Ординатура / Офтальмология / Английские материалы / Clinical Ophthalmology A Systematic Approach 7th Edition_Kanski, Bowling_2011

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Trabeculectomy

Trabeculectomy lowers IOP by creating a fistula, to allow aqueous outflow from the anterior chamber to the sub-Tenon space. The fistula is protected or ‘guarded’ by a superficial scleral flap (Fig. 10.83). The procedure is usually performed when medical therapy has failed to achieve adequate control of IOP.

Fig. 10.83 Trabeculectomy principles. (A) Pathway of aqueous egress following trabeculectomy; (B) appearance frominside the eye following completion

Technique

aThe pupil is miosed.

b A bridle suture is inserted either into peripheral clear cornea superiorly or into the superior rectus muscle.

cA limbal or fornix-based flap of conjunctiva and Tenon's capsule is fashioned superiorly.

dEpiscleral tissue is cleared. An outline of the proposed superficial scleral flap is made with wet-field cautery.

eIncisions are made along the cautery marks through two-thirds of scleral thickness, to create a ‘trapdoor’ lamellar scleral flap (Fig. 10.84A). This flap may be rectangular (3 × 4 mm) or triangular, according to preference.

f The superficial flap is dissected forwards until clear cornea has been reached (Fig. 10.84B). g A paracentesis is made in superotemporal peripheral clear cornea.

h The anterior chamber is entered along the width of the trapdoor flap. i A block of deep sclera is excised with a punch (Fig. 10.84C).

jA peripheral iridectomy is performed in order to prevent blockage of the internal opening (Fig. 10.84D); some surgeons omit this step in pseudophakic eyes or those with a deep anterior chamber.

kThe superficial scleral flap is sutured at its posterior corners so that it is lightly apposed to the underlying bed.

lAlternatively, the flap may be sutured tightly with releasable or lysable sutures to reduce the risk of postoperative scleral flap leakage and shallow anterior chamber.

mBalanced salt solution is injected into the anterior chamber through the paracentesis. This tests the patency of the fistula and facilitates the detection of any holes or leaks in the flap.

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nConjunctiva/Tenon's capsule flap is sutured. Irrigation through the paracentesis is repeated to produce a bleb, which is then checked for leakage.

o A drop of atropine 1% is instilled; when no iridectomy has been performed, pilocarpine 2% may be used instead.

pA steroid and an antibiotic are injected under the inferior conjunctiva.

qSteroid-antibiotic drops are used four times daily for 1–2 weeks and then changed to prednisolone acetate 1% or dexamethasone 0.1% for a further 8–10 weeks.

Fig. 10.84 Trabeculectomy technique. (A) Outline of superficial scleral flap; (B) dissection of superficial scleral flap; (C) excision of deep scleral tissue with a punch; (D) peripheral iridectomy

Shallow anterior chamber

A shallow anterior chamber may be due to (a) pupillary block, (b) overfiltration or (c) malignant glaucoma (aqueous misdirection). Severe and sustained shallowing is uncommon (Fig. 10.85A and B), the chamber re-forming spontaneously in most cases. However, those that do not may develop severe complications such as peripheral anterior synechiae, corneal endothelial damage (Fig. 10.85C) and cataract (Fig. 10.85D).

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Fig. 10.85 Shallow anterior chamber. (A) Peripheral iris-corneal apposition; (B) pupillary border-corneal apposition; (C) lenticulo-corneal apposition resulting in corneal oedema; (D) cataract following inappropriate management

(Courtesy of J Schuman, V Christopoulos, D Dhaliwal, M Kahook and R Noecker, from Lens and Glaucoma, in Rapid Diagnosis in Ophthalmology, Mosby 2008 – fig. A)

Pupillary block

Pupillary block may occur with a non-patent peripheral iridectomy.

1Signs

•High IOP and flat bleb.

•Negative Seidel test.

•Iris bombé with a non-patent iridectomy.

2Treatment involves YAG laser to the pigment epithelium at the iridectomy site if the anterior iris stroma appears to have been largely penetrated, or a new laser iridotomy is performed.

Overfiltration

Overfiltration may be caused by scleral flap leakage due to insufficient resistance to outflow by the lamellar scleral flap, but bleb leakage through an inadvertent buttonhole or due to inadequate closure of the conjunctiva and Tenon capsule is perhaps the most common cause.

1Signs

•Low IOP with a well formed bleb in a scleral flap leak and flat in a bleb leak.

•Seidel test is negative in a scleral flap leak and a positive in a bleb leak (Fig. 10.86A).

•The cornea may manifest signs of hypotony such as folds in Descemet membrane.

•Choroidal detachment may be present (Fig. 10.86B).

