Horner syndrome (Horner’s syndrome) results from an interruption of the sympathetic nerve supply to the eye and is characterized by the classic triad of miosis (ie, constricted pupil), partial ptosis, and loss of hemifacial sweating (ie, anhidrosis). The term Horner syndrome is commonly used in English-speaking countries, whereas the term Bernard-Horner syndrome is common in France. Von Passow syndrome is an association of Horner syndrome with iris heterochromia (heterochromia iridis).