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Pupillary response is a physiological response that varies the size of the pupil between 1.5 mm and 8 mm, [1] via the optic and oculomotor cranial nerve. A constriction response , [2] is the narrowing of the pupil, which may be caused by scleral buckles or drugs such as opiates/opioids or anti-hypertension medications.
Convergence of the eyes, or the orientation of the visual axis of each eye towards an object in order to focus its image on each fovea, is the first of the three responses. This can be observed by the cross-eyed movement of the eyes when a finger is held up in front of a face and moved towards the face. Next, constriction of the pupil occurs.
The pupillary sphincter muscle and pupillary dilator muscle control the iris to adjust the size of the pupil to adjust how much light enters into the eye. The pupillary dilator muscle increases the pupillary diameter and it is arranged radially, but the pupillary sphincter muscle is responsible for the constriction of the pupil's diameter and ...
The pupil constricts when the iris sphincter muscle is stimulated and contracts. In humans, it functions to constrict the pupil in bright light (pupillary light reflex) or during accommodation. [citation needed] In lower animals, the muscle cells themselves are photosensitive causing iris action without brain input. [5]
Conversely, parasympathetic stimulation causes contraction of the circular muscle and constriction of the pupil. The mechanism of mydriasis depends on the agent being used. It usually involves either a disruption of the parasympathetic nerve supply to the eye (which normally constricts the pupil) or overactivity of the sympathetic nervous ...
When light is shone into right eye, right pupil constricts. Direct reflex of the right pupil is unaffected, The right afferent limb, right CN II, and the right efferent limb, right CN III, are both intact. The left consensual reflex is lost. When the right eye is stimulated by light, left pupil does not constrict consensually.
Tonic pupils are fairly common – they are seen in roughly 1 out of every 500 people. A person with anisocoria (one pupil bigger than the other) whose pupil does not react to light (does not constrict when exposed to bright light) most likely has Adie syndrome – idiopathic degeneration of the ciliary ganglion.
The Marcus Gunn pupil is a relative afferent pupillary defect indicating a decreased pupillary response to light in the affected eye. [3] In the swinging flashlight test, a light is alternately shone into the left and right eyes. A normal response would be equal constriction of both pupils, regardless of which eye the light is directed at.