Ординатура / Офтальмология / Английские материалы / Glaucoma Surgery_Trope_2005

See the chapter on releasable sutures for methods to close the flap utilizing this technique.

11.Suturing the conjunctival flap: In the case of a fornix-based flap, it is very important to execute closure carefully, avoiding any conjunctival laxity and thus postoperative leakage. Two sutures are inserted in a purse-string fashion at either end of the incision, drawing the conjunctiva tightly across the limbus. The suture ends are buried, thus avoiding postoperative discomfort. If there is still laxity or retraction of the flap, a mattress suture can be used, spanning the two end sutures. Some surgeons prefer a continuous suture to close fornix-based flaps plus two wing sutures.

With a limbal-based flap, it is essential to ensure that the incision is tightly sutured, making it water-tight. A useful method is to use a mattress stitch (absorbable 8.0 vicryl suture), taking bites of the conjunctiva and Tenon‘s capsule of the distal edge of the incision, followed by Tenon’s and conjunctiva of the proximal edge in turn. Each bite is locked in succession. If Mitomycin is used, we recommend closing limbal flaps in two separate layers using 8/0 vicryl sutures.

12.Reformation of the anterior chamber: At the end of the procedure, it is important to reform the anterior chamber, using saline injected through the paracentesis, ensuring that the chamber is of good depth and the tension reasonable (tested by pressing gently on the central cornea with a blunt instrument). This avoids a shallow anterior chamber postoperatively, and possibly also helps prevent hypotony or choroidals.

13.Antibiotics/steroids/patch: Some surgeons use subconjunctival antibiotics at the conclusion of the procedure, but we recommend a topical antibiotic/ steroid combination (Tobradex).

We do not patch the eye after surgery (7). A plastic shield is used to cover the eye and the patient is instructed to start their postoperative drops (Tobradex QID and Atropine 1% BID) 4 h postsurgery. We recommend discontinuing the atropine after a few days if the chamber is deep. We discontinue the antibiotic steroid combination after 4 days and switch to a topical steroid drop (prednisone QID or more often if needed) for an additional 6 weeks or until the bleb is quiescent without active vacularization (8).

2.POSTOPERATIVE CARE

At the first postoperative visit, it is important to check the IOP, the state of the anterior chamber and fundus, and the morphology of the drainage bleb.

If the IOP is raised on the first day, it is possible to apply gentle localized pressure with a sterile cotton bud to the edge of the scleral flap, thus separating the edges of the wound and allowing egress of aqueous into the subconjunctival space. If this fails to reduce the IOP to a satisfactory level, the releasable suture can be adjusted, or, if all else fails, fully released. A fixed suture can also be released, if necessary, by means of laser suture lysis (9,10), using the argon laser. See relevant chapters for further descriptions of these techniques.

In most cases, the releasable suture is removed at the first or second postoperative week. However, if the IOP is at an optimum level, the releasable suture described earlier can be left in situ permanently, as the exposed parts of the suture usually become covered by epithelium within about 4 weeks.

The approach to the management of postoperative problems such as shallowing of the anterior chamber, bleb leakage, and so on is dealt with in another chapter.

3.CONCLUSION

Trabeculectomy is an effective procedure that maintains IOP control at a satisfactory target level for a long period of time.

It is essential to develop a safe and careful surgical technique, keeping in mind the aims and potential pitfalls of the procedure, in order to ensure good results and prevent complications.

REFERENCES

1.Cairns JE. Trabeculectomy: preliminary report of a new method. Am J Ophthalmol 1968; 66:673 679.

2.Watson PG. Surgery of the glaucomas. Br J Ophthalmol 1972; 56:299 305.

3.Lerner SF. Small incision trabeculectomy avoiding Tenon’s capsule: a new procedure for glaucoma surgery. Ophthalmology 1997; 104:1237 1241.

4.Carrillo M, Buys Y, Faingold D, Trope GE. Prospective randomized study comparing lidocaine 2% jelly versus subtenons anesthesia for trabeculectomy surgery. Brit J Ophthalmol 2004; 88:1004 1007.

5.Shuster JN, Krupin T, Kolker AE, Becker B. Limbus versus fornix based conjunctival flap in trabeculectomy: a long term randomized study. Arch Ophthalmol 1984; 102:361 362.

6.Traverso CE, Tomey KF, Antonios S. Limbal vs fornix based conjunctival trabeculectomy flap. Am J Ophthalmol 1987; 104:28 32.

7.Trope GE, Buys YM, Flanagan J, Wang L. Is a tight patch necessary after trabeculectomy? Br J Ophthalmology 1999; 83:1006 1007.

8.Roth SM, Spaeth GL, Starita RJ et al. The effect of postopertive corticosteroids on trabeculect omy and the clinical course of glaucoma: five year follow up study. Ophthamic Surg 1991; 23:724 729.

9.Lewis RA. Laser suture lysis and releasable sutures. In: Weinreb RN, Mills RP, eds. Glaucoma Surgery. Principles and Techniques. 2nd ed. San Francisco: American Academy of Ophthal mology, 1991:60 63.

