A 58-year-old woman presents with sudden severe pain in the right eye, nausea, vomiting, and diminished vision. The cornea appears steamy, the pupil is mid-dilated and fixed, and the eye is hard on palpation. Gonioscopy reveals a closed angle. What is the mechanism of intraocular pressure rise in this condition?

• A Pupillary block leading to forward bowing of peripheral iris obstructing the trabecular meshwork ✓
• B Increased aqueous production by the ciliary body
• C Episcleral venous pressure elevation due to carotid-cavernous fistula
• D Trabecular meshwork dysfunction from accumulation of pseudoexfoliation material

Explanation

Acute primary angle-closure glaucoma (PACG) occurs when aqueous cannot flow from the posterior to the anterior chamber through the pupil, causing posterior chamber pressure to bow the peripheral iris anteriorly, occluding the trabecular meshwork. This pupillary block mechanism is most commonly precipitated in anatomically predisposed eyes (shallow anterior chamber, thick lens, short axial length). Mid-dilation maximises pupillary block by opposing iris against the lens without the miotic benefit of a very constricted or very dilated pupil.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.