Walsh & Hoyt: Drug Effects

The iris is easy to see because it is suspended in a clear fluid behind a clear cornea. Thus, the actions of the sphincter and dilator muscles on the size of the pupil can be monitored easily. Parasympathetic and sympathetic neural impulses to the iris muscles can be modified by drugs at the synapses and at the effector sites, because it is at these locations that the transmission of the impulses depends on chemical mediators. Thus, the pupil can be and frequently is used as an indicator of drug action. Drugs that dilate the pupils. Parasympatholytic (anticholinergic) drugs. Sympathomimetic (adrenergic) drugs. Muscle relaxants. Drugs that constrict the pupils. Parasympathetomimetic (cholinergic) drugs. Sympatholytic (antiadrenergic) drugs. Other drugs that affect the pupil. Iris pigment and pupillary responses to drugs.