Trabeculectomy and glaucoma treatment

Fistulizing surgery - trabeculectomy is most often performed to reduce intraocular pressure in patients with glaucoma. Trabeculectomy allows to reduce intraocular pressure, since during the operation a fistula is created between the inner parts of the eye and the subconjunctival space with the formation of a filtration pad.

Cairns reported the first operations in 1968. A number of existing techniques make it possible to create and maintain filter pads in a functional state, avoiding complications.

Description of Trabeculectomy

Currently, any type of regional anesthesia is used (retrobulbar, peribulbar, or injection of anesthetic under Tenon's capsule). Local anesthesia is possible using 2% lidocaine gel, 0.1 ml of 1% lidocaine solution intracameral and 0.5 ml of 1% lidocaine solution subconjunctivally from the upper temporal quadrant so that a conjunctival ridge is formed over the superior rectus muscle.

Trabeculectomy is best performed in the superior limbus because low-lying filtration pads are associated with a higher risk of infectious complications. The globe can be rotated downwards using a superior straight traction suture (4-0 or 5-0 black silk) or a corneal traction suture (7-0 or 8-0 black silk or Vicryl on an atraumatic needle).

A base-to-limbus or fornix conjunctival flap is created using Wescott scissors and dissecting forceps (without teeth). A fornix-based flap is preferred when the limbus already has scarring from previous surgeries; this flap is more likely to be associated with cystic pads. When creating a base-to-limbus flap, the conjunctival incision is made 8 to 10 mm posterior to the limbus. The incision in the conjunctiva and Tenon's capsule should be extended by approximately 8 to 12 mm. The flap is then mobilized anteriorly to expose the corneoscleral sulcus. When creating a base-to-fornix flap, the conjunctiva and Tenon's capsule are separated. A limbal peritomy of approximately 2 o'clock (6 to 8 mm) is sufficient. Blunt dissection is performed posteriorly.

The scleral flap should completely cover the fistula formed in the sclera to provide resistance to the outflow of fluid. Fluid will flow around the scleral flap.

Variations in the shape and size of the scleral flaps are unlikely to have much effect on the outcome of the surgery. The flap thickness should be between one-half and two-thirds the thickness of the sclera. It is important to dissect the flap anteriorly (approximately 1 mm of cornea) to ensure that the fistula extends to the scleral spur and ciliary body. Before opening the globe, a corneal paracentesis is performed with a 30- or 27-gauge needle or a sharp point blade. A block of tissue is then excised from the corneoscleral junction.

First, two radial incisions are made with a sharp blade or scalpel, starting from the transparent cornea, and extended back approximately 1-1.5 mm. The radial incisions are spaced approximately 2 mm apart. A Vannas blade or scissors are used to connect them, thus separating a rectangular flap of tissue. Another method involves an anterior corneal incision, parallel to the limbus and perpendicular to the axis of the eye, allowing access to the anterior chamber. A Kelly or Gass perforator is used to excise the tissue.

When performing an iridectomy, care should be taken to avoid damaging the iris root and ciliary body, as well as bleeding. The scleral flap is first closed with two single interrupted 10-0 nylon sutures (in the case of a rectangular flap) or with one suture (if the flap is triangular).

Sliding knots are used to achieve a tight seal of the scleral flap and normal drainage of fluid. Additional sutures can be used to better control the drainage of fluid. After suturing the scleral flap, the anterior chamber is filled through a paracentesis, and drainage occurs around the flap. If drainage appears excessive or the depth of the anterior chamber decreases, the sliding knots are tightened or additional sutures are placed. If fluid does not flow through the scleral flap, the surgeon may loosen the sliding knots or place tight sutures, skipping some of them.

Relaxing sutures may be used. Externally placed relaxing sutures are easily removed and are effective in cases of inflamed or hemorrhagic conjunctiva or thickened Tenon's capsule.

For a limbal-based flap, the conjunctiva is closed with a double or single continuous suture of 8-0 or 9-0 absorbable suture or 10-0 nylon. Many surgeons prefer to use round needles. For a fornix-based flap, a tight conjunctival-corneal junction must be created. This can be accomplished using two 10-0 nylon sutures or a mattress suture along the edges of the incision.

After wound closure, the anterior chamber is filled with balanced salt solution via paracentesis using a 30-gauge cannula to elevate the conjunctival pad and assess leakage. Antibacterials and glucocorticoids can be injected into the inferior fornix. Eye patching is individualized based on the patient's vision and the anesthesia method used.

