8.3New Minimally Invasive, Sclerothalamotomy Ab Interno Surgical Technique

8.3.1Introduction to the Sclerothalamotomy Ab Interno

Trabeculectomy, Þrst described in the 1960s [1Ð3], was the surgical procedure of choice for glaucoma till recently. The original intention of trabeculectomy was to the bypass the resistance of the trabecular meshwork by channeling aqueous humor directly to the SchlemmÕs canal. It soon became evident that successful reduction in IOP following trabeculectomy was clearly related to the presence of a subconjunctival Þltering bleb [4]. Despite initial success, there was a progressive rate of failure of trabeculectomy due to subconjunctival Þbrosis in the Þltering bleb in most cases. Trabeculectomy was also associated with serious vision-threatening complications like postoperative choroidal effusions and hemorrhage, delayed bleb leaks, and bleb-related infections including endophthalmitis. These complications were seen more frequently when wound-healing agents like 5-ßuorouracil (5-FU) and MMC were used.

The concept of trabecular meshwork bypass as a surgical principle for glaucoma treatment evolved from the discovery that pathologic outßow resistance was caused primarily by the juxtacanalicular trabecular meshwork and, in particular, by the inner wall of the SchlemmÕs canal [5, 6]. A further study showed that 35% of the outßow resistance arises distally to the inner wall of the SchlemmÕs canal [7].

The more recent methods of nonpenetrating deep sclerectomy and viscocanalostomy, Þrst described by Fjodorov [8] and Stegmann [9], respectively, attempted at improving uveoscleral outßow and were therefore not considered depending on the presence of a Þltering bleb. In 1976, Benedikt [10] described a surgical technique for glaucoma in which the ciliary body was exposed (i.e., a form of penetrating sclerectomy). He successfully reported long-term IOP regulation in 27 of 38 cases (63.2%) involving hemorrhagic, aphakic, and irreversible angle-closure glaucoma after initially failed Þltering surgery. This technique was the basis for the later development of perforating deep sclerectomy by the authors of this study. This technique used

since 1985 was termed sclerothalamectomy [11]. Spiegel et al. [12] have described a new surgical technique involving the use of an implanted tube, the trabecular meshwork bypass tube shunt, which should provide a direct connection between SchlemmÕs canal and the anterior chamber. This surgical technique avoids the technical difÞculties related to the nonpenetrating surgical procedures. Sclerothalamotomy ab interno evolved from sclerothalamectomy, and this subchapter will explain the surgical technique and comment on the results of this technique used to control IOP in glaucoma patients.

8.3.1.1Indications for the Sclerothalamotomy Ab Interno

The main indication for the sclerothalamotomy ab interno procedure is insufÞcient response to medical treatment of IOP. Patients with primary open-angle glaucoma and juvenile glaucoma are good candidates for such a procedure.

8.3.2 Anesthesia

This procedure can usually be performed under local anesthesia. Nonetheless, for anxious or uncooperative patients, or for those unable to stay calm, general anesthesia is preferred. In most cases, a local procedure provides enough relaxation and analgesia to ensure safe and precise surgery. Sub-tenon anesthesia is the procedure of choice as it provides excellent analgesia as well as akinesia. Subconjunctival or topical anesthesia can be considered in cooperative patients.

8.3.3 Surgical Technique

The aim of this technique is to create a new space, a sort of cavity, in the sclera by performing a deep sclerotomy ab interno. The so-called sclera thalami are made using a diathermy probe inserted in the anterior chamber. The sclerothalamotomy ab interno is performed under gonioscopic view using a gonioscopy lens. The main advantage of this technique is that the anterior chamber

is not penetrated; only a paracentesis is made to insert the probe. The IOP is gently lowered after the trabecular meshwork and SchlemmÕs canal are locally removed by the diathermy probe. Aqueous humor is then collected through intrascleral drainage pathways draining into episcleral veins, similar to one of the routes proposed for deep sclerectomy.

8.3.3.1 Preparation

A clear cornea incision (1.2 mm wide) is placed in the temporal upper quadrant using a diamond knife. A second corneal incision is performed 120¡ apart from the Þrst followed by any injection of Healon GVª. The high-frequency diathermy probe (Oertli, Switzerland) consists of an inner platinum electrode which is isolated from the outer coaxial electrode. The platinum probe tip is 1 mm in length, 0.3 mm high, and 0.6mm in width and is bent posteriorly at an angle of 15¡ (Fig. 8.39a, b). The external diameter of the probe measures 0.9 mm. The modulated 500 kHz current generates a temperature of approximately 130¡C at the tip of the probe. The setup provides high-frequency power dissipation in the vicinity of the tip. As a result, heating of tissue is locally very limited and is applied as a rotated ellipsoid.

Fig. 8.40 Insertion of the high-frequency diathermy probe (Oertli) through the temporal corneal insertion

8.3.3.2 Diathermy Probe Insertion

The high-frequency diathermy probe is inserted through the temporal corneal insertion (Fig. 8.40). Visual inspection of the target zone (opposite iridocorneal angle) is observed by a four-mirror gonioscopic lens (Fig. 8.41). The high-frequency tip penetrates up to 1 mm nasal into the sclera through the