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Mydriasis

 

 
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Mydriasis
 
 
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Mydriasis is an excessive dilation of the pupil
Pupil

The pupil is the sphere that is located in the center of the Iris of the eye and that controls the amount of light that enters the eye. It appears black because most of the light entering the pupil is absorbed by the biological tissue inside the eye....
 due to disease
Disease

A disease or medical condition is an abnormal condition of an organism that impairs bodily functions, associated with specific symptoms and Medical signs....
, trauma
Physical trauma

Physical trauma refers to a body injury. A trauma patient is someone who has suffered serious and life-threatening physical injury with the potential for secondary complications such as Shock , respiratory failure and death....
, or the use of drug
Drug

A drug, broadly speaking, is any chemical substance that, when absorbed into the body of a living organism, alters normal bodily function....
s. Normally, the pupil dilates in the dark
Dark

Dark may refer to:*Darkness, the absence of light*The Dark, the name of several works of fiction*Evil, sinister or malign*dark , a term used to describe a broadcasting service that has ceased transmission...
 and constricts
Constriction

Sorry, no overview for this topic
 in the light
Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
 to improve vividity at night and to protect the retina
Retina

The vertebrate retina is a light sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera....
 from sunlight damage during the day. A mydriatic pupil will remain excessively large even in a bright environment. Sometimes colloquially referred to as a "blown pupil
Blown pupil

Blown pupil is an informal medical term used by physicians and nurses to refer to sudden pupillary dilation and loss of ability to constrict in response to light....
."

The opposite, constriction of the pupil, is referred to as miosis
Miosis

Miosis is constriction of the pupil of the eye. This is a normal response to an increase in light but can also be associated with certain pathological conditions, microwave radiation exposure and certain drugs....
.
e are two types of muscle
MUSCLE

MUSCLE is public domain, multiple sequence alignment software for protein and nucleotide sequences.MUSCLE is integrated into UGENE bioinformatics tool as a plugin....
 that control the size of the iris
Iris (anatomy)

The iris is a membrane in the eye, responsible for controlling the amount of light reaching the retina. The iris consists of pigmented fibrovascular tissue known as a stroma of iris....
: circular
Iris sphincter muscle

The Iris sphincter muscle is a muscle in the part of the eye called the iris. It encircles the eye, appropriate to its function as a constrictor....
 muscle and radial
Iris dilator muscle

The Iris dilator muscle , is a smooth muscle of the eye, running radially in the iris and therefore fit as a dilator. It is innervated by the sympathetic system, which acts by releasing noradrenaline, which acts on a1-receptors.....
 muscle.






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Mydriasis is an excessive dilation of the pupil
Pupil

The pupil is the sphere that is located in the center of the Iris of the eye and that controls the amount of light that enters the eye. It appears black because most of the light entering the pupil is absorbed by the biological tissue inside the eye....
 due to disease
Disease

A disease or medical condition is an abnormal condition of an organism that impairs bodily functions, associated with specific symptoms and Medical signs....
, trauma
Physical trauma

Physical trauma refers to a body injury. A trauma patient is someone who has suffered serious and life-threatening physical injury with the potential for secondary complications such as Shock , respiratory failure and death....
, or the use of drug
Drug

A drug, broadly speaking, is any chemical substance that, when absorbed into the body of a living organism, alters normal bodily function....
s. Normally, the pupil dilates in the dark
Dark

Dark may refer to:*Darkness, the absence of light*The Dark, the name of several works of fiction*Evil, sinister or malign*dark , a term used to describe a broadcasting service that has ceased transmission...
 and constricts
Constriction

Sorry, no overview for this topic
 in the light
Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
 to improve vividity at night and to protect the retina
Retina

The vertebrate retina is a light sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera....
 from sunlight damage during the day. A mydriatic pupil will remain excessively large even in a bright environment. Sometimes colloquially referred to as a "blown pupil
Blown pupil

Blown pupil is an informal medical term used by physicians and nurses to refer to sudden pupillary dilation and loss of ability to constrict in response to light....
."

The opposite, constriction of the pupil, is referred to as miosis
Miosis

Miosis is constriction of the pupil of the eye. This is a normal response to an increase in light but can also be associated with certain pathological conditions, microwave radiation exposure and certain drugs....
.

