A man in his fifties seeks the attention of an ophthalmologist after suffering from a severe migraine. The man notes his drooping left eyelid, as well as a contracted pupil (Beck, 1988, p. 234). The man is later diagnosed with oculosympathetic paralysis, also known as Horner's syndrome (Kanski, 1990, p.65). The main ocular symptoms of Horner's disease are unilateral ptosis and miosis of the affected eye. This syndrome is caused by a dysfunction of the sympathetic nervous system and can have a multitude of etiologies (Kanski, 1990, p.65). This article aims to explain and explore the various causes, clinical features and diagnostic tests that an eye care professional can use to diagnose Horner syndrome. The sympathetic pathway is part of the autonomic nervous system and is responsible for preparing to combat Horner's syndrome. or flight response of the body (Remington, 1998, p. 253). The sympathetic nervous system's path starts from the hypothalamus, where it then travels to the lateral gray matter of the spinal cord. The path extends from the thoracic segments to the segments of the upper lumbar spine. The parts of interest responsible for the innervation of ocular structures are found in segments T-1 to T-3 (Remington, 1998). The sympathetic nerve fibers that innervate the ocular structures are composed of preanglionic fibers and exit the ventral root of the spinal cord, ascending to the superior cervical ganglion. The superior cervical ganglion synapses with postganglionic fibers, which form the sympathetic carotid plexus around the internal carotid artery. The nerve then divides into numerous routes, with some extensions traveling along the trigeminal nerve to ultimately innervate the trigeminal nerve; iris and ciliary muscles, smooth muscles of the ...... middle of paper ...... external to the sympathetic nervous system pathway, like a tumor in which it could be removed. Works Cited Beck, RW (MD), , Smith, CH (MD). (1988). Neuro-ophthalmology: A problem-oriented approach. United States of America: Little, Brown and Company. Cogan, DG (MD). (1972). Neurology of the eye muscles, (2nd ed.). Illinois: Thomas Books. Geeraets, W. J. (1976). Ocular syndromes, (3rd ed.). Philadelphia: Lea & Febiger. Kanski, J.J., Dafydd, J.T. (1990). The eye in systemic diseases, (2nd ed.). Scotland: Cambus Litho Ltd. Laskaris, G. (1998). Color Atlas of Oral Diseases, (3rd ed.). Athens: Litsas Medical Publications. Retrieved from http://books.google.ca/books?id=sZLOsiHlwt4C&pg=PA14&dq=facial+hemiatrophy&hl=en&ei=O-vXTrfaIMeBgwewr-z6Dg&sa=X&oi=book_result&ct=book-thumbnail&resnum=2&ved=0CDcQ6wEwAQ#v=onepage&q=facial% 20hemiatrophy&f=false