8.2.2 Anesthesia

MPGS with the Ex-PRESSª implant can usually be performed under local anesthesia. General anesthesia is needed only in young uncooperative patients or disorientated patients. Sub-tenon anesthesia is probably the safest and the most efÞcient of the different types of local anesthesia as it provides excellent analgesia as well as akinesia. Subconjunctival or topical anesthesia can be considered in very cooperative patients.

8.2.3Surgical Technique and Potential Modifications

A fornix-based conjunctival ßap is formed in an upper quadrant (Fig. 8.26). A 5 × 5 mm limbus-based scleral ßap of approximately 50% depth is created taking care that the dissection passes the vascular arcade and reaches clear cornea. At the surgeonÕs discretion, Mitomycin C (MMC) 0.02% can be applied under the conjunctiva and the scleral ßap (Fig. 8.27). A preincision is made into the anterior chamber under the scleral ßap, in the lower part of the blueÐgrey transition zone between the white sclera and clear cornea (Fig. 8.28). Misplacement of the preincision can lead to inadequate device positioning. A preincision that is too scleral might lead to iris touch whereas a preincision that is too corneal might cause anterior migration of the device. The size of the preincision differs according to the model of the Ex-PRESSª used. A 25 gauge needle is recommended for the P models. For the X models, a 23 gauge needle is needed to allow an easy insertion of the Ex-PRESSª. The needle should be held nearly parallel to the iris plane and aimed at the pupil while entering the anterior chamber in order to ensure proper positioning of the device. The anterior chamber is then Þlled with a viscoelastic material through a separate paracentesis.

An alternative to the use of viscoelastic during the operation is the use of an anterior chamber maintainer (ACM) with balanced salt solution (BSS). The ACM provides intraoperative control of the IOP and a deep A/C throughout the operation.

Recently, the Ex-PRESS is mounted on a selfrelease device for ease of handling (Fig. 8.29). The

Fig. 8.26 A fornix-based conjunctival ßap is created and a 5 × 5 mm, 50% depth scleral ßap is dissected at the 12 oÕ clock position

Fig. 8.27 Application of Mitomycin C under the conjunctival and scleral ßap

Fig. 8.28 A preincision (anterior chamber penetration) is made in the lower part of the grey zone between the white sclera and clear cornea. A 25 gauge needle is used for the P model and a 23-gauge needle is used for the X model

Fig. 8.29 The Ex-PRESSª mini-shunt mounted on a selfrelease device

Fig. 8.30 The Ex-PRESSª is inserted into the anterior chamber via the preincision

implant is inserted into the anterior chamber via the preincision site (Figs. 8.30 and 8.31).

The scleral ßap is then securely sutured, using 10/0 nylon sutures, to cover the Ex-PRESSª implant plate. The sutures are usually placed at the distal corners of the ßap and at 1/4 the distance between the limbus and the corner of the scleral ßap (Fig. 8.32). The conjunctiva is sutured securely back in place (Fig. 8.33). Once correctly placed, the ßange of the device lies ßat under the scleral ßap with the conjunctiva completely covering the scleral ßap, and the device body should lie parallel to the iris. At the end of the operation, most of the surgeons prefer to leave a certain amount of standard viscosity viscoelastic material in the A/C in order to prevent immediate postoperative over Þltration, hypotony,

Fig. 8.32 The scleral ßap is secured back in place with four tight 10/0 nylon sutures

and loss of A/C. The suggested amount of viscoelastic material differs with each model of the Ex-PRESSª. It might also differ according to the personal technique of the scleral ßap size, shape, and suturing. The P models with its rounded body will need approximately onethird of the A/C Þlled with viscoelastic. The X models with their square-shaped bodies will need two-thirds of the A/C Þlled with viscoelastic.

Some users of the Ex-PRESSª prefer to create a limbal-based conjunctival ßap and a smaller triangular (3 × 3 mm) scleral ßap. In that case, one 10/0 nylon suture might sufÞce to secure the scleral ßap, whereas the conjunctiva is closed with a running absorbable suture.

Some surgeons, who were familiar with NPGS prior to the Ex-PRESS introduction, suggest adding a deep sclerectomy under the superÞcial scleral ßap without opening SchlemmÕs canal [35]. This modiÞed deep sclerectomy creates an intrascleral space that might enhance intrascleral bleb formation and lessen subconjunctival bleb formation (Figs. 8.34Ð8.38). This technique is particularly suited for intractable cases, although no studies have been published yet on its added efÞcacy.

Fig. 8.35 Ex-PRESSª model X200 inserted under a scleral ßap. Note the appearance of the mild diffuse bleb 2 years after the operation

Fig. 8.37 Ex-PRESSª model R50 inserted under a scleral ßap. Note the elevated scleral ßap forming an intrascleral bleb