(A)

Fig. 34-26  (A) Moorfields Bleb Grading System. The bleb is assessed either photographically or at the slit-lamp, and characterized with respect to height and to vascularity in three zones: central bleb, peripheral bleb, and non-bleb. An elaborate photographic set of standards is available, as well as a standardized form for reporting (www.blebs.net). (1) Central bleb area: an estimation into five categories of percentages (0%, 25%, 50%, 75%, and 100%) is made of the relative size of the central demarcated area of the bleb relative to the visible conjunctival field superiorly. Often this is confined to the area over the scleral flap; in a uniform bleb, central and peripheral estimations are congruent. (2) Peripheral bleb area: the maximal extent of the bleb is assessed using a similar scale of five percentage estimations. This parameter assesses the maximal diffusion area of the bleb, as evidenced by slight bogginess or guttering at the edges. (3) Bleb height:

in reference to the standardized photographs, the maximal central bleb height is scaled as flat, low, moderately elevated, or maximally elevated.

(4) Vascularity: considered the most important prognostic parameter for bleb failure, this scale is applied to three areas: the central demarcated bleb, the bleb’s peripheral extent of diffusion, and the surrounding non-bleb conjunctiva. Five grades of vascularity are used: avascular, normal, mild vascularity, moderate vascularity, and severe vascularity. Subconjunctival blood is also notated.

roughly 10 or 12 mmHg in 6–8 weeks. Factors that contribute to surgical failure include intrinsic difficulties (e.g., eye with previous surgery or trauma, ocular-surface disease with conjunctival inflammation) and intraoperative factors (e.g., use of superior rectus suture, inexperience­ with trabeculectomy technique, etc.).97

Surgical options and modifications

A number of intraoperative modifications of the original trabeculectomy procedure have been popularized. Although every surgeon has individual preferences, none of the variations below have demonstrable superiority over its alternatives.

Triangular versus rectangular flap

A triangular scleral flap is easier to dissect in a single plane towards the limbus than is a rectangular flap. Sometimes a single suture at the apex is sufficient for closure.

Early trabeculectomy technique specified a rectilinear 4-mm 6-mm long scleral flap overlying a 3-mm wide 1.5-mm deep sclerostomy.A ‘short-flap’ modification reduces these dimensions to a 3-mm long 3-mm wide rectangular flap. This was developed to more nearly approximate full-thickness filtration while keeping the chamber retention aspects of the guarded filter.This technique has advantages when used in conjunction with postoperative lasering of flap sutures because of the ease in visualizing subconjunctival sutures so close to the limbus. The scleral flap extends less than 1 mm from the sclerostomy on all sides. Sutures at each distal corner are tied securely to retain the chamber. Additional flap sutures may be used as desired. Because the flap is small, it leaks more freely; this could be too much if excessive cautery near the edges is employed. If enhanced filtration is desired, the scleral flap sutures can be lasered or released postoperatively.Theoretically this technique combines the advantages of guarded and full-thickness filtration.

Note that both the triangular and rectangular scleral flaps are cut down to the limbus itself. In contrast, either a scleral tunnel approach or the Moorfields Safer Surgery technique specifically avoid bringing the flap edges so far anteriorly, to facilitate posterior aqueous flow away from the limbus.

Postoperative lasering, adjustment, or release of sutures

If the scleral flap has been secured with 9-0 or 10-0 nylon sutures, the sutures may be cut in the postoperative period with the argon green, argon blue-green, diode, or krypton red laser.98 (The yttrium- aluminum-garnet (YAG) laser can also cut sutures but is capable of rupturing conjunctival and episcleral blood vessels, possibly leading to subconjunctival hemorrhage; hence it is rarely used.) Laser suture lysis is greatly facilitated by compressing the overlying conjunctiva to visualize the suture.This can be done without magnification with the edge of a four-mirror Zeiss gonioprism98b or with the Hoskins laser suture lens (see Figs 32-4 and 32-5).99 High-magnification suturelysis contact lenses are commercially available (e.g., Mandlekorn lens [Fig. 34-27] or Blumenthal lens [Fig. 34-28A]), which, without coupling gel, both blanche the conjunctiva and intensify the power density of the laser beam (Fig. 34-28B). Such lenses are enormously helpful with argon, krypton, and diode slit-lamp delivery lasers.

