Miosis caused by high doses ofopiates. The person also showsptosis of both eyelids and an inattentive look at the camera, a sign ofaltered level of consciousness caused by the sedative effect of the drug.
Light entering the eye strikes three differentphotoreceptors in theretina: the familiarrods andcones used in image forming and the more newly discoveredphotosensitive ganglion cells. The ganglion cells give information about ambient light levels, and react sluggishly compared to the rods and cones. Signals from photosensitive ganglion cells have multiple functions including acute suppression of the hormonemelatonin,entrainment of the body'scircadian rhythms and regulation of the size of the pupil.
The retinal photoceptors convert light stimuli into electric impulses. Nerves involved in the resizing of the pupil connect to thepretectal nucleus of the highmidbrain, bypassing thelateral geniculate nucleus and the primaryvisual cortex. From the pretectal nucleus neurons send axons to neurons of theEdinger-Westphal nucleus whosevisceromotor axons run along both the left and rightoculomotor nerves. Visceromotor nerve axons (which constitute a portion ofcranial nerve III, along with the somatomotor portion derived from the Edinger-Westphal nucleus) synapse onciliary ganglion neurons, whose parasympathetic axons innervate theiris sphincter muscle, producingmiosis.