2Treatment depends on the cause and degree of shallowing.

aInitial conservative treatment in eyes without lens-corneal touch is observation, with atropine to prevent PAS formation and malignant glaucoma.

bSubsequent treatment if the above measures are ineffective involves temporary tamponade of the conjunctiva to enhance spontaneous healing by simple pressure patching, a large diameter soft bandage contact lens, a collagen shield or a Simmons shell designed for the purpose.

cDefinitive treatment often consists of inserting additional conjunctival sutures, and if necessary placing a transconjunctival scleral flap suture. If potentially serious shallowing is present, the anterior chamber can be reformed with a viscoelastic. Choroidal detachments rarely require drainage.

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Fig. 10.86 (A) Positive Seidel test; (B) choroidal detachment

Malignant glaucoma

Malignant glaucoma is rare but serious. It is caused by anterior rotation of the ciliary processes and iris root, often with aqueous misdirection (ciliolenticular block); blockage of aqueous flow occurs in the vicinity of the pars plicata of the ciliary body, so that aqueous is forced backwards into the vitreous.

1Signs

•High IOP and absent bleb.

•Negative Seidel test.

2Treatment

aInitial treatment is with mydriatics (atropine 1% and phenylephrine 10%) to dilate the ciliary ring and increase the distance between the ciliary processes and the equator of the lens, thereby tightening the zonule and pulling the lens posteriorly into its normal position. Intravenous mannitol may be used if mydriatics are ineffective in order to shrink the vitreous gel and allow the lens to move posteriorly.

bSubsequent treatment if medical therapy fails is with Nd:YAG laser fired through the iridectomy in order to disrupt the anterior hyaloid face, reduce the vitreous volume and break any ciliary block. In pseudophakic eyes, laser posterior capsulotomy and disruption of the anterior hyaloid face should be performed. Cyclodiode may be effective in some cases. Pars plana vitrectomy is performed if laser therapy fails: sufficient vitreous gel is excised to allow free flow of aqueous to the anterior chamber.

Failure of filtration

Diagnosis

A normally functioning bleb should be slightly elevated, avascular and show superficial microcysts (Fig. 10.87A). Poor filtration is indicated by increasing IOP and a bleb with one of the following appearances:

1Flat without vascularization (Fig. 10.87B).

2 Vascularized bleb due to episcleral fibrosis (Fig. 10.87C).

3Encapsulated bleb (Tenon cyst) which typically develops 2–8 weeks postoperatively. It is characterized by a localized, highly elevated, dome-shaped, firm, fluid filled cavity of hypertrophied Tenon capsule with engorged surface blood vessels (Fig. 10.87B).

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Fig. 10.87 Filtering blebs. (A) Normal; (B) flat non-functioning; (C) vascularized; (D) encapsulated – Tenon cyst

Causes

Causes of failure can be classified according to the site of blockage:

1Extrascleral causes include (a) subconjunctival and episcleral fibrosis and (b) occasionally bleb encapsulation.

2Scleral causes include (a) an over-tight suturing of the scleral flap, and (b) gradual scarring in the scleral bed may lead to obstruction of the fistula at that level.

3Intraocular causes are uncommon and include (a) blockage of the sclerostomy by vitreous, blood or uveal tissue and (b) obstruction of the internal opening by a variety of thin membranes derived from surrounding cornea or sclera.

Management

Management of filtration failure depends on the cause and may involve one or more of the following:

1Ocular compression in an effort to force outflow through the surgical fistula may be performed by (a) digital compression through the lower lid with the eyes closed and the patient looking straight ahead or (b) at the slit-lamp with a moistened sterile cotton bud at the edge of the scleral flap in an attempt to promote outflow.

2Suture manipulation may be considered 7–14 days postoperatively if the eye has high IOP, a flat bleb and a deep anterior chamber. Releasable sutures can be cut or released according to the technique of initial placement. Argon laser suture lysis is useful if releasable sutures have not been used. It may be performed through a suture lysis lens or a Zeiss four-mirror goniolens.

3Needling of an encysted bleb may be performed at the slit-lamp or operating microscope under topical anaesthesia. It can be augmented with 5-fluorouracil to enhance the success rate.

4Subconjunctival injection of 5-fluorouracil may be used in the first 7–14 days to suppress episcleral fibrosis; 5 mg (0.1 mL of 50 mg/mL solution) is injected approximately 10 mm away from the bleb and can be repeated as necessary.

Late bleb leakage

1Cause is disintegration of conjunctiva overlying the sclerostomy following previous operative application of antimetabolites, particularly mitomycin C. Necrosis of the surface epithelium results in transconjunctival drainage of aqueous.

