Anisocoria (Unequal Pupils)



What is anisocoria?

Anisocoria is a condition in which the pupil of one eye differs in size from the pupil of the other eye. Your pupils are the black circles in the center of your eyes, and they are usually the same size.

Babies born with different sized pupils may not have any underlying disorder. If other family members also have similar pupils, then the pupil size difference could be genetic and is nothing to worry about. Also, for unknown reasons, pupils may temporarily differ in size. If there are no other symptoms and if the pupils return to normal, then it is nothing to worry about.

Unequal pupil sizes of more than 1 mm that develop later in life and do NOT return to equal size may be a sign of an eye, brain, blood vessel, or nerve disease.

How common is anisocoria?

Slight differences in pupil sizes are found in up to 1 in 5 healthy people. Most often, the diameter difference is less than 0.5 mm, but it can be up to 1 mm. It can occur in patients in any gender at any age. Please discuss with your doctor for further information.

Which signs and symptoms can anisocoria usually be associated with?

Related signs and symptoms include:

  • Drooping eyelid (ptosis)
  • Problems moving your eye
  • Eye pain
  • Fever
  • Headache
  • Reduced sweating
  • Blurred vision
  • Double vision
  • Loss of vision
  • Nausea
  • Stiff neck


What causes anisocoria?

Causes of anisocoria can include:

  • Direct trauma to the eyes or a concussion; bleeding inside the skull
  • Certain eye medications. For example, pilocarpine eye drops used to treat glaucoma may cause the pupil of the treated eye to be smaller than the other pupil.
  • Inflammation of the iris. Iritis (anterior uveitis) can cause anisocoria that usually is accompanied by eye pain.
  • Adie’s tonic pupil. This benign condition (also called Adie’s pupil, tonic pupil, or Adie’s syndrome) typically causes one pupil to be noticeably bigger than the other. The affected pupil also does not react to light. In most cases, the cause of Adie’s pupil is unknown. But it can be associated with eye trauma (including trauma caused by complicated cataract surgery), lack of blood flow (ischemia) or an infection.
  • Neurological disorders. A number of conditions that damage nerves in the brain or spinal cord can cause anisocoria. One of the most significant of these is Horner’s syndrome. People with nervous system disorders that cause anisocoria often also have a drooping eyelid, double vision and/or strabismus. Brain disorders associated with anisocoria include strokes, hemorrhage (spontaneous or due to head injury) and, less commonly, certain tumors or infections.

Other possible causes include:

  • Inflammation of your optic nerve
  • Brain tumor
  • Aneurysm
  • Seizure (pupil size difference may remain long after seizure is over)
  • Excess pressure in one eye caused by glaucoma
  • Increased intracranial pressure, because of brain swelling, intracranial hemorrhage, acute stroke, or intracranial tumor
  • Infection of membranes around the brain (meningitis or encephalitis)
  • Migraine headache
  • Tumor, mass, or lymph node in the upper chest or lymph node causing pressure on a nerve may cause decreased sweating, a small pupil, or drooping eyelid all on the affected side
  • Diabetic occulomotor nerve palsy
  • Prior eye surgery for cataracts

The conditions mentioned above are some common causes of anisocoria. Consult with your doctor for an accurate diagnosis.

Risk factors

What increases my risk for anisocoria?

There are many risk factors for anisocoria, such as:

  • A nervous system problem
  • A history of damage to the eye
  • Risk of having a stroke
  • A viral infection
  • Adie’s tonic pupil (when one pupil does not respond to light as well as the other pupil)

Please consult with your doctor for further information.

When to see your doctor

When should I see my doctor?

You should contact your doctor if you or your loved one has persistent, unexplained, or sudden changes in pupil size.

  • Always seek immediate medical attention if differing pupil size occurs along with
  • Blurred vision
  • Double vision
  • Eye sensitivity to light
  • Fever
  • Headache
  • Loss of vision
  • Nausea or vomiting
  • Eye pain
  • Stiff neck

On noticing one of these symptoms or having any questions, please consult with your doctor. Everyone’s body acts differently. It is always best to discuss with your doctor to get the best solutions for your situation.

Lifestyle changes & home remedies

What are some lifestyle changes or home remedies that can help me manage anisocoria?

These following lifestyles and home remedies might help you cope with anisocoria:

  • If you have benign anisocoria and one pupil is bigger than the other, ask your eye doctor about photochromic lenses. These eyeglass lenses will darken automatically in sunlight to reduce any light sensitivity (photophobia) you may be experiencing.Photochromic lenses also will protect your eyes from harmful UV rays and high-energy blue light — especially the eye with the larger pupil if it doesn’t react normally to light.

Some cases of anisocoria are impossible to predict or prevent. But you can take steps to reduce your risk of developing uneven pupils. For example:

  • Report any changes to your vision to your doctor immediately.
  • Wear a helmet while playing contact sports, cycling, or horseback riding.
  • Wear protective gear while using heavy machinery.
  • Wear your seatbelt while driving.

If you have any questions, please consult with your doctor for the best solutions.

Hello Health Group does not provide medical advice, diagnosis or treatment.


Review Date: March 11, 2019 | Last Modified: March 11, 2019

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