## Anatomical Basis of Primary Angle-Closure Glaucoma ### Most Common Predisposing Factor **Key Point:** Short axial length (hyperopia) is the single most common anatomical predisposing factor for primary angle-closure glaucoma (PACG). Hyperopic eyes have a naturally crowded anterior segment, bringing the iris and lens into closer proximity to the cornea. ### Mechanism of Angle Closure in PACG 1. **Shallow anterior chamber** — consequence of short axial length 2. **Narrow angle** — iris and lens are positioned anteriorly 3. **Pupillary block** — relative pupillary block occurs when the pupil dilates, causing the iris to bow forward and occlude the trabecular meshwork 4. **IOP spike** — aqueous humour cannot drain, leading to acute elevation ### Anatomical Risk Factors in PACG | Feature | Role in PACG | |---------|---------------| | **Short axial length** | Most common predisposing factor; creates crowded anterior segment | | **Thick lens** | Contributory but less common as primary factor | | **Anterior lens position** | Results from short eye; not primary | | **Iris bombé** | Occurs *after* angle closure (secondary phenomenon) | | **Narrow angles** | Consequence of short axial length, not cause | ### Clinical Pearl **High-Yield:** Hyperopic patients (especially women, who have shorter eyes on average) are at highest risk. The combination of hyperopia + female sex + age >40 years = classic PACG risk profile. Screening with gonioscopy or anterior segment OCT is recommended in all hyperopic patients with narrow angles. ### Why This Matters - **Preventive strategy:** Laser peripheral iridotomy (LPI) in fellow eye of PACG patients and in asymptomatic narrow-angle eyes reduces risk of acute attack by ~50% - **Refractive surgery consideration:** LASIK in hyperopic patients can paradoxically increase PACG risk by further reducing anterior chamber depth [cite:Kanski & Bowling 9e Ch 8]
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