Next, I cut a 6×6 mm square of donor acellular dermis graft [Alloderm Regenerative Tissue Matrix, Acellular Human Dermis (thickness=0.79 to 1.78 mm), Lifecell, Branchburg, NJ] with scissors (Fig. 4). This graft is laid on the episcleral bed over the exposed segment of tube and tucked beneath the anterior and posterior conjunctival flaps (Fig. 5). The graft should seem oversized for the space, so that there will be a gap of 2 to 3 mm between the conjunctival edges. No sutures are placed in the dermis graft. Rather, the graft will become “caged in” by the conjunctival closure. I close conjunctiva with a running horizontal mattress (meandering) suture of 7-0 polyglactin (Fig. 6). The suture should pull light tension only on the conjunctiva. There will remain the 2 to 3 mm gap over the dermis graft. An attempt at tight, complete conjunctival closure will result in wound dehiscence, from cheese-wiring of the suture through the tissue. Instead, the gap is allowed to heal (epithelialize) by secondary intention. At follow-up visits, epithelial healing may be monitored using topical fluorescein at the slit lamp, which easily differentiates epithelium (glistening, with little or no stain uptake) from bare graft collagen (stain uptake similar to corneal stroma).
The traction suture is removed from the cornea (if present). I inspect the anterior chamber to assure that the chamber depth and the tube position have not changed as a result of the procedure. Remember that no entry of any kind has been made into the anterior chamber with my method. After the lid speculum and drapes have been removed, a combination of antibiotic/corticosteroid ointment is applied, and the eye is protected with a rigid shield. Postoperative follow-up includes 1 day and 1-month visits.
RESULTS OF TUBE REVISION
Descriptions in the literature of the follow-up results of tube revision procedures have been limited. In the 1 patient for whom Gedde et al revised rather than removed the tube, the eye was reported as phthisical at 1-year follow-up. Brandt2 reported that at 8 months' follow-up, the dura mater patch graft seemed well tolerated, without surrounding or overlying conjunctival reaction. Lama and Fechtner4 reported follow-up for 1 case at 15 months and the other at 8 months. Both eyes demonstrated intact overlying conjunctiva and no evidence of thinning of the donor scleral patch graft. The autologous scar tissue patch used by Puustjärvi et al5 was reported to be a smooth and partly translucent area covering the former operated area with a well-healed conjunctival covering at 3 months. Billson et al6 described 3 pediatric patients in whom resiting a Molteno tube under a half-thickness scleral flap was performed. All 3 cases were simply described as “stable” 4 to 7 years postoperatively. The 4 patients of Joos et al7 who underwent posterior repositioning of a tube for recurrent erosion had no further recurrent erosions during follow-up, which was 1 to 42 months at most.
In my series of tube revisions with acellular dermis graft, there have been 30 cases over 4 years. The period of follow-up observation was 1 to 42 months, with a median period of 12 months. Twenty-nine of the procedures created good tissue coverage initially over the tube with secondary epithelialization of the graft. None had active infection preceding the revision, so culturing and preoperative treatment of infection were moot. There were no extrusions of the dermis graft. All tubes remained in stable position in the anterior chamber without loss of drainage function. Some of the grafts seemed to maintain their original thickness, whereas others seemed to thin partially with time. Complications are discussed in the next section.
COMPLICATIONS OF TUBE REVISION SURGERY
The literature lists some complications of revision surgery for tube exposure. Phthisis bulbi1 realistically followed from endophthalmitis, which was a sequela of tube exposure. Recurrent tube erosion,7 tube migration toward the corneal endothelium,3 and cystoid macular edema2 have been described as the result of revision surgery.