10.Macken P, Buys Y, Trope GE. Laser suture lysis. Br J Ophthalmol 1996; 8:398 401.

1.PRINCIPLES OF NONPENETRATING GLAUCOMA SURGERY

Nonpenetrating glaucoma surgery (NPGS) selectively targets the pathological structures responsible for the increase in intraocular pressure (IOP) (1,2). This is done without penetration into the eye (3). In this respect, NPGS is essentially extraocular surgery as opposed to other surgical modalities that necessitate eye penetration. The avoidance of penetration into the eye reduces the risk of hypotony and its sequelae.

In primary and in some cases of secondary open-angle glaucoma, the main aqueous outflow resistance is thought to be located at the level of the juxtacanalicular trabeculum and the inner wall of Schlemm’s canal (4). These two anatomic structures are removed during NPGS. The principal behind this technique was first proposed by Zimmerman (1,2), and he used the term ab externo trabeculectomy to describe it.

Kozlov (5) suggested a variation on ab externo trabeculectomy in an attempt to increase the aqueous outflow facility. He extended the dissection anteriorly into peripheral corneas for an extra 1 2 mm removing the corneal stroma behind Descemet’s membrane (Fig. 6.1). This has been termed deep sclerectomy. Postoperatively, the main aqueous outflow occurs at the level of the anterior trabeculum and Descemet’s membrane, the so-called trabeculo-Descemet’s membrane (TDM).

In viscocanalostomy, as described by Stegmann et al. (6), the aqueous filters through the TDM to the surgically created scleral space, as in deep sclerectomy, but it does not form a subconjunctival filtering bleb because the superficial scleral flap is tightly closed. From the scleral space, the aqueous reaches Schlemm’s canal ostia, which are surgically opened, and dilated with viscoelastic.

2.INDICATIONS FOR NPGS

Most published trials have evaluated efficacy of NPGS in primary and secondary openangle glaucoma. In cases where the angle is grossly distorted or closed, NPGS should not be performed.

2.1.Open-Angle Glaucoma

NPGS has been advocated as a safer option to trabeculectomy in open-angle glaucoma (7). Instead of excising a portion of peripheral cornea and trabecular meshwork, NPGS targets the presumed site of pathology, namely the inner wall of Schlemm’s canal and the juxtacanalicular meshwork.

2.2.Glaucoma Patients with High Myopia

Conventional glaucoma surgery in patients with high myopia carries a higher risk of complications. One study (8) reported on the results of NPGS in highly myopic

Figure 6.1 (See color insert) Sclerectomy, ab externo trabeculectomy, deep sclerectomy.

glaucoma patients. Two out of 21 patients developed choroidal detachments, one of which was secondary to blunt trauma to the operated eye. This low rate of complication is attributed to the gradual intraoperative IOP reduction with NPGS.

2.3.Pigmentary Glaucoma

NPGS is a potential therapy for pigmentary glaucoma; NPGS targets the site of the pathology, namely the pigment loaded trabecular meshwork.

2.4.Exfoliative Glaucoma

NPGS is an option in exfoliative glaucoma. One study (9) reported 2-year acceptable IOP control rates in patients with exfoliative glaucoma. They also reported a low incidence of complication with NPGS.

2.5.Congenital Glaucoma

Tixier and co-workers (10) were the first to report on NPGS in congenital glaucoma. Nine of 12 operated eyes were ,16 mmHg at 10 months without medications. They concluded that NPGS is at least as effective as trabeculectomy in congenital glaucoma with fewer complications.

3.RELATIVE CONTRA-INDICATIONS TO NPGS

There are no published reports on NPGS in primary angle closure glaucoma. This is not surprising considering the principles behind NPGS and its presumed mechanisms of function. Likewise, secondary angle closure aetiological entities are a relative contraindication. The descision, though, depends on the degree of angle closure.

4.ABSOLUTE CONTRA-INDICATIONS

4.1.Neovascular Glaucoma

Neovascular glaucoma is an absolute contra-indication to NPGS. The condition of the angle structures and the pathological state of the trabeculum provide little chance of surgical success.

chamber (AC) at this point. In patients with congenital glaucoma, Schlemm’s canal localization is more difficult to find, because it is often more posteriorly situated.

Tip: The best way to perform this last part of the dissection is to make two careful radial corneal cuts without penetrating down to anterior trabecular meshwork or Descemet’s membrane. This is performed with a 15-degree diamond knife or with No. 11 stainless-steel blade with the bevel side facing up.

When the anterior dissection between corneal stroma and Descemet’s membrane is completed, the deep scleral flap is cut at its anterior edge using the diamond knife. At this stage, there should be a diffuse percolation of aqueous through the remaining TDM.

The juxtacanalicular trabeculum and Schlemm’s endothelium are then removed using a small blunt forceps (Fig. 6.4).

