Ординатура / Офтальмология / Английские материалы / Glaucoma Surgery_Trope_2005

Figure 7.7 (See color insert) Paracentesis with microsharp blade.

cornea. This creates the path through which the silicone tube will be passed. The distal cut end of the silicone tube is then grasped with a tying forceps, while at the same time the anterior lip of the entry tunnel is elevated, allowing the eye to be steadied, facilitating the entry of the tube into the anterior chamber (Fig. 7.9). A tube inserter manufactured by ASSI may also be used for this purpose. If peripheral anterior synechiae are present, the tube may have to be passed more anteriorly to avoid the peripheral iris. If this become necessary, it is imperative to ensure that the anterior edge of the graft is far enough anterior to totally cover the tube.

The preplaced 10/0 suture around the tube is now tied, fixating the tube to the sclera. If a 3/0 supramid suture had been placed into the tube, then prior to inserting the tube, venting slits are made in the sides of the tube, which will lie beneath the graft. These slits may be made by passing the needle of the 10/0 suture through the tube or by slitting

Figure 7.8 (See color insert) Use of 22 or 23 gage needle to create passage for silicone tube into anterior chamber.

Figure 7.11 (See color insert) Pericardium sutured to sclera. Tube tied off with 70 Vicril at junction with plate.

The conjunctiva is then closed by suturing the free ends of the conjunctiva, located by the preplaced sutures, to their original position at the limbus (Fig. 7.12). Two wing sutures are needed for the limbal reattachment of the conjunctiva, using an episcleral insertion at the limbus, and then passing the needle through the free edge of the conjunctiva close to where the preplaced marker sutures were placed. The conjunctiva is brought forward to completely cover the scleral/pericardial patch and if this is not achieved, a further one or two sutures placed at the limbus may needed to accomplish this. The relieving incisions of the conjunctivae are also sutured. All of these suturings being done with 7/0 vicril sutures. Prior to closure of the conjunctiva, the previously placed supramid suture protruding from the plate end of the draining implant is brought forward under the conjunctiva, so that it protrudes beyond the limbus. After the conjunctiva has been

Figure 7.12 (See color insert) Suturing conjunctiva to limbus and showing availability of supramid suture for removal at a later date.

sutured at the limbus, the supramid suture is trimmed, so that it just protrudes beyond the limbus from under the conjunctiva (Fig. 7.12). Edema of the conjunctiva will just cover the suture and it may easily be grasped at a later date, when it needs to be removed from the tube. This allows the suture to be removed from the tube without having to disturb the conjunctiva.

Tip 1: If the tube and scleral patch are bulky and apply pressure to the overlying conjunctiva, the limbal wound can retract exposing the graft. To prevent this, we recommend using half thickness scleral patch grafts. In such situations, we prefer to close the conjunctiva at the limbus with a continuous 8/0 vicryl limbal suture.

If a fornix-based conjunctival flap is used, we recommend closure of tenons first (using a continuous suture) followed by a continuous conjunctival suture (i.e., closed in two layers). This is particularly important if the tube has been inserted from below, as conjunctival wound healing is often poor in the inferior quadrants.

2.6.Insertion of a Double Plate Molteno Implant

The use of a double plate Molteno implant requires modification of the insertion technique. The device is labeled right or left side, indicating that the plate to which the tube entering the anterior chamber is attached will be placed on the nasal side. However, it is more practical to have the primary plate placed in the supero-temporal quadrant, where more space allows for easier placement of the plate, the tube, and the scleral patch. This is achieved by placing a left-labeled double plate implant in the right eye and vice-versa. In placing a double plate, a fornix-based conjunctival flap is once again fashioned from the limbus, but is now extended 1808. Relieving incisions are made parallel to the upper borders of the lateral and medial rectus muscles. The nasally placed plate is sutured to the sclera between the medial and the superior rectus muscles 7 10 mm behind the limbus, using the same technique as described for a single plate. The superior rectus muscle is isolated with a muscle hook, and the conjunctiva is carefully dissected from the muscle sheath. This allows the second plate to be passed over the muscle and to be placed in the temporal quadrant between superior and lateral rectus muscles. The laterally placed plate is sutured to the sclera 7 10 mm behind the limbus, in the manner described for the medial plate. The silicone tube is handled in the same manner as described for a single-plate implant. In addition, the tube connecting the two plates is tied off with a 7/0 vicril suture, which will release in about 2 3 weeks, at which an adequate capsule over the second plate will prevent excessive hypotony. The conjunctiva is resutured to the limbus utilizing the preplaced 4/0 silk suture markers to ascertain correct anatomical placement of the conjunctiva to the limbus. The conjunctiva is sutured with two interrupted 7/0 vicril sutures, the initial placement of the suture being from the limbus through episcleral tissue. If the conjunctiva does not fit snugly to the limbus, further interrupted 7/0 vicril sutures can be inserted. The relieving incisions along the upper borders of the medial and lateral rectus muscles are sutured with a continuous 7/0 vicril suture. The previously placed supramid suture is handled as described for single-plate implants.

