Vasoactive intestinal polypeptide immunoreactive nerve fibres in the human eye

Immunohistochemistry applied to whole-mount preparations was used to investigate the presence and distribution of vasoactive intestinal polypeptide (VIP) immunoreactive nerves in the non-retinal part of the human eye. The choroid has a dense perivascular supply of VIP immunoreactive nerve fibers, and some free nerve endings within the stroma. These nerves enter the choroid in ciliary nerves and also as perivascular networks around the ciliary arteries. Occasional choroidal VIP immunoreactive nerve cell bodies are seen. The ciliary body stroma, close to the iris root has a dense circumferential plexus of VIP immunoreactive nerve fibers that occur both singly and in bundles. The iris root has a circumferential arrangement of bundles from which VIP immunoreactive nerve fibres travel radially in the stroma. They supply the pupillary region with numerous free nerve endings; the sphincter pupillae is not supplied by these nerves. The cornea is devoid of VIP immunoreactive nerves. These findings, together with existing knowledge of the physiological actions of VIP, indicate that VIP immunoreactive nerves are likely to be involved in the functioning of several ocular tissues.