Abstract
Purpose: :
To provide a comprehensive description of the human corneal innervation using modified whole mounts.
Methods: :
Human corneas from donors aged 19-83 years with death-to-fixation times of <18 hours were obtained from registered eye banks. The central core of each cornea was removed with a 6.5mm trephine and the peripheral cornea was cut into temporal and nasal halves. Five serial 100 micron-thick sections were cut from each specimen in a cryostat in a posterior-to-anterior direction at which point the remaining tissue, consisting of approximately 50-100 microns of anterior stroma and the entire corneal epithelium, was thawed in PBS to yield an anterior-cornea whole mount. Specimens were incubated overnight in 0.01% hyaluronidase and 0.1% EDTA in 0.1M PBS, pH 5.3 to enhance permeability. Corneal nerves were stained immunohistochemically with neurotubulin primary Ab (TUJ1, Covance, Inc.) and standard ABC-DAB methodology.
Results: :
An average of 74 evenly spaced stromal nerve bundles entered the peripheral cornea at the limbus. These fibers gave rise to a modest midstromal nerve plexus consisting of branched, medium-sized nerve bundles. Anterior-cornea whole mounts from the central and peripheral cornea provided comprehensive, three-dimensional demonstrations of subepithelial and subbasal nerve architecture. The subepithelial plexus comprised a tortuous network of delicate, highly anastomotic fibers that was most dense in the peri-central cornea. The subbasal plexus in the central cornea consisted of uniformly-spaced thick subbasal nerves separated from one another by an anastomotic network of much thinner fibers. Subbasal nerves in the central cornea coursed, in general, in a 6-12 oclock direction. Subbasal nerves in the peripheral cornea coursed in a predominantly radial direction; however, many peripheral subbasal nerves (especially in older corneas), coursed parallel or oblique to the corneoscleral limbus. The mean distance between thick subbasal nerves was 108 microns in the central cornea and 229 microns in the intermediate/peripheral cornea. Intraepithelial nerve terminals, which degenerate rapidly after death, were visualized inconsistently in this study; however, many anterior-cornea whole mounts contained several areas of excellent nerve terminal staining suitable for morphologic analyses.
Keywords: innervation: sensation • cornea: tears/tear film/dry eye • cornea: basic science