Index
You look in the mirror and notice that the black dot in the middle of your eyes is larger than normal. What’s going on?
That point is your pupils, the openings that allow light to enter your eye so you can see.
The muscles in the colored part of your eye, called the iris , control the size of your pupil. Your pupils get bigger or smaller, depending on the amount of light around you.
In low light conditions, your pupils open or dilate to let in more light. When it’s bright, they get smaller, or narrow, to let in less light.
Sometimes your pupils can dilate without any change in light. The medical term for this is mydriasis . Medicines, injuries and illnesses can all cause this eye condition.
Mydriasis (/mɪdraɪ.əsɪs/) is pupil dilation, which usually has a non-physiological cause, or sometimes a physiological pupillary response. Non-physiological causes of mydriasis include illness, trauma, or drug use.
Normally, as part of the pupillary light reflection , the pupil dilates in the dark and contracts in the light to respectively enhance the intensity at night and to protect the retina from damage caused by sunlight during the day.
A mydriatic pupil will remain excessively large even in a bright environment. The excitation of the radial fibers of the iris that increases the pupillary opening is known as mydriasis.
More generally, mydriasis also refers to the natural dilation of the pupils, for example in low light conditions or under sympathetic stimulation.
An informal term for mydriasis is an exhaled pupil, and it is used by medical providers. It is generally used to refer to a fixed unilateral mydriasis, which could be a symptom of elevated intracranial pressure.
The opposite, the constriction of the pupil, is known as miosis. Both mydriasis and miosis can be physiological. Anisocoria is the condition of one pupil that is more dilated than the other.
Benign unilateral episodic mydriasis
This condition means that only one pupil is dilated.
It is called “benign” because it is not related to any serious condition, but it can sometimes affect young women with migraines. The pupil usually returns to normal size within a few hours, but can last for several days.
Mystery of the mydriatic pupils
The authors describe the case of a 27-year-old man who was examined for vertigo and blurred vision. In the objective clinical case there was a slight confusion, in the physical examination the broad symmetric mydriasis predominated.
Later other similar patients were found. Atropine poisoning was proven. The source of the alkaloid was poppy seed contaminated with henbane seeds (Hyoscyamus niger), in bakery products served in the works canteen.
Mechanism
There are two types of muscles that control the size of the iris: the iris sphincter, made up of circularly arranged muscle fibers, and the iris dilator, made up of radially arranged muscle fibers.
The sphincter is innervated by the parasympathetic nervous system (signaled by nerves) and the dilator by the sympathetic nervous system.
Sympathetic stimulation of adrenergic receptors causes contraction of the radial muscle and subsequent dilation of the pupil. In contrast, parasympathetic stimulation causes contraction of the circular muscle and constriction of the pupil.
The mechanism of mydriasis depends on the agent used. It usually involves an interruption of the supply of the parasympathetic nerve to the eye (which normally constricts the pupil) or an overactive sympathetic nervous system (SNS).
The diameter of the pupil also increases in reaction to cognitive tasks that require memory and attention, and this phenomenon is used as an indicator of mental activation (“arousal”) in psychophysiological experiments.
Effects edit
The natural release of the hormone oxytocin can cause mild to moderate mydriasis.
Autonomic neuropathy
Parasympathetic fibers travel with cranial nerve III, the common ocular motor nerve, to innervate the circular layer of the eye muscle (sphincter of the pupils).
Damage to this nerve typically manifests as mydriasis, since the sympathetic supply to the pupil, which causes mydriasis, is unaffected, and therefore unopposed.
Multiple disorders of the central nervous system, eg. epilepsy, stroke, and impending brain herniation are also known to cause temporary mydriasis.
A brain catastrophe, or a rapidly increasing brain mass, can cause compression of the common ocular motor nerve.
Traumatic
In cases of head injury or orbital trauma (eye injury), the sphincter of the iris (the muscle responsible for closing the pupil) or the nerves that control it can be damaged, reducing or eliminating the normal reflection of pupillary light.
