Trabeculectomy

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].

Trabectome

This is a trabectome procedure performed on a patient with moderate severity open angle glaucoma. Trabectome is a minimally invasive glaucoma surgery (MIGS) developed by Baerdveldt and Chuck where the trabecular meshwork is electrocauterized, irrigated, and aspirated under gonioscopy to improve the drainage of aqueous humor and reduce intraocular pressures.

Procedure
Topical TetraVisc is first administered to the eye. The patient’s head is rotated 30 degrees away from the surgeon and the microscope tilted 30 degrees toward the surgeon. The patient’s axial core can be rotated if turning the neck proves difficult. The gonioscope lens is used to visualize the trabecular meshwork, the pigmented line between Schwalbe’s line and the scleral spur. A 1.7 mm temporal clear corneal and uniplanar incision is made 2 mm anterior to the limbus.

While applying continuous irrigation to deepen the angle, the Trabectome handpiece is introduced into the anterior chamber under gonioscopic visualization, and the end of the device was inserted into the inferonasal trabecular meshwork. When properly inserted, the trabecular meshwork should enter between the electrode tip and the footplate, causing the footplate to be obscured by the trabecular meshwork. The handpiece is used to ablate trabecular meshwork at a setting of flow 3 and 0.7 mW. It is rotated superiorly to create a 120 degree cleft, exposing the outer white wall of Schlemm’s canal. Care must be taken to prevent outward push on Schlemm’s canal by applying a slight inward pull during ablation. The handpiece may need to be readjusted as it is rotated in a counter-clockwise fashion.

The handpiece is removed from the anterior chamber. The patient’s head is returned to a neutral position, and BSS was used to exchange viscoelastic from the anterior chamber through the temporal wound. BSS is to irrigate red blood cells from the Schlemm’s canal collector channels. The gonioscope is used to verify the cleft. At the conclusion of the case, the intraocular chamber is formed and pressure checked to be appropriate via digital palpation.

Indications
Trabectome is indicated for narrow-angle [1], open-angle, and secondary glaucoma with uncontrolled intraocular pressures and progressive nerve injury refractory to maximal or tolerable medication management [2]. As a MIGS, trabecome can be considered in initial stages of glaucoma due to its safety and quick routine recovery. Reduction of drops due to side effects, costs, or poor compliance are reasons to offer this procedure to patients [3]. Trabectome surgery can also be performed in conjunction with cataract surgery, in pseudophakic and phakic eyes, and after trauma, scleral buckle [4], laser trabeculoplasty [5], or failed trabeculectomy or tube shunt [6,7].

Contraindications
Contraindications are few but the most common is pathology that limits gonioscopic view of the angle (active neovascular glaucoma, uveitis, corneal edema etc).

Setup
Patient’s head is rotated 30 degrees away from the surgeon and the microscope rotated 30 degrees toward the surgeon to provide optimal surgical approach.

Preoperative Workup
The patient’s glaucoma stage and type are identified. History taking should involve asking patients about trauma and prior eye surgeries. 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 Landmark
Trabecular meshwork should be identified as the pigmented line between Schwalbe’s line and the scleral spur. Care must be taken to not ablate the ciliary body band. Blood reflux from Schelmm’s canal collector channels to confirm the ablation target can be induced by burping the main incision. After ablation, the cleft should be verified. The pigmented line from the trabecular meshwork should no longer be visible and only the outer wall of Schlemm’s canal seen.

Advantages/Disadvantages
Numerous studies have looked at the efficacy of trabectome surgery. Intraocular pressure drops to the mid-teens and decreasing the number of medications in most cases [8]. Unlike trabeculectomy or tube shunts, there is little scarring, the conjunctiva is preserved, the recovery is predictable, and there are less complications [3]. Patients with higher IOPs stand to benefit with greater reductions in IOPs than those with lower IOPs. There is limited data on the long-term success rate of trabectome surgeries. Studies following patients after surgery show that trabectome alone has a 70% success rate at 1 year but only 22% at 2 years [9,10,11].

Complications/Risks
The most common complications are transient hyphema, peripheral anterior synechiae, corneal injury, and transient IOP spikes of 10 mmHg or higher. Surgical failure can be due to incomplete or improper removal of the trabecular meshwork as well as damage to the ciliary body band or surrounding tissues [12]. The rate of serious vision-threatening complications, such as hypotony, cyclodialysis cleft, choroidal hemorrhage, and endophthalmitis, is <1% [13].

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