What Causes Pupil Dilation?


Pupil dilation, also called mydriasis, can be not only a reaction to low light, but also the result of certain drugs and recreational medications, as well as trauma and some serious brain conditions. You should see your doctor if your pupil or pupils dilate and do not return to normal size.

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The pupils are round black circles located in the center of the iris (the colored part of the eye) through which light enters the eye. They are constantly changing in size. When the pupil is enlarged, it is called dilation. This usually occurs in low light conditions to allow more light to enter the eyes.

On the other hand, the pupils become narrower (or smaller) in bright conditions to minimize the amount of light entering the eye.

In addition to responding to light, the pupils can also dilate after taking certain medications and recreational drugs, although the pupils generally return to normal size after the drug wears off. These are normal reactions.

However, there are times when one or both pupils are dilated for abnormal reasons that could be a sign of a serious condition affecting the brain, including:

  • Career
  • Internal bleeding
  • Tumor
  • Head injury

If one or both pupils remain dilated, in situations where the change in size is not related to lighting or drug use, you should seek immediate medical attention .


Pupils can dilate not only in low light, but for a variety of additional reasons, including medications or drugs, eye exams, injuries, and certain medical conditions, among others. Mydriasis (dilated pupils) can occur in both eyes or in only one eye (in this case, it is known as anisocoria).

Medication or drug use

Health professionals can determine when certain medications or the use of other medications are causing a person's pupils to dilate because their pupils do not respond normally to light stimuli, in particular, they do not narrow when the eye is exposed to large amounts of light.

Pupil dilation caused by the use of medications or drugs is often accompanied by the following symptoms:

  • Changes in mental health
  • Dry Skin
  • Hot
  • Redness
  • Myoclonus (sudden involuntary muscle contractions, tremors, or spasms)
  • Seizures
  • Urinary retention

In situations involving holin block poisoning, symptoms may also include:

How long does it take for dilated pupils to return to normal after taking medication?

After health professionals confirm that a patient's prolonged period of pupillary dilation was caused by drugs or drugs, the patient can expect their pupils to return to normal as the effect of the drug wears off. There is no set deadline for this. The effects of different drugs and medications vary greatly, and the duration of the pupil dilation is no exception.

However, we know that the amount of time it takes for a person's pupils to return to normal is related to the half-life of a particular drug or drug. So if your healthcare provider can determine the cause of your enlargement, they can provide you with information about the half-life of the medication so that you can better understand how long the enlargement will last.

Vision test

During a comprehensive eye exam, an ophthalmologist or ophthalmologist will most likely put eye drops in the patient's eyes, causing the pupils to dilate. The drops begin to work in about 20-30 minutes. When they do this, it gives the optometrist the opportunity to verify certain pupillary responses, some of which can reveal neurological problems, as well as to know the state of the internal structures of the eye, including the retina , vitreous humor, and optics . nerve . , blood vessels (choroid) and macula.

Expanding drops typically take several hours to come together, so it might be a good idea to ask someone to drive you to your appointment if possible .


Trauma to the eyes or brain can also cause dilated pupils. It is usually a blunt, closed injury that damages the sphincter muscle of the iris, which is responsible for constricting the pupil or one of the pathways in the brain that controls it. It can also cause bleeding inside the skull, which can cause the pupils to dilate.

In addition to trauma, eye injuries can also occur as a result of intraocular surgeries such as cataract removal and corneal transplantation, or after retinal procedures .

Medical conditions

In addition to medications and injuries, dilated pupils (in one or both eyes) can also be the result of a number of conditions, including:

  • Brain aneurysm
  • Brain tumor or abscess (eg, pontine lesions)
  • Excessive pressure in one eye due to glaucoma
  • Brain edema
  • Intracranial hemorrhage
  • Acute stroke
  • Intracranial tumor
  • Increased intracranial pressure
  • Infection of the lining of the brain (meningitis or encephalitis)
  • Migraine
  • Capture
  • A tumor, lump, or lymph node in the upper chest or lymph node
  • Horner syndrome
  • Diabetic common ocular motor nerve palsy

Other reasons

Finally, there are several additional causes of pupil dilation. For example, recent research has shown that elevated levels of oxytocin , the hormone "love" or "affection," can cause dilated pupils in situations of attraction, mood, or emotional response to someone or something .

There is also evidence that a person's pupils can dilate in situations where they are highly focused on something, including making decisions .

When to call your healthcare provider

If you have persistent or unexplained changes in pupil size, it's time to discuss it with your healthcare provider. If any of these changes were sudden and / or recent, or after an eye or head injury, it could be a sign of a very serious condition.

If the pupil dilation (in one or both eyes) is accompanied by certain symptoms, it may be a sign of an emergency that requires immediate medical attention. These symptoms include:

  • Blurry vision
  • Double vision
  • Sensitivity of the eyes to light.
  • Hot
  • Headache
  • Loss of sight
  • Nausea or vomiting
  • Eye pain
  • Stiff neck muscles

Get the word of drug information

Our pupils not only have an important function of regulating the light entering our eyes, but they can also indicate a variety of other health problems, from those that resolve on their own to those that require immediate medical attention.

The next time you look in the mirror, pay attention to the size of your pupils. You can also dim and turn on the lights in the room to see how your pupils react. This will give you a general idea of how your pupils usually look and how they usually react to light. It would be helpful to go ahead, for example, if you notice that your pupils are different from their normal size or react as usual to light.

In such situations, it is best to consult with your healthcare professional about this symptom, unless of course it is accompanied by any of the above symptoms, which may indicate a medical emergency. In this case, seek immediate medical attention.

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