2Complications of untreated leaks include infection and hypotony maculopathy (see Ch. 14).

3Signs

•Low IOP and an avascular cystic bleb.

•Seidel testing may initially be negative with only multiple punctate staining areas (sweating) being seen. Later the formation of a hole results in gross leakage with a positive test.

•Shallow anterior chamber and choroidal detachment may be present in severe cases.

4 Treatment is difficult. The following are some of the methods used, none of which are universally successful. a Initial treatment is as for early postoperative overfiltration but is seldom successful.

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bSubsequent treatment depends on whether the leakage involves merely ‘sweating’ or is due to a hole.

•Sweating blebs may be treated by injection of autologous blood into the bleb, ‘compression’ sutures or a transconjunctival scleral flap suture.

•Full thickness holes usually require revisional surgery, such as conjunctival advancement to hood the existing bleb, free conjunctival patch autografts with removal of the existing bleb and scleral grafts to limit flow through the sclerostomy.

Bleb-associated bacterial infection and endophthalmitis

Glaucoma filtration-associated infection is classified as limited to the bleb (blebitis) or endophthalmitis, although there is some overlap. The incidence of blebitis following trabeculectomy with mitomycin has been estimated to be up to 5% per year but many studies show a for lower rate.

Pathogenesis

Adjunctive antifibrotic agents (mitomycin C, 5-fluorouracil) are frequently used to increase the success of glaucoma filtration surgery. The use of these agents can lead to a very thin-walled drainage bleb (Fig. 10.88A) that significantly increases the risk of late-onset infection. The infection presumably gains access directly through the thin and avascular wall of the drainage bleb. All patients with such blebs should be warned of the possibility of late infection and strongly advised to report immediately should they develop a red and sticky eye, or blurred vision (RSVP – red, sticky, visual loss, pain).

1Risk factors include blepharitis, higher does of mitomycin, long-term topical antibiotic use, an inferior or nasally placed bleb, and bleb leak. Late bleb leaks should be treated aggressively to reduce the risk of infection.

2Pathogens. The most frequent are H. influenzae, Streptococcus spp., and Staphylococcus spp. The often poor visual prognosis is related to the virulence of these organisms.

Fig. 10.88 (A) Thin-walled bleb; (B) blebitis; (C) endophthalmitis with hypopyon

Blebitis

Blebitis describes infection without vitreous involvement.

1Presentation is with mild discomfort and redness.

2Signs

•A white bleb that appears to contain inflammatory material (Fig. 10.88B).

•Anterior uveitis may be absent.

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• The red reflex is normal.

3Investigation. A conjunctival swab should be taken; a sample should not be aspirated from within the bleb.

4Treatment

•Topical ofloxacin and cefuroxime (or vancomycin 50 mg/mL) hourly.

•Oral co-amoxiclav 500/125 mg t.i.d. and ciprofloxacin 750 mg b.d. for 5 days; azithromycin 500 mg daily for 5 days is an alternative.

Endophthalmitis

1Presentation is with a short history of rapidly worsening vision, pain and redness.

2Signs

•White milky bleb containing pus.

•Severe anterior uveitis that may be associated with hypopyon (Fig. 10.88C).

•Vitritis and impairment of the red reflex.

3Treatment involves topical and systemic therapy as for blebitis. Intravitreal antibiotics as for acute post-operative endophthalmitis following cataract extraction (see Ch. 9) should be considered if there is no early response.

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Non-penetrating surgery

Overview

In non-penetrating filtration surgery the anterior chamber is not entered and the internal trabecular meshwork is preserved, thus reducing the incidence of postoperative overfiltration and hypotony and its potential sequelae. Two lamellar scleral flaps are fashioned and the deep flap excised leaving behind a thin membrane consisting of trabeculum/Descemet membrane through which aqueous diffuses from the anterior chamber to the subconjunctival space. The surgery is technically challenging and requires meticulous dissection of a deep scleral flap without entering the delicate anterior trabecular meshwork.

Indications

The main indication for non-penetrating surgery is POAG, although other open-angle glaucomas may also be amenable. In general the IOP reduction is less than that achieved by trabeculectomy, so that topical medication often needs to be recommenced. Conventional filtration is therefore still the procedure of choice when the target IOP is in the low teens though it is probably associated with a lower risk of ‘snuffing out’ central vision when advanced damage is present.

Technique

1Deep sclerectomy in which a Descemet window is created, that allows aqueous seepage from the anterior chamber (Fig. 10.89). Subsequent egress is subconjunctival resulting in a shallow filtration bleb, as well as along deeper suprachoroidal routes. The longterm results can be enhanced by using a collagen implant at the time of surgery and postoperative application of Nd:YAG laser to the meshwork at the surgical site using a gonioscope (goniopuncture).

