Purpose: To determine pathways of sympathetic nerves from the orbital apex to the eyelids in human cadaver tissue using immunohistochemistry.
Methods: Human cadaver orbit tissue was sectioned and immunolabeled with a monoclonal antityrosine hydroxylase antibody.
Results: In the orbital apex, the nasociliary, frontal, lacrimal, and maxillary branches of the trigeminal nerve demonstrated intense staining upon entering the orbit. Immunoreactive axons from the nasociliary and frontal nerves were observed to join the extraocular motor nerves in the posterior orbit. A plexus of immunolabeled nerves was observed to accompany the ophthalmic artery as it entered the orbital apex. The ophthalmic artery and its branches throughout the orbit demonstrated staining of nerve fibers in the peripheral muscularis. The nasociliary nerve contributed sympathetic branches to the ciliary ganglion. Nerves passing through the ciliary ganglion and a few ganglion cell bodies demonstrated mild to moderate tyrosine hydroxylase reactivity. Axons within the short and long ciliary nerves demonstrated strong tyrosine hydroxylase reactivity and were observed to enter the posterior sclera and the suprachoroidal space. The lacrimal gland demonstrated mild pericapillary staining and occasional stromal nerve fibers reactive to the antityrosine hydroxylase antibody. Müller muscle and the inferior tarsal muscle possessed a strong tyrosine hydroxylase-reactive nerve supply that appeared to originate from the anterior terminal branches of the nasociliary and lacrimal nerves.
Conclusions: Sympathetic nerves enter the orbit via the first and second divisions of the trigeminal nerve and a plexus of nerves surrounding the ophthalmic artery. Extraocular motor nerves receive a sympathetic nerve supply from the sensory nerves in the posterior orbit. Some ciliary ganglion cell bodies demonstrated tyrosine hydroxylase-like reactivity, suggesting a sympathetic modulatory role for the ciliary ganglion. Sympathetics innervate ocular structures via the posterior ciliary nerves. Sympathetic axons travel anteriorly in the orbit via the nasociliary and lacrimal nerves to innervate the sympathetic eyelid muscles. Sympathetic nerves also travel with the frontal branch of the ophthalmic nerve to innervate the forehead skin. The ophthalmic artery and all of its branches contain a perivascular sympathetic nerve supply that may be involved in regulation of blood flow to ocular and orbital structures.