Which of the following is the primary mechanism of elevated intraocular pressure in primary angle-closure glaucoma?

Explanation

## Mechanism of Primary Angle-Closure Glaucoma **Key Point:** Pupillary block is the PRIMARY mechanism in angle-closure glaucoma. The lens-iris contact at the pupil creates a pressure gradient that pushes the peripheral iris forward, mechanically closing the drainage angle. ### Pathophysiology 1. **Pupillary Block (Central Mechanism)** - Contact between lens and iris at the pupil - Creates relative pressure difference between posterior and anterior chambers - Iris bows forward (iris bombé) - Peripheral iris apposes the trabecular meshwork 2. **Angle Closure Sequence** - Iris-trabecular contact → obstruction of aqueous outflow - IOP rises acutely (can exceed 40–60 mmHg) - Corneal edema develops - Pain and vision loss ensue ### Anatomical Risk Factors | Feature | Significance | |---------|-------------| | Shallow anterior chamber | Increased lens-iris proximity | | Short axial length (hyperopia) | Crowded angle anatomy | | Thick lens | Greater posterior pressure | | Narrow angle (< 20°) | Predisposition to closure | | Plateau iris | Angle closure without pupillary block | **High-Yield:** Pupillary block accounts for ~90% of primary angle-closure cases. Relief of pupillary block (via laser peripheral iridotomy) is the definitive treatment. **Clinical Pearl:** The mechanism is mechanical obstruction of the drainage angle, NOT a trabecular pathology—this distinguishes angle-closure from open-angle glaucoma.