## Anatomical Predisposing Factors in Primary Angle-Closure Glaucoma **Key Point:** Short axial length (hyperopia) is the single most common anatomical predisposing factor for primary angle-closure glaucoma (PACG). The hyperopic eye has a crowded anterior segment with a shallow anterior chamber, bringing the iris-lens diaphragm closer to the cornea. ### Mechanism of Angle Closure in Hyperopia In hyperopic eyes: - Shorter axial length reduces anterior chamber depth - Lens is positioned more anteriorly relative to the cornea - Iris is pushed forward, narrowing the angle recess - Pupillary block becomes more likely with any iris-lens contact ### Comparative Anatomy Table | Feature | Hyperopic Eye (PACG Risk) | Myopic Eye (PACG Safe) | | --- | --- | --- | | Axial length | Short (< 21 mm) | Long (> 24 mm) | | Anterior chamber depth | Shallow (< 2.5 mm) | Deep (> 3.5 mm) | | Lens position | Anterior | Posterior | | Angle configuration | Narrow | Wide | | Pupillary block risk | High | Low | **High-Yield:** PACG is rare in myopic eyes because the longer axial length creates a deeper anterior chamber and wider angle. ### Secondary Anatomical Factors 1. **Increased lens thickness** — contributes but is less common as primary factor 2. **Anterior iris insertion** — increases angle crowding but less frequent than short axial length 3. **Posterior iris bowing** — occurs *after* angle closure begins (secondary phenomenon), not a predisposing cause **Clinical Pearl:** Screening for PACG risk in hyperopic patients (refraction > +3.00 D) with shallow anterior chamber is standard practice. Prophylactic laser peripheral iridotomy is indicated in fellow eyes of acute PACG patients. [cite:Parson's Diseases of the Eye 22e Ch 8]
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