Open Angle Glaucoma surgery

Surgery

• Surgery therapy of glaucoma is undertaken when:

1. medical therapy is not appropriate, not tolerated, not effective, or not properly utilized by a particular patient
2. the glaucoma remains uncontrolled with either documented progressivedamage or a very high risk of further damage.

• Surgery is usually the primary approach for infantile and pupillary-blockglaucoma.
• When surgery is indicated, the clinical setting must guide the selection of the appropriate procedure.

1. trabeculectomy and its variations
2. non-penetrating filtration procedures
3. glaucoma drainage tube implants
4. angle surgery for congenital glaucoma
5. ciliary body ablation.
6. iridectomy
7. gonioplasty

Surgery For Open Angle Glaucoma

• Surgery is indicated when IOP cannot be maintained by nonsurgical therapies at a level considered low enough to prevent further pressure-related damage to theoptic nerve or visual field loss. Surgery has traditionally been considered only

when medical therapy has failed and is associated with long-term risks of blebassociated problems, cataracts, and infection.

• The glaucoma may be uncontrolled for various reasons:

1. Maximal medical therapy fails to adequately reduce IOP
2. The amount of medical therapy necessary to control IOP is not well tolerance or places the patient at unacceptable risk
3. Optic nerve cupping or visual field loss is progressing despite apparent “adequate” reduction of IOP with medical therapy.
4. The patient cannot comply with the necessary medical regimen

Laser Trabeculoplasty (LTP)

• Mechanism of action

• LTP stimulates the growth of trabecular meshwork endothelial cells → restorestrabecular meshwork function → improves the outflow facility

• Indications

1. Patients with glaucoma on maximum tolerated medical therapy who require lower IOP and in whom the angle is open on gonioscopy.
2. LTP effectively reduces IOP in patients with POAG, pigmentary glaucoma, and exfoliation syndrome. Aphakic and pseudophakic eyes may respond less favorably than phakic eyes; therefore, LTP may be more effective before than after cataract surgery.
3. The role of initial LTP in POAG is at least as effective as medications for the first 2 years. LTP may postpone the need for conventional surgery or additional medications. When effective, LTP is expected to lower IOP 20%-25%.

• Relative contraindications

1. Inflammatory glaucoma
2. Membrane in the angle
3. Young patients who have developmental defects.
4. The lack of effect in the fellow eye

• Preoperative evaluation

1. Optic nerve evaluation
2. Visual field examination
3. Gonioscopy to check that the angle must be open. The amount of pigment in the angle will help determine the laser settings for argon laser; a more pigmented angleresponds to lower laser energy

• Argon laser procedure

1. Set at 300-1000 mW, 50 um, and 0.1 second.Laser beam is focused through a gonio lens at the junction of the anterior unpigmented and the posterior pigmented edge of the trabecular meshwork.
2. Laser energy was applied to the entire circumference (360°) of the trabecular meshwork. End point: blanching of the trabecular meshwork or production of a tiny bubble. If a large bubble appears, the power is reduced.
3. Application to the posterior trabecular meshwork tends to produce inflammation, pigment dispersion, prolonged elevation of IOP, and PAS.
4. Diode laser procedure: is similar; set at 600-1000 mW, 75 um, and 0.02second.

• Complications

1. Transient rise in IOP (occurs in 20% of patients), usually evident within thefirst 2-4 hours after treatment. Topical medications shown to blunt the IOPspikes include alpha2-agonists, beta blockers, pilocarpine, and topical CAIs. Hyperosmotic agents, oral CAIs, and ice packs may be helpful in eyes with IOP spikes not responsible to topical medication.
2. Low-grade iritis
3. Persistent elevation of IOP requiring filtering surgery
4. Hyphema
5. Formation of PAS
6. Re-treatment of an angle that has been fully treated has a lower success rate and a higher complication rate than does primary treatment. If initial LTP fails tobring IOP under control, a trabeculectomy should be considered.

Selective Laser Trabeculoplasty

• Q-switched 532 nm Nd:YAG laser trabeculoplasty,the laser targets intracellular melanin.

