Eye Miosis: Causes, Treatment, and Diagnosis of Constricted Pupil

Princess A.
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Eye Miosis: Causes, Treatment, and Diagnosis of Constricted Pupil

It is absolutely normal for a pupil to change their size in response to changing light conditions. They tend to widen in the dark to let in more light. And reversely, they tend to constrict or get narrow in bright lighting conditions to prevent too much light from getting in. A situation whereby pupils look abnormally small and do not change as expected is called miosis or myosis.

Miosis can occur in one or both eyes. When it affects only one eye, it’s also called anisocoria. Another name for miosis is pinpoint pupils. When your pupils are excessively dilated, it’s called mydriasis.

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However, there are many causes of miosis. It can be a symptom of certain brain and nervous system conditions. It can also be induced by many types of drugs and chemical agents. Read on to learn more about the causes of miosis, how it is diagnosed, and also how it is treated. 

Here is a list of what you should expect in this post:


What is Eye Miosis?

Eye miosis or myosis is a medical term that refers to the constriction of the pupil. It changes the normal pupil size that is, it makes the pupil shrink. The non-medical term for eye miosis is constricted pupils or pinpoint pupils. What is the size of pinpoint pupils?

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The pupil is the round, dark central opening in your eye. This is where light comes in. The normal pupil size in bright light situations is between 2 to 4 millimeters, but in low light situations, pupil size is from 4 to 8 millimeters. The size of miotic pupils or pinpoint pupils is 2 millimeters or less.

How is miosis diagnosed?

Your doctor will examine your pupils, usually with the aid of a flashlight or other light source. The doctor will look at your pupils in a dimly lit place, because it’s natural for pupils to be constricted in a brightly lit location, especially outdoors. The doctor will ask you to look at a faraway object. Then will also check:

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  • The size of your eyelid opening
  • The size and shape of your pupils
  • The position of your pupils
  • Whether your pupils are equal in size
  • How your pupils react to bright light

The answer to each of these questions can help identify the possible cause of the miosis. Normal pupil size is 2 to 4 millimeters in bright light and 4 to 8 millimeters in the dark. Your doctor can measure your pupils in both eyes to see how well they shrink and grow.


What are the causes and treatments of eye miosis?

Several conditions and drugs can cause pinpoint pupils, including:

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1. Age

It’s normal for a newborn’s pupils to stay small for about 2 weeks so her eyes have extra protection from bright light. Your pupils tend to get smaller as you get older, too. The muscles that work your pupils can get weak and have a tough time opening them. This can make it harder for you to see at night.

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2. Genes

Being born without the muscle that controls your pupils or with pupil muscles that aren’t formed correctly is called congenital miosis or myosis. You get it when one or both of your parents pass down a problem gene to you. It can happen in one eye or both eyes. If you have it, you may also be shortsighted and have trouble seeing things far away.

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3. Prescription opioids or narcotics

Some medications have opioids or narcotics in them. Opioids, including morphine, are drugs commonly used for pain relief. Opioids can affect a person psychologically and are highly addictive. People often take prescription opioids in pill form to treat severe post-surgical pain, such as from dental surgery, or for long-term pain.

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Prescription opioids that may cause pinpoint pupils include:

  • Methadone
  • Oxycodone
  • Morphine
  • Hydrocodone
  • Codeine

Methadone is often used to help a person who has an opioid dependency recover from their addiction slowly and with manageable withdrawal symptoms. As well as pinpoint pupils, symptoms of an opioid overdose include:

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  • Pale or wet face
  • Blue or purple fingernails
  • Slow breathing
  • Slow heartbeat
  • Flaccid body
  • Vomiting
  • Loss of consciousness


A person experiencing an overdose of opioids will be given naloxone, which blocks the effects of opioids. A doctor might also refer them to a treatment and recovery program if they have a drug dependency.

4. Hypertension medications

Some medications prescribed for high blood pressure (hypertension) can also cause pinpoint pupils or miosis. These include:

  • Tetrahydrozoline
  • clonidine


Anyone who thinks their hypertension medication may be causing pinpoint pupils should speak to their doctor. The doctor may also be able to prescribe a different form of medicine.

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5. Horner’s syndrome

Horner’s syndrome is a collection of symptoms resulting from damage to the nerves connecting the brain to the face or eye. Decreased pupil size (miosis) and drooping eyelids on one side of the face are typical symptoms.


There’s no specific treatment for Horner’s syndrome. If your doctor can find the underlying condition, they’ll treat that. It could be due to stroke, brain tumor, or spinal cord injury, or there may be no discoverable cause.

6. Cluster headaches

A cluster headache produces very severe pain around or above the eye, in your temple, or forehead. It occurs only on one side of your head, and recurs at different intervals, depending on the type of cluster headache you have (chronic or episodic). Miosis is one of the common accompanying symptoms.

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Acute cluster headaches are treated with oxygen inhalation, triptans, ergotamine, and topical lidocaine nose drops.

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7. Inflammation

Swelling inside your eye can make it hard for your pupils to get bigger. Sometimes this happens if you’ve injured your eye. It may also be because of a condition called uveitis, which is swelling in your iris, the part that gives your eye its color and the tissues around it.


If your pupils are small because of inflammation in your eye, your doctor can give you long-lasting dilating drops (atropine or homatropine) that make your pupils wider.

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Some other causes of miosis include:

  • Neurosyphilis (a bacterial infection in your brain that comes from untreated syphilis, a sexually transmitted disease).
  • intracranial hemorrhage and brain stem stroke( A hemorrhage or stroke happens when the blood supply to your upper brain stem (Pons) is cut off by a burst artery or a blockage).
  • Severe lack of vitamin D

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There is no specific treatment for miosis or myosis because it is not a disease, however, it can be a symptom of one. The diagnosis will guide your treatment options.

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When should I seek help?

Anyone experiencing pinpoint pupils with no apparent cause should see a doctor as soon as possible. Many of the causes of pinpoint pupils are serious medical conditions, such as opioid dependency or pesticide poisoning. Early intervention can help prevent life-threatening complications.

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