Ординатура / Офтальмология / Английские материалы / Oxford American Handbook of Ophthalmology_Tsai, Denniston, Murray_2011

308 CHAPTER 10 Glaucoma

Glaucoma drainage device (GDD) surgery

The tube versus trabeculectomy (TVT) study compared Baerveldt drainage implants with trabeculectomy with MMC in patients with previous ocular surgery (either a failed trabeculectomy or prior cataract surgery), and at 1 year demonstrated that trabeculectomy patients obtain lower IOPs with fewer medications, but had higher incidences of hypotony and require more reoperations.

The study determined that Baerveldt implants maintain IOP control comparable to that with antimetabolite-augmented trabeculectomy.

Indication

When to operate

Historically, GDD surgery was reserved for patients who were at high risk for failure due to fibrosis of the sclerectomy or conjunctiva. More commonly, GDDs are used for the same indications as for trabeculectomy: inadequate IOP, progression of glaucomatous damage, or intolerance of medical therapy.

GDDs may be more appropriate in children and in patients with lid disease or lifestyles that predispose to trabeculectomy bleb infections (gardening, swimming, etc)

Which tube

Nonvalved implants (Baerveldt/Molteno) require ligation sutures, as resistance is provided by the encapsulated plate. Filtration prior to encapsulation can lead to profound hypotony. Valved implants (Ahmed) have a leaflet-type valve set to around 10 mmHg and require no ligation suture.

Many surgeons use only one type of tube, on the basis of their training and comfort level. Some surgeons vary the type of tube used according to the clinical scenario: a patient with very high IOP (neovascular glacuoma) who needs immediate IOP lowering may receive an Ahmed valve implant; a patient who is intolerant of medications, has moderately elevated IOPs, and can tolerate 4–6 weeks of higher IOPs may receive a Baerveldt implant.

Modifications of the Baerveldt to allow drainage prior to release of the ligation suture involve the placement of small, full-thickness slits in the tube between the anterior chamber and the ligature, allowing some restricted flow out of the tube.

Method

Standard GDD placement with fornix-based limbal incision is described here.

•Consent: explain what the operation does and the possible complications, including encapsulation with return to high IOP, hypotony, hemorrhage, worsened vision, and risk of acute postoperative infection as well as corneal scarring, cataract formation, exposure of the implant, and double vision.

•Preoperative: consider stopping aqueous suppressants a couple of days before surgery.

•Prep with 5% povidone iodine and drape.

•Place corneal traction suture superotemporally.

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•10 mm limbal peritomy with 2 mm radial relaxing incisions at ends of limbal incision.

•Dissect a subtenon’s pocket between the superior and lateral rectus.

•Ahmed implant.

•Prime the Ahmed valve with balanced salt solution (BSS) on a 30g cannula.

•Measure 8 mm posterior to the limbus and suture the Ahmed plate to globe with partial-thickness scleral passes of 8-0 nylon, rotate knots.

•Baerveldt implant.

•Ligate tube about 1 mm from plate with 7-0 Vicryl suture (will dissolve and open the tube in about 4–6 weeks).

•Use BSS on a cannula to verify watertight ligation of tube.

•Capture superior and lateral rectus muscles with muscle hooks and pass plate wings under muscles.

•With plate anteriorly against muscle insertions, suture plate to globe with partial-thickness scleral passes of 8-0 nylon, rotate knots.

•Four or more venting tube slits can be created with a paracentesis blade or the needle of the 7-0 Vicryl suture placed between the anterior chamber and the ligature.

•Create a paracentesis and consider addition of viscoelastic solution.

•Trim the tube to length with a bevel up, aiming for about 2 mm in the eye.

•Use a 23g needle to enter the anterior chamber from about 1.5 mm posterior to the limbus, aiming to have the needle (and ultimately the tube) parallel with the iris, without contacting intraocular structures.

•Verify the tube position; if not ideal, then remove the tube, close the sclerostomy with 10-0 nylonsuture (instead of 8-0 vicryl), and repass the 23g needle in another position.

•Suture the tube to the sclera with 8-0 Vicryl or 10-0 nylon

•Secure scleral reinforcement graft (tutoplast sclera or pericardium) over the tube with 8-0 Vicryl.

•Close conjuctiva with wing or running suture.

•Use topical antibiotic (e.g., gatifloxacin 4x/day) and steroid (e.g., prednisolone acetate 1% four times a day initially, tapering down over 2 months).

•Review at 1 day and 1 week, then according to result.

310 CHAPTER 10 Glaucoma

Glaucoma drainage device: complications

Intraoperative complications

•Conjunctival flap damage: button holes, especially if previous surgery.

•Bleeding may be conjunctival, scleral, from the iris, or, most seriously, suprachoroidal.

•Scleral perforation with retinal damage.

•Damage to crystalline lens from improper needle pass or tube position.

•Wound leak from damaged conjunctiva or inadequate closure.

Early postoperative complications

Shallow AC

Grade as for trabeculectomy. Pay extra attention to the potential for damage caused by tube against corneal endothelium or crystalline lens.

