Eye Miosis

Pupils are the black centers of your eyes. The medical term for small, constricted pupils is miosis. Eye miosis can be caused by many things, including using opioids or having a stroke.


An eye with miosis has a small, constricted pupil.
Miosis of the eye, also known as pinpoint pupils, can be caused by many things, including poisons, eye disease and injury.

What is eye miosis?

Miosis of the eye refers to having small or constricted pupils. The condition is also called pupillary miosis. Pupils are the black circles in the middle of your eyes. With miosis, the muscles of your iris (the colored part of your eye) tighten around your pupil. These muscles control whether your pupils are large or small. Another name for miosis is pinpoint pupils.

Typically, your pupils get bigger or smaller when light enters your eyes. When there’s a bright light, your pupils get smaller. When it’s dark, your pupils get larger. If you have miosis, your pupils stay small even if the light changes.

The size of your pupils also changes when you look at an object that is close to you. Pupils get smaller when are focused on something that is closer rather than farther away.

Miosis of the pupils can be on one side (unilateral) or both sides (bilateral). These conditions can also be thought of as monocular (one eye) and binocular (two eyes).


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What is the difference between miosis and mydriasis?

Miosis is the opposite of mydriasis (dilated pupils), where the black centers of your eyes are extremely large.

What is intraoperative miosis?

During cataract surgery, your pupils might contract (intraoperative miosis). Surgeons prefer pupils that are open to about 7 millimeters (mm) to do surgery. There are some issues related to small pupils, including something called intraoperative floppy iris syndrome (IFIS). Providers have developed devices, medications and strategies for dealing with intraoperative miosis.

IFIS can happen if you’ve used alpha-1-adrenergic receptor antagonist medications in the past. The drugs treat high blood pressure and benign prostatic hyperplasia (an enlarged prostate). It can also happen if you take other medications designed to constrict your pupils.


Possible Causes

What are the most common causes of miosis?

There are several reasons you might have small pupils, including the following:

Miosis caused by opioids and other medications

Some drugs will cause your pupils to become very small. Pinpoint pupils are a known result of taking opioids and barbiturates. Other drugs, such as myotic drugs like pilocarpine, make pupils small. Pilocarpine is a medicine used to treat glaucoma and dry mouth. Miosis caused by opioids is present in both eyes.

Miosis caused by Horner’s syndrome

Horner’s syndrome is a condition that affects your eyes and part of your face. It happens because of a disruption of the pathway of the sympathetic nerves that connect your brain stem to your eyes and face. The nerves control involuntary functions like dilation and constriction of the pupils of the eye. Oculosympathetic palsy or Bernard-Horner syndrome are other names for Horner’s syndrome. Miosis caused by Horner’s syndrome is monocular (one-sided).

Miosis caused by poisoning

You can develop miosis of the pupils because of poisoning. Poisons that cause miosis include organophosphates, benzodiazepines and clonidine.

Miosis caused by uveitis

Uveitis describes a group of diseases that cause pain in your eyes, redness and inflammation. The disease affects the middle part of the eye known as the uvea, along with the retina and the sclera. The sclera is the white part of your eye. The retina is the innermost part of the eye that senses colors and lights and sends images to the brain.

Miosis caused by iritis

Iritis is the medical term for inflammation (swelling) of the iris. The iris is the colored part of your eye. Muscles in your iris control your pupil.

Miosis caused by an injury to your brain or eye, including a brainstem stroke

If your eye is injured, it can swell and be painful. This can make it more difficult for the pupil to change sizes. Miosis can also happen after a stroke that happens in the pons area of the brainstem (a Pontine stroke) or bleeding in the skull or brain.

Miosis caused by neurosyphilis (Argyll Robertson pupils)

Argyll Robertson pupils are constricted pupils in someone who has late-stage syphilis. When syphilis goes untreated, the germ that causes it can enter the cerebral spinal fluid. Even though there is a treatment for syphilis, a sexually transmitted infection, a significant number of people don’t get treatment.

Miosis caused by synechiae, or inflammatory adhesions between parts of the eye

Sometimes, inflammation causes adhesions between parts of the eye that are located next to each other. Adhesions happen when tissues of two organs or parts stick together, usually because of scar tissue.

Miosis caused by cluster headaches

Cluster headaches get their name from how they affect you. They come on in clusters or groups before going away. Each headache may last about 30 minutes and you can have up to eight of these headaches within a period of 24 hours. Cluster headaches sometimes produce symptoms similar to Horner’s syndrome, meaning that miosis and drooping affect one side of your face.

Care and Treatment

How is miosis treated?

The treatment of miosis depends on the reason that you have miosis. Treating miosis often means that you must treat the underlying condition. For instance, if your pupils are small because of drugs you’ve taken, you’ll need to stop taking the drugs that cause pupils to constrict.

Your provider may prescribe medications, often eye drops, to treat eye conditions like uveitis or iritis. These may include anti-inflammatory drugs like steroids or anti-infectives. Your provider might prescribe sumatriptan for cluster headaches.

Your provider may recommend surgery if you have Horner’s syndrome that’s caused by tumors. Your provider may treat strokes with medications or procedures to bust or remove blood clots.


How can miosis be prevented?

You can prevent drug-induced miosis by avoiding the drugs that cause pupils to become small. These include opioids. You may want to talk with your provider about using alpha-1-adrenergic receptor antagonist medications or pilocarpine, especially if you may need cataract surgery soon.

If you participate in sports, you should make sure to wear the correct safety equipment. Also, use safety equipment if you have a job that recommends goggles or other types of protective gear.

When To Call the Doctor

When should miosis be treated by a healthcare provider?

You should get treatment from your healthcare provider for nearly all of the conditions that can cause miosis.

A note from Cleveland Clinic

The pupils in your eyes get bigger or smaller depending on how much light enters or what they’re focusing on. When your pupils are much smaller than normal and don’t respond as they normally do to light or focus changes, you have miosis. This condition can have many causes. You should contact your healthcare provider about most of them, as some causes can be serious.

Medically Reviewed

Last reviewed on 07/27/2022.

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