Mechanism

There are two types of muscle
MUSCLE

MUSCLE is public domain, multiple sequence alignment software for protein and nucleotide sequences.MUSCLE is integrated into UGENE bioinformatics tool as a plugin....
 that control the size of the iris
Iris (anatomy)

The iris is a membrane in the eye, responsible for controlling the amount of light reaching the retina. The iris consists of pigmented fibrovascular tissue known as a stroma of iris....
: circular
Iris sphincter muscle

The Iris sphincter muscle is a muscle in the part of the eye called the iris. It encircles the eye, appropriate to its function as a constrictor....
 muscle and radial
Iris dilator muscle

The Iris dilator muscle , is a smooth muscle of the eye, running radially in the iris and therefore fit as a dilator. It is innervated by the sympathetic system, which acts by releasing noradrenaline, which acts on a1-receptors.....
 muscle. The former is innervated by the parasympathetic nervous system
Parasympathetic nervous system

The parasympathetic nervous system is a division of the autonomic nervous system , along with the sympathetic nervous system and enteric nervous system ....
, the latter by the sympathetic nervous system
Sympathetic nervous system

The Sympathetic Nervous System is a branch of the autonomic nervous system along with the enteric nervous system and parasympathetic nervous system....
. Sympathetic stimulation of a1 adrenergic receptors causes the contraction
Muscle contraction

Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may #Eccentric contraction, #Concentric contraction or #Isometric contraction....
 of the radial muscle, and subsequent dilation of the pupil. Conversely, parasympathetic stimulation cause 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 causes contraction of the pupil), or overactivity of the sympathetic nervous system
Sympathetic nervous system

The Sympathetic Nervous System is a branch of the autonomic nervous system along with the enteric nervous system and parasympathetic nervous system....
 (SNS).


Causes


Physiological

Natural release of the hormone oxytocin
Oxytocin

Oxytocin is a mammalian hormone that also acts as a neurotransmitter in the brain.It is best known for its roles in female reproduction: it is released in large amounts after distension of the cervix and vagina during labor, and after stimulation of the nipples, facilitating childbirth and breastfeeding, respectively....
 can cause mild to moderate mydriasis. Strong sexual arousal can often lead to very enlarged pupils, rather than the minor dilation observed during sexual affection. Orgasm
Orgasm

An orgasm is the conclusion of the Human sexual response cycle#Plateau phase of Human sexual response cycle, and may be experienced by both males and females....
 has been reported to lead to pupillary block in a single case in combination with an ocular precondition. Here the parasympathetic and sympathetic stimulation lead to sphincter muscle stimulation during pupillary dilation in the dark, while ciliary contraction caused zonular relaxation leading to pupillary block and angle-closure in combination with pre-existing narrow chamber angle
Anterior chamber

The anterior chamber is the fluid-filled space inside the eye between the iris and the cornea's innermost surface, the endothelium. Aqueous humor is the fluid that fills the anterior chamber....
.

Pathological

The parasympathetic nervous supply which causes constriction of the pupil, or miosis
Miosis

Miosis is constriction of the pupil of the eye. This is a normal response to an increase in light but can also be associated with certain pathological conditions, microwave radiation exposure and certain drugs....
, is supplied by cranial nerve III, the oculomotor nerve
Oculomotor nerve

The oculomotor nerve is the third of twelve paired cranial nerves. It controls most of the eye's movements, constriction of the pupil, and maintains an open eyelid....
. Damage to this nerve typically manifests itself as mydriasis, because the sympathetic
Sympathetic

The word sympathetic means different things in different contexts.* In neurology and neuroscience, the sympathetic nervous system is a part of the autonomic nervous system....
 supply to the pupil which causes mydriasis remains unaffected, and therefore unopposed. Multiple central nervous system
Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
 disorders e.g. epilepsy, stroke are known to lead to temporal mydriasis as well.

