A 52-year-old woman presents with sudden onset of severe pain in the right eye, headache, nausea, and vomiting. Slit-lamp examination reveals corneal oedema, a mid-dilated fixed pupil, and shallow anterior chamber. IOP measures 58 mmHg. Gonioscopy of the fellow eye shows a Van Herick grade I angle. Which mechanism best explains the acute pressure elevation in this patient?
- A Trabecular meshwork degeneration with progressive outflow obstruction
- B Relative pupillary block causing iris bombe and angle closure ✓
- C Episcleral venous pressure elevation from arteriovenous fistula
- D Uveal congestion and ciliary body rotation rotating lens-iris diaphragm anteriorly
Explanation
Acute primary angle-closure glaucoma is caused by relative pupillary block: aqueous accumulates behind the iris, bowing it forward (iris bombe), which mechanically blocks the trabecular meshwork and causes rapid IOP elevation. The mid-dilated pupil position maximises iris-lens contact and pupillary block. Option A describes open-angle glaucoma. Option C (Sturge-Weber, carotid-cavernous fistula) presents with elevated episcleral venous pressure without rapid pain. Option D describes malignant (ciliary block) glaucoma, which occurs post-operatively with a flat anterior chamber rather than the classic APAC picture.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.