Complications after glaucoma surgery

Statistics show that when performing glaucoma surgery in the early stages, good immediate and long-term results are obtained, in most cases, stabilization of visual functions is noted. However, complications after surgery are possible.

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Anterior chamber depth reduction

One of the frequent complications after trabeculectomy and may be associated with: pupillary block, hyperfiltration, malignant glaucoma. Pronounced prolonged reduction of the depth of the anterior chamber is rare and usually recovers on its own. In other cases, more serious complications may occur: formation of anterior peripheral synechiae, endothelial dystrophy of the cornea, cataract, hypotony and associated maculopathy.

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Grade

There are 3 degrees of grinding of the anterior chamber depth.

• Grade 1: displacement of the iris to the back surface of the cornea.
• Grade 2: Contact between the edge of the pupil and the cornea.
• Grade 3: Corneolenticular contact, which may lead to endothelial degeneration and cataract formation.

Reasons

• Obvious peripheral iridectomy and iris configuration that excludes the occurrence of pupillary block.
• Monitoring the condition of the filter cushion.
• Seidel's test with instillation of 2% fluorescein solution into the conjunctival cavity or onto a filtration pad. In the presence of external filtration, fluorescein dissolved in aqueous humor is determined in the red-free light of a slit lamp, which has a bright green color in contrast to a 2% fluorescein solution with a less intense color.
• Intraocular pressure control.
• Examination of the fundus to rule out choroidal detachment.

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Iridectomy hole

Cause: Non-functioning peripheral iridectomy.

Signs: high intraocular pressure, flat filtration pad, negative Seidel test, iris bombage, presence of non-perforating iridectomy.

Treatment: argon laser excision of the pigment sheet in the area of the existing iridectomy hole if its perforation is incomplete, or new laser iridectomy.

Pupillary block

Reasons

• Excessive filtration through the scleral flap area occurs due to its insufficient adaptation. It can be prevented by tight suturing of the scleral bed. In the early postoperative period, it is possible to enhance the outflow by cutting the scleral sutures with an argon laser or by loosening them with sliding knots. These actions are effective for up to 10 days after surgery;
• excessive filtration through the cushion (external filtration) in the presence of an opening in the conjunctival suture area or insufficient suturing of the conjunctiva and Tenon's capsule.

Signs

• Hypotension.
• The filtration cushion is expressed due to excess filtration in the area of the scleral flap.
• The Seidel test is negative in case of hyperfiltration in the area of the scleral flap and positive in case of external filtration.
• Descemet's membrane folds in hypotension.
• In some cases - choroidal detachment.

Treatment depends on the cause and extent of the anterior chamber collapse.

• initial conservative therapy is carried out in the absence of iridocorneal contact;
  • Instillations of 1% atropine to maintain mydriasis and prevent pupillary block.
  • Instillation of beta-blockers or oral acetazolamide to reduce aqueous humor production and promote healing while temporarily decreasing fistula drainage.
  • Point zones of external filtration are sealed with cyanoacrylate or fibrin glue, but large conjunctival defects or wound diastasis are eliminated surgically.
  • Often these measures result in restoration of the anterior chamber within a few days.
• follow-up therapy is carried out if conservative therapy is ineffective. Conjunctival tamponade is possible to speed up healing by applying pressure to the surgical area. Soft contact lenses with a large diameter, a collagen frame or a special Simmons shield are used as a bandage. If the measures taken do not lead to deepening of the anterior chamber within a few hours, further actions are ineffective;
• final therapy is carried out in case of progressive grinding of the anterior chamber and the risk of developing corneolenticular contact (or already existing):
  • The anterior chamber of the eye is filled with air, sodium hyaluronate or gas (SF ₆ ).
  • Choroidal detachment is drained only when the level is very high or there is a risk of contact between the bubbles (“kissing” choroid).
  • The scleral flap and conjunctiva are re-sutured, which can be difficult to perform due to the loose structure of the operated tissues.

Ciliary block

Atypical aqueous outflow syndrome is a rare but very serious complication.

Causes: blockage of the outflow of aqueous humor through the pars plicata of the ciliary body with its reverse (retrograde) outflow into the vitreous body.

Signs: shallow anterior chamber combined with high intraocular pressure, absence of a filtration cushion and a negative Seidel test.

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Treatment

Initial conservative therapy.

