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Dilated pupils (mydriasis)


Although some people may have congenitally dilated pupils , the truth is that their presence reveals moods , possible poisonings or critical health situations that require medical attention.

What is mydriasis?

The pupils are the black dots that we see in the center of the eyes, which are covered by the cornea and surrounded by the iris, and which are responsible for graduating the passage of light to the retina.

Through the muscle fibers of the iris (dilator and sphincter) the pupil contracts or dilates in reaction to light. In this way, it is natural for the pupil to contract in bright light, while if it is scarce, the pupil will enlarge to optimize vision.

Precisely, the retraction receives the name of myosis and the dilatation mydriasis. However, if our pupils are permanently dilated, if this alteration in their size occurs suddenly or affects one of the eyes, this abnormal mydriasis alerts us to a health problem, which requires the inspection and assessment of the ophthalmologist.

Causes of dilated pupils

Pupil dilation occurs as a physiological response to exposure to light rays, but it is not the only acting agent. There are other factors that affect the muscles of the iris and that modify the size of the pupils:

  • Emotions . Anger causes constriction while arousal or sexual attraction dilates the pupils.
  • Certain poisons or chemicals . The bark of the black carob tree produces intoxication and, therefore, dilation. Drugs, for their part, have a direct impact on the pupils: opiates contract them and cocaine or marijuana dilate them.
  • Drugs such as atropine, eye drops, antidepressants or antihistamines, administered in large doses, alter the response of the pupil to light.
  • Diseases, neurological or ophthalmological .

When should we be concerned about dilated pupils?

Pupillary dilation is a frequent practice in the ophthalmologist’s office

There are different kinds of pathologies that explain abnormal mydriasis and require us to consult a specialist, especially if the change is sudden or recurrent.

This enlargement of the pupils will be alarming if it is accompanied by other symptoms such as:

  • Blurred or double vision
  • Loss of vision
  • Headache .
  • Fever .
  • Nausea and vomiting
  • Eye pain or sensitivity to light.
  • Neck stiffness.

Neurological diseases

Edema or brain tumors can produce anisocoria or disparity in pupil dilation: in one eye exaggerated and in the other minimal. Extreme dilation in both eyes is usually due to the ingestion of toxins.

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Adie Syndrome , associated with neurological dysfunction, affects only one eye in 80% of cases. The pupil dilates suddenly, compromising vision, since light rays do not penetrate perpendicularly.

It is usually preceded by a viral disease such as herpes zoster infection or diabetes . It mainly affects young women and, as it is a nervous disorder, it has no treatment. Over time the pupil will get smaller.

For its diagnosis, the ophthalmologist must examine the eye in depth and rule out other pathologies such as:

  • Argyll Robertson’s pupils : start in one eye to end up involving both. It presents as a small, irregular pupil that does not respond to light stimuli.
  • Parinaud’s Syndrome : affects both eyes and is caused by a brain tumor. There is no physiological reaction to light. However, visual acuity and focusing ability are not impaired.

Brain trauma

An accident or trauma can damage the trigeminal nerve (the one in charge of controlling things related to the face) and cause permanent dilation of the pupils, along with paralysis, jaw pain or migraine .

Symmetric arreactive mydriasis

The pupils remain dilated despite being exposed to bright light. It is usually indicative of the existence of severe brain damage , as occurs in cardiorespiratory arrests.

Syndrome Claude – Bernard – Horner

The contraction of one of the pupils can lead us to believe that the other is dilated. The carotid artery injury, a lung tumor or brain damage are its triggers, also causing the eye to sink and the eyelid to fall.

Ophthalmic disease

If the mydriasis is not due to any neurological pathology, the cause will be found in a structural lesion of the eye that is interfering with the well-being of the eye . A tear caused by a blow, glaucoma or ischemia of the iris are possible anomalies that explain it.

Does it require treatment?

For a correct diagnosis and treatment, the specialist must consider the particularities of each case taking into account the age of the patient, their medical history and the specific cause that could be masking an underlying disease.

Tackling this associated pathology will condition the choice of treatment, requiring surgical intervention in the event of a neurological cause.

Going to the ophthalmologist before any sudden or suspicious change will be of great help to face the situation early, thus avoiding setbacks that could endanger our health and well-being.


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Hello Readers, I am Nikki Bella a Psychology student. I have always been concerned about human behavior and the mental processes that lead us to act and think the way we do. My collaboration as an editor in the psychology area of ​​Well Being Pole has allowed me to investigate further and expand my knowledge in the field of mental health; I have also acquired great knowledge about physical health and well-being, two fundamental bases that are directly related and are part of all mental health.

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