Tip: Just before attempting to grasp the inner wall of Schlemm’s canal with the forceps, the area should be dried, this greatly facilitates the process of stripping.

Finally, the superficial scleral flap is closed and secured with two loose 10/0 nylon sutures. Note that the procedure has evolved into a combined deep sclerectomy and ab externo trabeculectomy.

5.1.3.The Use of Implants

The original idea (5,11) behind using implants in NPGS was to avoid collapse of the superficial flap over the TDM and the remaining sclera. The first implant was a collagen implant placed in the scleral bed and secured with a single 10/0 nylon suture (Fig. 6.5).

The implant was processed from porcine scleral collagen. It increased in volume after contact with aqueous and is slowly resorbed within 6 9 months leaving a patent scleral space for aqueous filtration. Other implants currently available are the reticulated

Figure 6.4 (See color insert) Peeling of the innerwall of Schlemm’s canal and juxtacanalicular trabeculum.

Figure 6.5 (See color insert) Implantation of a collagen implant.

hyaluronic (12) acid implant resorbing in 3 months or the T-shaped hydrophilic acrylic implant, which is nonabsorbable. The role of implants in nonpenetrating surgery is still controversial, but studies comparing deep sclerectomy with an implant vs. without (13) seems to show greater success rates with implant use.

5.2.Viscocanalostomy

In the case of viscocanalostomy, high viscosity hyaluronic acid is injected into the two surgically created ostia of Schlemm’s canal, aiming at dilating both the ostia and the canal. The viscoelastic agent is also placed in the scleral bed. The superficial scleral flap is tightly sutured in order keep the viscoelastic in place and to force the aqueous percolating through the TDM into the two ostia.

6.Nd:YAG GONIOPUNCTURE AFTER NPGS

When filtration through the TDM is insufficient, Nd:YAG goniopuncture is performed (14). Using a gonioscopy contact lens, the aiming beam is focused on the semitransparent TDM. Using the free running Q-switched mode, with a power of 4 5 mJ, 2 15 shots are applied. This results in the formation of microscopic holes through the TDM allowing direct passage of aqueous from the AC to the subsuperficial flap space (also termed decompression chamber or intrascleral bleb). The success rate of Nd:YAG laser goniopuncture is 50%. The success of goniopuncture depends mainly on the thickness of the TDM, hence the importance of sufficiently deep dissection.

By opening the TDM, however, goniopuncture converts a nonperforating filtration procedure into a perforating one. Nevertheless, the combined complication rates of deep sclerectomy and goniopuncture are significantly lower than the complication rates associated with trabeculectomy (15).

7.COMPLICATIONS OF NONPENETRATING SURGERY

Nonpenetrating surgery has a lower complication rate than conventional trabeculectomy (16,17), with or without antimetabolites. Complications of NPGS are considered intraoperative, early postoperative or late postoperative. Comprehensive knowledge of these complications, as well as an understanding of the best ways to deal with them, help to make appropriate management decisions.

7.1.Intraoperative Complications

7.1.1.Perforation of the TDM

The commonest intraoperative complication of nonpenetrating surgery is perforation of the TDM. Perforations occur in 30% of the first 10 20 cases. After the initial learning phase, surgeons can expect perforations in 2 3% of cases. Different types of perforations are as follows.

Transverse Tear. This occurs at the junction of the anterior meshwork and Descemet’s membrane, the weakest point of the TDM corresponding to Schwalbe’s line on gonioscopy. A perforation at this level will usually lead to the formation of a long tear, followed by immediate iris prolapse.

TDM Holes. Holes may occur in the TDM during the anterior deep dissection with the knife. Holes may be small with no loss of depth of the AC or large and accompanied by shallow or flat AC and/or iris prolapse.

Management. The two factors that determine the management of a TDM perforation are the depth of the AC and the presence of iris prolapse.

Small holes with no iris prolapse or loss of AC depth should be ignored, and the surgery continued. Perforations with shallow or flat AC and no iris prolapse should be dealt with in order to prevent subsequent iris prolapse or peripheral anterior synechia formation. Viscoelastic material should be injected through a paracentesis, into the AC under the TDM window to reform the AC and reposition the iris. The smallest possible amount of viscoelastic material should be used to avoid postoperative ocular pressure spikes. In addition, an implant can be placed on the perforation site to tamponade the hole. The superficial scleral flap should be tightly sutured with 6 8 10/0 nylon sutures once the AC has been reformed and the iris pushed back.

Iris prolapse accompanying a larger hole is an indication for a peripheral iridectomy. The superficial flap should be tightly closed after viscoelastic material has been inserted into the surgically created scleral space so as to increase the outflow resistance. Because the scleral space left after deep sclerectomy decreases the aqueous-humor outflow resistance, very tight superficial scleral-flap closure is of great importance (18).

7.2.Early Postoperative Complications

7.2.1.Wound Leak

Wound leaks or positive Seidel test occurs with the same frequency after trabeculectomy and nonpenetrating surgery and are often due to inadequate conjunctival wound closure.