Fig. 5 Ocular sympathetic pathways. Hypothalamic sympathetic fibers comprise a polysynaptic system as they descend to the ciliospinal center. This intra-axial tract is functionally considered the “first-order neuron.” The second-order neuron takes a circuitous course through the posterosuperior aspect of the chest and ascends in the neck in relationship to the carotid system. Third-order neurons originate in the superior cervical ganglion and are distributed to the face with branches of the external carotid artery and to the orbit via the ophthalmic artery and ophthalmic division1 of the trigeminal nerve.