A 58-year-old woman presents with acute onset eye pain, blurred vision, and halos around lights. Examination reveals a shallow anterior chamber, mid-dilated non-reactive pupil, corneal edema, and intraocular pressure of 58 mmHg. Which single feature best distinguishes acute primary angle-closure glaucoma from acute secondary angle-closure glaucoma?

Explanation

## Distinguishing Primary from Secondary Angle-Closure Glaucoma ### Key Discriminating Feature **Key Point:** The fundamental distinction between primary and secondary angle-closure glaucoma is the *absence or presence of an identifiable underlying cause*. Primary angle-closure occurs in anatomically predisposed eyes with no secondary precipitant, while secondary angle-closure has a demonstrable etiology. ### Comparison Table | Feature | Primary Angle-Closure | Secondary Angle-Closure | |---------|----------------------|------------------------| | **Underlying cause** | None (anatomic predisposition alone) | Identifiable cause present | | **Common causes of secondary** | — | Lens swelling, inflammation (uveitis), neovascularization, posterior synechiae, trauma, silicone oil | | **Anterior chamber** | Shallow bilaterally | May be shallow or normal | | **Pupil** | Mid-dilated, non-reactive | Varies with cause | | **Corneal edema** | Present in acute attack | Present in acute attack | | **IOP elevation** | Severe (>40 mmHg) | Severe (>40 mmHg) | | **Gonioscopy findings** | Angle closure without other abnormality | Angle closure + secondary pathology | ### Clinical Pearl **Clinical Pearl:** In primary angle-closure, gonioscopy shows appositional or synechial closure of the angle with an otherwise normal iris and lens. In secondary angle-closure, you will identify the *cause* — e.g., a swollen cataractous lens, iris neovascularization, posterior synechiae from inflammation, or evidence of trauma. ### High-Yield Discriminator **High-Yield:** The diagnostic criterion is **absence of secondary cause**. Both conditions present with identical acute symptoms (pain, halos, corneal edema, mid-dilated pupil, high IOP). The distinction is made by: - Detailed history (trauma? inflammation? lens intumescence?) - Gonioscopy (angle anatomy vs. secondary pathology) - Imaging (OCT, ultrasound biomicroscopy) - Examination of the lens and iris ### Why Other Features Are Not Discriminators - **Corneal edema, mid-dilated pupil, elevated IOP:** These are present in *both* primary and secondary angle-closure during acute attack. They reflect the acute rise in pressure, not the underlying etiology. - **Shallow anterior chamber:** While typical of primary angle-closure, secondary angle-closure can also present with angle closure in some cases (e.g., lens swelling, posterior pushing mechanisms). **Mnemonic:** **PACE** — **P**rimary = **A**natomic predisposition **C**ause-**E**xclusion (no secondary cause identified).