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Pupillary response

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Pupillary response

Pupillary response

Pupillary response is a physiological response that varies the size of the pupil, via the optic and oculomotor cranial nerve. This response results in either constriction (miosis),[1] narrowing the pupil, or dilation (mydriasis), widening the pupil. Dilation of the pupil occurs when the smooth cells of the radial muscle, controlled by the sympathetic nervous system (SNS), contract. Constriction of the pupil occurs when the circular muscle, controlled by the parasympathetic nervous system (PNS), contracts.

The responses can have a variety of causes, from an involuntary reflex reaction to exposure or inexposure to light — in low light conditions a dilated pupil lets more light into the eye — or it may indicate interest in the subject of attention, or sexual stimulation.[2] The pupils contract immediately before REM sleep begins.[3] A pupillary response can be intentionally conditioned as a Pavlovian response to some stimuli.[4]

The latency of pupillary response (the time in which it takes to occur) increases with age.[5] Use of central nervous system stimulant drugs and some hallucinogenic drugs can cause dilation of the pupil.[6]

In ophthalmology, intensive studies of pupillary response are conducted via videopupillometry.[7]

Anisocoria is the condition of one pupil being more dilated than the other.

Scheme showing sympathetic and parasympathetic innervation of the pupil and sites of lesion in a Horner's syndrome.
Sympathetic connections of the ciliary and superior cervical ganglia.
Pupillary responses
Constriction Dilation
Muscular mechanism Relaxation of iris dilator muscle Activation of iris dilator muscle
Cause in pupillary light reflex Increased light Decreased light
Other physiological causes Accommodation reflex Fight-or-flight response
Corresponding non-physiological state Miosis Mydriasis

See also


  1. ^
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  3. ^
  4. ^
  5. ^
  6. ^
  7. ^

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