Definition
This condition occurs when one pupil is a different size from the other one.

Alternative Names
Enlargement of one pupil; Pupils of different size; Anisocoria

Considerations
Occasionally, differing pupil size is inherited and there is no underlying disorder. If other family members also have this condition, then pupil size is probably genetic and is nothing to worry about.

Occasionally, and for unknown reasons, pupils may differ in size. If there are no other symptoms and if the pupils return to normal, then the transient condition is nothing to worry about.

Head injuries that cause differing pupil sizes are usually curable with early recognition of danger signs and medical treatment. Complications, however, can be life-threatening or cause permanent disability.

Common Causes
Bleeding inside the skull caused by head injury
Brain tumor or abscess
Infection of membranes around the brain caused by meningitis or encephalitis
Expanding brain lesion such as an aneurysm
Excess pressure in one eye caused by glaucoma
Birth injury, tumor in the chest, or lymph-node pressure that may be accompanied by decreased sweating on the side with a dilated pupil or drooping eyelid on the affected side
Eye-drops

Home Care
Treatment depends on the cause of the enlargement of one pupil. For example:

For pupil size inequality caused by a head injury, get immediate medical help.
For pupil size inequality caused by a tumor, follow prescribed therapy. Stay active as strength allows. Work and exercise moderately. Rest when tired.
For pupil size inequality caused by meningitis or encephalitis, follow prescribed therapy and rest in bed in a darkened room.
For pupil size inequality caused by acute glaucoma, avoid emotional upset, which raises pressure in the eye. Don't smoke. Tobacco constricts blood vessels, reducing the blood supply to the eye. Follow prescribed therapy that may include eye drops to lower pressure inside the eye, diuretics to decrease fluid pressure in the eye, or pain relievers. After treatment, resume normal activities, but avoid fatigue. A low-salt diet is recommended.

Call your health care provider if

Differing pupil size follows an eye or head injury -- get medical help immediately!
Differing pupil size is accompanied by headache, nausea or vomiting, blurred vision, or double vision.
Differing pupil size is accompanied by fever, headache that worsens when bending forward, stiff neck, or eyes sensitive to light -- get medical help immediately!
There is severe eye pain and loss of vision -- get medical help immediately!
Differing pupil size is persistent or unexplained.

What to expect at your health care provider's office
The medical history will be obtained and a physical examination performed.

Medical history questions documenting differing pupil size in detail may include:

Is this a new finding?
When did it start?
What other symptoms are also present?
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 (photophobia)?
Is there eye pain?
Is there loss of vision?

The physical examination will include a neurological examination.

Diagnostic tests that may be performed include:
Blood studies such as CBC and 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 skull
X-rays of the neck

Intervention:
Depending on the diagnosis, medications may be prescribed including cortisone (to diminish swelling of the brain tissue), anticonvulsant drugs (to control seizures), pain relievers, antibiotics (for bacterial meningitis), or anticancer drugs.

After seeing your health care provider, you may want to add a diagnosis related to enlargement of one pupil to your personal medical record.