• Instillation of mydriatics (atropine 1% and phenylephrine 10%) to achieve maximum cycloplegia. This increases the distance between the ciliary processes and the equator of the lens, compressing the zonular zone and returning the lens to its normal position.
• If mydriatics are ineffective, mannitol is administered intravenously to reduce the volume of the vitreous body and displace the lens posteriorly.
• Decreasing aqueous humor production to control intraocular pressure.

Follow-up therapy if drug treatment is ineffective.

• Nd:YAG-Aa3epOM through the iridectomy hole, the hyaloid membrane is destroyed and the ciliary block is eliminated. In pseudophakia, the posterior capsulotomy is performed first, then the anterior hyaloid membrane is destroyed.
• Pars plana vitrectomy is performed when laser therapy is ineffective. Sufficient volume of vitreous removed allows aqueous humor to move freely to the anterior chamber. If vitrectomy is not possible due to fluid accumulation, aspiration should be performed using a needle inserted 3.5 mm just beyond the limbus toward the center of the eyeball.

"Dysfunction" of the filter cushion

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Clinical course

Satisfactory filtration: low intraocular pressure and a pronounced type 1 or 2 filtration pad.

• type 1 - thin-walled and polycystic cushion, often with transconjunctival filtration;
• Type 2 - low, thin-walled, diffuse filtration zone, avascular relative to the surrounding conjunctiva. Conjunctival epithelial microcysts are clearly visible at high magnification.

Filtration cushion "dysfunction": increased intraocular pressure and type 3 or 4 filtration cushion.

• type 3 - due to episcleral fibrosis, the scleral flap is not associated with microcysts and has characteristic dilation of superficial blood vessels;
• Type 4 - encapsulated filtration pad (Tenon's cyst), which appears 2-8 weeks after surgery as a limited, fluid-filled formation with depressions in the hypertrophied Tenon's capsule and superficial blood vessels.

The recesses retain aqueous humor and block filtration; sometimes the ophthalmotonus level does not change due to adequate functioning of adjacent zones. Risk factors: previous operations with conjunctival dissection, laser trabeculoplasty, use of local sympathomimetics, and an encapsulated filtration pad on the fellow eye.

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Reasons for failures

Extraocular

• Subconjunctival and episcleral fibrosis are the most common causes of failure, but a properly formed cushion is never delimited. Intra- or postoperative subconjunctival hemorrhage increases the risk of subsequent fibrosis.
• Encapsulation of the filtration cushion.

Scleral

• Excessive tension of the scleral flap.
• Gradual scarring in the scleral bed area, which leads to blockage of the fistula.

Intraocular

• Blockage of the sclerostomy opening by vitreous body, blood or uveal tissue.
• Blockage of the internal opening by various thin membranes from the surrounding tissues (cornea or sclera). This may be the result of poor surgical technique.

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Tactics for unfavorable outcomes

Depends on the etiology and is eliminated as follows.

Compression of the eyeball to enhance the outflow of aqueous humor through the created fistula.

• finger massage-compression through the lower eyelid with closed eyes and looking forward. Pressure is applied for 5-10 seconds, after which the filtration zone is monitored. If the fistula is completely closed, the level of intraocular pressure and the state of the filtration cushion will not change. With effective compression, the intraocular pressure will decrease and the filtration shaft will increase. The patient needs to independently repeat the massage several times a day;
• local compression with biomicroscopic control under local anesthesia using the application of a moistened cotton swab, which is placed in the area of the projection of the scleral flap to improve outflow.

Manipulations with scleral sutures are possible on the 7-14th day after surgery if there is high intraocular pressure, a flat cushion and a deep anterior chamber.

• adjustable stitches can be loosened or removed depending on the technique used to apply them;
• Argon laser suturolysis of scleral sutures is possible if adjustable sutures have not been used. Such sutures are cut through a special Hoskins goniolens or a four-mirror goniolens. The duration of laser exposure is 0.2 sec, the light spot size is 50 μm and the power is 500-700 mW.

Needling of the cystic cushion is performed under local anesthesia and biomicroscopic control. 1 ml of a balanced solution is administered subconjunctivally. The needle is also used to create 2 mm micro-incisions in the fibrous wall of the cystic cushion without violating the integrity of the conjunctiva.

Subconjunctival injections of 5-fluorouracil 7-14 days after surgery to suppress episcleral fibrosis are used at a dose of 5 mg (0.1 ml at 50 mg/ml), inserting the needle at a distance of 10 mm from the filter pad.

