Architecture of human corneal nerves

Area of Science:

• Ophthalmology
• Neuroscience
• Microscopy

Background:

• Corneal innervation is crucial for sensation and wound healing.
• Previous studies, primarily light microscopy, described radially oriented stromal nerve bundles forming a subbasal plexus.
• The precise orientation, size, and postmortem changes of these fibers remain incompletely understood.

Purpose of the Study:

• To determine the orientation of nerve fibers in the human corneal subbasal plexus.
• To analyze the size and morphology of these nerve fibers.
• To investigate postmortem changes affecting corneal nerve integrity.

Main Methods:

• Corneas from enucleated eyes (melanoma patients and postmortem pairs) were marked for orientation.
• Serial "en face" semithin sections were used for light microscopy to study orientation and postmortem changes.
• Ultrathin cross-sections were analyzed to determine nerve fiber size.

Main Results:

• Significant degeneration of nerve fibers was observed 13.5 hours postmortem.
• Nerve fiber bundles exhibited a distinct orientation pattern: 9-3 hours, then 12-3 hours after bifurcation, and 9-3 hours after a second bifurcation.
• Corneal innervation density was uniform in central and central-peripheral areas, with significantly lower density in the peripheral cornea. Mean fiber diameters were 0.4 micron (central) and 0.67 micron (peripheral).

Conclusions:

• The human corneal subbasal nerve plexus forms a dense, regular meshwork with uniform density across central and central-peripheral regions.
• The majority of identified nerve fibers, based on their size, are classified as C-fibers.
• Postmortem changes rapidly degrade corneal nerve structures, highlighting the importance of timely analysis.