Traumatic

In cases of head injury
Head injury

Head injury refers to Physical trauma to the head . This may or may not include injury to the human brain . However, the terms traumatic brain injury and head injury are often used interchangeably in the medical literature....
 or orbit trauma (eye injury)
Eye injury

Physiology or chemical injuries of the eye can be a serious threat to Visual perception if not treated appropriately and in a timely fashion. The most obvious presentation of ocular injuries is redness and pain of the affected eyes....
, the iris sphincter
Iris sphincter muscle

The Iris sphincter muscle is a muscle in the part of the eye called the iris. It encircles the eye, appropriate to its function as a constrictor....
 (the muscle responsible for closing the pupil) or the nerves controlling it can be damaged, reducing or eliminating reactivity
Reactivity

Reactivity refers to the Reaction rate at which a chemical substance tends to undergo a chemical reaction in time. In pure chemical compounds, reactivity is regulated by the physical properties of the sample....
 to light.

Drugs

Anticholinergic
Anticholinergic

An anticholinergic agent is a substance that blocks the neurotransmitter acetylcholine in the central nervous system and the peripheral nervous system....
s such as atropine
Atropine

Atropine is a tropane alkaloid extracted from deadly nightshade , jimsonweed , Mandrake and other plants of the family Solanaceae. It is a secondary metabolite of these plants and serves as a hard drug with a wide variety of effects....
, hyoscyamine
Hyoscyamine

Hyoscyamine, pronounced hi-oh-SYE-uh-meen, is a chemical compound, a tropane alkaloid. It is the levorotary isomer to atropine. It is a secondary metabolite found in certain plants of the Solanaceae family, including henbane, mandrake , jimsonweed , and deadly nightshade ....
, and scopolamine
Scopolamine

Scopolamine, known by the names levo-duboisine and hyoscine, is a tropane alkaloid Medication with muscarinic antagonist effects. It is obtained from plants of the family Solanaceae , such as henbane, jimson weed and Angel's Trumpets , and corkwood ....
 antagonize the muscarinic acetylcholine
Muscarinic acetylcholine receptor

Muscarinic receptors, or mAChRs, are G protein-coupled receptor acetylcholine receptors found in the plasma membranes of certain neurons and other Cell s....
 receptors in the brain. By blocking these receptors, the pupils are no longer capable of constriction and dilation results.

Many hallucinogens induce mydriasis. The psychedelic
Psychedelic

The word 'psychedelic' is an English term coined from the Greek language words for "soul," ???? , and "manifest," d???? . A psychedelic experience is characterized by the perception of aspects of one's mind previously unknown, or by the creative exuberance of the mind liberated from its ostensibly ordinary fetters....
s, including LSD
LSD

Lysergic acid diethylamide, LSD, LSD-25, or acid, is a semisynthetic psychedelic drug of the ergoline family. Its unusual psychological effects, which include visuals of colored patterns behind the eyes in the mind, a sense of time distorting, and crawling geometric patterns, have made it one of the most widely known psyched...
, magic mushrooms, mescaline
Mescaline

Mescaline or 3,4,5-trimethoxyphenethylamine is a naturally-occurring psychedelic alkaloid of the phenethylamine class. It is mainly used as a recreational drug, an entheogen, and a tool to supplement various practices for transcendence , including in meditation, psychonautics, art projects, and psychedelic psychotherapy....
, 2C-B
2C-B

2C-B or 4-bromo-2,5-dimethoxyphenethylamine is a Psychedelics, dissociatives and deliriants of the 2C's, an Empathogen-entactogen. It was first synthesized by Alexander Shulgin in 1974....
, and DMT
Dimethyltryptamine

Dimethyltryptamine , also known as N,N-dimethyltryptamine, is a naturally-occurring tryptamine and potent psychedelic drug, found not only in many plants, but also in trace amounts in the human body where its natural function is undetermined....
, to name a few, all do so by agonizing the serotonergic
Serotonin

Serotonin is a monoamine neurotransmitter synthesized in serotonergic neurons in the central nervous system and enterochromaffin cells in the gastrointestinal tract of animals including humans....
 5-HT2A
5-HT2A receptor

The mammalian 5-HT2A receptor is a subtype of the 5-HT2 receptor which belongs to the serotonin receptor family and is a GPCR ....
 receptors in the brain. The dissociatives such as ketamine
Ketamine

