A 55-year-old woman on long-term atropine therapy for chronic obstructive airway disease develops progressive blurred vision, eye pain, and headache. Intraocular pressure (IOP) is measured at 42 mmHg (normal: 10–21 mmHg). Which investigation is most appropriate to establish the diagnosis and guide management?

Explanation

## Anticholinergic-Induced Acute Angle-Closure Glaucoma: Diagnostic Approach ### Clinical Context Anticholinergic drugs (atropine, scopolamine, antihistamines, tricyclic antidepressants) cause pupillary dilation (mydriasis) and cycloplegia. In susceptible individuals—those with anatomically narrow anterior chamber angles—mydriasis can precipitate acute angle-closure glaucoma by pushing the peripheral iris forward, mechanically obstructing the trabecular meshwork. ### The Pathophysiology ```mermaid flowchart TD A[Anticholinergic drug administered]:::action --> B[Pupillary dilation mydriasis]:::outcome B --> C{Anterior chamber angle?}:::decision C -->|Narrow angle predisposition| D[Iris pushed forward]:::outcome D --> E[Trabecular meshwork obstruction]:::outcome E --> F[IOP rises acutely]:::urgent F --> G[Acute angle-closure glaucoma]:::urgent C -->|Normal/wide angle| H[No angle closure]:::outcome ``` ### Why Anterior Chamber Depth Measurement is Diagnostic **Key Point:** Anterior chamber depth (ACD) directly assesses the anatomical risk factor for angle closure. Narrow ACD (<2.5 mm) predisposes to angle-closure glaucoma when mydriasis occurs. **High-Yield:** The investigation of choice for suspected angle-closure glaucoma is **gonioscopy** (direct visualization of the angle) or **anterior chamber depth measurement** (A-scan ultrasound or OCT). ACD measurement is non-contact, rapid, and quantifies the anatomical risk. ### Investigation Comparison | Investigation | Purpose | Diagnostic Value in Angle-Closure | |---|---|---| | **Anterior chamber depth (A-scan/OCT)** | Measures ACD; identifies narrow angles | **Gold standard for anatomical risk assessment** | | Gonioscopy | Direct visualization of angle structures | Gold standard for angle assessment but requires expertise; not always available acutely | | Dilated fundus exam | Assesses optic disc cupping, retinal changes | Shows chronic glaucoma changes; not diagnostic of acute angle closure | | Perimetry (visual fields) | Detects glaucomatous field defects | Useful for monitoring chronic glaucoma; not diagnostic of acute angle closure | | Tear osmolarity/Schirmer | Assesses dry eye | Unrelated to angle-closure glaucoma | ### Clinical Pearl **Anticholinergic-induced angle-closure glaucoma is a medical emergency.** Acute IOP elevation (>40 mmHg) causes corneal edema, severe eye pain, blurred vision, and rapid optic nerve damage. The diagnosis is confirmed by: 1. **Elevated IOP** (>21 mmHg; often >40 mmHg acutely) 2. **Narrow anterior chamber angle** (ACD <2.5 mm on A-scan/OCT or closed angle on gonioscopy) 3. **Acute symptoms** (eye pain, blurred vision, headache, nausea) 4. **Temporal relationship** with anticholinergic drug exposure ### Why Other Investigations Are Inadequate - **Dilated fundus exam:** Shows optic disc changes (pallor, cupping) in chronic glaucoma but does not identify the acute angle-closure mechanism or narrow angle anatomy. - **Perimetry:** Detects glaucomatous visual field loss but is time-consuming and not diagnostic of acute angle closure; reserved for chronic glaucoma monitoring. - **Tear osmolarity/Schirmer:** Evaluates dry eye syndrome; unrelated to angle-closure glaucoma pathophysiology.