Drugs
The neurotransmitter norepinephrine regulates many physiological processes in the body and brain, including conscious muscle groups and the involuntary muscles of the autonomic nervous system (such as the dilation or constriction of the opening of the pupil through the muscles of the iris).
When it is intended to be a useful effect, various drugs such as Tropicamide are used as mydriastic agents during surgery.
Anticholinergics such as atropine, hyoscyamine, and scopolamine antagonize muscarinic acetylcholine receptors in the eye. By blocking these receptors, the pupils are no longer capable of constriction and dilation.
Which is critical in eye surgery procedures like LASIK that require uninterrupted access to the inner eye through the pupillary opening, requiring the eye to be paralyzed and anesthetized before the procedure can continue.
Mydriatic
A mydriatic is an agent that induces the dilation of the pupil. Medications such as tropicamide are used in medicine to allow examination of the retina and other deep structures of the eye, and also to reduce painful spasm of the ciliary muscles.
Phenylephrine (for example, Cyclomydril) is used if a strong mydriasis is needed for surgery. One of the effects of administering a mydriatic is intolerance to bright light (photophobia).
Intentionally induced mydriasis through mydriatics is also used as a diagnostic test for Horner syndrome.
About 15 to 30 minutes after this treatment, the pupils will dilate, allowing the specialist to take a good look at both the retina and the optic nerve.
Being able to see these components of the eye can provide key indicators of eye health and signs of serious problems.
Eye exams can be done to detect problems, such as glaucoma, macular degeneration, and other conditions that threaten vision. The effects of the eye drops usually wear off in 4 to 6 hours.
Causes of dilated pupil
Medical personnel, including nurses, physicians, and pharmacists, are especially prone to accidental instillation of mydriatic agents.
Instillation of 1% pilocarpine helps differentiate pharmacologic mydriasis from other causes of a large, non-reactive pupil. With the parasympathetic denervation of the pupil of oculomotor palsy or a tonic pupil of Adie, the answer is immediate miosis.
Failure to notice any change on the side of the mydriatic pupil is strong clinical evidence for drug dilation, provided the pupillary sphincter muscle is anatomically intact.
There are many different potential causes for mydriasis, including:
Medicines
Some medications can affect the muscles that control the pupils and prevent them from getting smaller when light enters. These medications include:
- Atropine (Atropen), which treats heart rhythm problems, stomach problems, and some types of poisoning.
- Antihistamines , such as diphenhydramine, decongestants, such as pseudoephedrine, anti-nausea medications such as dimenhydrinate. Medicines for Parkinson’s, such as amantadine (Symmetrel) and carbidopa-levodopa (Sinemet).
- Tricyclic antidepressants such as amitriptyline (Elavil) and desipramine (Norpramin), botulinum toxin (Botox, Myobloc), and anti-seizure medications, such as phenobarbital (Luminal) and topiramate (Topamax).
Drug use
Dilated pupils are a sign that someone has used illegal drugs, such as:
- Cocaine.
- Amphetamines.
- LSD.
- Ecstasy.
These drugs affect the muscle that widens the pupil, decreasing the way it reacts to light.
So even in a bright room, the eyes remain dilated. Withdrawal of these drugs can also cause the pupils to remain wide open.
Floors
Some plants, such as Jimson’s herb, angel’s trumpet, and members of the belladonna family, can cause the pupils to dilate.
A person can inadvertently find these plants by inhaling particles or touching the flowers in the garden.
Oxytocin
Increases in oxytocin levels tend to dilate the pupils. Oxytocin is a hormone that supports human connection and reproduction.
It supports women during childbirth, promotes bonding with babies, and also affects testosterone levels. Studies have linked oxytocin and pupil dilation to attraction and positive social interaction.
Brain injury or disease
The pressure that builds up inside your brain after a head injury, stroke, or tumor can damage the muscles in your iris that normally cause your pupils to open and close.
One or both of your pupils may be fixed in the dilated position and cannot react to light. If that happens, you should see a doctor right away.
If you’ve had a head injury, your doctor or nurse may shine a light in your eye during the exam to see if the pupils get smaller.
Eye wound
An injury to the eye can damage the nerves or muscles in your iris that control the size of your pupil. This can also happen after eye surgery, such as cataract removal or corneal transplantation.
