Ординатура / Офтальмология / Английские материалы / The Glaucomas Volume 1 Pediatric Glaucomas_Sampaolesi, Zarate_2009

Step 3

The most important step of NPDS involves the removal of the internal elements of resistance. If this membrane is not removed the intraocular pressure will fail to be regulated (Fig. 15.48).

Fig. 15.48 Dissection of the inner wall of the Schlemm canal with its endothelium, juxtacanalicular tissue, and the external corneoscleral trabecular meshwork (left). Schematic representation of the tissue removed and of its previous locations

(center), where only the internal corneoscleral trabecular meshwork and the uveal trabecular meshwork, which, together with the Descemet membrane form the trabecular Descemet membrane, are left (bottom right)

Step 4

At this step, the implant is secured to the sclera with a nylon 10-0 suture (Fig. 15.49).

Implants may be made of different materials. In our first 60 patients, we used the implant manufactured by Staar Surgical AG (Nidau, Switzerland). It is a cylindrical collagen implant measuring 2.5 mm in length and 1 mm in diameter processed from lyophilized

American porcine scleral collagen, which is sterilized using a radiation procedure. The water content of the hydrated device is 99%. This implant is resorbed within 6–9 months after surgery, as demonstrated by ultrasound biomicroscopy (UBM). In the last 22 cases, we used the corneal implant SKGEL 3.5 (Laboratoire Corneal, Paris, France). This implant is triangular and it is made of sodium hyaluronate.

Complications of Surgery

Triangular Flap Dissected Too Superficially

The dissection of the triangular flap is not deep enough for the resection of the external wall of the Schlemm canal. The graph at the center of the figure shows the key element allowing the surgeon to find the Schlemm canal. The most posterior darker blue sector (between 3 and 4 in the blue area) indicates the location of the Schlemm canal (Fig. 15.50).

The external wall of the Schlemm canal must be dissected with a round cutting spatula specially designed for this purpose by Grieshaber (Fig. 15.51). This dissection can be made with direct illumination or under transillumination (Fig. 15.52).

To find the Schlemm canal, it is very important to view the surgical area with direct illumination and with transillumination (the Minsky maneuver). The area is transilluminated by the optical fiber of the microscope supported by the cornea, and separated from it by one of the white triangles used for drying, but embedded in physiological solution to prevent the cornea from overheating (Fig. 15.53). In Fig. 15.53a, the view is in direct illumination and in Fig. 15.53b, transillumination. Transillumination clearly reveals the location of the Schlemm canal (white arrows).

In Fig. 15.54, the external wall of the Schlemm canal of the same case has been completely removed.

Fig. 15.50 Image seen if the dissection has failed to be done on the correct plane and it is not deep enough for the resection of the external wall of the Schlemm canal by means of the triangular flap. All three areas are visible but the open Schlemm

canal is not (left). The schematic representation at the center shows the key element for the surgeon to find the Schlemm canal: the most posterior darker blue sector (between 3 and 4) of the blue area

In this case, when the surgeon tries to remove part of the second flap, the iris prolapses because a perforation of the internal wall has been made (Fig.15.55). If this occurs, the surgical procedure should invariably be turned into a trabeculectomy.

The goal of step 1 (uproofing the Schlemm canal) is to remove the external wall to clearly expose the canal. This step is shown in Fig. 15.56.

In step 2, the surgeon removes the external elements with Mermoud forceps [62], as shown in Fig. 15.57a. When this step is perfectly done, the space between the scleral spur and the Schwalbe line is enlarged, and aqueous humor percolation is observed (Fig. 15.57b, c).

Fig. 15.57a–c The second critical step is number 2. It is necessary to remove the internal elements, internal wall of the Schlemm canal, juxtacanalicular tissue, and the external part of the corneoscleral trabecular meshwork in order to regulate

the intraocular pressure. It should be kept in mind that between the internal and external part of the corneoscleral trabecular meshwork there is a natural cleavage pane

The ultrasound biomicroscopy in Fig. 15.58 shows, from left to right, the conjunctival tissue with aqueous humor, separating it from the quadrangular scleral flap, and two parallel lines behind it corresponding to the implant, where the nylon suture securing it can be seen. The implant is surrounded by aqueous humor and the scleral lake is seen behind it. The intrascleral lake and the trabeculo-Decemet membrane, 8 months later, are shown in Fig. 15.58b. The implant is reabsorbed.

Figure 15.59 illustrates the typical appearance of the chamber angle after NPDS. The dark area (Fig. 15.59a) on the external wall of the chamber angle is the scleral lake (1), which can be clearly seen full of liquid with a fine slit cut (b). Figure 15.59a shows the Schlemm canal and the trabecular meshwork, which have become convex, raised toward the interior of the anterior chamber, because they have been displaced, and therefore, deformed, by the cylindrical implant.

Fig. 15.59a–c Typical appearance of the chamber angle after NPDS. The Schlemm canal and the trabecular meshwork have become convex, raised toward the interior of the anterior chamber, because they have been displaced by the cylindrical

implant, which deforms them. In a, the dark area seen by diffuse illumination on the external wall of the chamber angle is the scleral lake, which, in b, is seen full of liquid with a fine slit cut. c UBM of the same case