Adrenoceptors affect accommodation by modulating cholinergic activity.

In an attempt to clarify the functional role of adrenoceptors in accommodation, the effects of various adrenergic agents on the state of accommodation were studied. Fifty-two emmetropic, visually normal subjects (24.6 +/- 0.42 years old) participated in this study. Using an infrared optometer, the far and near points of accommodation were measured by a quasistatic method. Tonic accommodation and accommodative adaptation were also investigated. All these parameters were measured before and after topical application of various adrenergic agents. Both bunazosin hydrochloride (0.1%) and phenylephrine hydrochloride (5%) had no effect on tonic accommodation and accommodative adaptation. However, bunazosin hydrochloride increased the near point of accommodation. Timolol maleate (0.5%) and isoproterenol hydrochloride (3.0%) did not affect tonic accommodation. Isoproterenol hydrochloride evoked a hyperopic shift of the far point of accommodation by 0.23 +/- 0.42 diopters (D). Additionally, accommodative adaptation was increased by timolol maleate (0.36 +/- 0.62 D) and decreased by isoproterenol hydrochloride (0.18 +/- 0.48 D). These results indicate that both alpha and beta adrenoceptors affect accommodation. Activation of alpha adrenoceptors increased the near point of accommodation and activation of beta adrenoceptors decreased accommodative adaptation, which suggests that activation of adrenoceptors may modify parasympathetic activity; hence, affecting the state of accommodation.