This article discusses the benefits of the widely used technique of laser suture lysis and explores newer alternatives of releasable, compression sutures and adjustable sutures.
LASER SUTURE LYSIS
About the Technique
Laser suture lysis can be an excellent option, because it allows surgeons to place tight sutures and release them predictably.4 A great advantage of this approach is that the ophthalmologist need not master a new intraoperative procedure. The technique involves the transconjunctival application of laser energy to the sutures in the scleral flap. The laser energy causes the sutures to heat and dissolve, thus lysing and effectively cutting them. Suture lysis eliminates local tension on the scleral flap at the site of the suture and thereby permits an increase in aqueous flow.
Conjunctival compression causes blanching that allows the surgeon to visualize the scleral flap suture. Compression is accomplished with either the corner of a four-mirror lens or other specially designed lenses that focus the laser energy on the suture (Figure 1). Asking the patient to look down and having an assistant help lift the patient's upper eyelid generally improves the surgeon's access to the scleral flap area. Laser suture lysis most commonly involves an argon laser, although a krypton or diode laser may also be used. Typical settings on the argon laser are a 50-µm spot size, 20- to 100-millisecond duration, and 250 to 1,000 mW of power.
Figure 1. During laser suture lysis, a Hoskins (Ocular Instruments, Bellevue, WA) or similar lens compresses and blanches the conjunctiva and exposes the scleral flap suture. Laser energy lyses the suture, thus releasing tension on the scleral flap and increasing the flow of aqueous. The superior periphery of the Hoskins lens contains a flange or retractor that acts to lift the upper eyelid.
Special Considerations
At times, laser suture lysis may result in ocular pain from the early postoperative placement of a lens in the area of surgery. There is also a risk of trauma to or dehiscence of the conjunctival flap. Moreover, problems of visualization that prevent suture lysis tend to occur in the eyes that most need the sutures released, particularly those with thick, inflamed Tenon's tissue or blood. Making long suture passes intraoperatively increases the likelihood that the surgeon will visualize a clear area of the suture. In the setting of thick Tenon's tissue, prolonged compression of the area with a lens may in some cases blanch the underlying tissue and permit suture lysis. Laser-induced perforation of the conjunctival flap may occur, especially in the presence of blood. After trabeculectomy with adjunctive mitomycin C, such punctures may result in chronic wound leaks.5 If the surgeon does not find an area free of blood but he can visualize the suture, using a red laser may permit lysis without perforation.
Laser suture lysis also poses problems related to convenience and cost, because it usually involves the cutting of multiple sutures over time. For many ophthalmologists, the procedure must be scheduled at an off-site location that requires reimbursement for the use of its laser. Even moving patients to a laser room multiple times within one's own office is inefficient and inconvenient, especially when these individuals are elderly and relatively immobile. Moreover, after releasing sutures, ophthalmologists typically recheck patients' IOPs and apply digital pressure as necessary to mobilize the bleb, thereby necessitating a return trip to the examining room. If a portable and easily transferable argon laser is available, moving it onto and off the slit lamp will allow the patient to stay in one room for the examination, laser treatment, and postlaser checks.
INTERRUPTED, EXTERNALIZED SUTURES IN THE SCLERAL FLAP
About the Technique
To avoid the obstacles of laser suture lysis, surgeons have developed approaches such as interrupted, externalized releasable sutures. The most widely used technique for these sutures was developed by Cohen and Osher.6 These scleral flap sutures can be removed predictably even in the presence of hemorrhagic, thickened, or edematous conjunctiva. Lens-induced pain, trauma, or risk of a perforated conjunctival flap during laser suture lysis are avoided, and access to a laser is not required. Using traditional interrupted sutures such as those in a conventional scleral flap minimizes the learning curve with the procedure.
The surgeon places a slipknot on the interrupted suture over its position on the scleral flap (Figure 2). The slipknot involves making four suture loops to ensure that the suture will remain in place until the surgeon judges its removal to be appropriate. The end of the suture is brought out beneath the conjunctival reflection to the corneal surface. If the suture is left loose there, it may cause the patient discomfort or result in infection. To ensure that the suture remains flat on the cornea and no loose ends are present, the surgeon places an additional suture pass in the cornea, pulls the end tight, and cuts it flush with the corneal surface, thus creating a flat suture loop with no exposed suture end. During removal of the suture, lifting the suture loop exposes the suture's end and ensures that the suture is always accessible for removal. Several such sutures may be placed around the perimeter of the scleral flap, and they are removed sequentially as necessary.
Figure 2. In the technique for releasable interrupted sutures described by Cohen and Osher,6 a 10–0 nylon suture passes from the sclera (1) to the apex of the scleral flap (2) to create an interrupted suture (A, cross-section B). Four throws in the suture (1) with subsequent grasping of the suture loop (2) create a slip-knot (C). The suture then passes through the base of the scleral flap (3), under the conjunctival reflection, and to the corneal surface (4). A loop next passes over the corneal surface. The suture finally enters the corneal stroma (5) then reemerges at the corneal surface (6) where the surgeon cuts it flush with the cornea. Pulling the suture loop on the corneal surface upward exposes the end of the suture. Tension on the suture's end loosens the slipknot and removes the suture.