A number of additional potential complications, although not published, can be foreseen, and efforts should be made to minimize the risk of these. The likelihood of de novo infection as the result of revision surgery must be minimized with attention to sterile technique and the use of preoperative and postoperative topical antibiotics. Hypotony, with attendant choroidal effusion and/or suprachoroidal hemorrhage, can be avoided by not entering the anterior chamber and by avoiding dislodging the tube from its fistula. Of course, a dislodged tube can be replaced easily, but the intraocular pressure drops quickly to near 0 mm Hg. In this event, the anterior chamber should be reinflated with balanced salt solution after tube replacement, to restore moderate pressure. If the tube is inadvertently transected during dissection of the tissues, then it should be repaired using one of several tube splicing techniques. However, tube splicing is beyond the scope of this discussion. A needle puncture or small nick in the tube wall, absent transection, rarely warrants repair.
Wound dehiscence is a risk. Realistically, all wounds closed by my method are “dehisced,” because of the 2 to 3 mm intentional gap between the conjunctival edges. The risk is of cheese-wiring the suture through tissue, wider dehiscence, and even loss of the dermis graft. The most reliable hedge against this is to resist the impulse to tighten the polyglactin closure. A loosely meandering polyglactin suture that “cages in” the dermis graft is more likely to remain intact for weeks than a taut closure. When cheese-wiring and further dehiscence do occur, close observation is the management of choice. Most wounds will go on to completely epithelialize the dermis graft. In the unlikely event of displacement or loss of the dermis graft during postoperative follow-up, the revision procedure must be repeated with a fresh graft, or using one of the variations described in the literature.1–7
Hemorrhage is a potential complication, but rarely a serious problem. Most wounds ooze copiously during dissection, because the tissue is previously disturbed and fibrovascular. The surface bleeding is easily accessible with fine-point bipolar cautery. Postoperative surface bleeding is rare and may emanate from suture erosion through conjunctival vessels. Suprachoroidal hemorrhage may theoretically occur as a sequela of anterior chamber penetration with loss of intraocular pressure or of scleral perforation with a sharp instrument reaching the highly vascular ciliary body or choroid.
Potential complications may occur to the equatorial plate. Buttonhole defects created in the posterior conjunctiva could result in plate exposure, which can lead to complete extrusion in some cases. The fluid-filled bleb space may be breached, with sudden egress of aqueous humor and loss of intraocular pressure. In the event of a breached bleb, the opening of the fibrous bleb wall may be closed with polyglactin suture, avoiding incorporating epithelium. The intraocular pressure may be partially restored by injecting viscoelastic into the anterior chamber through a paracentesis incision. The risk of these complications may be minimized by careful, deliberate dissection.
Epithelial entrapment and epithelial inclusion cyst formation are potential complications. The risk of these may be minimized by, first, the decision to operate sooner rather than later in the course of the tube exposure (allowing for less extensive undergrowth of epithelium beneath the tube) and, second, by careful dissection, scraping, and cautery of the underpass of epithelium on the episclera. A rare potential complication of breaching the bleb space would be epithelialization, or “marsupialization,” of the posterior bleb lining.
The rate of complications for my series of tube revisions, over 4 years, is 5 of 30 patients. Four of them involved tube reexposure and 2 involved endophthalmitis. One patient developed a tube reexposure 6 months after successful revision with acellular dermis graft. He underwent a second revision procedure with acellular dermis graft, and had no further complications 6 months later. A second patient developed tube reexposure 20 months after a revision that had healed well. Because the eye was blind (no light perception), she opted to undergo removal of the tube 30 months after the revision rather than have another revision operation. The third patient developed what is better described as wound dehiscence, with tube exposure and graft retraction posteriorly 1 month after the revision. There was not complete extrusion of the graft. Because his eye had very poor vision, he opted for removal of the tube 3 months after the revision.
The fourth patient developed reexposure of her tube 6 months after the revision procedure. However, the graft and epithelial covering were healed and intact—the new exposure was posterior to the acellular dermis graft and close to the plate. This was treated with another revision and a second acellular dermis graft posterior to the first. This failed to epithelialize completely and 4 months later she developed endophthalmitis requiring a vitreous tap, intravitreal antibiotics, and removal of the tube. The fifth patient developed endophthalmitis 2 months after the revision procedure. By that time, the graft was well epithelialized and the conjunctival surface was free of aqueous leaks. He was treated successfully with vitrectomy and intravitreal antibiotics and his tube remained well-covered 29 months later. Because he had no signs of infection at the time of the revision, I conjecture that the infection, however slow to become evident, was introduced at the time of the revision procedure or the early postoperative period before complete epithelial healing.
