June Newsletter: How Your Ophthalmologist Can Help with Constricted Pupils

June Newsletter: How Your Ophthalmologist Can Help with Constricted Pupils

Close up shot of constricted pupil.

How Your Ophthalmologist Can Help with Constricted Pupils

Your pupils constantly change size, allowing you to see well in dark and light environments. In some cases, pupils become too small, which can interfere with vision and may be a sign of an underlying health problem. A visit to the ophthalmologist can help you determine if constricted pupils are a cause for concern.

What Are Constricted Pupils?

Tiny muscles in your eyes called the iris sphincter muscles control the size of your pupils. In dark conditions, your pupils enlarge to help more light enter your eyes. The opposite happens in bright environments. Normal pupils decrease in size to 2 to 4 millimeters in bright conditions and dilate (expand) to 4 to 8 millimeters in dim light, according to All About Vision. If your pupils are less than 2 millimeters in size, you may be diagnosed with miosis (constricted pupils).

How Can I Tell If I Have Constricted Pupils?

Constricted pupils are usually very noticeable. In fact, they're known as "pinpoint" pupils because they are so small. Miosis can affect one or both eyes. If just one eye is affected, the condition is called anisocoria. It's not unusual to have pupils that are slightly different sizes, according to the American Academy of Ophthalmology. If your pupils have always been different sizes, this may be completely normal for you. A sudden change in pupil size can be a sign of a serious underlying health condition in some cases.

What Causes Constricted Pupils?

Miosis can be caused by:

  • A Brain Injury. A blow to the head may be the reason for your constricted pupils. If you've hit your head and notice smaller-than-normal pupils, go to the emergency room immediately.
  • Stroke. Strokes occur when a blockage interferes with blood flow to the brain or if a blood vessel inside the brain bursts. Strokes damage the brain and may affect the part of the brain that controls the iris sphincter muscles, making it difficult for your eyes to dilate.
  • Medication Side Effects. Some antihistamines, antipsychotics, opioids, glaucoma or dementia drugs, muscle relaxants, high blood pressure, or anti-anxiety medications may constrict your pupils.
  • Nicotine Use. Smoking or vaping may increase your risk for constricted pupils.
  • Cluster Headaches. You might notice a change in pupil size while you're having a cluster headache. These painful headaches happen in groups and cause pain on one side of the head, watery eyes, and nasal discharge.
  • Horner's Syndrome. Horner's syndrome affects the nerves on one side of the face and can occur when nerve signals to the brain are disrupted by a stroke, spinal cord injury, swollen lymph glands, aortic aneurysm, tumor, or a torn artery. The neurological condition can also be present at birth.
  • Other Neurological Conditions. Other neurological conditions, including Adie's tonic pupil and third nerve palsy, could make your pupils smaller.
  • Inflammation. Inflammation in your iris or inside your eye can make it harder for the sphincter to change the size of your pupils.
  • Other Causes. Exposure to toxic chemicals in pesticides could cause constricted pupils, as could an eye injury or aging.

Treatments for Constricted Pupils

During your visit to the ophthalmologist's office, your eye doctor will conduct several tests to see how your pupils react to light. If your ophthalmologist suspects a health problem is causing miosis, you may be referred to a specialist or your family doctor. In some cases, blood or urine tests, or diagnostic tests, like X-rays, computerized tomography (CT) or magnetic resonance imaging (MRI), may be needed to make a diagnosis and create a treatment plan.

If constricted pupils are a temporary problem, you may not need any treatment. For example, if you have cluster headaches, your pupils will return to normal once the headache ends. Changing the dosage or trying an alternate drug can be helpful if your symptoms are caused by a medication. Talk to your ophthalmologist and family doctor before making any changes to your medications.

Your doctor may prescribe medications or eyedrops if constricted pupils are caused by inflammation in the iris or the middle of the eye. If your pupils narrowed after an eye injury, you may need surgery to improve your vision.

Seek immediate medical care if you notice any of these symptoms in addition to constricted pupils:

  • Dizziness
  • Balance Problems
  • Head Injury
  • Eye Pain
  • Changes in Vision

Worried about constricted pupils? Contact our office to schedule an appointment with the ophthalmologist.


All About Vision: What Do Small Pupils Mean and When Should You See a Doctor?, 12/8/2022


American Academy of Ophthalmology: What Is Aniscoria, 5/2/2023


Ophthalmology Breaking News: Pupil Size and the Brain: Exploring the Science of Miosis, 10/16/2023


WebMD: What Is Eye Miosis?, 3/9/2023


Merck Manual: Horner Syndrome, 7/2023



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