What is the definition or description of: horner syndrome?

Definition: A persistently small pupil (miosis) A notable difference in pupil size between the two eyes (anisocoria) Little or delayed opening (dilation) of the affected pupil in dim light Drooping of the upper eyelid (ptosis) Slight elevation of the lower lid, sometimes called upside-down ptosis Little/no sweating (anhidrosis) either on the entire side of face or isolated patch of skin on the affected side.