Incisional Surgery for Open Angle Glaucoma

1. The goal of filtering surgery (fistulizing procedure) is to create a new pathway(fistula) for the bulk flow of aqueous humor from the anterior chamber throughthe surgical defect in the sclera into the subconjunctival and sub-Tenon’s space.
2. The filtering procedure most commonly used is guarded trabeculectomy.

• Indications: a patient with glaucoma on maximum tolerable medical therapy (MTMT) who has had maximal laser benefit and whose optic nerve function is failing or is likely to fail.The physician can determine that the patient is at MTMT only by advancing therapy beyond the tolerated level and documenting intolerance. An alternative concept is core therapy, in which treatment consists of those medications likelyto work well in combination.
• Relative contraindications

1. Blind eye → ciliary body ablation is a better alternative for lowering IOP
2. Active anterior segment neovascularization (rubeosis iridis) or active iritis → the underlying problem should be addressed first, or a surgical alternativesuch as tube implant surgery should be considered.
3. Sustained extensive conjunctival injury or extremely thin sclera fromextensive prior surgery or necrotizing scleritis.
4. Younger or aphakic/pseudophakic patients.
5. Black patients.
6. Patients with uveitic glaucoma or with previously failed filtration procedures

• Preoperative evaluation

1. The patient must be medically stable for an invasive ocular procedure under local anesthesia.
2. Control of preoperative inflammation with corticosteroids helps to reducepostoperative iritis and scarring of the filtering bleb.
3. Anticholinesterase agents should be discontinued if possible and replacedtemporarily by alternative medications at least 2-3 weeks before surgery toreduce bleeding and iridocyclitis.
4. IOP should be reduced as close as possible to normal levels before surgery isperformed, to minimize the risk of expulsive choroidal hemorrhage.
5. Antiplatelet medications should be discontinued.
6. Systemic hypertension should be controlled.
7. Patient should be informed :

• The purpose and expectations of surgery: to arrest or delay progressive visual loss caused by their glaucoma.
• Glaucoma surgery alone rarely improves vision.
• Glaucoma medications may still be required postoperatively
• Surgery may fail completely
• Vision could be lost as a result of surgery
• Glaucoma may progress despite successful surgery
• Patients with far advanced visual field loss or field loss that is impinging on fixation are at risk for total loss of central acuity following a surgical procedure. The possible mechanism of this phenomenon include:

• Cystoid macular edema
• Early postoperative IOP spiking
• Shifting of the lamina, further compromising remaining axons
• Optic nerve ischemia, possibly related to regional anesthesia

Trabeculectomy

• A guarded partial-thickness filtering procedure performed by removing ablock of limbal tissue beneath a scleral flap. The scleral flap providesresistance and limits the outflow of aqueous, thereby reducing the complications associated with early hypotony (such as flat anterior chamber, cataract, serous and hemorrhagic choroidal effusion, macular edema, and optic nerve edema)
• The use of antifibrotic agents (such as mitomycin-C and 5-fluorouracil),combined with techniques of releasable sutures or laser suture lysis, enhancesthe longevity of guarded procedures.
• Succesful trabeculectomy surgery:

1. Involves reducing IOP and avoiding or managing complications
2. Depends on appropriate and timely postoperative intervention to influencethe functioning of the filter.
3. Complete healing of the epithelial and conjunctival wound with incompletehealing of the scleral wound is the goal of this procedure.

• Trabeculectomy procedure :

• Preoperative evaluation
• Exposure.

• A corneal traction suture or superior rectus bridle suture can rotate the globe down, giving excellent exposure of the superior sulcus and limbus.

• Conjunctival wound.

• Fornix-based conjunctival flap → provides better exposure at the limbus; more difficult to achieve a water-tight closure.
• Limbal-based conjunctival flap → technically more challenging but allows for a secure closure well away from the limbus.

• Scleral flap (3-4 mm trapezoidal or rectangular flap).

• The flap is dissected anteriorly into clear cornea.

• Paracentesis

• To control the anterior chamber through instillation of BSS or viscoelastic
• Allows for gradual lowering of IOP
• Intraoperative testing of the patency of the filtration site as well as of the integrity of the conjunctival closure.

