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A human adult exhibiting voluntary control over his iris muscles, where he can cause his pupil to dilate and constrict on command. A dilation response , is the widening of the pupil and may be caused by adrenaline; anticholinergic agents; stimulant drugs such as MDMA, cocaine, and amphetamines; and some hallucinogenics (e.g. LSD). [2]
Mydriasis is frequently induced by drugs for certain ophthalmic examinations and procedures, particularly those requiring visual access to the retina. Fixed, unilateral mydriasis could be a symptom of raised intracranial pressure. The opposite, constriction of the pupil, is referred to as miosis. Both mydriasis and miosis can be physiological.
Nerves involved in the resizing of the pupil connect to the pretectal nucleus of the high midbrain, bypassing the lateral geniculate nucleus and the primary visual cortex. From the pretectal nucleus neurons send axons to neurons of the Edinger-Westphal nucleus whose visceromotor axons run along both the left and right oculomotor nerves .
Certain drugs cause constriction of the pupils, such as opioids. [7] Other drugs, such as atropine, LSD, MDMA, mescaline, psilocybin mushrooms, cocaine and amphetamines may cause pupil dilation. [8] [9] The sphincter muscle has a parasympathetic innervation, and the dilator has a sympathetic innervation.
What it looks like: Some of the signs of opioid overdose include unconsciousness, slow or shallow breathing, choking or gurgling sounds, discolored skin, and constricted “pinpoint pupils ...
The short-term physiological effects of cocaine include [11] constricted blood vessels, dilated pupils, and increased temperature, heart rate, and blood pressure. Some users of cocaine report feelings of restlessness, irritability, and anxiety. In rare instances, sudden death can occur on the first use of cocaine or unexpectedly thereafter.
Additionally, nicotine can cause constriction of the blood vessels, reducing blood flow to the eyes and making them more vulnerable to damage and disease. [30] It is recommended that smokers exhibiting signs and symptoms of retinopathy engage in smoking cessation to improve their quality of life.
The ptosis of Horner syndrome can be quite mild or barely noticeable (partial ptosis). [7] When anisocoria occurs and the examiner is unsure whether the abnormal pupil is the constricted or dilated one, if a one-sided ptosis is present then the abnormally sized pupil can be presumed to be on the side of the ptosis. [citation needed]