Trabeculectomy, the Ex-PRESS Mini Glaucoma Shunt, and the Xen Gel Stent

Marlene R. Moster

Augusto Azuara-Blanco

TRABECULECTOMY

Guarded filtration surgery, or trabeculectomy, lowers the intraocular pressure (IOP) by creating a fistula between the inner compartments of the eye and the subconjunctival space (i.e., filtering bleb; Fig. 24-1). Cairns¹ reported the first series in 1968. A number of techniques are available to assist in establishing and maintaining the function of filtration blebs and avoiding complications (see below).

Trabeculectomy is the most commonly used surgical procedure in patients with glaucoma, but its role is constantly evolving. Trabeculectomy has been compared with initial topical medical treatment as an initial treatment for glaucoma in a large randomized controlled trial.² It seems that patients presenting with more advanced disease had slower visual field progression if their primary intervention was surgical rather than medical. Trabeculectomy as the primary surgical intervention in glaucoma has been recently questioned, but a randomized comparative study between trabeculectomy and Baerveldt glaucoma drainage device did not show any difference in mean IOP after 5-year follow-up.³

REFERENCES

1. Cairns JE. Trabeculectomy: preliminary report of a new method. Am J Ophthalmol. 1968;(66):673-679.

2. Musch DC, Gillespie BW, Lichter PR, Niziol LM, Janz NK; CIGTS Study Investigators. Visual field progression in the Collaborative Initial Glaucoma Treatment Study: the impact of treatment and other baseline factors. Ophthalmology. 2009;116(2):200-207.

3. Gedde SJ, Schiffman JC, Feuer WJ, Herndon LW, Brandt JD, Budenz DL; Tube versus Trabeculectomy Study Group. Treatment outcomes in the Tube versus Trabeculectomy (TVT) study after five years of follow-up. Am J Ophthalmol. 2012;153(5):789-803.

FIGURE 24-1. Trabeculectomy filtering bleb. A slit-lamp view of an eye that underwent trabeculectomy 3 months earlier (A and B). Note the nonlocalized elevation of the conjunctiva.

SURGICAL TECHNIQUE

• Any type of regional anesthesia (retrobulbar, peribulbar, and sub-Tenon) can be used. Topical anesthesia is also possible, with topical 2% lidocaine gel, 0.1 mL of intracameral 1% nonpreserved lidocaine (Fig. 24-2), and 0.2 mL of subconjunctival 1% lidocaine injected from the superior temporal quadrant to balloon the conjunctiva over the superior rectus muscle (Fig. 24-3).

• Trabeculectomy should be done at the superior limbus, because inferiorly located blebs are associated with a much higher risk of bleb-associated infections.

• A fixation or traction suture is used to keep the eye in downward position, giving a good area of exposure.

A corneal traction suture in the quadrant of the planned surgery (7-0 or 8-0 black silk or nylon, or 8-0 Vicryl on a spatulated needle) is the preferred option of the authors. The needle is passed through clear, midstromal cornea approximately 2 mm from the limbus for approximately 3 to 4 mm.
Alternatively, a superior rectus traction suture (4-0 or 5-0 black silk on a tapered needle) can be used to rotate the globe inferiorly and bring the superior bulbar conjunctival into view. Using a muscle hook to rotate the globe downward, the conjunctiva and superior rectus are grasped with toothed forceps and the threaded needle is passed through the tissue bundle (Fig. 24-4).

• A limbus-based (Fig. 24-5) or fornix-based (Fig. 24-6) conjunctival flap is made with Westcott scissors and nontoothed utility forceps. A fornix-based flap is more likely to be associated with diffuse blebs.

When forming limbus-based flaps, the conjunctival incision is placed 8 to 10 mm posterior to the limbus. The conjunctival and Tenon wound should be lengthened to approximately 8 to 12 mm cord length. The flap is then extended anteriorly to expose the corneoscleral sulcus.
When making fornix-based flaps, the conjunctiva and Tenon are disinserted. Approximately, a 2-clock-hour limbal peritomy (6 to 8 mm) is sufficient. Blunt dissection is carried posteriorly.

• A scleral flap is then dissected. The scleral flap should completely cover the fistula to provide resistance to the aqueous outflow. The aqueous will flow around the scleral flap.

The differences in the shape or size of the scleral flap probably have little effect on surgical outcome. The flap thickness should be between one-half and two-thirds (Fig. 24-7).
It is important to dissect the flap anteriorly (approximately 1 mm into the clear cornea) to ensure that the fistula is created anterior to the scleral spur and the ciliary body.

• A corneal paracentesis is made before opening the globe (Fig. 24-8) with either a 30- or a 27-gauge needle or a sharp point blade. A block of tissue at the corneoscleral junction is then excised.

Two radial incisions are made first with a sharp blade or knife starting in the clear cornea, and extending posteriorly approximately 1 to 1.5 mm. The radial incisions are made approximately 2 mm apart. The blade or Vannas scissors are used to connect the incisions; thereby, a rectangular piece of tissue is removed (Fig. 24-9).
Alternatively, an anterior corneal incision, parallel to the limbus and perpendicular to the eye, is made to enter into the anterior chamber, and a Kelly or Gass punch is used to excise the tissue.