Generally the sutures should usually be cut within the first three postoperative weeks to enhance filtration before irrevocable scar-

ring occurs. The outside window may extend as far as 8 weeks if mitomycin-C is used intraoperatively100–102 and there is little con-

junctival inflammation in the interim. Because mitomycin-C and other antimetabolites delay tight wound healing for many weeks, a

late wound leak or hyperfiltration with hypotony can follow suture lysis.103–107 Often, however, small, pinpoint bleb leaks from the laser

beam will spontaneously heal within a few days, in the temporary reduction or absence of steroids, and use of antibiotic drops. Gentle digital pressure on the globe through the lid or directly on the posterior edge of the scleral flap will often open the wound and

Fig. 34-27  Mandlekorn contact lens for laser suture lysis.

(Courtesy of Ocular Instruments.)

elevate the bleb if it fails to do so spontaneously after the suture is cut. Laser suture lysis is also useful to release sutures that are inducing astigmatism and/or to enhance filtration after combined cataract and trabeculectomy surgery.

If the suture can be seen clearly, it can be cut with a single application of argon laser energy delivered at 400 mW for 0.1 second with a 50-  m spot size. Unfortunately, it can be very difficult to visualize and cut sutures through an inflamed, thickened and failing bleb. Careful focus with the laser maximizes energy delivery and minimizes collateral tissue damage. Blood overlying the suture may prevent suture visualization or cause excessive absorption of the laser energy, potentially leading to a conjunctival hole.Though such a small breach may leak aqueous, a reduction in topical steroids and patience usually effect spontaneous healing within a few days.

Several alternative methods have been described. Though not widely available in an office setting, an endolaser probe to compress the conjunctiva overlying the suture has been used in cutting sutures under a conjunctival flap.108 An ingenious adaptation of the standard scleral flap closure can allow visualization and laser lysis of these sutures with slit-lamp gonioscopy in the postoperative period, independent of the conjunctival appearance and dependent only on sufficient corneal clarity for gonioscopy.109 This technique is adaptable to any variation of trabeculectomy technique; it is illustrated here using a standard #10-0 nylon for closing the scleral flap (Figs 34-29 through 34-34). So long as the anterior chamber remains deep and there is no internal obstruction of the trabeculectomy stoma (by iris, blood, debris, etc.), this technique reliably and elegantly bypasses difficulties of subconjunctival edema

Fig. 34-29  A #10-0 nylon suture passed through flap base, seen from above.

Fig. 34-31  Suture passed through posterior bed of flap.

or hemorrhage which can obscure sutures which might require lysing.

Laser suture lysis may not be a viable clinical option if a suitable laser is simply neither available nor accessible in the postoperative

period: hence many surgeons prefer using releasable sutures at the time of trabeculectomy.62,64b,110 This approach has proven to be a simple,

Fig. 34-28  (A) Blumenthal contact lens for laser suture lysis. (B) Pressure on lens

focally blanches and compresses conjunctiva, enhancing visualization for laser suture lysis.

(Courtesy of Volk Instruments).

Fig. 34-30  A #10-0 nylon suture passed through flap base, seen overhanging sclerostomy.

Fig. 34-32  Two sutures suspended over stoma before closing flap.

low-cost, and efficacious way to influence postsurgical filtration in the first several weeks postoperatively.111–113 Several techniques have

been described: they essentially begin with a #10-0 or #9-0 nylon suture through the perilimbal cornea, bringing it out through the hinged area of the scleral flap, and then closing the flap edge with a slip knot; several such stitches can be placed. Postoperatively at the slit lamp, the corneal end of the suture can be grasped with a forcep and removed; the mechanical disruption of the flap edge by this maneuver is felt efficacious in disrupting adherence between the flap and its scleral bed, thus facilitating aqueous egress. To avoid a loose