Clinical implications of reported timolol-induced side effects

Since its approval by the Food and Drug Administration (FDA), timolol has been widely used for the treatment of open-angle glaucoma. Contrary to the clinical trials before FDA approval, many reports of possible ocular and systemic side effects have now appeared. Cardiovascular, respiratory, and gastrointestinal systemic effects occur relatively often and are attributable to beta-adrenergic antagonism, but central nervous system (CNS) effects are not so explainable. The most frequent ocular side effects are instillation pain and blurred vision, often requiring discontinuation of timolol. Superficial punctate keratitis and associated reduced corneal sensitivity have been reported and pose a risk for affected contact lens wearers. The incidence of side effects in two prospective studies was about 20%, with some 40% of those having to discontinue timolol. Of optometric interest are reports that timolol increases the electro-oculogram (EOG) ratio (Arden Index), and that it may be used to lower intraocular pressure in acute angle closure when pilocarpine alone is unsuccessful.