Glaucoma described a group of disorders characterised by a loss of visual field associated with cupping of the optic disc and optic nerve damage. While glaucoma is generally associated with raised intra-ocular pressure, it can occur when the intra-ocular pressure is within normal range.
The most common cause of glaucoma is primary open-angle glaucoma (chronic open-angle glaucoma), where drainage of the aqueous humor through the trabeular meshwork is restricted. The condition is ofter asymptomatic, but the patient may present with significant loss of visual field. Patients with ocular hypertension are at high risk of developing primar open-angle glaucoma.
Acute angle-closure glaucoma occurs when the outflow of aqueous humour from the eye is obstructed by bowing of the iris against the trabecular meswork; it is a medical emergency that requires urgent reduction of intra-ocular pressure to prevent loss of vision. Patient with acute angle-closure glaucoma should be referred immediately for specialist opthalmology assessment and treatment.

Brimonidine tartrate, a selective alpha₂-adrenoceptor agonist, is thought to lower intraocular pressure by reducing aqueous humour formation and increasing uveoscleral outflow. It is licensed for the reduction of intraocular pressure in open-angle glaucoma or ocular hypertension in patients who cannot tolerate beta-blockers; it may also be used as adjunctive treatment when intraocular pressure inadequately controlled by other therapy.