As the popularity of tube shunts for the treatment of glaucoma continues to grow, so, too, do the options for materials with which to cover these devices. Historically, surgeons favored sclera or processed pericardium for patch grafts, with the latter currently more popular owing to its greater availability and ease of use. A recent shortage of Tutoplast processed pericardium (IOP Inc., Costa Mesa, CA), however, has prompted ophthalmologists to seek alternatives to avoid delaying patients' surgery. Pericardium is also available from New World Medical, Inc. (Rancho Cucamonga, CA). Investigators are exploring other materials for use as patch grafts to cover the tubes of drainage implants.

Another reason to use alternative materials is cosmesis, because many patients complain about seeing the white patch under their conjunctiva. I find this reaction to be more common among younger patients who do not have sufficient age-related ptosis to cover the patch completely and among patients with a wide palpebral fissure. An additional benefit of a clear graft is that it facilitates the lysis of a ligature suture around a nonvalved tube shunt. This article reviews the currently available alternatives to sclera and pericardium.

CORNEA
The clarity of donor corneal tissue gives it a cosmetic advantage over sclera and pericardium. In addition, corneal tissue may be more enduring than pericardium. Over time, most pericardial patch grafts may thin, thereby increasing the risk of the erosion of the tube. Although mechanical forces and poor positioning may have more to do with a tube's erosion, a thinned patch may contribute to the problem.

The two main disadvantages of corneal tissue are its availability and cost. Surgeons cannot keep a large supply of donor cornea on hand to accommodate a busy 2 months of surgery. Moreover, the facility fee for scleral reinforcement with a patch graft is fixed, and using a more expensive material only decreases the facility's bottom line. This may not be a major issue for surgeons who operate in a hospital setting. For those who operate in an ambulatory surgery center, however, the added $150 to $200 per case for corneal tissue versus less expensive alternatives is usually prohibitive. A third drawback to donor cornea is that its use involves extra administrative time pre- and postoperatively. For example, the staff must coordinate getting corneal tissue in time for a case and must fill out the donor and recipient data forms.

AMNIOTIC MEMBRANE
A less expensive alternative to corneal tissue is amniotic membrane. Bio-tissue, Inc. (Miami, FL), developed amniotic membrane for the coverage of tube shunts. Unlike the thin membranes used for ocular surface reconstruction, Amniograft-G (Figure 1A) is approximately 300 to 400 µm thick—almost 10 times the thickness of standard amniotic membrane. Amniograft-G comes on a piece of paper, which is soaked in a preserving fluid inside a sterile plastic peel pack (Figure 1B).

I have used Amniograft-G as is but, more recently, have been folding it over to create a 600- to 800-µm patch. I use fibrin tissue glue to fixate all of my patch grafts to the sclera over the tube. The technique has been especially helpful with amniotic membrane, because it eliminates any manipulation of the graft that may occur during suturing. In the past year, I have used amniotic membrane to cover approximately 15 tubes with no cases of erosion to date. The cosmetic result is similar to that of corneal tissue.

A possible disadvantage is that amniotic membrane may dissolve over a short period of time. I have noted a persistent elevation in the area where the graft is placed, however, that is likely due to the host-cell migration of conjunctival cells that integrate into the graft. Anterior segment optical coherence tomography demonstrates the persistence of the membrane over time, but longer follow-up is needed (Figure 2). It is also possible that amniotic membrane exerts anti-inflammatory and anti-scarring actions.

The pricing of Amniograft-G is similar to that of pericardium. If its protective effect over the tube proves to be enduring, thick amniotic membrane may be an excellent alternative to corneal tissue in terms of cosmesis, cost, and biocompatibility.

PORCINE SUBMUCOSAL TISSUE
In addition to Tutoplast, IOP Inc. manufactures a new material for scleral reinforcement that can be used to cover a tube. Both products are packaged similarly, but KeraSys is porcine submucosal tissue. A significant advantage of this material is that there is an almost unlimited supply. In addition, it does not carry the same risk of disease transmission as corneal tissue. KeraSys is a thinner, more pliable version of the company's TarSys, which oculoplastic surgeons use for reconstructing the eyelid.

During the last shortage of pericardial tissue, I tried KeraSys. It is far more rigid than Tutoplast but becomes easier to manage after soaking. Because I use fibrin tissue glue, the material's rigidity was not a problem, but it might be more difficult to suture than pericardium. It is also unclear how this bioengineered lamellar patch graft will behave over time. The tissue is mildly opaque (Figure 3) but was not visible under the conjunctiva except for the raised edges of the graft. KeraSys therefore offers similar cosmetic advantages to cornea and amniotic membrane. During early follow-up, it also seems to be an enduring material. The raised edges of the graft were still visible in the eyes I treated even after several months, but the follow-up period had not yet reached 6 months at press time.

At present, IOP Inc. uses the same pricing for KeraSys and Tutoplast.

CONCLUSION
Most glaucoma surgeons have extensive experience with pericardium, which is likely the most commonly used patch graft to cover a tube. At times, however, its availability is limited, and this material offers suboptimal cosmesis. Donor cornea can be used even if the conjunctiva cannot be completely closed. Availability, administrative issues, possible disease transmission, and cost remain barriers to the regular use of corneal tissue as a patch graft over a tube shunt. Amniograft-G and KeraSys seem to be promising, but greater follow-up is needed to determine their long-term effectiveness for preventing the tube's erosion.

Steven R. Sarkisian, Jr, MD, is a clinical assistant professor at The Dean A. McGee Eye Institute of the University of Oklahoma in Oklahoma City. He acknowledged no financial interest in the products or companies mentioned herein. Dr. Sarkisian may be reached at (405) 271-1093; steven-sarkisian@dmei.org..