The origin of the arteries supplying the posterior circulation include the aorta and the great vessels in the chest (e.g., innominate, vertebral, subclavian arteries) followed by the cervical and intracranial parts of the vertebral arteries, the basilar arteries and perforating vessels, and the terminal artery the posterior cerebral arteries. The most common causes of strokes involving the posterior circulation include atherosclerosis, embolism, and dissection. The brainstem including the medulla also contains vestibular-otolith pathways and the ocular sympathetic pathway which can produce skew deviation, nystagmus, or Horner syndrome respectively.Īpproximately 20-25% of ischemic stroke involve the posterior circulation. The midbrain-or mesencephalon- and pons have several functions which include involvement in the afferent and efferent pupillary and ocular motor (efferent) pathways. The midbrain, pons, and medulla oblongata are components of the brainstem which control basic body functions such as consciousness, breathing, proprioception, heart rate, and blood pressure. Brainstem stroke syndromes are a subtype of strokes which lead to ischemia of the structures of the brainstem. Visceromotor nerve axons (which constitute a portion of cranial nerve III, along with the somatomotor portion derived from the Edinger-Westphal nucleus) synapse on ciliary ganglion neurons, whose parasympathetic axons innervate the iris sphincter muscle, producing miosis.Posterior circulation strokes involving the brainstem can result in subsequent ophthalmologic manifestations. 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. 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. The retinal photoceptors convert light stimuli into electric impulses.
Signals from photosensitive ganglion cells have multiple functions including acute suppression of the hormone melatonin, entrainment of the body's circadian rhythms and regulation of the size of the pupil. The ganglion cells give information about ambient light levels, and react sluggishly compared to the rods and cones. Light entering the eye strikes three different photoreceptors in the retina: the familiar rods and cones used in image forming and the more newly discovered photosensitive ganglion cells. In some rare cases, when exposed to mustard gas.Pilocarpine eye drops and all other parasympathomimetics.Mirtazapine, a noradrenergic and specific serotonergic antidepressant ( NaSSA).Some cancer chemotherapy drugs, including camptothecin derivatives.Serotonin antagonists, such as Ondansetron (an anti-emetic) known by its brand name Zofran.Cholinergic agents such as acetylcholine.Antipsychotics, including risperidone, haloperidol, chlorpromazine, olanzapine, quetiapine.Imidazolines such as clonidine, naphazoline, oxymetazoline and tetrahydrozoline.Products containing nicotine such as cigarettes, chewing tobacco or gum.Opioids such as fentanyl, morphine, heroin and methadone (the notable exception being pethidine).Patient also shows ptosis of both eyelids and an inattentive look at the camera, a sign of altered level of consciousness caused by the sedative effect of the drug.
Hemorrhage into pons ( intracranial hemorrhage).Senile miosis (a reduction in the size of a person's pupil in old age).Anisocoria is the condition of one pupil being more dilated than the other. The opposite condition, mydriasis, is the dilation of the pupil.
Miosis, or myosis (from Ancient Greek μύειν ( múein) 'to close the eyes'), is excessive constriction of the pupil.
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