Sympathetic Innervation (Horner's Syndrome)

Sympathetic innervation to the eye mediates the action of the iris dilator and contractor muscles (via “double-reciprocal innervation”), the smooth muscle of the orbit & the Muller’s muscles of the upper & lower eyelids. This pathway originates in the hypothalamus, exits the spinal chord with the ventral thoracic roots and synapses in the cranial cervical ganglion, adjacent to the tympanic bullae. Post-ganglionic fibers follow the ophthalmic division of the trigeminal nerve before entering the eye via the long ciliary nerves. Partial or complete interruption of sympathetic innervation to the ocular structures results in a group of symptoms referred to as “Horner’s Syndrome”, comprising variable combinations of pupillary miosis, third eyelid protrusion, enophthalmos and/or upper lid ptosis.