Anisocoria is unequal pupil size. The pupil is the black part in the center of the eye. It gets larger in dim light and smaller in bright light.
Enlargement of one pupil; Pupils of different size; Eyes/pupils different size
Slight differences in pupil sizes are found in up to 1 in 5 healthy people. Usually, the diameter difference is less than 0.5 mm, but it can be up to 1 mm (0.05 inch).
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 is possibly genetic and 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.
The use of eyedrops is a common cause of a harmless change in pupil size. Other medicines that get in the eyes, including medicine from asthma inhalers, can change pupil size.
Other causes of unequal pupil sizes may include:
Bleeding inside the skull caused by head injury
Brain tumoror abscess
- Excess pressure in one eye caused by
- Increased intracranial pressure
- Infection of membranes around the brain (
- Migraine headache
- Seizure (pupil size difference may remain long after seizure is over)
- 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 eyelidall on the affected side (Horner syndrome)
Treatment depends on the cause of the unequal pupil size. You should see a doctor if you have sudden changes in pupil size.
Call your health care provider if
You should see a doctor if you have persistent, unexplained, or sudden changes in pupil size. The new development of different sized pupils may be a sign of a very serious condition.
If you have differing pupil size after an eye or head injury, get medical help immediately.
Always seek immediate medical attention if differing pupil size occurs along with:
Eye sensitivity to light
Loss of vision
Nausea or vomiting
What to expect at your health care provider’s office
Your health care provider will perform a physical exam and ask questions about your symptoms and medical history, including:
- Is this new for you or have your pupils ever been different sizes before?
- When did it start?
- What other symptoms do you have?
- Is there a headache?
- Is there nausea?
- Is there vomiting?
- Is there blurred vision?
- Is there double vision?
- Is there a fever?
- Is there a stiff neck?
- Are the eyes light-sensitive (
- Is there eye pain?
- Is there loss of vision?
Tests that may be done include:
- Blood studies such as
CBCand blood differential
- Cerebrospinal fluid studies (
lumbar puncture) CT scan of the head EEG Head MRI scan Tonometry(if glaucoma is suspected) X-rays of the neck
Treatment depends on the cause of the problem.