NdrYAG laser is used in two cases:

• internal action to open a fistula blocked by any tissue detected during gonioscopy, although the filtration cushion has been formed;
• External transconjunctival exposure in late episcleral fibrosis of the filtration bleb.

Revision of the surgical site to control the existing fistula or creation of a new one in a different location. In such cases, adjunctive antimetabolite therapy may improve the success of the surgical intervention.

Drug therapy is prescribed when the surgery performed is not effective enough.

Late external filtration cushion fistula

Cause: diastasis of the conjunctiva above the sclerostomy zone after the use of antimetabolites, especially mitomycin C, and necrosis of the superficial epithelium of the conjunctiva.

Complications of undiagnosed fistulas: corneal dystrophy, formation of anterior peripheral synechiae, hemorrhagic suprachoroidal detachment, chorioretinal folds, hypotony, maculopathy, intraocular infection.

Signs

• Hypotension and avascular cystic cushion.
• The Seidel test is initially negative, only numerous areas of blurred spots (sweating) are noted. Later, when the opening is formed, a positive test is recorded with a pronounced external fistula.
• In some cases, a shallow anterior chamber and choroidal detachment are noted.

Treatment is difficult (none of the methods presented below are universal).

• Initial measures for severe hyperfiltration in the early postoperative period are rarely successful;
• The next steps depend on whether the filtration is simply sweating or is due to a hole being formed.
  • "Sweating" filter pads can be blocked by injection of autologous blood, the use of tissue glue or tension sutures.
  • In the presence of a complete opening, revision of the surgical area is required with plastic surgery of the filtration cushion with a conjunctival flap, excision of the existing cushion and suturing of the sclera to limit the outflow through the scleral opening.

Hypotension and avascular cystic cushion

A thin-walled filter pad with a positive Seidel test after the use of antimetabolites is a potential entry point for infection. The patient should be warned to contact a physician if redness, discharge, or blurred vision occurs. Traumatic manipulations (e.g., insertion of contact lenses or gonioscopy) should be avoided.

Other risk factors include complete drainage (eg, Scheie thermosclerostomy), low or atypical location of the filtration zone, and prolonged antibiotic instillation after surgery.

Blebites

The vitreous body is not involved in the process.

They manifest as moderate discomfort and redness, which usually last for several days.

Signs

• Paleness of the filtration cushion (the so-called “milky” cushion).
• Signs of anterior uveitis may be absent (stage 1) or present (stage 2).
• The fundus reflex is unchanged.

Treatment: fluoroquinolone or other drugs used in the treatment of bacterial keratitis. This is usually sufficient, but the patient must be observed for some time to exclude the possibility of vitreous involvement in the inflammatory process.

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Blebitis associated with endophthalmitis

They manifest themselves acutely, with a sharp deterioration in vision, pain and redness.

Signs

• Light yellow "milky" filter pad.
• Clinical presentation of severe uveitis with hypopyon.
• Bitrate and the emergence of pathological reflex.

Treatment: vitreous biopsy and intravitreal antibiotics.

In this regard, trabeculectomy is performed to further reduce ophthalmotonus. This non-penetrating type of intervention involves cutting out two scleral flaps and excising the deep layers of the sclera while preserving a thin membrane consisting of the trabecula and Descemet's membrane, through which aqueous humor leaks from the anterior chamber into the subconjunctival space.

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Deep sclerectomy

1. A conjunctival incision is made with the base towards the fornix.
2. A thin superficial scleral flap is separated down to the transparent part of the cornea.
3. A second scleral flap 4 mm wide is cut from the deep layers of the sclera to the area of Schlemm's canal.
4. A collagen drain is placed into the scleral bed.
5. Free reposition of the superficial scleral flap is performed with suturing of the conjunctival incision.

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Viscocanalostomy

1. A conjunctival flap is formed with the base towards the fornix.
2. A superficial flap of the sclera is cut out to 1/3 of its thickness.
3. The second flap is cut from the deeper layers so that it provides access to the Schlemm's canal.
4. A high-molecular viscoelastic is injected into the lumen of Schlemm's canal using a special hollow needle.
5. A "window" is created in Descemet's membrane by carefully dissecting the sclera under a deep scleral flap in the area above Schlemm's canal, and then this area of the sclera is excised.
6. The superficial scleral flap is tightly sutured to minimize subconjunctival drainage of aqueous humor and form a filtration cushion.
7. Viscoelastic is injected into the sclerotomy area.
8. The conjunctiva is sutured.

Despite successful treatment, the risk of recurrence of infection remains.