Pupillary response is a

physiological Physiology (; ) is the science, scientific study of function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a branches of science, subdiscipline of biology, physiology focuses on how organisms, organ syst ...

response that varies the size of the pupil between 1.5 mm and 8 mm, via the optic and oculomotor cranial nerve. A constriction response (

miosis Miosis, or myosis (), is excessive constriction of the pupil.Farlex medical dictionary
citing: ...

), is the narrowing of the pupil, which may be caused by scleral buckles or drugs such as

opiates An opiate is an alkaloid substance derived from opium (or poppy straw). It differs from the similar term ''opioid'' in that the latter is used to designate all substances, both natural and synthetic, that bind to opioid receptors in the brain ( ...

/ opioids or anti-hypertension medications. Constriction of the pupil occurs when the circular muscle, controlled by the

parasympathetic nervous system The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The autonomic nervous system is responsible for regulat ...

(PSNS), contracts, and also to an extent when the radial muscle relaxes. Voluntary pupil dilation

A dilation response (

mydriasis Mydriasis is the Pupillary dilation, dilation of the pupil, usually having a non-physiological cause, or sometimes a physiological pupillary response. Non-physiological causes of mydriasis include disease, Physical trauma, trauma, or the use of c ...

), is the widening of the pupil and may be caused by

adrenaline Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands a ...

;

anticholinergic Anticholinergics (anticholinergic agents) are substances that block the action of the acetylcholine (ACh) neurotransmitter at synapses in the central nervous system, central and peripheral nervous system. These agents inhibit the parasympatheti ...

agents;

stimulant Stimulants (also known as central nervous system stimulants, or psychostimulants, or colloquially as uppers) are a class of drugs that increase alertness. They are used for various purposes, such as enhancing attention, motivation, cognition, ...

drugs such as

MDMA 3,4-Methylenedioxymethamphetamine (MDMA), commonly known as ecstasy (tablet form), and molly (crystal form), is an empathogen–entactogenic drug with stimulant and minor Psychedelic drug, psychedelic properties. In studies, it has been used ...

cocaine Cocaine is a tropane alkaloid and central nervous system stimulant, derived primarily from the leaves of two South American coca plants, ''Erythroxylum coca'' and ''Erythroxylum novogranatense, E. novogranatense'', which are cultivated a ...

, and

amphetamines Substituted amphetamines, or simply amphetamines, are a chemical class, class of compounds based upon the amphetamine structure; it includes all derivative (chemistry), derivative compounds which are formed by replacing, or substitution reacti ...

; and some

hallucinogen Hallucinogens, also known as psychedelics, entheogens, or historically as psychotomimetics, are a large and diverse class of psychoactive drugs that can produce altered states of consciousness characterized by major alterations in thought, mo ...

ics (e.g. LSD). 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. Pupillary light reflex

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 finance and economics, interest is payment from a debtor or deposit-taking financial institution to a lender or depositor of an amount above repayment of the principal sum (that is, the amount borrowed), at a particular rate. It is distinct f ...

in the subject of attention or arousal, sexual stimulation,

uncertainty Uncertainty or incertitude refers to situations involving imperfect or unknown information. It applies to predictions of future events, to physical measurements that are already made, or to the unknown, and is particularly relevant for decision ...

, decision conflict, errors, physical activity or increasing cognitive load or demand. The responses correlate strongly with activity in the locus coeruleus

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a Chemical synapse, synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell. Neurotra ...

system. The pupils contract immediately before REM sleep begins. A pupillary response can be intentionally conditioned as a Pavlovian response to some stimuli. 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. 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. In

ophthalmology Ophthalmology (, ) is the branch of medicine that deals with the diagnosis, treatment, and surgery of eye diseases and disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a ...

, intensive studies of pupillary response are conducted via videopupillometry.

Anisocoria Anisocoria is a condition characterized by an unequal size of the eyes' pupils. Affecting up to 20% of the population, anisocoria is often entirely harmless, but can be a sign of more serious medical problems. Causes Anisocoria is a common cond ...

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

References

{{Nonverbal communication Sexual arousal Pupil

See also

References