A 58-year-old man presents to the ophthalmology clinic with a 3-day history of right eye pain and blurred vision. On examination, the right pupil is mid-dilated (5 mm) and fixed to light, while the left pupil reacts normally. Extraocular movements are intact. Visual acuity is 6/9 in both eyes. Slit-lamp examination reveals ciliary injection and keratic precipitates. Intraocular pressure is 42 mmHg in the right eye. What is the most likely explanation for the pupillary finding?

Explanation

## Clinical Diagnosis: Acute Angle-Closure Glaucoma with Pupillary Involvement ### Pathophysiology of the Fixed Mid-Dilated Pupil **Key Point:** In acute angle-closure glaucoma, the mid-dilated fixed pupil results from acute iris ischemia due to severely elevated intraocular pressure (IOP), causing transient paralysis of the iris sphincter muscle. The sequence of events: 1. Sudden angle closure → IOP spike (often >40 mmHg) 2. Iris ischemia from compromised iris blood supply 3. Sphincter muscle paralysis → pupil becomes fixed in mid-dilated position (4–6 mm) 4. This is a **reversible** finding if IOP is lowered promptly ### Clinical Features Supporting This Diagnosis | Feature | Finding | Significance | |---------|---------|---------------| | IOP | 42 mmHg | Markedly elevated, typical of acute angle closure | | Pupil size | Mid-dilated (5 mm) | Characteristic of iris ischemia | | Pupil reactivity | Fixed | Sphincter paralysis from ischemia | | Ciliary injection | Present | Acute anterior uveitis from angle closure | | Pain + blurred vision | 3 days | Classic acute presentation | | Keratic precipitates | Present | Inflammatory response to angle closure | ### Differential Consideration: Why Not Adie's Tonic Pupil? **Warning:** Adie's tonic pupil presents with a **dilated, slowly reacting pupil** (not fixed), and is associated with **normal IOP** and **absent deep tendon reflexes**. The acute presentation with high IOP and ciliary injection excludes Adie's. ### Recovery After Treatment **Clinical Pearl:** Once IOP is controlled with topical/systemic agents or laser peripheral iridotomy, the iris ischemia resolves and pupillary light reflex typically returns within hours to days. This reversibility distinguishes it from permanent third nerve palsy. **High-Yield:** The mid-dilated fixed pupil in acute angle closure is a sign of **iris ischemia**, not true neurological palsy — it is an **emergency sign** requiring immediate IOP reduction. ### Mnemonic: AACD Pupil **AACD** = **A**cute **A**ngle-Closure **D**ilated pupil - **A**cute onset (hours to days) - **A**cute IOP elevation (>40 mmHg) - **C**iliary injection + keratic precipitates - **D**ilated, fixed pupil (iris ischemia) [cite:Khurana Comprehensive Ophthalmology Ch 7]