3.THE EXPRESS GLAUCOMA SHUNT

Within the past few years, a new mini-glaucoma shunt has been introduced (4), labeled the Express Mini-glaucoma Shunt. The shunt is a stainless steel “tube” that measures ,3 mm in length and 400 mm in diameter. The device has a penetrating tip that is inserted into the anterior chamber. Behind the tip is a spur to prevent extrusion of the device and at the

proximal end, there is an external flange that prevents over-penetration. The Express is intended to reduce IOP in patients with glaucoma, where medical and conventional surgical treatments have failed, indications similar to those for other drainage implants. Originally designed for insertion as a minimally invasive procedure, more recently the insertion of the Express under a trabeculectomy flap has been described. The Express is implanted through a simple four-step procedure.

1.Inject viscoelastic material into the anterior chamber through a paracentesis opening.

2.A small 1 2 mm incision is made in the conjunctiva, 10 mm from the limbus.

3.A 25 gage needle is inserted through the conjunctival incision and guided subconjunctivally to the limbus, where it is used to penetrate into the anterior chamber.

4.The Express is then introduced into the anterior chamber, via the introducer, which is passed along the same subconjunctival pathway. The introducer is then withdrawn, the spur keeping the Express in position.

An alternative method of implantation, is to place the Express under a scleral flap (5). A standard trabeculectomy is performed up to the stage of entry into the anterior chamber. Instead of removing corneoscleral tissue, the Express shunt is inserted into the anterior chamber beneath the scleral flap, without the addition of a peripheral iridectomy. If so desired, an antimetabolite such as mitomycin C or 5 Fu may be used, as one might do in a standard trabeculectomy. The flap is then sutured over the mini-shunt with interrupted sutures or a releasable suture. The use of the shunt in this way is a modified nonpenetrating and penetrating glaucoma procedure. Early results with the shunt placed under a flap have been encouraging, particularly with regard to eliminating such complications as hypotony and erosion associated with the original technique of subconjunctival insertion.

4.GENERAL PRINCIPLES REGARDING THE INSERTION OF ALL GLAUCOMA DRAINING IMPLANTS

Utilize a fornix-based flap, as this places the conjunctival incision at the furthest distance from the draining bleb eliminating the possibility of erosion and leakage through the conjunctiva.

In nonvalved implants, a stent within the silicone tube needs to be placed to prevent post-operative hypotony.

If deciding to place the tube via the pars plana, a total vitrectomy needs to be done to avoid blockage of the tube by vitreous (see chapter elsewhere in this book).

If superior quadrants are not available, the implant may be placed inferiorly. In doing so, the patient should be warned of the possibility of diplopia where binocular vision is present. When placing the implant inferiorly instead of using sclera or pericardium, half thickness cornea should be used to cover the silicone tube as this affords a better cosmetic result. If an Ahmed valve is used inferiorly using a limbal-based flap, the conjunctiva must be and closed in two layers.

REFERENCES

1.Molteno ACB, Straughn JL, Anker E. Long tube implants in the management of glaucoma. SA Fr Med J 1976; 50:1062 1066.

2.Sherwood MD, Smith MF. Prevention of early hypotony associated with Molteno implants by a new occluding stent technique. Ophthalmology 1993; 6:515 520.

3.Freedman J. Drainage implants. In: Yanoff M, Duker J, eds. Ophthalmology. London: Mosby, Section 12, 32.1 32.6.

4.Kaplan Messas A, Traverso C, Sellem E, Zagorski Z, Belkin M. The Ex Press minature glaucoma implant in combined surgery with cataract extraction: prospective study. ARVO, Fort Lauderdale, FL, 2002.

