A 35-year-old man presents with sudden-onset right eye pain, blurred vision, and a mid-dilated pupil that is poorly reactive to light. On examination, the right pupil is 5 mm and reacts sluggishly to direct light stimulus. The left pupil is 3 mm and reacts briskly. There is no afferent pupillary defect. Which investigation is most appropriate to confirm acute angle-closure glaucoma as the underlying cause of the pupillary abnormality?

Explanation

## Diagnosis: Acute Angle-Closure Glaucoma with Pupillary Changes The clinical presentation—sudden pain, blurred vision, mid-dilated poorly reactive pupil, and absence of APD—is classic for acute angle-closure glaucoma (ACG). The pupil becomes mid-dilated and fixed due to iris ischemia from markedly elevated intraocular pressure (IOP). ### Why Gonioscopy is the Investigation of Choice **Key Point:** Gonioscopy is the gold standard for direct visualization of the anterior chamber angle and confirmation of angle closure. Gonioscopy allows: 1. Direct visualization of the iridocorneal angle 2. Assessment of angle width (Shaffer grading: Grade 0–4) 3. Identification of peripheral anterior synechiae (PAS) 4. Confirmation of angle-closure mechanism (pupillary block vs. plateau iris) 5. Differentiation from other causes of elevated IOP ### Role of Other Investigations | Investigation | Purpose | Limitation in ACG Diagnosis | |---|---|---| | **AS-OCT** | Non-contact imaging of anterior chamber angle | Useful for screening but less direct than gonioscopy; cannot assess dynamic angle changes during provocative maneuvers | | **Applanation Tonometry** | Measures IOP | Confirms elevated IOP (typically >40 mmHg in ACG) but does NOT diagnose the mechanism of angle closure | | **Pupillography** | Quantifies pupillary light reflex dynamics | Assesses pupillary function but does NOT visualize the angle or confirm angle closure | **High-Yield:** In acute ACG, IOP is markedly elevated (often >50 mmHg), but the diagnosis rests on gonioscopic confirmation of angle closure, not on IOP measurement alone. ### Clinical Pearl Gonioscopy in acute ACG may be challenging due to corneal edema from high IOP. If corneal clarity is poor, AS-OCT or ultrasound biomicroscopy (UBM) can be used as adjuncts, but gonioscopy remains the definitive test once the cornea clears (after IOP-lowering therapy). **Warning:** Do not confuse pupil reactivity with angle status. A fixed mid-dilated pupil in acute ACG is due to iris ischemia and sphincter muscle paralysis, not primary pupillary nerve pathology. The angle closure is confirmed by gonioscopy, not by pupillary examination alone.