8/1/2023 0 Comments Hippus pupil reactionThe contralateral efferent limb causes consensual light reflex of the contralateral pupil. The ipsilateral efferent limb transmits nerve signals for direct light reflex of the ipsilateral pupil. Each afferent limb has two efferent limbs, one ipsilateral and one contralateral. ![]() Postganglionic nerve fibers leave the ciliary ganglion to innervate the ciliary sphincter. Each Edinger-Westphal nucleus gives rise to preganglionic parasympathetic fibers which exit with CN III and synapse with postganglionic parasympathetic neurons in the ciliary ganglion. The pretectal nucleus projects crossed and uncrossed fibers to the ipsilateral and contralateral Edinger-Westphal nuclei, which are also located in the midbrain. ![]() The efferent limb is the pupillary motor output from the pretectal nucleus to the ciliary sphincter muscle of the iris. Ganglion cells of the retina project fibers through the optic nerve to the ipsilateral pretectal nucleus. Anatomically, the afferent limb consists of the retina, the optic nerve, and the pretectal nucleus in the midbrain, at level of superior colliculus. Each efferent limb has nerve fibers running along the oculomotor nerve ( CN III). The afferent limb has nerve fibers running within the optic nerve ( CN II). The pupillary light reflex neural pathway on each side has an afferent limb and two efferent limbs. Right consensual pupillary reflex is the right pupil's indirect response to light entering the left eye, the contralateral eye.Right direct pupillary reflex is the right pupil's response to light entering the right eye, the ipsilateral eye.Left consensual pupillary reflex is the left pupil's indirect response to light entering the right eye, the contralateral eye.Left direct pupillary reflex is the left pupil's response to light entering the left eye, the ipsilateral eye.Thus there are four types of pupillary light reflexes, based on this terminology of absolute laterality (left versus right) and relative laterality (same side versus opposite side, ipsilateral versus contralateral, direct versus consensual): A consensual pupillary reflex is response of a pupil to light that enters the contralateral (opposite) eye. A direct pupillary reflex is pupillary response to light that enters the ipsilateral (same) eye. The terms direct and consensual refers to the side where the light source comes from, relative to the side of the reacting pupil. When light is shone into only one eye and not the other, it is normal for both pupils to constrict simultaneously. Right pupillary reflex means reaction of the right pupil, whether light is shone into the left eye, right eye, or both eyes. Left pupillary reflex refers to the response of the left pupil to light, regardless of which eye is exposed to a light source. Pupillary reflex is conceptually linked to the side (left or right) of the reacting pupil, and not to the side from which light stimulation originates. Pupillary reflex is synonymous with pupillary response, which may be pupillary constriction or dilation. Whereas, the pupil is the passive opening formed by the active iris. It may be helpful to consider the Pupillary reflex as an ' Iris' reflex, as the iris sphincter and dilator muscles are what can be seen responding to ambient light. By analogy with a camera, the pupil is equivalent to aperture, whereas the iris is equivalent to the diaphragm. ![]() The pupil is the dark circular opening in the center of the iris and is where light enters the eye. Light shone into one eye will cause both pupils to constrict. Thus, the pupillary light reflex regulates the intensity of light entering the eye. A greater intensity of light causes the pupil to constrict ( miosis/myosis thereby allowing less light in), whereas a lower intensity of light causes the pupil to dilate ( mydriasis, expansion thereby allowing more light in). The pupillary light reflex ( PLR) or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity ( luminance) of light that falls on the retinal ganglion cells of the retina in the back of the eye, thereby assisting in adaptation of vision to various levels of lightness/darkness. The W-shaped pupil of the cuttlefish dilating when the lights are turned off
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