Specific treatment will depend on the underlying cause, but in general, if there is a risk of corneal decompensation from lenticulocorneal and/or tube-corneal touch, urgent measures are required to reform the AC or to restrict flow into the tube (e.g., balanced salts, viscoelastic, or gas).

Low IOP/hypotony

Manage as for trabeculectomy; it may be a result of a non-tight sclerostomy, faulty valve (Ahmed), incomplete ligature (Baerveldt, Molteno), or aqueous hyposecretion.

High IOP

Early

This may result from failure to prime the valved tube, inadequate or absent venting slits on a ligated nonvalved tube, or tube occlusion with fibrin, blood, viscoelastic, vitreous, etc. Many times, IOP will improve with time and can be managed temporarily with topical IOP-lowering agents. Occasionally, AC tap, anterior chamber tissue plasminogen activator (tPA), or tube irrigation or revision is necessary.

If intraocular structures such as the iris are occluding the tube, a 27g needle, argon laser iridoplasty, or Nd:YAG iridotomy can be used to clear the obstruction. Occasionally, surgical revision is necessary.

Late

Valve failure or occlusion (fibrin, vitreous, etc) or encapsulation of plate and mechanical restriction of aqueous diffusion may result in high IOP. Needle bleb (± 5-FU injection), and IOP should decrease. If IOP is still high, then the tube or valve is occluded.

Diplopia

This may improve over time. If persistent in primary gaze, consider tube revision or removal. If present only in extreme gaze and IOPs are well controlled, balance the risk of glaucomatous damage with revision or removal of the implant with disability from diplopia.

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Exposure of implant

Excise down-growth of epithelium that prevents proper wound closure. Reinforce exposed portion of implant with donor tissue (sclera, pericardium, cornea, etc). Advance conjunctiva, if possible, or place conjunctival graft. If exposure persists, consider removing implant.

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314 CHAPTER 11 Uveitis

Anatomy and physiology

Uveitis describes intraocular inflammation of both the uveal tract itself and neighboring structures (e.g., retina, vitreous, optic nerve). Uveitis is relatively common with an incidence of around 15 new cases per 100,000 population per year. Acute presentations (often recurrences) make a significant contribution to emergency ophthalmic presentations.

Anatomy

The uveal tract comprises the iris, ciliary body, and choroid.

Iris

The iris is the most anterior part of the uveal tract. It extends from a relatively thin root in the anterior chamber angle to the pupil. It is divided by a collarette into the central pupillary zone and the peripheral ciliary zone.

The anterior surface is made of connective tissue with an incomplete border layer overlying the stroma that contains the vessels, nerves, and sphincter pupillae. The sphincter pupillae is a ring of true smooth muscle supplied by the short ciliary nerves (CN III) under parasympathetic control. The posterior surface comprises an epithelial bilayer.

The anterior layer is lightly pigmented and contains the radial myoepithelial processes of the dilator pupillae that extend from the iris root. These are supplied by two long ciliary nerves (CN V1) under sympathetic control.

The anterior layer is continuous with the pigmented outer layer of the ciliary body. The posterior epithelial layer is cuboidal, densely pigmented, and continuous with the nonpigmented inner layer of the ciliary body.

Ciliary body

The ciliary body comprises the ciliary muscle and ciliary epithelium, arranged anatomically as the pars plana and pars plicata (containing approximately 70–80 ciliary processes). The ciliary epithelium is a cuboidal bilayer arranged apex to apex with numerous gap-junctions.

The inner layer is nonpigmented, with high metabolic activity, and posteriorly is continuous with the neural retina. The outer layer is pigmented and posteriorly continuous with the retinal pigmented epithelium (RPE).

Choroid

The choroid is a vascular layer extending from the ora serrata (where it is 0.1 mm thick) to the optic disc (0.3 mm thick). From the inside out, it comprises Bruch’s membrane (RPE basement membrane, collagen, elastin, collagen, choriocapillaris basement membrane), the choriocapillaris (capillary layer), the stroma (medium-sized vessels in Sattler’s layer, large vessels in Haller’s layer), and the suprachoroid (a potential space).

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Physiology

Iris

Pupillary functions include light regulation, depth of focus, and minimization of optical aberrations. The iris also maintains the blood–aqueous barrier (tight junctions between iris capillary endothelial cells) and contributes to aqueous circulation and outflow (uveoscleral route). In inflammation, there is breakdown of the blood–aqueous barrier, leading to flare and cells in the anterior chamber (AC).

Ciliary body

The nonpigmented layer contributes to the blood–aqueous barrier (tight junctions between nonpigmented epithelial cells). The nonpigmented and pigmented layers together are responsible for aqueous humor production. Contraction of the ciliary muscle permits accommodation and increases trabecular outflow. The ciliary body also contributes to the uveoscleral outflow route.

Choroid

With 85% of the ocular blood flow (cf. <5% for the retina), the choroid provides effective supply of oxygen and nutrients, removal of waste products, and heat dissipation. It may also have a significant role in ocular immunity.