What Is Horner Syndrome?

Horner syndrome is an uncommon neurologic condition marked by a droopy upper eyelid (ptosis), a small pupil (miosis), and reduced sweating on one side of the face (facial anhidrosis). The article explains it doesn’t occur by itself; it results from damage to the sympathetic nervous system, particularly the oculosympathetic pathway. Causes can include stroke, brain tumor, or spinal cord injury. Diagnosis and treatment focus on identifying and managing the underlying condition. Symptoms are typically unilateral, though in newborns it can also cause iris heterochromia. Additional signs may include facial flushing, blurred vision, or eye pain depending on the cause.