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Intraoperative use of antimetabolites

Mitomycin-C and 5-fluorouracil are used to reduce postoperative subconjunctival fibrosis, which is especially important when there is a high risk of unsuccessful surgery. The use of antimetabolites is associated with both greater success and a high complication rate in primary trabeculectomies and high-risk surgeries. The risk/benefit ratio should be considered for each patient individually.

Mitomycin-C (0.2-0.5 mg/ml solution) or 5-fluorouracil (50 mg/ml solution) is applied for 1-5 min with a cellulose sponge soaked in the solution of the preparation. The entire sponge or a piece of it of the required size is placed above the episclera. It is possible to apply the preparation under the scleral flap. The conjunctival-Tenon layer is thrown over the sponge so as to avoid contact of mitomycin with the edges of the wound. After application, the sponge is removed, the entire area is thoroughly washed with a balanced salt solution. Plastic devices collecting the outflowing liquid are replaced and disposed of in accordance with the rules for the disposal of toxic waste.

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Post-operative care

Local glucocorticoid instillations (1% prednisolone solution 4 times a day) are gradually discontinued after 6-8 weeks. Some doctors use nonsteroidal anti-inflammatory drugs (2-4 times a day for 1 month). Antibacterial drugs must be prescribed for 1-2 weeks after surgery. In the postoperative period, cycloplegic drugs are used individually in patients with a shallow anterior chamber or severe inflammation.

If there is a high probability of developing early complications (vascularized and thickened filtration pads), it is recommended to perform repeated subconjunctival applications of 5-fluorouracil (5 mg in 0.1 ml of solution) during the first 2-3 weeks.

Digital pressure on the eyeball in the area of the inferior sclera or cornea through a closed lower eyelid, as well as pinpoint pressure on the edge of the scleral flap with a moistened cotton swab, can be useful for elevating the filtration pad and reducing intraocular pressure in the early postoperative period, especially after laser suture lysis.

Suture lysis and removal of relaxing sutures are necessary in cases of high intraocular pressure, flat filtration pad, and deep anterior chamber. Before performing laser sutolysis, gonioscopy should be performed to ensure that the sclerostomy is open and there is no tissue or thrombus in its lumen. Suture lysis and removal of relaxing sutures should be performed in the first 2-3 weeks after surgery; the result can be successful even a month after surgery when taking mitomycin-C.

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Complications of trabeculectomy

Complication	Treatment
Conjunctival openings	Purse-string suture with 10-0 or 11-0 thread on a round (“vascular”) needle
Early superfiltration	If the anterior chamber is shallow or flat but there is no lens-corneal contact, use cycloplegics, reduce the load, and avoid the Valsalva maneuver. If there is lens-corneal contact, urgent reconstruction of the anterior chamber is necessary. In case of complications, re-suture the scleral flap.
Choroidal effusion (choroidal detachment)	Observation, cycloplegics, glucocorticoids. Drainage is indicated for large effusions associated with a shallow anterior chamber.
Suprachoroidal hemorrhages
Intraoperative	Try to suture the eye and carefully tuck in the prolapsed choroid. Intravenous mannitol and acetazolamide.
Postoperative	Observation, control of intraocular pressure and pain. Drainage is indicated after 7-10 days in cases of persistent shallow anterior chamber and unbearable pain.
Incorrect direction of liquid flow	Initial drug treatment includes intensive local cycloplegics and mydriatics, local and oral fluid suppressants and osmotic diuretics. In pseudophakic eyes - hyaloidotomy with a neodymium YAG laser or anterior vitrectomy through the anterior chamber In phakic eyes - phacoemulsification and anterior vitrectomy. Vitrectomy through pars plana
Encapsulation of the pad	Observation first. Fluid suppressants for elevated intraocular pressure. Consider 5-fluorouracil or surgical revision.
Late filtration pad fistula	In case of minor leakage, observation and local application of antibacterial drugs. If the leakage is prolonged, surgical revision (conjunctival plastic surgery)
Chronic hypotension	For maculopathy and vision loss - subconjunctival blood injection or surgical revision of the scleral flap
Inflammation of the filtration pad, endophthalmitis	Infection of the eye pad without involvement of intraocular structures - intensive treatment with strong broad-spectrum antibacterial drugs. Footpad infection with moderate anterior segment cellular reaction - intensive local treatment with strong antibacterial drugs. Pad infection with severe anterior segment cellular reaction or vitreous involvement: vitreous sampling and intravitreal antibacterial administration

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