Trabeculectomy

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Author: Thanh-Thao Vu
Published:
Specialties: Ophthalmology
Schools: Gavin Herbert Eye Institute, University of California Irvine
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Aqueous humor is drained from the eye via the trabecular meshwork or the uveoscleral pathway. Trabeculectomy is performed to lower intraocular pressure in glaucoma patients by means of creating an ostium in the anterior chamber connected to a partial thickness scleral flap covered by conjunctiva. This allows aqueous humor to be filtered into the subconjunctival space and out of the eye via the venous system.

Procedure

First, a partial thickness traction suture using a 6-0 Vicryl is passed through the superior cornea to rotate the eye inferiorly and expose the superior quadrant. Sharp curved Vannas scissors and 0.12 forceps are used to create a conjunctival limbal peritomy superiorly at the 3 o’clock hour position. The peritomy may be placed near the limbus or fornix. Mini Westcott scissors are then used to bluntly dissect and undermine the conjunctiva and Tenon’s layer to expose the sclera posteriorly, nasally, and temporally. Hemostasis can be achieved with light cautery. Three instrument wipe sponges are soaked with 0.4 mg/m of mitomycin C and then placed underneath the conjunctiva and Tenon’s layer and superior to the sclera nasally and temporally. They are left for 90 seconds and subsequently removed. Any remaining mitomycin C is irrigated with BSS.

Next, the eye is rotated inferiorly, and a #67 blade is used to create a 3.5 mm x 3 mm triangular scleral flap hinged at the limbus of about 50 to 75% thickness. Various shapes of the scleral flap can be made depending on surgeon preference (rectangular, trapezoidal etc.).  Straight tying forceps are used to lift the apex while a #67 blade is used to dissect beneath the flap anteriorly until the blue-gray zone of the limbus is exposed. At this point, a crescent blade is used to create a tunnel beneath the flap into the peripheral clear cornea. An anterior chamber paracentesis is created. An MVR blade is used to enter the anterior chamber through the tunnel and the sides of the blade are used to enlarge the opening.

A Kelley-Descemet punch is used to excise a corneal/trabecular block at the posterior lip of the wound until a clear ostium is observed under the flap. Colibri forceps are used to grasp and prolapse the peripheral iris tissue. An iridotomy is then performed using curved Vannas scissors. The anterior chamber is re-inflated with BSS.

A 10-0 nylon suture is then used to close the scleral flap with one suture at the apex and another at each base of the flap. The flap should be closed tightly enough to ensure the anterior chamber remains formed but loose enough to allow for drainage. Only the apical suture should be sealed most tightly to allow easier suture removal if the flap is too tight. Although not featured here, BSS can be injected through the paracentesis, and the flap confirmed to be watertight.

10-0 Vicryl is then used to close the conjunctiva against the limbus, forming a tight seal. The traction suture is then removed. At the conclusion of the case, subconjunctival injection of antibiotic and/or steroid can be given inferiorly. The anterior chamber should be formed and intraocular pressure appropriate. Wound leakage should be inspected with digital palpation.

Indications

Trabulectomy is indicated in glaucoma with uncontrolled intraocular pressures and progressive nerve injury refractory to maximal or tolerable medication management that is causing visual disability. Cost, compliance, side effects, inconvenience, and other factors should be considered when weighing the risks and benefits of trabeculectomy. Consideration should be made when glaucoma is moderate to advanced in severity, rapidly progressive, or failed prior laser surgery.

Contraindications

Contraindications to trabulectomy are limited life expectancy, medical comorbidities that enhance the risks of undergoing surgery, and scarring of the superior conjunctiva.  Benefits should outweigh risks of the procedure.

Setup

Patient is prepared and draped in the usual sterile fashion for cataract surgery. Retrobulbar block can be administered.

Preoperative Workup

The patient’s glaucoma stage and type are identified. History taking should involve asking patients about trauma, prior eye surgeries, bleeding disorders, intake of blood thinners or aspirin, and inflammation or infection. A complete ophthalmic examination is performed, including intraocular pressure and assessment of the angles under gonioscopy. Nerve OCTs and Humphrey visual fields are also obtained. No bloodwork, EKG, or imaging are required. Anesthesia questionnaire is completed prior to the procedure.

Anatomy and Landmarks

The following anatomic structures should be identified: conjunctiva, Tenon’s, sclera, and iris. It is important that the flap consist of 50-75% scleral thickness. The traction suture should be placed in the superior cornea and the peritomy created at the 3 o’clock hour position.

Advantages/Disadvantages

IOP control, defined as IOP < 21 mmHg and reduction at least 20% from baseline, was maintained over 5 years on average after surgery [1]. Failure rates in a study that followed patients for 3 years were 13.9% at 1 year, 28.2% at 2 years, and 30.7% at 3 years [2]. Failure was defined as persistent hypotony or uncontrolled IOP.

Complications/Risks

Risk factors for trabeculectomy failure include previous eye surgeries, neovascular or uveitic glaucoma, African American ethnicity, and young age [3]. Early problems in the post-op period are elevated IOP or hypotony. Complications include bleb leak (6-11%), iris prolapse obstructing flow (1.1%), encapsulated bleb (6-12%), shallow anterior chamber (13%), ptosis (12%), serous choroidal detachment (11%), choroidal effusion (4%), new synechiae formation (5%), corneal edema (6%), endophthalmitis (3%), and suprachoroidal hemorrhage (0.7%) [2,4].

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