Technique
Exposure
In order to obtain adequate exposure, a partial-thickness suture can be passed through the superior cornea to rotate the eye inferiorly (Fig 13-4A). Alternatively, a superior rectus bridle suture can be placed (Fig 13-4B); however, its use has been reported to increase the risk of trabeculectomy failure.
Conjunctival incision
The conjunctival incision can be made in 1 of 2 locations. A fornix-based trabeculectomy conjunctival flap is created by making an incision adjacent to or slightly posterior to the limbus (Fig 5-13; Video 13-2), while a limbus-based trabeculectomy flap is created by making an incision 8–10 mm posterior to the limbus (Fig 6-13). Fornix-based trabeculectomies offer the advantages of better exposure, while limbus-based flaps reduce the risk of early wound leak because the incision is several millimeters away from the scleral flap. Fornix-based flaps are associated with more diffuse blebs.
VIDEO 13-2 Fornix-based trabeculectomy with running closure.
Courtesy of James A. Savage, MD.
Scleral flap
A partial-thickness scleral flap is created in the superior sclera, posterior to the limbus (Fig 7-13). This flap will ultimately cover the hole that allows aqueous to egress into the subconjunctival space. Whenever possible, the scleral flap is centered at 12 o’clock to help prevent postoperative bleb exposure and dysesthesia. Common flap shapes include triangular, rectangular, and trapezoidal.
Fistula creation
A paracentesis provides access to the anterior chamber to allow re-formation of the chamber with balanced salt solution or viscoelastic when needed. An incision into the anterior chamber is created under the scleral flap with a sharp blade. A corneoscleral block of tissue is removed (Fig 8-13), creating a fistula that allows aqueous to flow directly from the anterior chamber to the subconjunctival space. The fistula can be made freehand or with a trephining device such as a Kelly Descemet membrane punch. This fistula is typically centered underneath the scleral flap and is small enough so that the flap overlaps it on all sides.
Iridectomy
An iridectomy prevents iris from occluding the fistula (Fig 13-8D). Some surgeons do not perform an iridectomy in selected patients, as it is believed the risk of fistula occlusion is low in certain pseudophakic eyes. The risks of iridectomy (bleeding, inflammation) should be weighed against the risk of fistula obstruction.
Closure of scleral flap and conjunctiva
The scleral flap is secured (Fig 9-13) with several nylon sutures (typically 10-0 or 9-0), which are tightened to provide appropriate resistance to aqueous flow. Some surgeons preplace these sutures before entering the anterior chamber to facilitate quick closure. Releasable sutures in the flap allow for suture removal postoperatively without a laser (Video 13-3). After the sutures are tied, the anterior chamber is re-formed with balanced salt solution, and scleral flap tension is titrated to achieve the desired rate of egress of aqueous humor.
VIDEO 13-3 Placement of a releasable suture for flap closure.
Courtesy of Marlene Moster, MD.
Conjunctival closure must be watertight to prevent postoperative complications and to maximize the success of the surgery. For a limbus-based flap, the Tenon capsule and conjunctiva are closed separately or in a single layer by means of a running suture on a vascular needle. For a fornix-based trabeculectomy, the conjunctiva can be closed with 2 wing sutures or a running suture.
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.