Ketamine is a drug used in human and veterinary medicine developed by Parke-Davis in 1962. Its hydrochloride salt is sold as Ketanest, Ketaset, and Ketalar....
, DXM
Dextromethorphan

Dextromethorphan is an antitussive drug. It is one of the active ingredients used to prevent coughs in many Over-the-counter drug common cold and cough medicines....
, and PCP
Phencyclidine

Phencyclidine , also known as angel dust, is a dissociative drug formerly used as an anesthesia agent, exhibiting hallucinogenic and neurotoxic effects....
 do so as well via antagonism of the NMDA glutamate receptors. There have also been reports that the atypical psychedelic herb salvia divinorum
Salvia divinorum

Salvia divinorum, also known as Diviner?s Sage, ska Mar?a Pastora, or simply by the genus name Salvia, is a Psychoactive drug herb which can induce strong dissociative drug effects....
 causes mydriasis. It works via agonism of the ?-Opioid receptors in the brain. How the neurological changes induced by these drugs ultimately causes pupil dilation is unknown however.

Drugs that increase overall serotonin levels in general are capable of causing mydriasis in the same way as the 5-HT2A-mediated psychedelics. This is because serotonin (5-HT) itself is naturally responsible for normal 5-HT2A stimulation. Henceforth, in sufficient quantities serotonin is mydriatic and can even be mildly psychedelic, though the potentially fatal serotonin syndrome
Serotonin syndrome

Serotonin syndrome is a potentially life-threatening adverse drug reaction that may occur following therapeutic drug use, inadvertent interactions between drugs, overdose of particular drugs, or the recreational use of certain drugs....
 usually ensues before the psychedelia becomes overly-pronounced. Examples of such drugs include MDMA (as well as other MDxx
MDPEA

MDPEA, or 3,4-methylenedioxyphenethylamine, is a lesser-known Psychedelics, dissociatives and deliriants. MDPEA was first synthesized by Alexander Shulgin....
 compounds), fenfluramine
Fenfluramine

Fenfluramine is a drug that was part of the Fen-Phen anti-obesity medication . Also known as Pondimin, fenfluramine was introduced on the U.S....
, chlorphentermine
Chlorphentermine

Chlorphentermine is a stimulant drug which was used as an anorectic. Developed in 1962, it is the 4-chloro derivative of the better known appetite suppressant phentermine, which is still in current use....
, cocaine
Cocaine

Cocaine is a crystalline tropane alkaloid that is obtained from the leaves of the coca plant. The name comes from "coca" in addition to the alkaloid suffix -ine, forming cocaine....
, and many widely-prescribed antidepressant
Antidepressant

An antidepressant is a psychiatric medication used for alleviating major depressive disorder or dysthymia. Drug groups known as MAOIs, tricyclics, and second-generation antidepressants such as SSRIs, and serotonin-norepinephrine reuptake inhibitors are particularly associated with the term....
s such as the SSRIs, SNRI
Serotonin-norepinephrine reuptake inhibitor

Serotonin-norepinephrine reuptake inhibitors are a class of antidepressant used in the treatment of major depressive disorder and other mood disorders....
s, and MAOIs. Natural serotonin-boosting supplements such as L-Tryptophan and 5-HTP are also potentially capable of this in excessive doses.

The neurotransmitter
Neurotransmitter

Neurotransmitters are chemistry which relay, amplify and modulate signals between a neuron and another cell . Neurotransmitters are packaged into vesicles that cluster beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to receptors in the membrane on the postsynaptic side of...
 norepinephrine
Norepinephrine

Norepinephrine or noradrenaline is a catecholamine with dual roles as a hormone and a neurotransmitter.As a stress hormone, norepinephrine affects parts of the brain where attention and responding actions are controlled....
 (noradrenaline) regulates many physiological processes in the body and brain. One of them is the autonomic constriction and contraction of certain muscles. The psychoactive drug cocaine
Cocaine

Cocaine is a crystalline tropane alkaloid that is obtained from the leaves of the coca plant. The name comes from "coca" in addition to the alkaloid suffix -ine, forming cocaine....
 potently inhibits the normal reuptake of norepinephrine
Norepinephrine reuptake inhibitor