5.Dahan E, Carmichael T. The Ex Press minature glaucoma implant: implantation under a scleral flap. Fourth IGS Meeting, Barcelona, Spain, March 2003.

Consequently, there is a higher risk for intraoperative and postoperative complications. Complications associated with glaucoma implants can be classified as intraoperative, early postoperative, and late postoperative.

2.INTRAOPERATIVE COMPLICATIONS

2.1.Conjunctival “Button Hole” or Laceration

Manipulation of a friable conjunctiva may result in tearing or laceration of the conjunctiva, especially as these patients have often had previous surgical procedures involving conjunctival manipulation. Elevating the conjunctiva with balanced salt solution prior to cutting it allows the surgeon to delineate the areas of conjunctiva that are adherent to the underlying sclera and therefore more likely to perforate if elevated and thus can be avoided, decreasing the probability of lacerating the conjunctiva. If a tear is noted during surgery, attempts must be taken to close it with a 10/0 nylon on a BV needle. If the tear will not close, care should be taken to ensure the entrance to the anterior chamber is well covered by the patch graft under the tear and ensure there is no external aqueous leak. If there is none, it is likely that the conjunctiva will heal with vascularization of the patch. If there is an external leak, the implant may have to be removed, the wound tightly closed and the tube inserted in a new quadrant. Inability to accomplish adequate conjunctival closure at the end of the procedure can occur, especially if a thick patch graft is used such as full-thickness sclera or cornea. We recommend half-thickness cornea or sclera to cover the tube. Also, the conjunctiva has a tendency to contract, particularly in elderly patients. This problem can be minimized by marking the cut ends of the conjunctivae with sutures on disinsertion from the limbus, so that the ends can be identified at the end of the procedure and reattached to their correct anatomical area. If it still does not close, care must be taken to ensure the entrance wound is well covered by the patch graft. Then the conjunctiva is closed as close as possible to the limbus, as a small area of exposed patch graft does not pose a problem. The drainage occurs in a posterior situation so that if conjunctiva covers the plate and most of the patch graft, aqueous leakage is unlikely.

2.2.Tube Problems

The silicone tube may be cut too short and cannot adequately enter the anterior chamber. This can be remedied by splicing on more tube, utilizing a tube extender such as the one made by Ahmed (model TE), which is commercially available. It is advisable to always have a spare tube extender in case it is needed.

2.2.1.Tube Misdirection

A tube can be inserted too anteriorly or too posteriorly. If inserted too anterior, corneal endothelium will be damaged, and if inserted too posterior, iris or lens can be damaged. This complication is best avoided by correct placement of the introducing needle. The needle tract needs to be carefully planned, with the eye in the primary position with the needle track parallel to the iris plane. The needle track should start 1 2 mm posterior to the limbus in order to position the tube away from the corneal endothelium. The tube should enter the anterior chamber parallel to, but in front of the iris and lens, 1 2 mm behind the corneal endothelium. Careful assessment of the tube position is essential at the end of surgery and the tube should be repositioned anterior or posterior to the initial incision if it is too close to the endothelium or iris before the patient leaves the operating

room. In the postoperative period, if the tube is noted to touch the endothelium but this touch is localized, such as just the tip of the tube, this will not usually cause diffuse endothelial damage and may be left. If the tube touch is more extensive, that is, the whole intraocular portion of tube touches the endothelium, repositioning of the tube in the operating room should be seriously considered as extensive endothelial damage may result. If the tube is noted to touch the iris and is not blocked, it may be left alone. Misdirection of the tube into the posterior chamber is likely to happen in the presence of posterior synechiae, where the flexible tube follows the path of least resistance. This can be remedied by inserting an iris spatula through a limbal paracentesis opening to the site of entry of the tube and by guiding the tube above the spatula into the anterior chamber.

2.2.2.Vitreous Loss

A rare complication associated with plate insertion is the very deep placement of the fixating sutures with vitreous presentation at the insertion site. Should this occur, the sutures must be removed and the plate reattached at a different site. Should the eye become hypotonous, a careful examination of the retinal area is indicated and even if nothing is seen cryoablation at the perforation site is indicated. The patient should be followed up by a vitreoretinal specialist.

