Anisocoria is a condition characterized by an unequal size of the eyes' pupils.

Affecting up to 20% of the population, anisocoria is often entirely harmless, but can be a sign of more serious medical problems.

Anisocoria is a common condition, defined by a diameter difference of 0.4 mm or more between the sizes of the pupils of the eyes.

These cases may be due to brain mass lesions, which cause oculomotor nerve palsy.

Anisocoria in the presence of confusion, decreased mental status, severe headache, or other neurological symptoms can forewarn a neurosurgical emergency.