Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Horner syndrome ?
    ### Response:
    Horner syndrome is a disorder that affects the eye and surrounding tissues on one side of the face and results from paralysis of certain nerves. Horner syndrome can appear at any time of life; in about 5 percent of affected individuals, the disorder is present from birth (congenital).
    