Ординатура / Офтальмология / Учебные материалы / Atlas of Glaucoma Second Edition Choplin Lundy 2007

Tenon’s closure and run in the opposite direction as a standard unlocked running closure for the conjunctival closure (Figures 17.14a, 17.15a). Many different types of suture have been advocated for this closure including 9-0 Vicryl, 10-0 Vicryl, 9-0 PDS, and 10-0 nylon. Vascular needles have been very popular as well, and we have found 8-0 Vicryl on a BV needle to work well for limbus-based flaps. Our favorite technique is to use monofilament 9-0 Vicryl on a cutting needle, as it permits the suture to be ‘cinched’ down at the end of the double layer closure, adding an extra level of protection against leaks. Regardless of the suture used, a tightly closed, two-layer closure should prevent wound leak and lessen inflammation at the wound site.

A final comparison of the resultant bleb from the two surgery techniques is seen in Figure 17.16. Neither eye received intraoperative anitmetabolite, but both received a total of 10 mg of postoperative subconjunctival 5-fluorouracil. The bleb in Figure 17.16a has developed one bleb leak with blebitis. It seems unlikely that the bleb in Figure 17.16b will be as prone to this complication.

MODIFICATIONS

Releasable sutures

In cases in which the surgeon desires only minimal initial filtration, externalized releasable sutures should be considered. In these instances, and perhaps when antimetabolites are used, the surgeon may plan on tightly closing the scleral flap initially with a more aggressive outflow produced later from removal of the releasable suture when it is determined that a more copious drainage is necessary and safe. This lessens the likelihood of early postoperative complications

of overfiltration and flat chamber. Many surgeons also believe that removal of the externalized releasable suture is easier and safer than employing the analogous technique of postoperative laser suture lysis. The two techniques described below may be used with either limbus-based or fornix-based conjunctival flaps.

For the first technique, the initial pass of the 10-0 nylon suture begins on the clear cornea side of the limbus no more than about 1 mm onto clear cornea (Figure 17.17a). The needle is passed about half-thickness through cornea and sclera, exiting the sclera near the edge of the scleral flap (Figure 17.18a). The next pass is through the scleral flap into the edge of the scleral bed using the technique as described previously for routine scleral-flap closure (Figure 17.19a). The final pass of the suture is done back-handed simply reversing the initial pass of the suture, following a path roughly parallel to the initial suture pass, but far enough apart so that when the suture is eventually cut, there is enough suture exposed to be easily grasped (Figure 17.20a). The two ends of the suture are now exposed on peripheral clear cornea and are tied tightly with the ends trimmed at the knot (Figure 17.21a). One, or possibly two, of this type of suture may be placed on either side of the flap. The suture may be released in the postoperative period when deemed appropriate by the surgeon. This is done at the slit lamp under topical anesthesia by simply cutting through the exposed suture with a sharp-pointed blade or Vannas scissors and removing it with a slow, steady pull. This suture works quite well, but can cause significant postoperative astigmatism, can be irritating and can be difficult to remove, as there is a 90 angle between the scleral flap pass and the corneal exit site. When attempting to remove the suture, it should be pulled

down toward the floor, not out toward the slit lamp, to reduce the likelihood of breakage.

The second technique is astigmatically neutral, is not irritating and is easy to remove during the first 1–3 weeks postoperatively before fibrosis through the subconjunctival loop locks it in place. For a fornix-based rectangular flap, the initial pass is made in clear cornea entering about a millimeter anterior to the limbus about the location of the edge of the scleral flap. The suture is directed parallel to the limbus and exits the cornea in about the middle of the flap (Figure 17.17b). A second pass is made entering the cornea adjacent to the previous exit

site and directed to exit in the base of the scleral flap (Figure 17.18b). This should be a shallow pass. The next pass approximates the posterior lip of the flap to its bed (Figure 17.19b). A four-wrap throw is then made grasping the suture as it lies on the scleral flap (Figure 17.20b). The end of the suture is not pulled through, so that a loop forms (Figure 17.21b). Once the tension on the throw is adjusted, the needle tag end is cut short. The four wraps prevent the ‘knot’ from unraveling and yet allow the suture to be removed by grasping the ‘elbow’ in the suture as it lies on the cornea. The tag end is cut flush to the corneal surface.

