Anisocoria: Why Are My Pupils Different Sizes?
Quick answer: Anisocoria means the two pupils are different sizes. A small difference (under about 1 mm) is common and often harmless. A new difference that comes with a droopy eyelid, double vision, severe headache, eye pain or weakness needs emergency care, because it can signal a nerve or brain problem.
Noticed this in your own eyes? Book an eye examination (NPR 400) with an optometrist at Vision Concern Lazimpat, Boudha-Tushal or Makalbari. WhatsApp +977 9841466716.
Related service: Comprehensive eye examination (NPR 400) at Vision Concern Lazimpat, Boudha-Tushal and Makalbari.
What anisocoria means
The pupil is the black opening in the centre of the iris. Two muscles control its size: one makes it smaller in bright light and one widens it in dim light. When the two pupils differ in size, this is called anisocoria.
About one in five people have a slight, stable difference that never causes problems. This is called physiological anisocoria and the difference stays about the same in light and dark.
Common causes
- Physiological (harmless) anisocoria
- Eye drops or medicines, including some motion-sickness patches, inhalers and dilating drops
- Previous eye injury or eye surgery
- Inflammation inside the eye (iritis)
- Adie pupil, a slowly reacting enlarged pupil
- Horner syndrome, a small pupil with a slightly droopy lid
- Third-nerve palsy, an enlarged pupil with droopy lid and double vision
How it is checked
An optometrist compares the pupils in bright and dim light, checks how they react, looks at eyelid position and eye movements, and asks about medicines, drops and injuries. Old photos can help show whether the difference is new.
When to get urgent care
Go to an emergency department or eye hospital the same day if unequal pupils are new and come with a droopy eyelid, double vision, severe headache, eye pain, blurred vision, neck pain, confusion, weakness or a recent head injury.
How Vision Concern can help
Vision Concern optometrists in Kathmandu can examine your eyes, record what they find for comparison, update your glasses or contact lenses, and refer you to an ophthalmologist or eye hospital when medical treatment is needed. Vision Concern does not perform surgery or injections.
Frequently asked questions
Is it normal to have one pupil slightly bigger?
Yes. A small, stable difference is common and usually harmless, especially when vision is normal and there are no other symptoms.
Can eye drops cause unequal pupils?
Yes. Dilating drops, some allergy or glaucoma drops, and contact with medicines such as scopolamine patches can change one pupil’s size for hours to days.
Should I get unequal pupils checked?
Have any new difference checked. If it comes with headache, double vision, a droopy lid or eye pain, seek emergency care rather than waiting for a routine appointment.
This guide is general information from the Vision Concern editorial team. It is not a diagnosis and does not replace an eye examination or medical advice.
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