A constriction response (
miosis),[1] is the narrowing of the pupil, which may be caused by scleral buckles or drugs such as
opiates/
opioids or anti-hypertension medications. Constriction of the pupil occurs when the
circular muscle, controlled by the
parasympathetic nervous system (PSNS), contracts, and also to an extent when the
radial muscle relaxes.
A dilation response (
mydriasis), is the widening of the pupil and may be caused by
adrenaline;
anticholinergic agents;
stimulant drugs such as
MDMA,
cocaine, and
amphetamines; and some
hallucinogenics (e.g.
LSD).[2] Dilation of the pupil occurs when the smooth cells of the
radial muscle, controlled by the sympathetic nervous system (SNS), contract, and also when the cells of the iris sphincter muscle relax.
Some humans have the ability to exert direct and voluntary control over their
iris sphincter muscles and
dilator muscles, granting them the ability to dilate and constrict their pupils on command, regardless of lighting condition and/or eye
accommodation state.[14] However, this ability is very rare, and its potential use or advantages are unclear.
The latency of pupillary response (the time in which it takes to occur) increases with age.[15]
In
ophthalmology, intensive studies of pupillary response are conducted via videopupillometry.[16]
Anisocoria is the condition of one pupil being more dilated than the other.
^Aston-Jones G, Cohen JD (2005-07-21). "An integrative theory of locus coeruleus-norepinephrine function: adaptive gain and optimal performance". Annual Review of Neuroscience. 28 (1): 403–50.
doi:
10.1146/annurev.neuro.28.061604.135709.
PMID16022602.
S2CID535645.