Exposure of the operating field in the scleral phase. As an alternative to the traction suture, to achieve good exposure of the operating field in the scleral phase, the surgeon can wedge a suitably shaped merocel sponge into the blepharostat. With this maneuver, the surgeon can rotate the bulb (inferoversion) and this will provide him with easy access to the superior sector of the sclera. Once the scleral phase of the operation has terminated, the sponge is removed and the eye bulb returns to its original position to allow the subsequent phases of the surgery on the cornea or in the AC to be performed

Preparation of scleral bed. In the first phase of the operation, the surgeon creates a conjunctival-capsular flap at 12 o’clock, with a base at the limbus or the fornix; the width of the incision must be approximately 6–7 mm; in case of limbus based flap the incision is created about 8–10 mm from the limbus. The choice of the flap (with the base at the fornix or the limbus) depends substantially on the surgeon’s preference and the requirements of the individual case. The fornix based hinge is the more popular. Following the preparation of the conjunctival-capsular flap, the scleral bed and the surgical limbus are exposed (red line in Fig. 3.3; refer also to chapter “Anatomy”, Fig. 1.​3). Diathermy is used to stop any bleeding from the scleral surface; this procedure must be relatively conservative as it must not affect the scleral tissue. Prior to the creation of the conjunctival-capsular flap, the surgeon must control the position of the venous collectors (perforating) to avoid these being cut: it is extremely important to avoid detaching the conjunctiva at a point where it is will not be possible to perform the subsequent phases of the procedure due to perforating vessels presence. The surgeon should delicately rub a blunt instrument (for example the closed arms of Westcott scissors) over the surface to create a transitory ischemia of the conjunctiva; this will provide a clear view where the venous collectors are positioned. In this way, the surgeon can select the most appropriate point to start the conjunctiva-capsular detachment

Creation of scleral flap . Once a suitable area has been identified, preferably lying between two venous collectors, the surgeon creates the scleral flap. This dissection should be extended for 1 mm in clear cornea (indicated by the broken red lines). The flap can be created in a range of different shapes and dimensions. Normally, it is trapezoidal (but it can be rectangular, square, triangular or circular); the dimensions can vary between 5 × 5 and 4 × 3 mm. The thickness is approximately 200–250 μm, that is approximately one-third of the scleral depth. The optimal depth of the incisions is indicated in the drawing with oblique red lines. Common mono-use blades or better a pre-calibrated diamond lancet can be used

(a) Scleral flap dissection . The scleral dissection is performed on a single plane parallel to the sclera at a depth of 200–250 μm. It can be completed using common bevel-up crescent knives, or with a specially-produced Grieshaber bevel-up knife. This incision extends for approximately 1 mm in clear cornea, just behind the limbus. The dissection is started from the posterior incision at the desired depth and is then extended anteriorly on the same surgical plane. For the correct execution of this maneuver, as the sclera is being cut, it is useful to hold the flap with Hoskin toothed forceps (for example Colibrì forceps) and pull the tissues gently: in this way, the scleral fibers will be pulled tight making it easier to identify and cut the fibrils with the crescent knife, creating a single cleavage plane. As mentioned before, the dissection is extended for approximately 1 mm in clear cornea. (b) Identification of surgical landmarks following scleral flap dissection. The drawing shows that below the scleral dissection the following structures are present: the flipped over scleral flap (F), the clear cornea (A) in an anterior position, the trabecular meshwork (gray line) which consists of parallel fibers (B) that merge with the white opaque scleral fibers (D). The junction between the gray trabecular meshwork (B) and the sclera (D) corresponds superficially (E) to the scleral spur (S). The Schlemm Canal (C) lies adjacent to the scleral spur (S). The surface landmark (E) of the scleral spur is an important surgical marker: it indicates the position of the scleral spur (S) and therefore indicates both the posterior margin of the corneo-scleral trabecular meshwork that the surgeon will remove during the trabeculectomy and the position of the Schlemm canal. As the surgeon is observing the eye from above, he can identify the following surgical landmark (in sequence and centripetally): the scleral spur, the trabecular meshwork, the Scwhalbe line and the cornea, or surgical limbus (also refer to chapter “Anatomy”, Fig. 1.​3). (c). Lateral section of relationship between internal structures and external surgical landmarks. See description of (c)

