What exactly is horner syndrome?

Nerve problem: Am impairment of sympathetic nerve activity that presents as ptosis(droopy eyelid), meiosis (constricted pupil) and anhydrosis (no sweating) on the same side of the face. While over 50% of the causes are benign it can indicate the presence od a tumor in the chest or neck.

Horner's syndrome: Horner's syndrome is interruption of the sympathetic nervous system input to the eye. This causes ptosis or drooping of the eyelid on the side of involvement, miosis or pupil constriction on the same side, and anhidrosis or lack of sweating on the same side of the face. This can be caused by many issues and needs further evaluation by an eye doctor asap.