“Horner syndrome is also known as Bernard-Horner syndrome or oculosympathetic palsy.  Horner syndrome is a condition that affects the face and eye on one side of the body. It is caused by the disruption of a nerve pathway from the brain to the head and neck.  Typically, signs and symptoms of Horner syndrome include decreased pupil size, a drooping eyelid and decreased sweating on the affected side of the face. Horner syndrome may be the result of another medical problem, such as a stroke, tumor or spinal cord injury. In some cases, no underlying cause can be found.”

MAYO CLINIC