Cutting Edge Glaucoma - Issue 2

12 • CUTTING EDGE - GLAUCOMA triangular flap as it allows adequate exposure of Schlemm canal and involves less scleral dis- section than a rectangular flap. 3. A one-half thickness scleral incision is then made with a no. 11 blade. Here we must bear in mind that the sclera in a buphthalmic eye is usually much thinner than in the adult eye. 4. The partial thickness scleral flap is then dissected toward the limbus using a no. 15 blade. The flap is held with Pierse-Hoskin forceps during the dissection. Care should be taken to main- tain the same plane while dissecting the scleral flap, especially near the limbus. 5. Surgical landmarks and anatomy of the limbal region should be carefully identified before one can proceed to the next step. Closest to the limbus is a transparent band of deep corneal lamellae, behind which is a narrow grayish-blue band, which is an external landmark of the trabecular meshwork. The grayish-blue band is followed by white, opaque sclera. The junc- tion of the posterior border of the grayish-blue band and the opaque sclera is the external landmark for finding Schlemm canal. In most eyes, this is situated between 2 and 2.5 mm behind the surgical limbus. The second landmark is one or more perforator vessels entering the sclera, indicating the area of Schlemm canal. Another landmark is a depression or dip at the area of Schlemm canal—the continuity of the two zones is not smooth; there is a dip between blue and white zone, which marks the junction. 6. A 2 × 2-mm-deep block is outlined without penetrating the anterior chamber (AC), which marks the area of the sclerostomy. 7. A central radial incision is then made across the scleral spur. The objective of this radial inci- sion is to cut the external wall of Schlemm canal and to avoid entering the AC. It is impor- tant to bear in mind that Schlemm canal is separated from the AC only by the trabecular meshwork. This is the most delicate step in the surgery and demands utmost microsurgical skill . Under high magnification the radial incision is gradually deepened with a no. 11 blade until it is carried through the external wall of Schlemm canal, at which point there is a gush of aqueous, occasion- ally mixed with blood. In our experience, a drop of aqueous is more common than a drop of blood. The dissection is carefully continued through the external wall until the inner wall is character- istically slightly pigmented and is composed of criss-crossing fibers. Vannas scissors are used to enlarge the lumen of the canal. Some surgeons confirm passage into the canal by passing a 6-0 nylon/prolene suture into the canal, as described by Smith [22]. 8. The internal arm of the trabeculotome is introduced into the canal with external parallel arm as a guide. Once 90% of the trabeculotome is within the canal, it is rotated into the AC until 75% of the probe arm length has entered, and the instrument is withdrawn. About 2–2½ clock hours of the internal wall of Schlemm canal and trabecular meshwork are disrupted by rotation of the trabeculotome into the AC. The same procedure is repeated on the other side. In total, about 100–120° of trabecular meshwork is opened by this technique. 9. Excess force should not be used while introducing the probe into the canal , to avoid creating a false passage. If the probe does not slip easily down the canal, it should be withdrawn and dissection of the outer wall continued until the surgeon is satisfied that all fibers of the outer wall are severed. The probe is then reintroduced into the canal to complete trabeculotomy.