Have you ever noticed which eye’s pupil is larger than the other is? This may present in a picture or in certain lighting. The medical term is anisocoria. At times it is harmless. But also it may be a sign of an eye issue or a health problem of the brain or nerves. By understanding what anisocoria causes you may be able to tell when to see a doctor.
What Is Anisocoria?
Your pupils’ job is to let in the proper amount of light. Generally they go through the process of changing at the same time in regard to light. In anisocoria one pupil is larger than the other. Also some healthy persons present with mild, long term differences. But unequal pupils sizes require a prompt medical evaluation. Also you may see a pupil size difference after an injury, medication exposure or from an underlying health issue.
What Are the Common Anisocoria Causes?
Here is what may account for different looking pupils. To understand the anisocoria causes we start with determining when the change began and what other symptoms may have appeared.
1. Natural Differences in Pupil Size
Some people are born with slightly unequal pupil sizes. This common variation may go on to do nothing. If the pupil size difference has always been there and does not cause other issues it may not require treatment. An ophthalmologist can determine if it is a normal variation.
2. Eye Drops and Medication Exposure
Certain eye drops which cause pupil dilation or constriction. Also report of accidental contact with different person’s medication which may also play a role in changing pupil size. These are some anisocoria causes. Report to your doctor of all medications and eye products you are using.
3. Eye Injuries or Previous Surgery
An injury may damage the iris that in turn affects pupil movement. Also past eye surgery may have changed how a pupil reacts to light. Report any new pupil size difference following an injury immediately, in particular if there is also pain or blurred vision.
4. Nerve or Brain Conditions
Some neurological issues affect the nerves which control pupil movement. This includes Horner syndrome and third cranial nerve palsy. Also at times we see serious conditions like an aneurysm or stroke which present acutely. Identifying anisocoria causes related to these conditions is key because some require urgent care.
Warning Signs That Need Urgent Attention
A report of a pupil size change is of greater concern when associated with other symptoms. Note for neurological eye signs which may include a drooping eyelid, double vision, or difficulty moving an eye. Also seek immediate assessment for a severe sudden onset headache, confusion, vomiting, or weakness.
If you see changes after a head injury do not wait for symptoms to go away. Suddenly note if unequal pupils size is which may go along with other neurological symptoms of a serious issue. In that case go to the emergency room right away.
Common Symptoms and Their Significance
| Observation | What it may indicate |
| Long-standing, mild difference without symptoms | A natural variation |
| Sudden change after eye drops | A medication effect |
| Different pupils after an injury | Possible damage to the eye or head |
| Drooping eyelid or double vision | Possible nerve involvement |
| Severe headache with sudden pupil changes | A potential medical emergency |
How do doctors diagnose anisocoria?
First they will ask when you noticed the issue and if it is a first time issue for you. Also they may look at old photos, go over your list of medications, and review any recent injuries.
During the exam the doctor will test for pupil response to bright and low light. Also they may check eye movement and vision. These tests help to tell the difference between benign unequal pupils and signs of a health issue. If the results are that of concern then we may do more in depth imaging or neurological evaluation.
Treatment Options
Treatment is based on what is at the root of the issue. A natural variation may only require watchful waiting. Medication related changes may improve once the effect wears off with appropriate medical guidance. Injuries and nerve related conditions require treatment per diagnosis.
Understanding what anisocoria causes helps doctors determine the best forward steps. Do not use eye drops which may change pupil size without professional advice.
Conclusion
A variation in pupil size is not to be taken as a sure sign of a serious issue but sudden changes are reason for concern. Identifying anisocoria causes and associated symptoms will help you to get the right care. At the first notice of a new change see a eye specialist. If it occurs with severe headache, vision changes, weakness, or after a head injury seek emergency care right away.
Frequently Asked Questions
1. Is it true that anisocoria is harmless at times?
Yes, a small stable difference may be normal. But if you develop unequal pupil size do see a doctor as soon as you can, even if you have no other symptoms.
2. When do I go to the emergency room?
Go to the emergency room for a sudden change in pupil size which may be accompanied by a very severe headache, double vision, drooping of the eyelids, weakness, confusion, or recent head injury. These neurological eye signs may indicate a serious condition.
3. Can drugs cause a different pupil size?
Yes. Some eye drops and medications may also cause that. Report to your health care provider any recent drug exposure and any new pupil size difference.
4. Does anisocoria, which is a difference in pupil size, always affect vision?
No. In some people it doesn’t. Also if you have blurred vision, eye pain or other neurological eye signs related to the eyes see prompt assessment.
5. How do we determine the cause?
Doctors note pupil reactions, eye movement and vision. Also they review medical history and may order additional tests. These actions help in the diagnosis of anisocoria causes and to determine what if any treatment is required.
Government and Official Medical References
1. MedlinePlus, U.S. National Library of Medicine: Anisocoria.
https://medlineplus.gov/ency/article/003314.htm
2. NSW Health, Government of New South Wales: Anisocoria (Unequal Pupils).
https://www.health.nsw.gov.au/outpatients/referrals/Pages/anisocoria.aspx
3. Government of Western Australia, Perth Children’s Hospital: Anisocoria (Unequal Pupil Size).
https://pch.health.wa.gov.au/For-health-professionals/Referrals-to-PCH/Prereferral-guidelines/Anisocoria-unequal-pupil-size
