Chronic simple glaucoma is a common disease in old age and lowering intraocular pressure is the treatment strategy. Although this can be achieved surgically, medical treatment with eye drops is more often prescribed. β-antagonists are the class of drug most often chosen, although other medical therapies are available. Systemic absorption of β-antagonist eye drops can cause unsuspected respiratory impairment. Physicians should be alert to the possibility of respiratory side-effects of topical therapy with β-antagonists and whenever such side-effects occur should use alternative treatments.