• Sclerotomy (with a punch or with sharp dissection).

• The size of the ostomy is determined by the scleral flap and the amount of overlap desired by the surgeon.
• A small amount of tissue should remain at the edges of the ostomy to allow for resistance to outflow from the flap.

• Iridectomy

• To lessen the risk of iris occluding the ostomy
• To reduce the risk of pupillary block

• Closure of scleral flap

• With the advent of laser suture lysis and releasable sutures, many surgeons close the flap relatively tightly to avoid early shallow chambers. After a few days, flap sutures are released to promote filtration.
• Flow should be tested around the flap before closing the conjunctiva.
• Leakage around the flap may be adjusted intraoperatively by the placement of additional sutures, removal of sutures, or application of cautery to shrink the wound edges.

• Closure of conjunctiva

• Fornix-based flap → conjunctiva is secured at the limbus
• Limbal-based flap → conjunctiva and Tenon’s capsule are closed separately or in a single layer.

• Postoperative management

• Topical antibiotics and corticosteroids
• Topical cycloplegic agents or mydriatics
• Sub-Tenon’s corticosteroids or a short course of systemic corticosteroids

• Antifibrotic agents

• 5-fluorouracil (5-FU), a pyrimidine analogue

• 5-FU → deoxynucleotide 5-fluoro-2’-deoxyuridine 5’-monophosphate (FdUMP) → interferes with DNA synthesis through its action on thymidylate synthetase
• Inhibits fibroblast proliferation; reduces scarring after filtering surgery.
• 50 mg/ml on a surgical sponge is used intraoperatively.
• A total of 5 mg in 0.1-0.5 cc can be injected postoperatively.

• Mitomycin-C (MMC), derived from Streptomyces caespitosus

• Acts as an alkylating agent after enzyme activation resulting in DNA crosslinking.
• Most commonly administered intraoperatively by placing a surgical sponge soaked in MMC within the subconjunctival space in contact with sclera at the planned trabeculectomy site.
• Concentrations are typically between 0.2 and 0.4 mg/ml with a duration of application from 1 to 4 minutes

• They should be used with caution in primary trabeculectomies on young myopic patients because of an increased risk of hypotony.
• Techniques allowing tighter initial wound closure of the scleral flap help toprevent early postoperative hypotony.

• The use of releasable flap sutures
• The placement of additional sutures that can be cut postoperatively.
• Laser suture lysis

• Early complications:

1. Infection
2. Hypotony
3. Flat anterior chamber
4. Aqueous misdirection
5. Hyphema
6. Formation or acceleration of cataract
7. Transient IOP elevation
8. Cystoid Macular Edema
9. Hypotony maculopathy
10. Choroidal effusion
11. Suprachoroidal hemorrhage
12. Persistent uveitis
13. Dellen formation
14. Loss of vision

• Late complications:

1. Leakage or failure of the filtering bleb
2. Cataract
3. Blebitis,
4. Endophthalmitis (bleb infection)
5. Symptomatic bleb (dysesthetic bleb)
6. Bleb migration
7. Hypotony

• Full Thickness Sclerotomy

1. A block of limbal tissue is removed with a punch, trephine, laser or cautery.
2. Advantages: IOP can be lowered and maintained at a lower level for long periods of time.
3. Disadvantages: higher incidence of postoperative flat anterior chamber, cataract, hypotony, choroidal effusion, leakage of filtering blebs, and endophthalmitis.

• Combined Cataract & Filtering Surgery

• Indications

1. Glaucoma that is uncontrollable either medically or after laser trabeculoplasty when visual function is significantly impaired by a cataract
2. Cataract requiring extraction in a glaucoma patient who has advanced visual field loss
3. Cataract requiring extraction in a glaucoma patient requiring medications to control IOP in whom medical therapy is poorly tolerated
4. Cataract requiring extraction in a glaucoma patient who requires multiple medications to control IOP

• Contraindications

1. Glaucoma that requires a very low target IOP
2. Advanced glaucoma with uncontrolled IOP and immediate need for successful reduction of IOP, thus Glaucoma surgery alone is preferred.