Horner Syndrome

Droopy lid, small pupil, and reduced sweating on one side

Overview

Horner syndrome is a combination of a mildly drooping upper eyelid, a smaller pupil, and sometimes reduced facial sweating on the same side, caused by interruption of the sympathetic nerve pathway to the eye and face. That pathway runs a long course from the brain down into the chest and back up the neck alongside the carotid artery, so causes are diverse, including stroke, tumors at the top of the lung, carotid artery dissection, and injury, while some cases are congenital or unexplained. It is named after the Swiss ophthalmologist Johann Friedrich Horner, who described it in 1869.