What causes small pupil and how to treat it?

Symptom Database

Small pupil, also known as pupil constriction or miosis, refers to a condition where the size of the pupil is abnormally reduced. On the other hand, pupil dilation or mydriasis is the opposite condition where the pupil size is larger than normal. The size of the pupil is controlled by the muscles in the iris, which respond to light and other stimuli. Abnormal pupil size can be indicative of various underlying conditions or disorders. In this article, we will explore the causes of small pupil and discuss potential treatment options.

Understanding Pupil Size

The pupil is the black circular opening in the center of the iris, which allows light to enter the eye. The size of the pupil is regulated by the iris muscles, specifically the sphincter muscle and the dilator muscle. The sphincter muscle constricts the pupil, making it smaller, while the dilator muscle dilates the pupil, making it larger.

Pupil size can vary depending on the lighting conditions and the body’s response to different stimuli. In bright light, the pupil constricts to limit the amount of light entering the eye, protecting the retina from excessive exposure. In dim light, the pupil dilates to allow more light to enter, enhancing vision in low-light conditions.

Causes of Small Pupil

1. Medications

Some medications, such as opioids, certain eye drops, and certain types of glaucoma medications, can cause pupil constriction as a side effect. These medications affect the muscles in the iris, leading to a smaller pupil size.

2. Eye Injuries

Eye injuries, particularly those affecting the iris or the muscles controlling pupil size, can result in small pupil. Trauma or damage to the eye can disrupt the normal functioning of the iris muscles, leading to abnormal pupil size.

3. Neurological Conditions

Neurological conditions, such as Horner’s syndrome, Adie’s syndrome, or third nerve palsy, can cause small pupil. These conditions affect the nerves that control the muscles in the iris, leading to abnormal pupillary response and constriction.

4. Eye Infections

Certain eye infections, such as iritis or uveitis, can cause inflammation in the iris, leading to pupil constriction. Infections can disrupt the normal functioning of the iris muscles, resulting in a smaller pupil size.

Treatment Options

The treatment for small pupil depends on the underlying cause. It is essential to identify and address the root cause to effectively manage the condition. Here are some potential treatment options:

1. Discontinuing Medications

If medications are causing pupil constriction, your healthcare provider may consider adjusting the dosage or switching to alternative medications that do not have this side effect. It is crucial to consult with a healthcare professional before making any changes to your medication regimen.

2. Treating Underlying Conditions

If small pupil is a result of an underlying condition, such as an eye infection or a neurological disorder, treating the underlying cause can help alleviate the symptoms. This may involve the use of antibiotics, anti-inflammatory medications, or other targeted treatments.

3. Pupil Dilation Drops

In some cases, pupil dilation drops may be used to temporarily counteract small pupil. These drops contain medications that relax the iris muscles, allowing the pupil to dilate. However, this is a temporary solution and should be done under the guidance of a healthcare professional.

4. Surgical Interventions

In certain situations, surgical interventions may be necessary to address the underlying cause of small pupil. For example, if an eye injury has damaged the iris or the muscles controlling pupil size, surgery may be required to repair the damage and restore normal pupillary function.


Small pupil, or pupil constriction, can be caused by various factors, including medications, eye injuries, neurological conditions, and eye infections. Identifying the underlying cause is crucial for determining the appropriate treatment approach. It is essential to consult with a healthcare professional for an accurate diagnosis and personalized treatment plan. By addressing the root cause, it is possible to manage small pupil and alleviate associated symptoms effectively.

Haroon Rashid, MD
Rate author
Urgent Care Center of Arlington, VA
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