Architecture of human corneal nerves.

PURPOSE The corneal innervation, mainly analyzed in light microscopical studies, has been described as radially oriented stromal nerve bundles that ramify as leashes in the subbasal plexus. The current study aims to determine the orientation, the size, and the postmortem changes of the nerve fibers in the subbasal plexus of the human cornea. METHODS Before processing for light and electron microscopy, the position of the corneas within the enucleated eyes of persons with melanoma and pairs of postmortem eyes was marked. The orientation and postmortem changes of the fibers were studied in serial "en face" semithin sections, and the size was determined in random, ultrathin cross-sections. RESULTS Thirteen and a half hours after death, the majority of the nerve fibers were degenerated or gone. Nerve fiber bundles in the subbasal plexus run first in the 9-3 hours direction, then after bifurcation in the 12-3 hours direction and after a second bifurcation again in the 9-3 hours direction. From the main straight bundles, single-beaded fibers branch and run obliquely. Quantification of the nerve fibers shows an equally dense innervated central and central-peripheral cornea (mean fiber diameter, 0.4 micron) and a five to six times lower innervated peripheral cornea (mean fiber diameter, 0.67 micron). CONCLUSIONS The nerve bundles in the subbasal plexus of the human cornea form a regular dense meshwork with equal density over a large central and central-peripheral area. Because of their size, the majority of the fibers can be classified as C-fibers.