2.2.3.Bleeding

Bleeding into the anterior chamber can occur, especially on introducing the tube into the anterior chamber where rubeosis iridis is present. To avoid this complication, the hypotony associated with tube insertion needs to be avoided, and this can be accomplished by either the use of an anterior chamber maintaining cannula attached to a bottle of balanced salt solution or the insertion of a viscoelastic substance prior to the tube introduction. The rubeotic vessels bleed when the surrounding pressure is lowered, therefore maintaining the intraocular pressure by balanced salt solution through the cannula or by inserting a viscoelastic material decreases the potential for bleeding from these vessels. The complication of suprachoirodal hemorrhage is more likely to occur in neovascular glaucoma or when there is uncontrolled intraocular pressure. The hemorrhage occurs when the eye is suddenly decompressed following tube introduction into the anterior chamber. This can be avoided by lowering the intraocular pressure preoperatively with appropriate medications and decompressing the eye slowly with a paracentesis prior to tube insertion. A small amount of aqueous should be removed in a controlled fashion until the eye is no longer hard. A prophylactic posterior sclerotomy can also be done prior to insertion of the tube. Intraocular pressure should be kept constant during insertion of the tube by inserting viscoelastic prior to tube insertion or with the use of an anterior chamber maintainer.

3.EARLY POSTOPERATIVE COMPLICATIONS

3.1.Flat Anterior Chamber

The commonest postoperative complication is the absence of the anterior chamber. This is most likely to occur with nonvalved implants, where no precaution has been taken to prevent postoperative hypotony. Nonetheless, this complication can occur with valved implants as well even with ligaturing of the tube. If the anterior chamber is shallow with iris corneal touch, it should be treated in the usual way with cycloplegics and aqueous suppressants. Transient shallow chambers usually resolve after a few days. If

sooner if the tube seems to be damaging the endothelium or is in contact with the lens. If the anterior chamber is flat, it may be reformed with the injection of a viscoelastic material through the paracentesis opening that was created intraoperatively. This may have to be repeated, but if the hypotony persists, the tube may have to be ligated in the operating room. Hypotony may be associated with the development of a suprachoroidal effusion. Large effusions may require the use of systemic steroids to eliminate them. Kissing choroidals will require suprachoroidal fluid drainage with the injection of gas and elimination of the cause of the hypotony, which usually means the tying off of the tube. The tube may be tied off by exposing it in its anterior position beneath the patch, which is where it is most accessible. A 5/0 vicryl suture may be used. This will dissolve at a later time. Alternatively, the tube may be removed from the anterior chamber, occluded with a prolene suture, and then reinserted. This suture can be released at an appropriate time using a YAG laser.

3.2.Blocked Tube

The tube may become blocked resulting in elevation of the intraocular pressure. The blockage may be due to blood, iris, or fibrin. Blood usually dissolves unless there is a full hyphema that may have to be washed out. Iris plugging the tube opening may be removed with a YAG laser. Fibrin responds well to intensive use of topical steroids, and if persistent can also be removed with a YAG laser. A large fibrinous exudate in the anterior chamber will respond to topical steroid use but may need a subconjunctival injection of steroid. Occasionally, an intense vitreitis is seen, particularly in neovascular glaucoma, which may require systemic steroid use.

3.3.Tube-Corneal Touch

Tube-corneal touch, if very localized and peripheral, can be left alone. It may produce some peripheral corneal decompensation in the region of contact without affecting the rest of the cornea. More extensive corneal touch can produce generalized corneal decompensation and the tube may need to be removed and repositioned.

3.4.The Hypertensive Phase

The hypertensive phase seen in most but not all glaucoma implant surgeries occurs 4 6 weeks postoperatively. The elevation of intraocular pressure may be treated with reduction of topical steroids and anti-glaucoma medications, but if very high, is best treated by draining using a 29 gage needle which is passed into the bleb under local anesthesia at the slit lamp, with the withdrawal of a quarter to a half cc of aqueous, without loss of the anterior chamber. This may have to be repeated on a weekly basis until the pressure returns to normal level. By decreasing the pressure within the bleb around the plate, ongoing fibrosis due to TGFb production is prevented, with the likelihood of a more successful outcome in bleb formation.

3.5.Iritis

Occasionally, a recurrent uveitis is seen in association with glaucoma implants. Care should be taken to ensure the tube is not eroding the peripheral iris or angle structures. If the iritis or iris erosion is mild it can be left alone or treated with low doses of