow up visit, four months after the surgery, the IOP was controlled well with a functional (filtering) device (figure 2).
Different devices have been developed that filtrate aqueous to a site away from limbus such as the equatorial subconjuctival space (1).
Similar types of implants are generally reserved for different glaucoma cases in which conventional filtering surgery has failed or is likely to fail.
Although aqueous shunts differ in design, the basic techniques for implantation are similar. For the
non-valve devices, there are a number of techniques to restrict flow in the early postoperative days, such as stenting the tube lumen or ligating the tube with a suture (1).
For the valve devices, restricting the flow is not necessary with devices that contain a flow restrictor, although hypotony and a flat AC can still sometimes occur with them (2).
Flat AC and hypotony caused by over-filtration are avoided by using valve device, an occlusion technique, or viscoelastic agents. However in some cases, flat AC is related to valve malfunction.
The valve mechanism is very sensitive and if the valve touches with a forceps during implantation, it might cause damage. It could also be damaged by forceful irrigation (3, 4).
Our case report shows that in case of valve malfunction, placing Nylon 5-0 suture into the tube shunt (removable suture) could be helpful to restrict the aqueous flow and give time to the fibrosis to work against over-filtration.
Spontaneous episodes of flat AC after Ahmed valve implantation in an eye can be well managed by inserting a removable suture into the Ahmed valve tube Another benefite from this thecnique was decrease risk of Ahmed Glaucoma Valve (AGV) exposure because tenon was very thin and conj very fragile too.
So we decided to new operation site and did not remove previous sutures.