Exposure
Exposure is obtained by passing a partial-thickness traction suture through the cornea. Typically, the first implant is placed in the superotemporal quadrant. The placement of a second implant, if required, is dependent on surgeon preference.
Incision
A conjunctival incision can be made either at the limbus (fornix-based flap) or 5–6 mm posterior to the limbus (limbus-based flap), depending on surgeon preference. Typically, about 90° of dissection is performed to provide ample space to implant the plate.
Placement of plate
The plate is then sutured onto the sclera about 8 mm posterior to the limbus. Prior to insertion, the muscles are identified to determine the appropriate location for the plate. For Baerveldt implants, the muscles must be isolated and lifted in order to place the wings of the plate underneath the rectus muscles. Nondissolving sutures are used to secure the plate. Care must be taken to avoid globe perforation, as the sclera is often relatively thin in this area.
Tube placement and management
The tube is cut to an appropriate length to ensure that it remains in the preferred location (pars plana, anterior chamber, or sulcus). If the tube is placed in the anterior chamber or the pars plana, the tube is cut bevel up. Alternatively, if the tube is placed in the sulcus, it is cut bevel down to prevent occlusion of the tube by the iris.
Valved devices must be primed to separate the leaflets of the valve. Nonvalved devices must be modified to prevent hypotony in the immediate postoperative period (Video 13-10). A dissolvable suture (or ligature) is tied around the tube near the tube–plate junction to restrict aqueous flow through the tube, thus allowing a capsule to form around the plate prior to dissolution of the suture. When the suture loosens (approximately 5–7 weeks postoperatively), resistance to flow from the capsule surrounding the plate prevents hypotony. A monofilament suture, called a rip cord, can be placed in or adjacent to the lumen of the tube and carried subconjunctivally. This rip cord can be pulled if necessary to lower the IOP within the first 6 weeks. Venting slits can be created between the ligature and the entry point of the tube into the eye to allow aqueous flow in the early postoperative period.
VIDEO 13-10 Intraoperative tube adjustments.
Courtesy of Chandrasekharan Krishnan, MD.
A 22- or 23-gauge needle is used to create an entry site for tube placement in the anterior chamber, ciliary sulcus, or pars plana (in a vitrectomized eye). When the tube is to be placed in the anterior chamber or sulcus, the needle is directed parallel to the iris in order to avoid tube–cornea touch. Some surgeons create a partial-thickness tunnel with the needle starting 3–6 mm posterior to the limbus.
Coverage of the tube can be reinforced with several different types of human donor materials (eg, cornea, pericardium, sclera), or the tube can be implanted through a long scleral tunnel or under a scleral flap (Video 13-11).
VIDEO 13-11 Tube coverage.
Courtesy of Chandrasekharan Krishnan, MD.
Closure
The conjunctiva is closed with dissolvable sutures. Fornix-based incisions can be closed with wing sutures, while limbus-based incisions can be closed with a running single- or 2-layer closure.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.