Acute angle-closure glaucoma
A sudden mechanical blockage of aqueous outflow at the iridocorneal angle causes a rapid, severe rise in intraocular pressure, producing an excruciatingly painful red eye with visual loss that is an ophthalmic emergency.
First principles
The disease is a plumbing problem: aqueous cannot leave the eye
Aqueous humour is produced by the ciliary body, flows from the posterior chamber through the pupil into the anterior chamber, and drains via the trabecular meshwork at the iridocorneal angle. In susceptible eyes (hypermetropic, with a shallow anterior chamber and a lens that thickens with age), the iris bows forward and crowds the angle. When the pupil becomes mid-dilated, in dim light or with a mydriatic, iris tissue bunches into the angle and seals the drainage pathway. Aqueous keeps being produced but cannot leave, so pressure rises rapidly.
Educational content pending clinical review. Not medical advice.