I would like to thank Glaucoma Today for inviting me to be a section editor of this column. I have always enjoyed reading GT, which has become a valuable educational resource on recent research, surgical techniques, and clinical strategy for both glaucoma specialists and readers from other specialities who share an interest in glaucoma. I look forward to highlighting with my fellow section editor, Jonathan Myers, MD, videos posted on Eyetube, which has become the premier online ophthalmic video resource.
For my first review, I selected “Retropupilary Artisan IOL and Ahmed Valve Implantation in Axenfeld-Rieger Patient” by A. John Kanellopoulos, MD. This video beautifully demonstrates the technique for implanting an Ahmed Glaucoma Valve (New World Medical) and shares some important tips (Figure). I congratulate Dr. Kanellopoulos on his instructive video, and I look forward to seeing more offerings from him on Eyetube.net.
POSITIONING THE PLATE
Although the superotemporal quadrant is the preferred position, the Ahmed Glaucoma Valve may be inserted in other quadrants when the superotemporal conjunctiva is unavailable. As Dr. Kanellopoulos explains, the device must not be pushed back so much that its posterior extent impinges on the optic nerve. While passing anchoring sutures, it is important for the surgeon to ensure that the plate does not encroach on the recti, which could disturb motility and cause diplopia. The valve should always be sutured such that the tube lies perpendicular to the limbus. Needless to say, the device should be primed before insertion.
COVERING AND INSERTING THE TUBE
Donor sclera is a good option for covering the tube. My preference is to create a thick, robust scleral flap measuring 5 × 5 mm to cover the tube, however, and to suture the flap over the tube such that it cannot move under the flap. Generally, I also place two radial sutures on either side of the tube where it emerges from under the flap. If dissecting a flap, I find it best to do so after suturing the valve in place so that the scleral flap can be marked out to cover the tube all around. This technique helps me to create a flap around the tube as it will lie in its final position. The strategy also ensures that the tube enters the eye in a straight line, without kinks, bends, or a change in direction. The securing suture at midlength of the tube helps to avoid dislodgement of the tube.
Whether placed in the anterior or posterior chamber, the tube needs to lie parallel to the iris to avoid iris pigment dispersion or iris plugging. A large, flaccid iris may require an iridoplasty. Insertion of the device must be carefully executed to avoid damaging the iris root or the ciliary body and causing hyphema. In eyes with a broken posterior capsule, I find it important to perform a thorough anterior vitrectomy and to clear all of the vitreous in the anterior chamber so as to keep vitreous from plugging the ostium.
PREVENTING CORNEAL DECOMPENSATION
Contact between the tube and corneal endothelium should be avoided at all costs, because it can result in corneal decompensation. For this reason, in pseudophakic eyes, I prefer to implant the tube in the posterior chamber between the iris and the IOL. I feel this location produces the same IOP-lowering effect while increasing the safety of the corneal endothelium. I keep the tube long enough that I can just see its tip; I direct the needle toward the posterior chamber parallel to the posterior iris surface. If required, the iris can be ballooned up by injecting an ophthalmic viscosurgical device underneath it to make insertion easier. I find that retroiridal positioning of the device maintains a safe distance between the tube and the corneal endothelium and that it avoids long-term corneal decompensation. I reserve anterior chamber placement for phakic eyes.
Before implanting the Ahmed Glaucoma Valve in the anterior chamber, it is important to look for and lyse any peripheral anterior synechiae. The device should not be placed in quadrants with dense iridocorneal adhesions that cannot be lysed, because they might result in anteroplacement of the tube with resultant corneal touch. In such cases, the surgeon can select a different quadrant or place the device in the posterior chamber after performing cataract extraction.
PREVENTING MIGRATION, EXTRUSION, AND EROSION OF THE TUBE
I find that migration, extrusion, and erosion of the tube can be prevented by (1) creating a robust 5 × 5-mm flap from the sclera (or donor sclera/preserved dura), (2) entering the eye via an oblique passage through the sclera so that the tube does not make any sudden turns, (3) keeping the needle entry for the tube into the eye as tight as possible, and (4) making an anchoring knot in the sclera around the tube to prevent it from shifting with extraocular movements. Tight sutures on the scleral flap on either side of the tube sandwich it under the flap, and if available, fibrin glue can be applied under the scleral flap to mold it around the tube. The glue, however, should not be allowed to seep posteriorly into the subconjunctival/Tenon pocket.
CONCLUSION
The Ahmed Glaucoma Valve has become a useful adjunct in the management of refractory glaucomas, but technique is as important here as in any other surgery to prevent postoperative disappointments.
Section Editor Soosan Jacob, MS, FRCS, DNB, is a senior consultant ophthalmologist at Dr. Agarwal's Eye Hospital in Chennai, India. She acknowledged no financial interest in the product or company mentioned herein. Dr. Jacob may be reached at dr_soosanj@hotmail.com.
Section Editor Jonathan Myers, MD, is an associate attending surgeon at Wills Eye Institute in Philadelphia.