Exposure of trabecular meshwork . Once the scleral flap has been created, the surgeon must proceed with the trabeculectomy. To expose the surgical limbus that includes the trabecular meshwork , the surgeon can add a viscoelastic substance (VES) to the flap that has been flipped-over. Alternately, one of his assistants can delicately catch the flap with non-traumatic forceps, for example, Hoskin forceps, and flip it over. Prior to the trabeculectomy and the basal iridectomy, as a precautionary measure, many surgeons will opt to position two nylon 10.0 sutures at the top of the flap (red arrow). The suture thread is only passed through the tissue and not knotted: in this way, after having completed the trabeculectomy and the basal iridectomy (the two critical phases of the operation), the surgeon will be able to close the flap immediately

Prior to the trabeculectomy, it is advisable to inject a small amount of dispersive VES (such as Viscoat) into the AC through a service incision to avoid a sudden loss in AC depth and to distance the iris during the trabeculectomy procedure

(a) Traditional trabeculectomy: scleral incision parallel to the limbus. In Cairns’s original technique, a first incision is created with a knife parallel to the limbus (anterior incision) in clear cornea (A), below the scleral flap, that penetrates into the AC. The plug of tissue to be removed (W) must measure 2 × 2 mm. It extends from the surgical limbus (L) located anteriorly to the scleral spur (located posteriorly) (S) indicated by the posterior edge of the gray band (E).

(b) Traditional trabeculectomy: completion of the creation of the sclero-corneal plug creation e its removal. Starting from the edge of the anterior incision parallel to the limbus, the surgeon creates another two radial incisions to reach the posterior edge of the surgical limbus, corresponding to the scleral spur (S). This will define three-sides of the piece of tissue to be removed. It can be flipped over with surgical forceps to expose the structures on the internal face, particularly the sclero-corneal trabecular meshwork for removal. This is finally removed with Vannas scissors, without emptying the AC. As mentioned above, prior to opening the AC, it is useful to inject some dispersive VES (Viscoat) onto the area where the trabeculectomy will be performed. This posterior incision is created just in front of the scleral spur (S), taking care to include the trabecular meshwork in the cut. To this end, the surgeon will expose the scleral spur by posteriorly flipping-over the sclero-corneal plug.

Removal of the block of trabecular meshwork tissue (trabeculectomy) is the crucial part of the procedure and can be performed in a number of ways—with knives, scissors, drills or scleral punches. The choice of instrument depends largely on the surgeon’s choice. However, the scleral punch would appear to guarantee smoother margins and a certain degree of standardization for the procedure.

Over the years, the main technical variations proposed for this type of procedure involve the shape of the scleral flap and the shape of the filtrating hole.

(c) Traditional trabeculectomy: surgeon’s view (from above). This drawing shows the final posterior incision for the removal of the trabecular meshwork plug (as in the previous drawing). Also shown is the surgeon’s view of the most important anatomical structures involved in a correct trabeculectomy with the conjunctival fornix based flap. The surgeon uses forceps to flip over the trabecular meshwork plug to expose the posterior surface. Moreover, using Vannas scissors, he will create the posterior incision anterior to the scleral spur (S), including the trabecular meshwork (T). The scleral spur (S) corresponds externally (E) to the junction between the white opaque sclera and the gray band (B). The drawing also indicates the scleral flap (F), the clear cornea (A), the iris (I) and the iris processes (IR).

(d) Exposure of different structures of trabecular meshwork following traditional trabeculectomy. The opening (window) created by the removal of the tissue plug can be observed. The insertion of the ciliary muscle (M) remains intact and anchored to the scleral spur (S). The Schlemm canal is not visible. The trabecular meshwork (T) lies along the radial wall of the opening (window).

The drawing also illustrates the clear cornea (A) and the junction (J) between the cornea and the sclera.

Adjacent to the radial wall of the opening (window), there is a portion of the scleral flap that has not been removed and this is a landmark for the internal structures: clear cornea (A), the gray band (B) that represents the external marker for the trabecular meshwork, and the external marker (E) of the scleral spur (S).

The radial wall has been removed on the side opposite of the opening (window). The anterior incision is located in clear cornea. The posterior incision is located just anterior to the scleral spur.

