A Better Way to Repair Large, Leaking Blebs

What to do when auto-graft is not feasible.

BY ANDREW RABINOWITZ, M.D.

Over the past quarter century, trabeculectomy with or without anti-metabolites such as mitomycin-C (MMC) or 5-fluorouracil (5-FU) has been the most commonly performed surgical procedure for management of uncontrolled intraocular pressure (IOP) in patients who fail to respond adequately to medications, or medications plus laser trabeculoplasty. Although there is growing interest in non-penetrating filtration procedures such as canaloplasty, trabeculectomy remains the most commonly performed first-line surgery for the management of uncontrolled IOP.

A common sequence for glaucoma surgeries includes trabeculectomy as the first procedure. When the initial trabeculectomy fails, a second trabeculectomy, usually with adjunctive anti-metabolites, is performed. If the second trabeculectomy fails, most glaucoma surgeons will use an aqueous shunt to attempt to gain control of IOP. Over the past decade, the use of aqueous shunts earlier in the sequence has become more prevalent. In certain glaucomas such as neovascular glaucoma (NVG), an aqueous shunt may be the most appropriate first-line surgery. This order has led to tens of thousands of patients who have undergone at least one trabeculectomy. Perhaps the most common long-term complication of trabeculectomy is the development of a bleb leak. This article will deal with the problems presented by bleb leaks while offering an innovative technique for repairing larger leaking blebs.

An Ophthalmic Emergency

The presence of a bleb leak must be viewed as an emergent event. Although many non-surgical treatments for sealing bleb leaks have been described, the gold standard is surgical repair of the leak. The use of tissue glues has not gained popularity due to its marginal success rate. The ideal treatment of a bleb leak may vary from case to case.

Bleb leaks associated with adjunctive MMC tend to be the most difficult to address. The use of MMC leads to large, spongiform, avascular blebs. The avascular nature of the tissue renders the conjunctival and Tenon's layers unable to repair themselves. Chronic friction between the upper lid and the surface of the bleb ultimately leads to breach of the epithelium and aqueous egress. A bleb leak is an ophthalmic emergency. Two potential consequences are hypotony and infectious endophthalmitis.

A Baerveldt Aqueous Shunt prior to implantation into the eye.

One technique for repairing a leaking bleb involves a "hooding" procedure. In this surgery, healthy conjunctiva and Tenon's layers are mobilized and brought down to cover the area of the leak. During this procedure, the area of ischemic tissue is surgically resected. This "hooding" technique is most successful for smaller leaks.

When the Bleb is Large

For leaks associated with MMC, the size of the bleb is generally too large to successfully "hood" the area. The repair of larger, often avascular blebs, requires replacing the compromised conjunctival and Tenon's layers with a conjunctival auto-graft. The auto-graft is actually a "patch graft" comprised of healthy conjunctiva and Tenon's layers from the patient's other eye or from another quadrant of the same eye.

The patch is created by mobilizing a free flap, consisting of both conjunctival and Tenon's layers. The size of the auto-graft must be at least 1 mm larger in all dimensions than the surface area of the leaking bleb. For example, if the leaking bleb measures 8 mm × 10 mm, then the auto-graft patch needs dimensions of no less than 9 mm × 11 mm. Obtaining a graft of these generous proportions often requires surgery to the inferior hemi-fields. Harvesting this graft requires meticulous surgical technique so as not to negatively effect the function of the lower eyelid. If a portion of the graft includes palpebral conjunctiva and/or palpebral Tenon's layers, the result can be foreshortening of the lower lid.

Once the auto-graft is harvested, it is properly oriented with respect to the anatomic limbus and sewn into place. The technique of surgically covering the ischemic bleb mandates strict attention to the tissue planes. The goal of this patch graft technique is to allow blood vessels to bridge the wound margins and allow both layers to become incorporated into the native tissue. This will ensure adequate long-term protection against recurrent bleb leaks.

The "Cover and Abandon" Approach

I have encountered a number of bleb leaks which ideally I would have preferred to repair using a conjunctival auto-graft. In some cases, I was unable to harvest an auto-graft of adequate dimensions. A lack of adequate conjunctiva and Tenon's layers for a conjunctival auto-graft can occur in patients who had been given postoperative 5-FU injections following their initial trabeculectomy. These postoperative injections, applied to prevent early bleb scarring, often lead to compromise of conjunctiva and Tenon's layers.

In cases where harvesting a conjunctival auto-graft is not feasible, I have adopted an alternative approach to repairing bleb leaks. In these instances, I use a "cover and abandon" approach to condemn the trabeculectomy site and then insert a Baerveldt Aqueous Shunt (Advanced Medical Optics, Santa Ana, Calif.) to provide adequate IOP control. This technique allows me to seal the leak, prevent future leaks and still maintain ideal IOP control in order to prevent glaucomatous progression.