• A peripheral iridectomy may then be performed. Iridectomy is not necessary in many
cases (e.g., pseudophakic eyes with open anterior chamber angle), but recommended in patients with a shallow anterior chamber and an angle-closure glaucoma.

The iris is grasped near its root with toothed forceps. It is retracted through the sclerostomy, and an iridectomy is performed with Vannas or DeWecker scissors (Fig. 24-10).
The iridectomy should avoid damage to the iris root and the ciliary body so as not to cause bleeding.

• The scleral flap is sutured initially with two interrupted 10-0 nylon sutures (in case of a rectangular flap; Fig. 24-11) or with one suture (in a triangular flap). Slipknots are useful to adjust the tightness of the scleral flap and the rate of aqueous outflow. Additional sutures can be used to better control the outflow.

During the suturing of the scleral flap, the anterior chamber is filled through the paracentesis, and the flow around the flap is observed. If flow seems excessive, or the anterior chamber shallows, the slipknots are tightened or additional sutures are placed. If aqueous does not flow through the flap, the surgeon may loosen the slipknots or replace tight sutures with looser ones.
In some situations, the scleral flap is tightly closed to avoid hypotony, for example, angle-closure glaucoma and high preoperative IOP. Releasable sutures can be used (Fig. 24-12) instead of interrupted ones. Externalized releasable sutures are easily removed and are effective in cases of inflamed or hemorrhagic conjunctiva or thickened Tenon capsule.

• Conjunctival closure in limbus-based flaps is done with a double or single running suture (Fig. 24-13), with an 8-0 or 9-0 absorbable suture, or with a 10-0 nylon suture. Many surgeons favor a round-body needle.

In fornix-based flaps, a tight conjunctival-corneal apposition is needed. Sutures (e.g., mattress 10-0 nylon suture; Fig. 24-14) at the edges of the incision can be used to anchor the conjunctiva to the cornea. Alternatively, the fornix-based flap can be closed with a running modified Condon suture technique. https://eyetube.net/video/closing-the-fornix-based-conjunctival-flap/

• After the wound is closed, a 30-gauge cannula is used to fill the anterior chamber with a balanced salt solution (BSS) through the paracentesis track to elevate the conjunctival bleb and test for leaks (Fig. 24-13). Antibiotics and corticosteroids can be injected in the inferior fornix.

• Patching the eye is individualized, depending on the patient’s vision and the anesthesia used.

Intraoperative Application of Antimetabolites

• To reduce postoperative subconjunctival fibrosis, especially important in patients with a high risk for failure, mitomycin C (MMC) (Fig. 24-15) is used. The use of antifibrotic agents is associated with a higher success rate, although the risk of complications may also increase. MMC (0.2 to 0.5 mg per mL solution) or 5-fluorouracil (5-FU; 50 mg per mL solution) is applied for 1 to 5 minutes using soaked cellulose sponges (Fig. 24-16) placed over the episclera. Application under the scleral flap is also possible. The conjunctival-Tenon layer is draped over the sponge, avoiding contact of the MMC with the wound edge.

• After the application, the sponge is removed and the entire area is irrigated thoroughly with BSS. The plastic devices that collect the liquid runoff (Fig. 24-17A) are changed and disposed of according to toxic waste regulations (Fig. 24-17B).

• Alternatively, MMC can be injected subconjunctivally. A tuberculin syringe on a 30-gauge needle can be used to inject 0.1 cc of MMC 0.4 mg per cc mixed with 0.1 cc of 1% nonpreserved lidocaine. The total volume is 0.2 cc. The injection is given under tenons/conjunctiva approximately 8 mm from the limbus in the temporal quadrant to avoid a buttonhole.

FIGURE 24-2. Topical anesthetic agents. A. Xylocaine 2% gel for topical application and lidocaine 1% nonpreserved for sub-Tenon or subconjunctival injection. B. Anesthetic preparations.

FIGURE 24-3. Ballooning of conjunctiva. Ballooning of the conjunctiva with nonpreserved lidocaine 1% (0.5 mL) using a 30-gauge sharp needle in the direction of the superior rectus muscle.

FIGURE 24-4. Traction suture placement. A. Placement of a superior rectus traction suture before a limbus-based trabeculectomy. B. Placement of a corneal traction suture for a limbal based conjunctival flap suture.

FIGURE 24-5. Limbus-based flap. Developing a limbus-based conjunctival-Tenon flap. A. The conjunctiva is grasped with forceps and elevated before the initial cut, and placed approximately 8 to 10 mm posterior to the limbus. B. The incision is extended laterally exposing the episclera.

FIGURE 24-6. A fornix-based flap. Developing a fornix-based conjunctival-Tenon flap. A. The conjunctiva is grasped with forceps and elevated before the initial cut. B. The conjunctival incision is done as anteriorly as possible at the limbus, extending 2 to 3 clock hours.

FIGURE 24-7. A partial-thickness flap. Developing a one-half to two-thirds partial-thickness scleral trabeculectomy flap with a fornix-based conjunctival flap (A and B) or with a limbal-based flap (C).

FIGURE 24-8. Corneal paracentesis. A corneal paracentesis is done temporally or nasally before creating the fistula. A sharp knife is used, and a long track is created.

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