Peripheral iridectomy

Surgical iridectomy may be required if a patent iridotomy cannot be achieved with a laser. Such situations include a cloudy cornea, a shallow or flat anterior chamber, and insufficient patient cooperation.

Cataract extraction

When pupillary block is associated with a visually significant cataract, lens extraction might be considered as a primary procedure. However, laser iridotomy may stop acute pupillary block, so that cataract surgery may be performed more safely at a later time. Cataract extraction combined with goniosynechialysis may be effective in patients with chronic angle-closure glaucoma following acute primary angle-closure glaucoma and in patients with primary angle closure unresponsive to laser iridotomy.

Harasymowycz PJ, Papamatheakis DG, Ahmed I, et al. Phacoemulsification and goniosynechialysis in the management of unresponsive primary angle closure. J Glaucoma. 2005;14(3):186–189.

Chamber deepening and goniosynechialysis

When PAS develop in cases of angle closure, iridotomy alone may not lower the IOP adequately. Chamber deepening through a paracentesis may break PAS of relatively recent onset. A viscoelastic agent and/or an iris or cyclodialysis spatula may be useful, in a procedure known as goniosynechialysis, to break synechiae.

Campbell DG, Vela A. Modern goniosynechialysis for the treatment of synechial angle-closure glaucoma. Ophthalmology. 1984;91(9):1052–1060.

Shingleton BJ, Chang MA, Bellows AR, Thomas JV. Surgical goniosynechialysis for angle-closure glaucoma. Ophthalmology. 1990;97(5):551–556.

Other Procedures to Lower IOP

Incisional and nonincisional procedures to control IOP include glaucoma drainage device implantation, ciliary body ablation, and cyclodialysis, as well as viscocanalostomy, canaloplasty, and other nonpenetrating procedures.

Glaucoma Drainage Device Implantation

Many different types of devices have been developed that aid angle filtration by shunting aqueous to a site away from the limbus, such as the equatorial subconjunctival space. Glaucoma drainage device implantation generally involves placing a tube in the anterior chamber, in the ciliary sulcus, or through the pars plana into the vitreous cavity. This tube is usually connected to an extraocular plate, which is attached to the sclera in the equatorial region of the globe, between the extraocular muscles; some devices employ 2 plates. Aqueous flows out through the tube and into the subconjunctival space in the region of the extraocular plate.

Glaucoma drainage devices can be broadly categorized as nonvalved devices, which have no flow restrictor, or valved devices, which have a flow restrictor (Table 8-2). The most popular nonvalved devices are the Molteno (Molteno Ophthalmic Ltd, Dunedin, New Zealand) and Baerveldt (Abbott Medical Optics, Santa Ana, CA) designs. The most widely used valved device is the Ahmed (New World Medical, Inc, Rancho Cucamonga, CA). A recently published study comparing the Ahmed glaucoma valve (AGV) and the Baerveldt glaucoma implant (BGI) found that the average IOP after 1 year was slightly higher in patients who received the AGV; however, there were fewer early

postoperative complications associated with use of the AGV than with the BGI. The size of the drainage device plate varies and can influence IOP control and complications postoperatively.

Table 8-2

The anterior chamber tube shunt to an encircling band (ACTSEB), described by Schocket, is another type of glaucoma drainage device. ACTSEB uses an encircling element intended for scleral buckling, and tubing, which is attached to the encircling band. A variation on ACTSEB can be used in eyes with a previously placed scleral buckle: angiocatheter tubing is passed into the anterior chamber via a needle track near the limbus and then threaded into the capsule surrounding a previously placed scleral buckle.

Budenz DL, Barton K, Feuer WJ, et al. Treatment outcomes in the Ahmed Baerveldt Comparison Study after 1 year of follow-up. Ophthalmology. 2011;118(3):443–452. Epub 2010 Oct 8.

Weinreb RN, Mills RP, eds. Glaucoma Surgery: Principles and Techniques. 2nd ed. Ophthalmology Monograph 4. San Francisco: American Academy of Ophthalmology; 1998:65–85.

Indications

The devices mentioned and similar types of implants have generally been reserved for difficult glaucoma cases in which conventional filtering surgery has failed or is likely to fail. However, glaucoma drainage device implantation may be used as a primary filtration procedure. The 3-year follow-up results of the Tube Versus Trabeculectomy study showed that tube-shunt (glaucoma drainage device) surgery had a higher success rate compared to trabeculectomy with MMC. Both procedures were associated with a similar reduction in IOP and use of supplemental medications. A glaucoma drainage device should be considered in the following clinical settings:

Failed trabeculectomy with antifibrotics: It may be appropriate to perform a second trabeculectomy in some clinical situations. However, when the factors that precipitated the initial failure cannot be modified, or when it is not technically possible to repeat the trabeculectomy, implantation of a glaucoma drainage device may be the procedure of choice.

Active uveitis: Although few randomized, prospective studies have been performed comparing trabeculectomy with antifibrotics to glaucoma drainage devices in the setting of active uveitis, the success rate of trabeculectomy is disappointingly low in most cases of active inflammation. In certain types of uveitis, for example, young patients with juvenile idiopathic arthritis, the success rate of trabeculectomy is low and glaucoma drainage device implantation is often the primary surgical treatment.

