Trabeculectomy Technique the Moorfields Safe Surgery System with New Adjustable Sutures
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SURGICAL PEARLS Trabeculectomy Technique The Moorfields Safe Surgery System with new adjustable sutures. BY PENG TEE KHAW, PHD, FRCS, FRCOPHTH, FRCP, FRCPATH, FIBIOL, FMEDSCI; ANNEGRET DAHLMANN, MD, FRCOPHTH; AND KAMIAR MIRESKANDARI, MD, FRCOPHTH his article presents a system of glaucoma surgery bleb is ultimately located under the upper lid. Otherwise, known as the Safe Surgery System that has evolved the chance of discomfort to the patient and of bleb-related at Moorfields Eye Hospital in London. The sys- complications such as leak and infection is markedly higher. T tem’s development is based on a need to improve If it is not possible to place the bleb under the patient’s the consistency of the surgery and its outcome, particularly upper lid, then we perform tube-drainage surgery instead. from the patient’s point of view. The use of strong antimetabolites such as mitomycin C TRACTION SUTURE (MMC) during trabeculectomy increases the risk of po- We always use a corneal traction suture to avoid a superi- tential complications, including hypotony with visual loss or rectus hematoma and to achieve maximal traction. Our and leaking as well as uncomfortable blebs that may lead to preference is a 7–0 black silk suture on a semicircular needle endophthalmitis. The Safe Surgery System is designed to (Figure 1). preserve visual acuity by minimizing hypotony and bleb- related complications while achieving a desirable postopera- CONJUNCTIVAL INCISION tive IOP. Table 1 highlights several ways in which the system We now only use fornix-based flaps, mainly because of the prevents complications. scleral exposure and controlled surgery they afford. This type of flap also eliminates the posterior incision of limbus-based POSITION OF FILTRATION AREA surgery that often results in a posterior restricting scar. We Our first step is carefully to assess and draw the lid’s posi- avoid radial, side-relaxing incisions. We dissect backward tion in relation to the superior limbus. We ensure that the with Westcott scissors to make a pocket approximately 10 to Figure 1. Placing a corneal traction suture averts hematoma Figure 2. The authors dissect over the rectus muscle and lift of the superior rectus muscle. the conjunctiva. 22 IGLAUCOMA TODAYIMARCH/APRIL 2005 SURGICAL PEARLS Figure 3. The ring of steel and anterior aqueous flow are visible. Figure 4. The authors cut a scleral pocket. 15 mm posteriorly and sufficiently wide to accommodate lowed a larger area of antimetabolite treatment, without the antimetabolite sponges. When dissecting over the supe- a posteriorly placed restricting scar. Similar blebs can be rior rectus tendon, we lift the conjunctiva to cut attach- achieved with a limbus-based flap, but the incision must ments while avoiding the tendon itself (Figure 2). be located quite posteriorly. Results are less consistent In the past, we relied on a limbus-based incision and an with this method, and we find it more difficult subse- antimetabolite due to our concern about postoperative quently to create the scleral flap and place sutures, par- leaks. Dr. Khaw’s clinical observation of all cystic blebs, ticularly in repeat trabeculectomies. however, led to his hypothesis that they had two things in common. The first was restricted posterior flow due to a SCLERAL FLAP ring of scar tissue, which he called the ring of steel. The sec- Our next step is to create an incision and a scleral pocket ond was a source of limbal drainage (Figure 3). The restrict- (similar to a phacoemulsification pocket), after which we cut ed flow from the posterior incision resulted in more focal, the two side incisions (Figure 4). We do not cut the side inci- cystic blebs, a finding that led us to convert to fornix-based sions right to the limbus in order to encourage posterior flow flaps. and reduce the incidence of cystic blebs. We cut the scleral With limbus-based flaps, the effects of treatment were flap before applying an antimetabolite. focal. Moreover, although their growth halted,1,2 the cells We try to make the largest flap possible. Leaving the side at the edge of the treatment area could produce scar tis- cuts at the limbus incomplete (1 to 2 mm from the limbus) sue and encapsulate the area, both of which resulted in a (Figure 5) forces the aqueous backward over a wide area to thin, cystic bleb. A fornix-based incision, by contrast, al- achieve a diffuse bleb. An aqueous jet at the limbus encour- TABLE 1. FEATURES OF THE SAFE SURGERY SYSTEM TO MINIMIZE COMPLICATIONS Prevent Hypotony Prevent Thin, Uncomfortable, Prevent Limbal Leaks of Aqueous Cystic Blebs New adjustable sutures for the scleral flap Large area of antimetabolite treatment Corneal groove-closure technique that can be gently titrated downward Continuous intraoperative infusion to Posterior diversion of aqueous by altering prevent intraoperative hypotony and scleral flap’s construction achieve accurate pressure titration Small sclerostomy punch Fornix-based flap to