Effects of topical application of adrenergic agents on refraction and accommodation]

In an attempt to clarify the functional role of adrenergic receptors on accommodation, effects of various adrenergic agents on the state of accommodation were studied. Fifty-two emmetropic normal subjects (age: 19-28 y) participated in this study. We examined the effect of the alpha agonist phenylephrine hydrochloride (5%), the alpha 1 antagonist adrenergic bunazosin hydrochloride (0.1%), the beta antagonist timolol maleate (0.5%), the beta 2 antagonist betaxolal hydrochloride (0.5%), and the beta agonist isoproterenol hydrochloride (3%). Using an infrared optometer, the refraction, far point and near point of accommodation, resting point of accommodation (empty-field accommodation and dark focus of accommodation), and accommodative adaptation were measured before and after topical application of various adrenergic agents. Application of bunazosin slightly but significantly decreased the near point of accommodation. Isoproterenol evoked a hyperopic shift on the far point of accommodation. None of the agents had any effect on the resting point of accommodation. Accommodative adaptation was increased by timolol and betaxolol, and decreased by isoproterenol. We surmised that beta adrenergic agents exerted an indirect influence on the parasympathetic nervous system. The activation of beta receptors produced a hyperopic shift on the far point of accommodation and decreased accommodative adaptation, which suggests that activation of adrenergic receptors may reduce parasympathetic activity, hence affecting the state of accommodation.