Special Considerations
Potential difficulties arise because the slipknot can become enveloped and infiltrated with episcleral tissue, which, after a short time, may preclude the suture's release. The suture loop on the corneal surface may also become loose and cause ocular discomfort or create a nidus for infection.
LIMITATIONS OF LOCALIZED INTERRUPTED SUTURES
Interrupted sutures individually only pin the scleral flap down at a single point. Because of the relatively short suture throws, there is no self-adjusting feature. Furthermore, the sutures typically pass full thickness through the flap near its base in the area of the sclerotomy. Such suture passes at times create small holes in the scleral flap that may stretch under tension and allow fluid to flow directly from the sclerotomy through the scleral flap. Operations in sclera compromised by previous surgery increase the risk of creating excessively large needle and suture track holes in the scleral flap.
Studies place the risk of a shallow chamber in the range of 33% to 54% in trabeculectomy with interrupted sutures,7,8 although the incidence of shallow chambers in one report was 14%.8 Careful study demonstrates that, even with multiple interrupted sutures, shallow chambers remain an issue9 and, at times, necessitate adjunctive measures such as large contact lenses, scleral shells, and the injection of viscoelastic agents into the anterior chamber.9,10
EXTERNALIZED COMPRESSION SUTURES OVER THE SCLERAL FLAP
About the Technique
Self-adjusting externalized compression sutures reduce the risk of shallow and flat chambers (Figure 3). In two prospective reports of my experience with the technique, my colleagues and I measured the anterior chamber depth objectively in more than 230 cases.1,2 The incidence of shallow chambers was 3%, and there were no flat chambers.
Figure 3. Dr. Johnstone uses two techniques together for releasable compression sutures. A suture passes from the sclera to the cornea under the conjunctival reflection, across the corneal surface, and then beneath the conjunctival reflection again (A1). A loosely tied horizontal mattress suture passes from the back of the scleral flap's surface to the scleral surface (A2). Tension on the posterior arm of the scleral flap suture uniformly compresses the entire back edge of the scleral flap into the scleral bed (A3). The left end of the corneal suture passes under the posterior arm of the horizontal mattress suture in the scleral flap (A4). Tensioning the corneal suture tightens the scleral flap suture (A5). Tying the corneal suture to itself creates an X-shaped area of elastic 10–0 nylon that uniformly compresses the entire anterior surface of the corneal flap. Dr. Johnstone rotates the knot of the corneal suture into the corneal stroma where it cannot become encased in episcleral tissue (A6). A second suture (B1) passes through the scleral wall, over the scleral flap's surface (B2), beneath the conjunctival reflection (B3), across the corneal surface, and then beneath the conjunctival reflection again (B4). Tying the suture to itself creates an area of gentle compression directly over the sclerotomy. Dr. Johnstone rotates the suture knot into the corneal stroma. The compression sutures are self-adjusting and easy to remove, because they are always accessible underneath the epithelium on the corneal surface.
In more than 3,500 cases, I have found the self-adjusting suture to be highly reliable at avoiding shallow chambers during the early postoperative period. Because the sutures adjust themselves, there is rarely a need to remove the cardinal X suture early. I can regularly avoid release during the first 2 weeks if I initially set the tension of the suture appropriately and judiciously use digital pressure to mobilize the scleral flap until the margins of the bleb become demarcated.11
The technique involves the placement of X-shaped compression sutures over the surface of the scleral flap. Because the sutures are long and elastic, they hold the flap down if the IOP is low and no aqueous flows. If the IOP rises, the elastic sutures permit the flap to rise, allowing the escape of aqueous through the sclerotomy. As the pressure drops, the elasticity of the nylon again causes compression of the flap and prevents the escape of more aqueous.
Initially, the surgeon passes a 10–0 nylon suture from cornea to sclera beneath the conjunctival reflection on both sides of the scleral flap (Figure 3A). The two ends of the suture are then laid aside. A second suture is placed at the posterior edge of the scleral flap in a horizontal mattress fashion with the knot tied loosely enough to allow the flap to elevate approximately 15º.
The left arm of the initial corneal suture is passed through the posterior arm of the scleral flap suture. Next, the surgeon pulls the left arm of the initial corneal suture forward and ties it to the right arm. Tensioning of the suture accomplishes two things. First, because the corneal suture passes through the posterior arm of the scleral flap suture, tension transmits directly to the anterior arm of the scleral flap suture and thus creates uniform tension along the entire back edge of the scleral flap. Second, the X created over the scleral flap distributes uniform compression over the entire anterior surface of the flap.
