Anisocoria and Horner Syndrome

What is anisocoria?

Anisocoria is a difference in size between the two pupils. It has several possible causes: in some people it is a normal variation without disease (physiological anisocoria), but it may also result from medicines or eye drops, previous eye trauma, or a neurological cause. Identifying the cause requires a focused clinical evaluation.

What is Horner syndrome?

Horner syndrome is a neurological cause of anisocoria resulting from damage somewhere along the sympathetic nerve pathway to the eye and face. It is classically described by a triad of ptosis (mild drooping of the upper eyelid), miosis (a smaller-than-expected pupil on the affected side), and anhidrosis (reduced sweating on the same side of the face), although not every patient has all three signs. Horner syndrome is one possible cause of anisocoria, not another name for it: most cases of anisocoria are not due to this syndrome.

When is urgent evaluation needed?

New or sudden anisocoria—especially with pain, eyelid drooping, double vision, weakness or other neurological symptoms—should be assessed promptly. Potential causes of Horner syndrome include serious conditions such as carotid artery dissection.

Where to receive an evaluation

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