DISCUSSION: KEY CONSIDERATIONS
Exposure of the tube of an ADI within a few millimeters of the limbus is not an infrequent long-term complication. Tube exposure that occurs within the first month of the original device implantation is recognized as a surgical wound dehiscence, and treated as such. This review discusses late tube exposure, typically years after the original surgery, and typically with a quiet eye. Most patients are unaware of a 1 to 2 mm tube exposure without infection. In fact, beyond a year after successful ADI implantation, tube exposure may be the most common complication. However, there are no data in the literature on rates of long-term (>1 y) complications of tubes exclusive of short-term (<1 y) complications. One study of the long-term outcomes of Ahmed valve implantation found that 3 of 78 eyes required revision for tube exposure.16 Although all eyes were observed for a minimum 3 years of follow-up, no mention was made of the timing (long-term or short-term) of the tube exposures.
I recommend that the surgeon, and subsequent nonsurgeon eye care personnel involved in the patient's care, bear in mind the following key considerations:
1. Each patient must be informed of his/her commitment to lifelong follow-up. After successful ADI surgery, the risk of complications of the hardware is ever present. Because of the lifelong risk of tube exposure and endophthalmitis, complacency and neglect could be very costly. Regular eye examinations for life are required. Also, he/she should be advised to avoid all eye rubbing—even though no data in the literature associate chronic eye rubbing with tube exposure.
2. Examine the ADI hardware at every visit. The surgeon, and subsequent nonsurgeon eye care personnel, must develop this habit. Tube position in the anterior chamber and its limbal crossing should be noted. Then the upper eyelid should be lifted while the patient gazes downward. At the slit lamp biomicroscope, the tube is inspected from limbus to plate, and the anterior edge of the plate and bleb (if possible) are inspected. Exposed hardware should be easy to identify. There is a rim of slight injection of the surrounding conjunctival vessels, and slight mucus or oil accumulation on the tube wall itself when exposure is present.
3. I recommend periodic eye examinations at intervals no longer than 12 months, for the life of the patient. One could argue that every 6 months is a more appropriate interval to detect early exposures and to minimize the chance of endophthalmitis.
4. Prophylactic antibiotics while awaiting surgery are of no proven value. Theoretically, they may be detrimental by selecting bacteria resistant to the antibiotic(s) used. There are no published data on reducing the incidence of endophthalmitis associated with tube exposure by using prophylactic antibiotics. In fact, there are few data on antibiotics for uninfected leaking trabeculectomy blebs. Wilensky17 reported that 2 of 12 patients with bleb leaks after trabeculectomy developed endophthalmitis. Because both had received prophylactic antibiotic therapy before endophthalmitis developed, Wilensky stated that “therefore, it would appear that such treatment does not afford major protection against the development of intraocular infection.” Prophylactic preoperative antibiotics are typically started 30 to 60 minutes before surgery.
5. An exposed tube in a prephthisical or phthisical eye (hand motions vision or worse) should simply be removed. Revision with a patch graft is too big an operation for an eye with no salvageable vision. Furthermore, the risk of later reexposure increases if the globe shrinks. In such a case, I recommend removing the tube from its limbal fistula, closing the fistula tightly with 7-0 polyglactin suture, and stretching the tube so as to transect it as closely as possible to the plate. The plate (if unexposed) need not be removed, as that again would be too big an operation for such an eye.
With attention to these considerations and to good intraoperative technique, one can achieve good tissue coverage of the tube while maintaining its drainage function.
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Keywords:© 2010 Lippincott Williams & Wilkins, Inc.
tube exposure; revision surgery; aqueous drainage implant; patch graft