Timolol

Timolol is a nonselective beta-adrenergic receptor blocker used mainly as eye drops to lower intraocular pressure and, orally, for some cardiovascular conditions.

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Beta blocker: A drug that blocks beta-adrenergic receptors activated by epinephrine and norepinephrine. Timolol belongs to this drug class and blocks both beta-1 and beta-2 receptors.
Glaucoma: A group of eye diseases involving characteristic optic nerve damage, often associated with elevated intraocular pressure. Timolol eye drops lower pressure to help prevent glaucomatous optic nerve damage.
Betaxolol: A beta-1-selective blocker used as an eye drop to lower intraocular pressure. Unlike nonselective timolol, betaxolol is less likely to block beta-2 receptors in the lungs.
Bradycardia: A heart rate slower than the normal range for a person's age and circumstances. Timolol can slow the heart by blocking cardiac beta-1 receptors.
Beta-adrenergic receptor: A cell-surface receptor activated by epinephrine and norepinephrine that regulates functions including heart rate and aqueous humor production. Timolol lowers eye pressure by blocking these receptors in the ciliary epithelium.
Ocular hypertension: Elevated intraocular pressure without the optic nerve damage that defines glaucoma. Timolol may lower pressure in people at risk of developing glaucoma.
Propranolol: An orally used nonselective beta blocker prescribed for cardiovascular conditions and migraine prevention. It shares timolol's nonselective receptor blockade but is used chiefly as an oral drug.
Bronchospasm: Contraction of airway smooth muscle that narrows the bronchi and can cause breathing difficulty. Systemic absorption of nonselective timolol can block airway beta-2 receptors and provoke bronchospasm.
Aqueous humor: The clear fluid that fills the front chambers of the eye and helps maintain intraocular pressure. Timolol eye drops reduce its production, lowering pressure inside the eye.
Migraine prophylaxis: Preventive treatment intended to reduce the frequency or severity of migraine attacks. Oral timolol is used for migraine prevention in some countries.