Anterior chamber-maintaining suture

In patients with a posterior chamber intraocular lens, the surgeon may wish to consider intraoperative placement of an anterior chamber maintenance suture in order to eliminate concern over a postoperative flat chamber. This suture should be placed at the beginning of the procedure, before the eye is entered, when the eye is still firm and the anterior chamber is deep. A 9-0 nylon suture, doublearmed with a straight needle, is passed from limbus to limbus to form a barrier to forward movement of the lens. The initial entry of the needle should be directed perpendicularly to the curve of the peripheral cornea just inside the conjunctiva. The entry point should be at the 8:30 o’clock position for a right-handed surgeon and the 3:30 o’clock position for a left-handed surgeon so that the intraocular pass of the needle will be in a forehand fashion. The needle is then passed across the anterior chamber just above the iris and lens and is externalized just on the corneal side of the limbus. The other arm of the suture is passed with a similar course parallel to the initial pass with the entry site 2–3 mm superior to the initial suture pass (Figure 17.22). The two free ends are then tied tightly with four or five throws to prevent slippage of the knot. The suture must be cinched tight enough to slightly deform the peripheral cornea at the entry and exit sites of the suture. The suture is trimmed flush with the knot. The patient is kept on topical antibiotics postoperatively as long as this suture is in place. The suture may be removed at any time that the surgeon believes the risk of postoperative flat chamber has passed.

Antimetabolites

Certain patients have been shown to have a poor success rate with the basic trabeculectomy technique

described above. The predominant risk factors for failure include neovascular glaucoma, aphakia, and previous intraocular surgery with residual scar tissue remaining. Many other factors are also known to predispose patients to failure of filtration surgery. Over the past decade the antimetabolites 5-fluorouracil (5-FU) and mitomycin have been used to improve the success rate of filtering surgery in these patients. 5-FU is administered via both postoperative subconjunctival injections, and topical application at the time of surgery. Mitomycin requires intraoperative application. There is no consensus among glaucoma surgeons as to the ideal method of intraoperative mitomycin application. Differences of opinion exist as to the ideal vehicle for mitomycin application, the concentration of mitomycin to be used, and the ideal application time. Peng Khaw has shown little additional release of drug from a cellulose sponge beyond three minutes of application. Regardless of the differing opinions over specific aspects of mitomycin usage, certain important principles will always apply. Whenever mitomycin is to be used, it must be applied prior to entry into the anterior chamber. If the surgeon prefers to place the mitomycin after dissection of the scleral flap, particular care must be taken not to enter the anterior chamber when extending the flap dissection anteriorly. Also, care must be taken to make certain that mitomycin does not come into contact with the edges of the conjunctival wound, especially if a fornix-based conjunctival flap has been dissected. When employing mitomycin with a fornix-based conjunctival approach, the surgeon must make certain that the limbal peritomy is broad enough and the dissection posterior enough to allow placement of the mitomycin sponge without contact to the wound edges. When using mitomycin, the surgeon should carefully titrate the amount of filtration so as to have control over the amount of

aqueous filtration obtained at the end of the case. This can be accomplished by modifications in dissection of the scleral flap, placement of the corneoscleral filtration site, and closure of the scleral flap, as discussed in detail previously. As Paul Palmberg has commented, it is particularly important to realize that antimetabolites do not cause immediate postoperative hypotony. Nor do they enable flow. They have no effect whatsoever on the scleral flap, but only allow whatever conditions are created at the time of surgery to be ‘fixed’. If the flap is poorly constructed so that it does not leak, no amount of antimetabolite will permit flow. If the flap is too loose, antimetabolites will inhibit any healing that might have eventually slowed down the aqueous flow, and hypotony will be assured.

Mitomycin may be applied with a cellulose sponge that has been thinned to approximately half of its original thickness and approximately half of its original length. The sponge is saturated with mitomycin, placed over the site of the intended filtration site, and the conjunctiva and Tenon’s is draped carefully over the sponge (Figures 17.23, 17.24a). Our preferred technique, however, is to use three or more 1–2-mm plegets of cellulose sponge placed over a broad area of the superior sclera. We do not place the antimetabolite anywhere near the location of the as-yet-to-be-formed scleral flap, but instead generally place one sponge on either side of the superior rectus and one sponge at about the muscle insertion. The cut conjunctival edge is held off the scleral surface to minimize its contact with the antimetabolite (Figure 17.24b). This broad application of antimetabolite attempts to prevent areas of focal bleb ischemia that are at high risk for subsequent breakdown and leak. We recommend either

Figure 17.22 Anterior chamber-maintaining suture. The anterior chamber-maintaining suture is double-armed 9-0 nylon on a straight Keith needle. The needle often needs to be bent near the suture insertion to facilitate grasping of the suture with the needle holder and passing it while avoiding the nose. The two arms are passed parallel to each other, exiting temporally (much easier because of the nose). In this photograph, the inferior pass has been made from photograph right to left. The superior pass is almost complete. The bent end of the needle is seen on the right, partly in the anterior chamber, and the needle holder is now being used to pull the needle across the anterior chamber. Counter traction can be applied by grasping the suture on the nasal side with a tying forceps to prevent a sudden springing of the needle base posteriorly against the IOL when it enters the anterior chamber. A view of the finished suture can be seen in Figure 17.1.