Cranial nerve neuropathy
Damage to the third cranial nerve can cause third nerve palsy, which interferes with the body’s ability to control the muscles of the eye and can cause mydriasis.
Infection, injury, diabetes, and migraines can damage this nerve, and people can be born with it, too.
Brain damage
Damage to the brain can cause increased pressure within the brain, which can affect eye health and damage nerves. The pressure can come from physical trauma or internal brain damage, such as a stroke.
eye trauma
When someone has an eye injury, it can damage the nerves that control the dilation of the pupil.
Tumor or aneurysmal compression of the third nerve variably affects the size of the pupil, depending on the location of the injury.
A large posterior communicating artery aneurysm, for example, distorts the subarachnoid portion of the third nerve and almost always causes mydriasis.
Concentration
When people concentrate, it can be related to the dilation of their pupils.
Researchers are using pupillometry practice or measuring pupil size to analyze emotions and intellectual tasks that cause pupils to dilate and constrict.
Signs and symptoms
The characteristic symptom of mydriasis is dilated pupils that do not get larger or smaller in response to changes in light.
When the pupils are dilated, the eyes become more sensitive to light. This can lead to blurred vision, as well as, in some cases, a general feeling of constriction around the forehead and eyes.
Some people may also experience headaches, dizziness, eye irritation, and trouble sleeping along with mydriasis.
When to see your doctor
See your doctor or ophthalmologist for an exam if your pupils are enlarged and do not get smaller in bright light.
Get emergency help if you have a head injury and your pupils look larger, especially if one pupil is larger than the other.
The doctor will examine your eyes. Imaging tests such as computed tomography (CT) or magnetic resonance imaging (MRI) may also be done to look for injury or other problems in the brain.
If mydriasis develops after an eye or head injury, a person should urgently seek medical treatment.
Treatment of mydriatic pupils
Treatment for mydriasis is determined by what caused the condition in the first place. Treatment approaches will try to protect the full functionality of the eyes.
For example, if the pupil dilation is caused by a reaction to medication, even though various drugs could cause students to return to normal size, many providers would simply recommend waiting for the effects of the drug to wear off and avoiding it in the future.
When mydriasis is caused by injury to the brain and eyes, more intense treatments come into play.
In extreme cases, a person may require surgery to repair damage to the nerves or structures in the eye. People can wear an eye patch while their eyes heal.
Low doses of pilocarpine, a drug generally used to treat glaucoma, can also be used to help narrow or narrow the pupils.
Complications
Many cases of mydriasis, particularly those caused by a reaction to plants or medications, will go away on their own, often within a few hours or days.
People with mydriasis will be more sensitive to light, as long as their pupils are dilated. It is best for the individual to wear sunglasses when outside and to stay away from bright lights. It is also a good idea to limit driving as much as possible.
If a person develops mydriasis after taking medication, they should avoid taking that medication in the future. They may be able to discuss finding an alternative treatment with the doctor who prescribed the drug.
People with mydriasis caused by an allergic reaction to a plant, such as angel’s trumpet, should take steps to limit their exposure to the plant in the future.
Since dilated pupils can be associated with recreational drug use, people with mydriasis may find themselves with embarrassing or uncomfortable questions about whether or not they are “on to something.”
How to manage mydriatic pupils
If a medicine caused your pupils to dilate, they should return to normal once the medicine wears off.
Try to avoid the drug in the future, if you can. If you need the medicine for a health problem, ask your doctor if you can try another medicine that does not affect your eyes.
As long as your eyes are dilated, they will be more sensitive to light than normal. Try to avoid bright places. Wear sunglasses when you go out. Sometimes dilated pupils can affect your vision. Ask your eye doctor if you need to avoid driving until your pupils return to normal size.
Panorama
There are many causes of mydriasis, some of which are temporary and will go away in a matter of hours, as a response to medications.
In severe cases, a person may have surgery to correct the underlying cause of an enlarged pupil, although this is not always necessary. If a person notices a dilated pupil without a clear cause, they should contact their doctor.
