Mydriasis pupil) or overactivity of the sympathetic nervous system (SNS). Pupil diameter also increases in reaction to cognitive tasks requiring memory and attention, and this phenomenon is used as an indicator of mental activation (‘arousal’) in psychophysiological experiments . Natural release of the hormone oxytocin can cause mild to moderate mydriasis. Parasympathetic fibers travel with cranial nerve III, the oculomotor nerve, to innervate the circular layer of muscle of the eye (sphincter pupillae). Damage to this nerve typically manifests itself as mydriasis, because the sympathetic supply to the pupil, which causes mydriasis, remains unaffected, and therefore unopposed. Multiple central nervous system
Mydriasis instance, the adrenoceptor agonist phenylephrine (e.g. Cyclomydril) is used if strong mydriasis is needed for a surgical intervention. Alternatively, anticholinergics (in particular, antimuscarinics) such as atropine, hyoscyamine, and scopolamine antagonize the muscarinic acetylcholine receptors in the eye. Blocking acetylcholine receptors, reduces the pupilary muscles' ability to constrict and causes dilation (which is critical in eye surgery procedures such as cataract surgery which require uninterrupted access to the inner eye via the pupilary aperture, thus requiring that the eye be both paralyzed and anesthetized before the procedure can go ahead. The antimuscarinic, tropicamide, may be used as a mydriastic agent during