2Viscocanalostomy involves the creation of a filtering window, identification and dilatation of Schlemm canal with high density viscoelastic. The superficial scleral flap is sutured tightly so that subconjunctival fluid outflow and bleb formation are minimized. The procedure probably causes inadvertent microscopic ruptures in the juxtacanalicular tissue and meshwork. A variation on this procedure involves the cannulation of the entire circumference of Schlemm canal with a microcatheter (canaloplasty).

Fig. 10.89 Non-penetrating filtration surgery: deep sclerectomy. (A) Dissection of scleral flap; (B) dissection into clear cornea exposing Schlemmcanal; (C) collagen implant; (D) shallow diffuse avascular bleb

(Courtesy of A Mermoud)

Trabectome

The Trabectome is a novel microelectrosurgical device which approaches the angle ab interno under direct vision using a gonioscopy lens, to remove a strip of trabecular meshwork and inner wall of Schlemm canal (‘trabeculotomy’). Whilst it does not seem to lower the intraocular pressure as effectively as trabeculectomy, the safety profile is better.

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Antimetabolites in filtration surgery

Indications

Adjunctive antimetabolites inhibit the natural healing response that may preclude successful filtration surgery. They should, however, be used with caution because of the serious nature of potential complications, and usually considered in the presence of known risk factors for failure of trabeculectomy. In uncomplicated glaucoma the use of low-dose antimetabolites may improve long-term control of IOP but this benefit should be weighed against possible complications such as corneal epithelial defects, chronic hypotony and late-onset bleb leakage.

1High risk factors

•Neovascular glaucoma.

•Previous failed trabeculectomy or artificial filtering devices.

•Certain secondary glaucomas (e.g. inflammatory, post-traumatic angle recession and iridocorneal endothelial syndrome).

2Intermediate risk factors

•Patients on topical medication (particularly sympathomimetics) for over 3 years.

•Previous conjunctival surgery.

•Previous cataract surgery.

3Lower risk factors

•Black patients.

•Patients under the age of 40 years.

5-fluorouracil

5-fluorouracil (5-FU) inhibits DNA synthesis and is active on the ‘S’ phase (synthesis phase) of the cell cycle. Fibroblastic proliferation is inhibited, but fibroblastic attachment and migration are unaffected. It is the antimetabolite of choice in elderly patients who have risk factors for failure. The drug can be used in one or both of the following ways:

1 Intraoperative application is as follows:

aThe conjunctival flap is dissected.

bA small cellulose sponge is soaked in a 50 mg/mL solution of 5-FU.

cThe sponge is placed under the dissected flap of Tenon's capsule at the site of filtration making sure that the edges of the conjunctival incision are not exposed to the drug.

dThe sponge is removed after 5 minutes.

e The space between the conjunctiva and episclera is thoroughly irrigated with balanced salt solution.

fThe trabeculectomy is completed.

2 Subconjunctival injection of 5 mg daily postoperatively for up to 7 days as follows: a The eye is anaesthetized with a cotton pledget soaked in amethocaine.

b 0.5 mL of 5-FU (50 mg/mL) is drawn up into a tuberculin syringe. c The 27-guage needle is exchanged for a 30-guage needle.

d The bubbles are shaken to the top of the syringe.

e0.4 mL of 5-FU is expressed so than only 0.1 mL remains in the syringe.

fThe contents of the syringe are injected subconjunctivally 180° away from the filtration site.

g Any reflux is caught on a dry cotton-tipped applicator or irrigated out.

Mitomycin C

Mitomycin C (MMC) is an alkylating agent rather than an antimetabolite, and selectively inhibits DNA replication, mitosis and protein synthesis. The drug inhibits proliferation of fibroblasts, suppresses vascular ingrowth and is much more potent than 5-FU. Optimum concentration and exposure time is not known and vary between 0.2–0.5 mg/mL and 1–5 minutes. In general, low or intermediate risk indicates use of a low concentration (0.2 mg/mL), whilst high risk implies the need for a higher concentration (0.4–0.5 mg/mL). Higher concentrations and extended exposure times are associated with an increased risk of complications. The technique of intraoperative application is the same as for 5-FU and great care should be taken to prevent contamination of the anterior chamber. MMC can also be applied externally to the bleb with a sponge in the postoperative period.

Complications

1 Corneal epithelial defects and postoperative wound leaks occur mainly after the use of 5-FU.

2Cystic thin-walled blebs may occur following the use of both 5-FU and mitomycin C and may predispose to chronic hypotony, late-onset bleb leak and endophthalmitis.

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