Corneal Nerve Fiber Structure, Its Role in Corneal Function, and Its Changes in Corneal Diseases

Figure 1

A putative architecture and distribution pattern of corneal nerve fibers of rats in normal (a) and their alterations after neonatal capsaicin treatment (b). Thick stromal subepithelial nerve fiber plexus are reactive to NsAchE. The NsAchE-positive (+) nerve plexus (indicated in blue) are resistant to capsaicin. On the other hand, NsAchE-negative (−) nerve fiber bundles showing dense interconnections (meshwork structure) reactive to neuropeptides and IB4 or TRPV1 seem to be subbasal leash fibers in rats cornea (indicated in orange). They are assumed to be destroyed (especially in the central portion) after neonatal capsaicin treatment (b), but NsAchE (+) nerves are never influenced by capsaicin. Probably, capsaicin-sensitive neurotrophic peptidergic nerve fibers are destroyed by neonatal capsaicin treatment resulting in the defect of epithelial cells (neuroparalytic keratitis) and desensitization to chemical or thermal stimuli. BEP: basal epithelial plexus of leash fibers, BL: Bowman’s layer, DEC: defect of epithelial cells, and SEP: subepithelial (stromal) plexus.