Pupillary response is a physiological response that varies the size of the pupil, either resulting in constriction (miosis) or dilation (mydriasis, expansion), via relaxation or contraction of the iris dilator muscle. The response 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 indicate sexual stimulation. The pupils contract immediately before someone falls asleep. A pupillary response can be intentionally conditioned as a Pavlovian response to some stimuli.
The latency of pupillary response (the time in which it takes to occur) increases with age. Use of central nervous system stimulant drugs and some hallucinogenic drugs can cause dilation of the pupil.
In ophthalmology, intensive studies of pupillary response are conducted via videopupillometry.
Anisocoria is the condition of one pupil being more dilated than the other.
| 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 | Fight-or-flight response | |
| Corresponding non-physiological state | Miosis | Mydriasis |
Read more about Pupillary Response: See Also
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