A 58-year-old woman presents with acute onset of severe eye pain, blurred vision, and halos around lights. Examination reveals a mid-dilated pupil, corneal edema, shallow anterior chamber, and intraocular pressure of 58 mmHg. Gonioscopy confirms angle closure. What is the drug of choice for immediate medical management before laser peripheral iridotomy?

Explanation

## Acute Angle-Closure Glaucoma: Medical Management Strategy ### Pathophysiology of Acute Attack In acute angle-closure glaucoma, the iris is pushed forward against the lens, mechanically obstructing aqueous outflow through the trabecular meshwork. IOP rises acutely to 40–80 mmHg, causing corneal edema, pain, and vision loss. ### First-Line Medical Agent: Acetazolamide **Key Point:** Acetazolamide is the drug of choice for acute angle-closure glaucoma because it acts via TWO mechanisms: 1. **Reduces aqueous humor production** by inhibiting carbonic anhydrase in the ciliary body (decreases IOP by 30–50%) 2. **Shrinks the vitreous volume**, pulling the lens–iris diaphragm posteriorly and deepening the anterior chamber—this mechanically relieves angle closure **High-Yield:** Acetazolamide is the ONLY drug that addresses the mechanical obstruction; all others merely reduce aqueous production or increase outflow without relieving the anatomical block. ### Dosing & Route - **IV acetazolamide 500 mg** (preferred in acute attack for rapid effect) - Oral 500 mg BD as alternative - Onset: 15–30 minutes IV; 1 hour oral ### Sequential Medical Management Algorithm ```mermaid flowchart TD A[Acute Angle-Closure Glaucoma]:::outcome --> B[Acetazolamide IV 500 mg]:::action B --> C[Topical beta-blocker<br/>+ alpha-2 agonist]:::action C --> D[Topical prostaglandin analogue<br/>contraindicated initially]:::urgent E[Corneal edema resolves?]:::decision C --> E E -->|Yes| F[Proceed to laser<br/>peripheral iridotomy]:::action E -->|No| G[Osmotic agent:<br/>IV mannitol]:::action G --> F ``` ### Why Acetazolamide Beats Other Options | Drug | Mechanism | Limitation in Acute ACG | |------|-----------|------------------------| | **Acetazolamide** | ↓ Aqueous production + shrinks vitreous (relieves mechanical block) | None—first-line | | Timolol (beta-blocker) | ↓ Aqueous production only | Does NOT relieve angle closure; IOP may remain dangerously high | | Latanoprost (PG analogue) | ↑ Uveoscleral outflow | **CONTRAINDICATED** in acute ACG—can worsen inflammation and angle closure | | Brimonidine (alpha-2 agonist) | ↓ Aqueous production + ↑ outflow | Weaker than acetazolamide; does NOT address mechanical block | **Clinical Pearl:** Prostaglandin analogues are avoided in acute angle-closure because they increase inflammation and can paradoxically worsen angle closure. ### Complete Acute Management Protocol 1. **Acetazolamide 500 mg IV** (immediately) 2. **Topical agents** (while awaiting acetazolamide effect): - Beta-blocker (timolol 0.5%) + alpha-2 agonist (brimonidine 0.2%) every 15 min × 1 hour - Avoid prostaglandin analogues 3. **Osmotic agent** if corneal edema persists (IV mannitol 1 g/kg) 4. **Laser peripheral iridotomy** once IOP controlled and cornea clears enough for visualization **Warning:** Do NOT delay laser iridotomy waiting for perfect IOP control—medical therapy is a bridge to definitive treatment, not a substitute. [cite:Parson's Diseases of the Eye 22e Ch 10]