Norepinephrine reuptake inhibitors , also known as noradrenaline reuptake inhibitors , are compounds that elevate the extracellular level of the neurotransmitter norepinephrine in the central nervous system by inhibiting its reuptake from the synapse into the presynaptic neuronal terminal....
 into presynaptic nerve terminals
Chemical synapse

Chemical synapses are specialized junctions through which neurons signal to each other and to non-neuronal cells such as those in neuromuscular junctions or glands....
 resulting in an increased level of extracellular
Extracellular

In cell biology, molecular biology and related fields, the word extracellular means "outside the cell ". This space is usually taken to be outside the plasma membranes, and occupied by fluid....
 norepinephrine. The released norepinephrine then proceeds to bind to adrenergic
Adrenergic receptor

The adrenergic receptors are a class of G protein-coupled receptors that are targets of the catecholamines. Adrenergic Receptor s specifically bind and are activated by their endogenous ligands, the catecholamines adrenaline and noradrenaline ....
 receptors and the biological effects of norepinephrine finally occur. When a solution of cocaine is dropped into the eye, this process takes place and the end result is dilation of the pupil. Cocaine itself is not typically used for this task however. Any potent norepinephrine reuptake inhibitor or release agent should be capable of such an effect.

The opiate
Opiate

In medicine, the term opiate describes any of the narcotic alkaloids found in opium, as well as any derivatives of such alkaloids....
s and opioid
Opioid

An opioid is a chemical substance that has a morphine-like action in the body. The main use is for analgesia. These agents work by binding to opioid receptors, which are found principally in the central nervous system and the gastrointestinal tract....
s such as morphine
Morphine

Morphine is a highly potent opiate analgesic Medication, is the principal active agent in opium, and is considered to be the prototypical opioid....
 and heroin
Heroin

Heroin is a opioid synthesized from morphine, a derivative of the opium poppy. It is the 3,6-acetate ester of morphine . The white crystalline form is commonly the hydrochloride salt diacetylmorphine hydrochloride, however heroin Freebase may also appear as a white powder....
 cause miosis
Miosis

Miosis is constriction of the pupil of the eye. This is a normal response to an increase in light but can also be associated with certain pathological conditions, microwave radiation exposure and certain drugs....
. Subsequently, mydriasis occasionally occurs during opioid rebound and withdrawal.

Mydriatics

A mydriatic is an agent which induces dilation
Dilation

Dilation or dilatation may refer to:In physiology:* Pupillary response, dilation of the pupil of the eye* Cervical dilation, the widening of the cervix in childbirth, miscarriage etc....
 of the pupil
Pupil

The pupil is the sphere that is located in the center of the Iris of the eye and that controls the amount of light that enters the eye. It appears black because most of the light entering the pupil is absorbed by the biological tissue inside the eye....
. Drugs such as tropicamide
Tropicamide

Tropicamide is a muscarinic anticholinergic.Other brand names include Mydriacyl....
 are used in medicine
Medicine

Medicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
 to permit examination of the retina
Retina

The vertebrate retina is a light sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera....
 and other deep structures of the eye, and also to reduce painful ciliary muscle
Ciliary muscle

The ciliary muscle is a muscle in the eye that controls the eye's accommodation for viewing objects at varying distances....
 spasm (see cycloplegia
Cycloplegia

Cycloplegia is paralysis of the ciliary muscle of the eye, resulting in a loss of accommodation . ...
). One effect of administration of a mydriatic is intolerance to bright light. Purposely-induced mydriasis via mydriatics is also used as a diagnostic test for Horner's Syndrome
Horner's syndrome

Horner's syndrome or Horner syndrome is a clinical syndrome caused by damage to the sympathetic nervous system. It is also known by the names Bernard-Horner syndrome or oculosympathetic palsy....
.

Cyclomydril is an ophthalmic medication intended to cause mydriasis, usually to allow an optometrist or ophthalmologist to perform a better visual inspection of the inside of an eye.

See also

  • Miosis
    Miosis

    Miosis is constriction of the pupil of the eye. This is a normal response to an increase in light but can also be associated with certain pathological conditions, microwave radiation exposure and certain drugs....
  • Anisocoria
    Anisocoria

    Anisocoria is a condition characterized by an unequal size of the pupils....