During a routine eye screening camp in rural India, you identify 12 patients with narrow angles on gonioscopy. You counsel them about the risk of acute angle-closure glaucoma. What is the most common trigger for an acute attack of primary angle-closure glaucoma in these asymptomatic narrow-angle patients?

## Triggers of Acute Primary Angle-Closure Glaucoma ### Most Common Trigger: Pupillary Dilation **Key Point:** Pupillary dilation (mydriasis) is the single most common trigger for acute angle-closure glaucoma in patients with anatomically narrow angles. When the pupil dilates, the iris tissue bunches up radially and is pushed forward by the lens, occluding the trabecular meshwork and blocking aqueous outflow. ### Mechanism of Pupillary Block ```mermaid flowchart TD A[Narrow angle + Hyperopia]:::outcome --> B[Pupil dilates]:::action B --> C[Iris tissue bunches radially]:::action C --> D[Iris pushed forward by lens]:::action D --> E[Trabecular meshwork occluded]:::action E --> F[Aqueous outflow blocked]:::action F --> G[IOP rises acutely]:::urgent G --> H[Acute angle-closure glaucoma]:::urgent ``` ### Common Triggers of Mydriasis in Clinical Practice | Trigger | Mechanism | Frequency in PACG | |---------|-----------|-------------------| | **Dim lighting** | Physiological pupil dilation | Most common | | **Topical mydriatics** (tropicamide, phenylephrine) | Pharmacological dilation | Common in eye clinics | | **Systemic anticholinergics** (antihistamines, antidepressants) | Systemic mydriasis | Moderate | | **Emotional stress** | Sympathetic activation → mydriasis | Moderate | | **Darkness/cinema** | Physiological response | Common | ### Why Other Options Are Wrong **Clinical Pearl:** While anterior chamber inflammation, accommodation changes, and hypertension can all occur in PACG, they are *not* the primary trigger mechanism. Pupillary dilation is the direct mechanical cause of angle closure in narrow-angle eyes. ### High-Yield: Prevention Strategy **Mnemonic: AVOID MYDRIASIS** — Patients with narrow angles should: - **A**void dim lighting and dark environments - **V**oid topical mydriatics (use miotics or prostaglandin analogues instead) - **O**btain laser peripheral iridotomy (LPI) prophylactically - **I**nform about systemic anticholinergics - **D**iscuss stress management - **M**onitor fellow eye - **Y**earn for gonioscopy screening in family members - **D**rug review (avoid antihistamines, tricyclic antidepressants) - **R**isk counselling before any mydriatic use - **I**ridotomy is definitive prevention - **A**void sympathomimetics - **S**creen hyperopic patients - **I**nform about acute symptoms (pain, haloes, blurred vision) - **S**urgical rescue (anterior chamber reformation) if acute attack occurs ### Clinical Correlation **Tip:** Always ask patients with narrow angles: "Do your symptoms occur in dim light, at the cinema, or at night?" This history is highly suggestive of pupillary dilation as the trigger. Prophylactic LPI is indicated in all narrow-angle eyes to prevent acute attacks. [cite:Kanski & Bowling 9e Ch 8]