Initiating the Procedure

In this surgery, the initial step is to use a blunt scissors to cut away the ischemic bleb from the healthy conjunctiva and Tenon's layers. Next, the blunt scissors are used to gently undermine the remaining conjunctiva and Tenon's layers and free up any adhesions between these layers and the sclera. This dissection is performed with great care so as not to perforate the sclera. The sclera often assumes a "spongiform" character in the years subsequent to filtration surgery due to the chronic bombardment of aqueous, which exits the eye through the scleral flap. Failure to identify the proper tissue planes can lead to inadvertent penetration of the globe.

Hemostasis is obtained by identifying and gently cauterizing any bleeders. Once adequate hemostasis is achieved, attention is turned to the ischemic, leaking bleb. The cautery tips are applied to the surface of the bleb. This is done to thermally heat up, shrink and flatten the bleb. A Weck-Cell sponge is soaked in 100% alcohol. This alcohol-soaked sponge is placed on the surface of the recently cauterized bleb. This application is applied to reduce the possibility of epithelial downgrowth into the eye. The alcohol is then thoroughly irrigated off of the tissues.

A pre-cut graft, composed of either processed pericardium or sclera, is then used to cover the entire trabeculectomy site. This graft is sewn onto the sclera with four interrupted 7-0 Vicryl (Ethicon, Piscataway, N.J.) sutures. The anchor points must be outside the margins of the ischemic bleb. This essentially closes off the scleral flap and prevents future aqueous egress from this site. This condemns this site, rendering it unable to contribute to IOP control.

Placement of the Shunt

The next step involves the placement of a Baerveldt Aqueous Shunt. The supero-temporal quadrant is carefully inspected, along with the superior and lateral rectus muscles. The borders of these muscles are stripped of any Tenon's adhesions. A Baerveldt 350 mm shunt is then placed under the superior and lateral rectus muscles. The plate is anchored to the sclera with two 7-0 Prolene (Ethicon) sutures. The knots are rotated into the eyelet holes to prevent erosion of the overlying conjunctiva. The tube is then ligated with a 7-0 Vicryl suture 1 mm to 2 mm anterior to the plate. The anterior aspect of the tube is then trimmed with an anterior facing bevel. A 22-gauge needle is then used to create a paracentesis tract into the anterior chamber. The tube is inserted into the anterior chamber via this tract.

The area where the tube is inserted into the anterior chamber must be unique to the trabeculectomy site. Often, this involves snaking the tube around the recently abandoned trabeculectomy site with an entrance into the chamber just nasal to the original bleb. The tube is then anchored to the sclera with two interrupted 9-0 nylon sutures. A 0.75 mm to 1.0 mm slit is made in the tube anterior the Vicryl tie-off. This will permit aqueous egress prior to opening of the 7-0 Vicryl tie-off. This 7-0 Vicryl tie-off will open between 4 to 5 weeks after surgery.

A second piece of processed sclera or pericardium is then used to cover the path of the tube from the limbus back to the base of the plate. This patch is anchored to the sclera with at least four interrupted 7-0 Vicryl sutures. At this point, the entire exposed extrascleral space is covered with processed pericardium or sclera. The covered area includes the initial trabeculectomy site and the newly placed aqueous shunt tubing. This surgical field is then closed in a watertight fashion by performing a two-layered closure. First, Tenon's layer is reopposed to the limbus laterally and superiorly with 7-0 Vicryl sutures. Finally, the conjunctiva is carefully brought just anterior to the limbus and closed with interrupted 7-0 Vicryl sutures. If the limbal aspect of the wound is not watertight at this stage, a running mattress suture can be placed using the 9-0 Vicryl suture on a vascular needle. This step, if necessary, ensures a watertight, Seidel-negative wound closure. Watertight closure is necessary to minimize postoperative hypotony and to lower the chance of postoperative infection.

Outcomes Have Been Positive

The combining of the "patch and abandon" closure of the initial bleb with the placement of an aqueous shunt allows for the repair of a leaking, large, avascular bleb in cases where a conjunctival auto-graft is not feasible. In addition to eliminating the emergent problem of an active wound leak, this combined procedure dramatically lowers the risk of long-term recurrent bleb-related complications by virtue of the fact that the bleb itself is condemned by the pericardial or scleral patch graft. In so doing, we provide excellent long-term IOP control without exposing the patient to recurrent bleb leaks. I have found this technique to be of profound benefit in cases which demand prompt wound closure in patients who require long-term IOP control.

In a majority of the cases I have performed using this technique, the short-term and long-term IOP levels achieved were at target levels. The postoperative recovery can take between 3 and 6 weeks. Once the external wounds are healed and scarred, the patient is again protected against bacterial endophthalmitis. Additionally, the posterior placement of the plate of the aqueous shunt lowers the risk of sight-compromising wound leaks. OM

Andrew Rabinowitz, M.D., is the glaucoma specialist at Barnet, Dulaney Perkins Eye Center, Phoenix, Ariz. His surgical techniques have been used in educational films demonstrating the appropriate uses of the Baerveldt Aqueous Shunt. He has no financial interest in any of the products mentioned in this article.