the use of the James Wise conjunctival closure technique with a fornix-based conjunctival flap, or the use of a limbus-based conjunctival flap when employing mitomycin, using a concentration of mitomycin of 0.4 mg/ml with an application time of 1–4 minutes. The length of application is individualized for each patient, depending on the characteristics of the patient, the type of glaucoma, and the health of the ocular tissues at the surgery site. The sponge is then removed from the field and the area of application is vigorously irrigated with approximately 10–15 ml of balanced salt solutions (BSS). With this technique, the mitomycin is applied prior to dissection of the scleral flap. This eliminates any chance of entering the anterior chamber prior to the mitomycin application and lessens the likelihood of a prolonged hypotony which may occur if mitomycin placement underneath the scleral flap results in complete ischemia with no healing at all in the bed of the flap, or mitomycin penetrates the thinned scleral bed and ablates part of the ciliary body.

SUMMARY

In many patients, glaucoma filtration surgery can halt or at least retard what would otherwise be relentlessly progressive vision loss from glaucoma. Filtration surgery requires diligent attention to details of performance. The planned approach and intraoperative execution of the procedure must be individualized for each given patient in order to maximize the likelihood of the desired result of glaucoma filtration surgery, preserved vision and preserved quality of life.

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INTRODUCTION

Although initially proposed in the 1950s by Epstein and Krasnov, non-penetrating glaucoma surgery (NPGS) emerged in the 1990s as a surgical alternative to the standard trabeculectomy. The promise of NPGS, according to its proponents, is an increased safety profile with equal efficacy of IOP lowering as compared to the standard trabeculectomy. In the absence of a full-thickness sclerostomy, filtration occurring in NPGS takes place across semi-permeable ocular structures, which provide a constant resistance to aqueous outflow. This circumvents large IOP fluctuations during the early post-operative period that can occur with trabeculectomy, which can lead to serious complications. Furthermore, in the absence of penetration in the anterior chamber, sudden decompression and the associated complications as well as intraocular inflammation, hyphema and infection are significantly reduced. Blebs that result from non-penetrating approaches are typically diffuse and low-lying as opposed to cystic and avascular blebs that are prone to leak and become infected as has been reported with trabeculectomy.

Currently, there are two procedures that are described as being NPGS: deep sclerectomy (DS) and viscocanalostomy (VC). The common principles as well as the difference between each procedure are presented in Figure 18.1.

MECHANISM OF ACTION

While the mechanism of IOP lowering is clear in standard trabeculectomy, there is debate as to how IOP is reduced by NGPS: first, where the filtration takes place; and second, where aqueous drainage occurs.

With respect to filtration, Grant demonstrated that 75% of the outflow resistance exists at the

juxtacanalicular trabecular meshwork (JCT), which is also where the altered resistance exists in primary open-angle glaucoma. Some surgeons consider that stripping of the inner wall of Schlemm’s canal (SC), which is also thought to remove the JCT in that region, is the principal mechanism of filtration in NPGS. This is clinically correlated with the increased percolation of aqueous noted after peeling of the inner wall of SC intraoperatively. Others have argued that microperforations are created in the trabeculo-Descemet’s window (TDW) during the surgical dissection of the deeper sclerocorneal flap and the peeling of the inner wall of SC. The physiological repair of these microperforations may result in elevated IOP postoperatively requiring laser goniopuncture of the TDW. A final theory is that aqueous filters through the TDW analogous to fluid movement across a semipermeable membrane. Experimental studies in rabbits have demonstrated limited ability for the TDW to function in this manner. However, the effect is probably more significant in humans in whom Descemet’s membrane is anatomically different and thinner.

Aqueous drainage is proposed to occur in a variety of mechanisms in NPGS. In DS, the superficial scleral flap is sewn loosely to the adjacent sclera to allow aqueous to seep from the scleral lake to the subconjunctival space, resulting in the formation of a bleb. In addition, ultrasound biomicroscopy studies have demonstrated hypoechoic areas in the supraciliary area deep to the aqueous lake as well as in the adjacent sclera, suggesting that aqueous drainage also occurs via uveoscleral and transscleral pathways (Figure 18.18). The additional drainage that occurs through these secondary pathways, as well as a lower flow rate, is probably why DS produces blebs that are lower compared to those of standard trabeculectomy despite achieving comparable IOP lowering.

In contrast to DS, the superficial scleral flap is securely sutured to the surrounding sclera