The conjunctival flap has its base at the fornix

(a, b) Trabeculectomy with scleral punch : (a) surgeon’s view from above; (b) side view. The scleral punch is an alternative to the traditional method.

This would appear to guarantee smoother edges and a more standardized trabeculectomy. First, the surgeon creates a full-depth 2 mm corneal incision, using trapezoidal blades. It is important that this incision lies on the Schwalbe line, meaning that it will be in front of the trabecular meshwork. The trabeculectomy is performed with the punch technique. The surgeon should make a visual check to ensure that the trabecular meshwork is included in the tissue removed. Sometimes it may be necessary to punch several times to obtain a satisfactory result.

(c) Trabeculectomy with scleral punch : surgeon’s view (from above) of the precise location of the tissue removal made with punch. The dotted black circle indicates the exact location of the bite, which must include the trabecular meshwork.

(d) Appearance of the trabeculectomy created with the punch technique. Observe the shape of the trabeculectomy, that includes the trabecular meshwork (T)

Basal iridectomy . Once the trabeculectomy has been completed, the surgeon continues with the basal iridectomy, that must be sufficiently wide to prevent the iris being involved in the stomia. To ensure that the iridectomy is the correct size, the root of the iris should be clearly visible: for this reason, pilocarpine eyedrops should be instilled prior to surgery to induce appropriate miosis. If the patient is affected by mydriasis, either because subjected to a combined phaco-trabeculectomy procedure or because there is a certain degree of mydriasis induced by the loco-regional anesthesia, an injection of acetylcholine in the AC may be useful. If this does not produce suitable miosis, the iris can be delicately distanced from the angle with the spatula.

For the basal iridectomy, the iris is caught through a scleral opening with dedicated fine toothed forceps, (iris or Colibrì forceps) and transported outside of the AC. On occasion, as soon as the AC is opened, the iris will tend to prolapse spontaneously through the incision. The iris is cut peripherally, parallel to the limbus, using Vannas or DeWecker scissors. The surgeon must pay attention to the stroma and to the pigmented layers of the iris to create a full-depth iridectomy.

During the iridectomy, the surgeon must check the position of the pupil: in this way, he will avoid cutting too close to the pupil. He must also take care to avoid removing the tissue too close to the iris root in order to reduce the risk of rupture of the base, iridodialysis or intraocular bleeding

(a) Suture placement . At this point, the surgeon positions one or two sutures in 10-0 nylon on the flap, if these have not already been positioned; the knots must always be recessed in the tissue. The knot that we prefer is the 1.1.1 Siepser—it is elegant and there is the possibility of adjusting the tension. Nylon is the most appropriate material for a laser section in the event of postoperative ocular hypertension.

As an alternative to nylon, an absorbing suture (10-0 vicryl) can be used to progressively increase the filtration (10-0 polyglactin reabsorbs in approximately 1 week), and the conjunctiva and Tenon capsule are sutured.

Some surgeons prefer to position 5 sutures on the flap.

With a flap with base at the fornix, two tobacco pouch sutures (in 10-0 nylon or 8-0 vicryl) positioned at 11 and 1 o’clock will cover the entire scleral flap and this will normally ensure that the incision is adequately sealed.

The creation of a flap with base at the limbus, on the other hand, necessitates a separate suture for the Tenon capsule (preferably in 8-0 vicryl) and for the conjunctiva (10-0 nylon).

(b) Final appearance (internal view) following trabeculectomy. The non-full thickness scleral flap (F) is repositioned and sutured with nylon suture 10.0 (P). Note the iridectomy (I), the trabecular meshwork window (W) and the Schlemm canal (C) that in this eye is positioned anteriorly to the scleral spur and hence was included in the removal of the sclero-corneal trabecular meshwork.

(c) Outflow of the aqueous humor following trabeculectomy. The surgery concludes with the introduction of a small quantity of BSS in the AC through the paracentesis that, through the trabeculectomy created, passes underneath the conjunctiva to form the bleb (indicated with the blue arrow in the drawing): this procedure provide the evidence that the surgical manuever was correctly performed. Any residual dispersive viscoelastic can be left in the AC, because it will not cause any important increase in IOP in the postoperative.