minimize posterior scarring Fornix-based conjunctival flap to opti- Bleb’s location under eyelid confirmed mize construction of the scleral flap MARCH/APRIL 2005 IGLAUCOMA TODAYI 23 SURGICAL PEARLS ages the formation of an anterior, focal cystic bleb. In preference is corneal shields rather than other sponges. contrast, a posteriorly directed, diffuse flow of aqueous Once cut in half and folded like a foldable lens (Figure 7A), from the incompletely cut sides of a large scleral flap the sponge fits through the entrance to the scleral pocket results in a more diffuse, noncystic bleb. We preplace without touching the conjunctival edges. Each sponge is sutures in the scleral flap while the eye is still firm, be- approximately 5 X 3 mm, and we insert about six of them cause suturing is more difficult after the eye has been into the pocket (Figure 7B). entered and is hypotonous. We treat as large an area as possible, including under the scleral flap. The polyvinyl alcohol sponges maintain their ANTIMETABOLITES integrity. In contrast, methylcellulose sponges fragment rela- Intraoperative Use tively easily, which increases the chance that small pieces of Our earlier article for Glaucoma Today3 covered patient sponge will remain in the wound. Enlarging the surface area risk factors for scarring, the risks of antimetabolite-related of treatment results in a more diffuse, noncystic area clini- complications, and our regimen with these agents. If intra- cally. It also prevents the development of the ring of steel, operative antimetabolites are indicated, we now use them which would otherwise restrict aqueous flow and promote after cutting the half-thickness scleral flap but before enter- the development of a raised, cystic, avascular bleb. ing the eye, because we have often found scar tissue in the subscleral space upon re-exploration. The other advantage Duration and Washout of Antimetabolite Treatment of cutting the flap first is that we can withhold antimetabo- We apply the antimetabolite for 3 minutes based on our lites if there is any problem with the scleral flap or scleral pharmacokinetic studies.5 If we need to vary the effect of integrity or any sign of aqueous’ leaking through the flap. MMC, we change its concentration but only use either 0.2 or 0.5 mg/mL. Alternatively, we apply 50 mg/mL of 5-fluo- Conjunctival Clamp rouracil intraoperatively and wash it out with 20 mL of BSS. We use a special conjunctival T clamp (Khaw Small Our pharmacokinetic experiments have shown a rapid Conjunctival Clamp, No. 2-686; Duckworth & Kent Ltd., uptake of the drug by the conjunctiva for 3 minutes during Hertfordshire, England) designed to hold back the conjunc- the application, after which the ocular tissue absorbs rela- tiva and to prevent exposing the cut edge of the conjuncti- tively little additional antimetabolite. In the period from 1 va to the antimetabolite. This clamp maintains a pocket for to 3 minutes, the dose delivered varies considerably, and antimetabolite treatment. Because our experiments have small, unavoidable inconsistencies in the time of delivery shown that the agent affects mainly the area it touches,4 cause a great variation in drug delivery. protecting the conjunctiva’s edge prevents wound leaks and dehiscence (Figure 6). Complication Rate An altered area of treatment (described earlier), our Type of Sponge aforementioned construction of conjunctival and scleral We use circular, medical grade, polyvinyl alcohol flaps, and our use of adjustable sutures (described later) sponges that are commonly employed during LASIK; our have dramatically reduced our incidence of short- and Figure 5. Limited side cuts to the scleral flap encourage the Figure 6. A special conjunctival T clamp holds tissue away posterior flow of aqueous. from the antimetabolite. 24 IGLAUCOMA TODAYIMARCH/APRIL 2005 SURGICAL PEARLS AB Figure 7. Polyvinyl alcohol sponges are folded (A) and inserted into the scleral pocket without touching the cut edge of conjunctiva (B). long-term complications. For example, the cystic areas imal chance of damaging the crystalline lens. Similarly, if we within the bleb have decreased from 90% to 29% (Fig- need to reform the anterior chamber intra- or postopera- ure 8). The rate of blebitis and endophthalmitis over 3 tively, we will introduce a cannula through an oblique para- to 5 years was 20% for older limbus-based techniques centesis and thereby minimize the chance of lenticular trau- with a smaller treatment area versus none during the ma. An inferiorly placed entry site will allow us access to the same period for the current technique.6 In 2004, Paul anterior chamber, if necessary, in the outpatient clinic. Palmberg, MD, of Miami told Dr. Khaw that his compli- cation rate also decreased in low-risk populations from INFUSION approximately 6% to 0.5%. If Dr. Palmberg’s and our sta- We use an anterior-segment infusion cannula (Lewicky; tistics were extrapolated to an approximate figure of Visitec Company, Sarasota, FL) on a three-way tap through 50,000 trabeculectomies with antimetabolites per year the paracentesis (Figure 10).