A 64-year-old woman in otherwise excellent health is referred by her optician to ophthalmology outpatients. The optician has noticed cupping of the optic disc and enlargement of the blind spot. Tonometry confirms the diagnosis of chronic simple (open angle) glaucoma. Choose the most appropriate drug from the choices below.

Chronic simple (open angle) glaucoma is one of the major causes of blindness. In contrast to acute (closed angle) glaucoma, its onset is insidious and painless. Initial treatment is with a topical beta-blocker, such as timolol, with the provison that significant systemic absorption may occur; the usual cautions and contraindications to beta-blockers should be observed. If initial treatment does not reduce intraocular pressure sufficiently, additional treatments may include parasympathomimetics (e.g. pilocarpine); selective alpha-2-adrenoceptor agonists (e.g. brimonidine); carbonic anhydrase inhibitors (e.g. dorzolamide) and prostaglandin analogues (e.g. latanoprost). If medical treatment fails, surgical trabeculectomy or laser trabeculoplasty may be necessary.