The knot of the corneal suture is next rotated into the cornea to prevent it from ever becoming encased in episcleral tissue. The suture remains under slight tension, which causes it always to be buried under the corneal epithelium and eliminates the risk of infection or the need for the suture's early release. Although the suture is generally removed within 3 months, it may be left in place for 2 or 3 years. Because the knot cannot become encased in episcleral tissue, it is always removable.
A second compression suture (Figure 3B) passes over the top of rather than through the scleral flap above the sclerotomy area. This configuration avoids buttonholes in the anterior portion of the flap near the sclerotomy. The suture passes through the scleral wall adjacent to the flap, over the flap's surface, and through the opposite scleral wall. The suture then passes from the sclera to the cornea, beneath the conjunctival reflection adjacent to the scleral flap, across the corneal surface, and then from the cornea to the sclera beneath the conjunctival reflection. Finally, the surgeon ties the suture to itself and rotates the suture knot into the cornea.
Special Considerations
There is a learning curve involved in operative management. As with other techniques, optimal suture tensioning is important. Emphasis must be placed on avoiding over tightening of the X suture, which may then require early suture release. For example, with proper adjustment, a full-depth chamber is maintained when the sutures are tied loosely enough so that the entire X of the elastic nylon may be easily elevated 2 to 3 mm above the corneal surface with upward pressure from a forceps. The elasticity of the long runs of suture creating the X will then recoil to the scleral flap surface with the forceps' release, thus ensuring the retention of chamber depth. When the sutures are properly tensioned, little or no astigmatism is induced, although cylinder from excessive tension may be an issue that only the suture's release resolves. The arrangement of sutures is quite forgiving and predictable, as an X configuration anywhere on the scleral flap surface provides uniform compression both over the scleral flap surface and along the entire back edge.
TRANSCONJUNCTIVAL ADJUSTMENT OF INTERRUPTED SUTURES
About the Technique
Surgeons have long had the ability to reduce IOP by means of various suture-release techniques, but there have been no practical alternatives to tighten the scleral flap and increase pressure when the IOP becomes too low. Recently described, the transconjunctival adjustment of interrupted sutures may offer a new approach to dealing with this vexatious issue. If the technique proves capable of reliably increasing the IOP, it will add a new dimension to the management of trabeculectomy.
Laboratory12 and clinical13 study explored the direct transconjunctival adjustment of interrupted sutures using specially developed, atraumatic forceps (Figure 4). The technique uses a 3- X 4-mm rectangular scleral flap with two 10–0 nylon sutures placed in its corners. The scleral flap sutures are the releasable type developed by Cohen and Osher6 (Figure 2). The surgeon adjusts the sutures postoperatively by grasping the suture knot through the conjunctiva and pulling it either toward or away from the cornea. In the clinical study,13 patients (n = 14) with an IOP higher than 15 mm Hg on day 1 had their suture tension decreased to reduce the pressure to a target range of 10 to 15 mm Hg. The mean IOP after adjustment was 10.7 mm Hg (SD = 3.6). No patient had a shallow chamber. Bleb needling was used as an adjunctive technique in 25% of the patients in the postoperative interval.
Figure 4. The surgeon uses two Khaw Transconjunctival Adjustable Suture Control Forceps (Duckworth & Kent Ltd, Hertfordshire, England) together to adjust the sutures. The round, smooth tips are designed to avoid trauma to or perforation of the conjunctiva during the sutures' transconjunctival adjustment.
Special Considerations
Limitations like those associated with laser suture lysis arise. They include the potential for trauma to or disinsertion of the conjunctival flap as well as the surgeon's inability to visualize and access the suture with thick Tenon's tissue or blood in the area. Although suture adjustment may be feasible immediately postoperatively, later adjustment may be compromised when the suture becomes enveloped and infiltrated by episcleral tissue.
The investigators reported the capability of rather reliably reducing the IOP by transconjunctival suture adjustment, but their ability to raise low IOP was less clearly characterized. With the currently widespread use of antimetabolites, the early and even rather late release or adjustment of sutures may at times result in an IOP that is lower than desired. A technique that can reversibly return the IOP to a normal level would be of great benefit in cases of persistently low IOP after suture lysis, release, or adjustment. Whether the transscleral suture adjustment technique can reliably increase IOP in patients whose IOPs fall and remain persistently below the desired level certainly warrants further study.
CONCLUSION
Releasable sutures reduce the risk of postoperative complications associated with low IOP and shallow anterior chambers. Various techniques are now available. Laser suture lysis is the most commonly used and offers the advantage of intraoperative simplicity. Other techniques such as externalized releasable sutures, releasable compression sutures, and the transscleral adjustment of sutures have been recently introduced as potential means for improving surgeons' ability to control IOP and chamber depth during the postoperative period.
Murray A. Johnstone, MD, is Consultant in Glaucoma for the Department of Ophthalmology at the Swedish Medical Center in Seattle. Dr. Johnstone may be reached at (206) 682-3447; murray_johnstone@hotmail.com.
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