Neovascular glaucoma: Eyes with neovascular glaucoma (NVG) are at high risk of trabeculectomy failure. In one prospective study, the 5-year success rate of trabeculectomy with 5-FU in NVG was 28%. When possible, panretinal photocoagulation is performed prior to glaucoma surgery in cases of NVG. When the IOP level is such that urgent surgery is required, or when the NVG does not respond to panretinal photocoagulation, a glaucoma drainage device is indicated. The management of NVG is likely to change with the use of anti–vascular

endothelial growth factor agents. These medications may decrease the risk of perioperative intraocular bleeding.

Inadequate conjunctiva: In patients who have undergone severe trauma or previous surgery involving conjunctiva (eg, retinal detachment surgery), trabeculectomy success may be reduced because these patients may have excessive conjunctival scarring. A glaucoma drainage device can be implanted, even in the presence of a scleral buckle. When a complete vitrectomy has been performed, the tube can be placed through the pars plana.

Aphakia: The success rate of conventional filtering surgery in aphakic eyes is low, even when MMC is used. Many surgeons use glaucoma drainage device implantation as a primary procedure in uncontrolled aphakic glaucoma.

Contact lens use: The need for contact lens use for vision rehabilitation is an important consideration. The use of a soft contact lens over a trabeculectomy bleb is a risk factor for bleb trauma and subsequent infection. The use of a soft contact lens following glaucoma drainage device implantation is not without risk, however, as the conjunctiva overlying the tube is more prone to erosion with contact lens use.

Contraindications

Glaucoma drainage device implantation may have a complicated postoperative course. Borderline corneal endothelial function is a relative contraindication for anterior chamber placement of a tube.

Preoperative considerations

The preoperative evaluation for glaucoma drainage device implantation is similar to that for trabeculectomy. During the ophthalmic examination, the clinician should note the findings of the motility examination, the status of the conjunctiva, the health of the sclera at the anticipated sites for the tube and external plate, the location of PAS near possible tube insertion sites, and the location of vitreous in the eye. The clinician should also note a previously placed scleral buckle.

Techniques

Although glaucoma drainage devices differ in design, the basic techniques for implantation are similar. The superotemporal quadrant is preferred over the superonasal quadrant, because surgical access is more easily achieved in the former. Valved devices must be primed before implantation. The extraocular plate is sutured between the vertical and horizontal rectus muscles, posterior to the muscle insertions. The tube portion of the device is then routed in 1 of 3 ways: anteriorly to enter the chamber angle; into the ciliary sulcus in a pseudophakic eye; or through the pars plana for posterior implantation in eyes that have had a complete vitrectomy. Typically, the tube is covered with tissue such as sclera, pericardium, or cornea to help prevent erosion through the conjunctiva. Dura should be avoided because of the potential risk of prion transmission.

For the nonvalved devices, there are a number of techniques to restrict flow in the early postoperative period, such as stenting the tube lumen or ligating the tube with a suture. Restricting flow is not necessary with devices that contain a flow restrictor, although hypotony and a flat chamber can still sometimes occur with them. Administering antifibrotic agents in doses similar to those used in trabeculectomy does not appear to improve the success of glaucoma drainage device surgery. For devices with 2 plates, the second plate and its interconnecting tube may be placed either over or under the superior rectus muscle; the distal plate is attached to the sclera in a manner similar to that in which the proximal plate is attached.

A confounding cause of hypotony can be leakage of aqueous around the tube at its entry site. In general, tubes should be introduced into the anterior chamber via a needle incision that is no larger

than the diameter of the tube (23 gauge for most tubes). When the patient’s eye has thin sclera or when the tube is introduced under a partial-thickness scleral flap, a tighter entry site (eg, 25 gauge) may be required.

Postoperative management

The IOP in the early postoperative period can be variable. With nonvalved devices in which the tube has been occluded, early IOP spikes are best managed medically. After sufficient time has passed for a capsule to form around the extraocular plate, the occluding suture is released for the nonvalved devices. As with trabeculectomy, topical corticosteroids, topical antibiotics, and cycloplegic agents are used. IOP elevation occurs around 2–8 weeks postoperatively, which probably represents encapsulation of the extraocular reservoir. Aqueous suppression can control the IOP, and this elevation usually improves or resolves spontaneously within 1–6 months.

Complications

Success rates have been encouraging, but the implant procedures share many of the complications associated with conventional filtering surgery. In addition, unique problems related to the tubes and plates arise. Early overfiltration in an eye with tube placement in the anterior chamber results in a flat chamber and tube–cornea touch. Tube–cornea touch can compromise the cornea; and even when no touch occurs, an area of corneal decompensation can appear near the tube. Eyes must be monitored for late complications such as tube erosion or plate migration. Ocular motility disturbances may also occur. Tube obstruction, plate migration, or tube erosion may require surgical revision. Table 8-3 lists several common complications of glaucoma drainage devices, along with methods for avoiding their development or managing them.

Table 8-3