Sensory supply of the anterior uvea: a light and electron microscope study.

We have studied the ultrastructural features of sensory nerve fibers in the ciliary body and the iris and their parent trigeminal ganglion cells, using intra-axonally transported horseradish peroxidase as a tracer. Unmyelinated nerve fibers of ipsilateral trigeminal origin were found in stroma of both the ciliary body and the iris. Most appeared in bundles of nerve fibers; but some were found singly. Two distinct types of varicosities were found, one containing both a few irregularly shaped vesicles and mitochondria, the other containing mitochondria only. The thin profiles of the axons between these varicosities or endings contained neurotubules and filaments. The trigeminal ganglion cells supplying the anterior eye were of a relatively small size (15-50 micron in diameter) and confined to the anteromedial part of the ipsilateral ganglion. These cells could not be classified according to the arrangement of their subcellular organelles. The morphological characteristics of the sensory nerve fibers and ganglion cells supplying the anterior uvea are consistent with the view that pain may be the predominant sensation mediated by these neurons.