A 58-year-old woman presents with acute onset severe eye pain, blurred vision, and nausea. Examination reveals a mid-dilated pupil, corneal edema, shallow anterior chamber, 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 defining difference between primary and secondary angle-closure glaucoma is the **absence or presence of an identifiable underlying cause**. ### Comparison Table | Feature | Primary Angle-Closure | Secondary Angle-Closure | | --- | --- | --- | | **Underlying cause** | None (anatomically predisposed eye) | Identifiable pathology (lens, inflammation, neovascularization, trauma, etc.) | | **Anterior chamber depth** | Shallow (anatomic predisposition) | May be normal or shallow depending on cause | | **Pupil position** | Mid-dilated (acute attack) | Variable, depends on etiology | | **IOP elevation** | Acute, severe (>40 mmHg) | Acute or chronic, variable severity | | **Corneal edema** | Present (due to high IOP) | Present (due to high IOP) | | **Gonioscopy findings** | Angle closure with no other pathology | Angle closure WITH identifiable secondary pathology | ### Clinical Pearl **Clinical Pearl:** In primary angle-closure glaucoma, the angle closes due to **pupillary block mechanism in an anatomically predisposed eye** (shallow anterior chamber, short axial length, thick lens, hyperopia). Gonioscopy reveals angle closure but no other abnormality. In secondary angle-closure glaucoma, there is an **identifiable structural or inflammatory cause** pushing or pulling the iris forward: - Lens-induced (phacomorphic, phacolytic, intumescent lens) - Inflammation-induced (posterior synechiae, iris bombe) - Neovascularization (rubeotic glaucoma) - Trauma or surgery - Aqueous misdirection (malignant glaucoma) ### High-Yield Distinction **High-Yield:** The **gonioscopic examination is critical**. In primary angle-closure, the angle is closed but otherwise normal. In secondary angle-closure, you will identify the **cause** (e.g., mature cataract, posterior synechiae, neovascular membrane, hemorrhage). ### Why Clinical Features Overlap Both conditions present with: - Acute severe pain and blurred vision - Corneal edema (from high IOP) - Mid-dilated pupil (from acute ischemia) - Elevated IOP (>40 mmHg) - Nausea and vomiting (from acute IOP spike) These **clinical presentations are identical**—the distinction requires **gonioscopy and history** to identify whether a secondary cause is present.