Possible non-muscarinic miotic action of echothiophate iodide in humans

The proposed non-muscarinic pupillary action of echothiophate iodide (EI) was investigated in humans. In 10 healthy volunteers the variations of the pupillary area, induced by EI eye drops, were evaluated by using an electronic pupillometer. When instilled alone, as well as after homatropine, EI caused pupillary constriction. The reduction of the homatropine-induced mydriasis by EI was not accompanied by any increase in the almost abolished pupillary response to light, thus excluding that an enhancement of the parasympathetic activity contributes to pupillary constriction. These findings suggest a non-muscarinic component in the EI-induced miosis, the nature of which remains to be elucidated.