Acute angle closure, iridotomy and lens extraction

Emergency Medical Hypotensive Ladder

Start pressure lowering urgently with contraindications checked. Perform definitive laser when visibility and mechanism permit; do not impose an absolute IOP cutoff as the sole prerequisite.

Step 1: Immediate Systemic & Topical Aqueous Suppression

• Systemic Carbonic Anhydrase Inhibitor: Acetazolamide 500 mg IV bolus (or 500 mg orally if the patient is not vomiting), followed by 250 mg orally every 8 hours. Directly decreases aqueous humor secretion by 30% to 40% through inhibition of ciliary epithelial carbonic anhydrase II.
• Topical Aqueous Suppressants:
  • Beta-Blocker: Timolol maleate 0.5% 1 drop.
  • Alpha-2 Agonist: Brimonidine tartrate 0.2% or Apraclonidine 1% 1 drop.
  • Topical Carbonic Anhydrase Inhibitor: Dorzolamide 2% 1 drop.
• Topical Corticosteroid: Dexamethasone 0.1% or Prednisolone acetate 1% every 15 to 30 minutes for the first 2 hours to suppress intraocular inflammation and prevent permanent PAS adhesion.

Step 2: Systemic Hyperosmotic Agents

Consider hyperosmotic treatment when severe pressure is not adequately controlled, assessing cardiac, renal and hydration risks rather than using one compulsory pressure/time trigger.

• Intravenous Mannitol 20%: Administer 1.0 to 2.0 g/kg (approximately 250 to 500 mL of 20% solution) via rapid intravenous infusion over 30 to 45 minutes.
• Mechanism: Rapidly elevates serum osmolarity relative to the ocular fluids, creating an osmotic gradient that draws water out of the vitreous body into the intravascular circulation. The resulting reduction in vitreous volume pulls the crystalline lens and iris-lens diaphragm posteriorly, opening the anterior chamber angle.
• Precautions: Contraindicated in patients with congestive heart failure (risk of acute pulmonary edema due to sudden intravascular volume expansion), severe renal failure, and dehydration.
• Oral Alternative: Glycerol 50% solution (1.0 to 1.5 g/kg orally over crushed ice); caution in diabetic patients (metabolized into glucose, precipitating ketoacidosis).

Step 3: Delayed Topical Miotics (Pilocarpine Protocol)

Definitive Procedural Interventions

Once the acute attack is broken, the cornea clears, and anterior chamber inflammation settles, definitive procedural intervention is indicated.

1. Neodymium:YAG Laser Peripheral Iridotomy (Nd:YAG LPI)

Nd:YAG LPI creates a full-thickness optical channel through the peripheral iris, allowing aqueous humor to flow directly from the posterior chamber to the anterior chamber, permanently bypassing pupillary block and flattening the iris contour.

• Pre-Treatment: Apraclonidine 1% or Brimonidine 0.2% instilled 30 minutes prior to prevent post-laser IOP spikes; Pilocarpine 1% instilled to stretch the peripheral iris stroma and make it thinner.
• Contact Lens: An Abraham or Wise iridotomy lens is applied, which features a high-power convex button (+66 D to +103 D) that magnifies the iris stroma, condenses the laser energy, and dissipates heat at the cornea.
• Site selection: Select a suitably thin peripheral iris site with consideration of lid coverage, anatomy and dysphotopsia risk. Superior placement does not eliminate dysphotopsia and is not mandatory in every eye.
• Laser settings are selected by iris pigmentation, mechanism, device and response; iridotomy and iridoplasty use different treatment targets.
• Confirmation of Patency: Successful full-thickness perforation is confirmed by: 1) a sudden plume of pigment, debris, and aqueous surging from the posterior chamber into the anterior chamber; 2) visible retroillumination through the iridotomy; and 3) direct visualization of the anterior lens capsule through the opening. The diameter should be at least 150 to 200 $\mu\text{m}$ to prevent spontaneous closure from pigment migration.
• Post-Laser Management: Measure IOP at 1 hour; prescribe topical prednisolone acetate 1% or dexamethasone 0.1% four times daily for 5 to 7 days.

2. Argon Laser Peripheral Iridoplasty (ALPI)

Argon laser peripheral iridoplasty is indicated when appositional angle closure persists after a patent iridotomy (plateau iris syndrome), or as emergency management when corneal edema prevents a definitive iridotomy during an acute attack.

• Laser Parameters: Large spot size (200 to 500 $\mu\text{m}$), long duration (0.5 seconds), and low power (200 to 400 mW).
• Mechanism: Low-energy, slow-burn photocoagulation applied to the extreme iris periphery causes contraction and shrinkage of the underlying stromal collagen, mechanically pulling the peripheral iris roll away from the trabecular meshwork without creating a full-thickness hole.

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Clear Lens Extraction: The Landmark EAGLE Trial

Historically, laser peripheral iridotomy was considered the universal first-line intervention for all presentations of primary angle closure. However, the crystalline lens is the primary anatomical driver of crowding in hyperopic eyes.

The Effectiveness in Angle-closure Glaucoma of Lens Extraction (EAGLE) trial, published in The Lancet in 2016, transformed international clinical practice. This randomized controlled trial compared primary clear lens extraction (CLE via phacoemulsification) with standard laser peripheral iridotomy (LPI) in 419 patients aged $\ge 50$ years with newly diagnosed PAC (with IOP $\ge 30$ mmHg) or PACG:

• EAGLE outcome: In the selected trial population, clear-lens extraction produced better health-status outcomes and a mean pressure 1.18 mmHg lower at 36 months than standard care. Interpret eligibility and treatment burden; this does not justify extraction for every angle-closure suspect or acute attack.
• Quality of Life: Patients treated with clear lens extraction reported significantly higher health-related quality of life, as measured by the European Quality of Life-5 Dimensions (EQ-5D) questionnaire.
• Cost-Effectiveness: While upfront procedural costs for phacoemulsification were higher, clear lens extraction was proven to be cost-effective over 3 years due to substantial reductions in long-term medication use, fewer clinical consultations, and avoided filtration surgeries.

Mechanism and Safety Before the Ladder

Acute closure requires prompt pressure lowering and definitive mechanism assessment. Check renal function, electrolyte/acid-base disease and contraindications before systemic acetazolamide; assess cardiac and respiratory contraindications before beta-blockers, and cardiac/renal status before hyperosmotics. Pilocarpine is appropriate for selected pupillary-block attacks after pressure reduction, not for aqueous misdirection or forward lens/iris displacement. LPI treats pupillary block but follow-up gonioscopy is required. Persistent closure may involve PAS, plateau iris or lens crowding. Iridotomy location is selected for anatomy and dysphotopsia risk, not compulsory superior placement. EAGLE enrolled adults at least 50 with PAC and IOP at least 30 mmHg or PACG; it excluded acute attacks and advanced disease and should not be extrapolated to every asymptomatic narrow angle.