Which anatomical feature is MOST important in predisposing an eye to primary angle-closure glaucoma?

Explanation

## Anatomical Predisposition to Primary Angle-Closure Glaucoma **Key Point:** Short axial length (hyperopia), anterior lens position, and a narrow angle are the **cardinal anatomical features** that predispose to primary angle-closure glaucoma. These create the ideal geometry for iris-lens contact and pupillary block. ### Anatomical Risk Factors | Feature | Effect on Angle Closure Risk | |---------|------------------------------| | **Short axial length** | Lens positioned anteriorly; iris-lens distance ↓ | | **Hyperopia** | Refractive consequence of short eye; crowded anterior segment | | **Narrow angle** | Reduced space between iris and trabecular meshwork | | **Thick, convex iris** | Greater surface area for lens contact | | **Anterior lens position** | Increased iris-lens contact, especially in mid-dilation | | **Small corneal diameter** | Crowded anterior segment anatomy | ### Why Short Axial Length Is Critical 1. **Geometric crowding** — in a short eye, all structures (lens, iris, ciliary body) are packed anteriorly 2. **Reduced iris-lens distance** — minimal space for aqueous flow between iris and lens surface 3. **Pupillary block vulnerability** — even mild pupil dilation can cause iris-lens contact 4. **Angle narrowness** — peripheral iris is naturally closer to the trabecular meshwork **Mnemonic:** **SAFE** eyes are at risk for angle closure: - **S**hort axial length - **A**nterior lens position - **F**emale (higher prevalence; smaller eyes) - **E**lderly (lens swells with age, moves forward) **Clinical Pearl:** A patient with hyperopia (short eye) presenting with acute eye pain, red eye, and mid-dilated pupil should raise immediate suspicion for angle-closure glaucoma. Gonioscopy will show a narrow or closed angle. [cite:Khurana Comprehensive Ophthalmology Ch 10] **High-Yield:** **Gonioscopy classification** (Shaffer grading) is used to assess angle width: - Grade 0–1 (narrow/closed) → high risk for angle closure - Grade 3–4 (open) → low risk Patients with narrow angles on gonioscopy should receive **prophylactic laser peripheral iridotomy** to prevent acute attacks. ### Why Other Options Are Wrong - **Long axial length (myopia)** — creates a *deep* anterior chamber and *wide* angle, which *protects* against angle closure - **Deep anterior chamber** — allows iris to fall back; angle remains open - **Thick ciliary body** — not a primary anatomical risk factor; aqueous production is normal in PACG