Educational Content: This article is for informational purposes only and does not constitute medical advice. Always consult a healthcare provider for diagnosis and treatment.
Definition of Horner syndrome
Medically reviewed by Min Clinic Staff | Updated: January 2026
Horner syndrome: A condition resulting from interruption of the sympathetic nerve pathways to the eye, resulting in the drooping of the upper eyelid on one same side (ptosis), the constriction of the pupil of that eye (miosis), and with the lack of sweating (anhidosis) and flushing of the affected side of the face. Also known as Horner-Bernard syndrome, Bernard syndrome, Bernard-Horner syndrome, and Horner ptosis.