Mechanism of haloperidol-induced miosis.

Haloperidol administration (iv) has been shown to produce miosis in dogs. In the present study on rabbits, haloperidol administration (iv) produced dose-related miosis but when administered intracerebroventricularly, it failed to produce any change in pupillary size. Higher degree of miosis was observed when haloperidol was administered directly into the anterior chamber of eye. Haloperidol pretreatment failed to significantly modify the mydriasis produced by phenylephrine or atropine. These observations suggest that the miosis produced by haloperidol is a peripheral effect, and also that the miosis is not mediated through the blockade of alpha adrenoceptors of radial muscles or stimulation of cholinoceptors of circular muscles of iris.