Ex vivo confocal microscopy of human corneal nerves

To evaluate the distribution, morphometry and the postmortem changes of the central and peripheral human corneal nerves by exvivo laser-scanning confocal microscopy (EVCM).

24 eyes from 14 cadavers were retrieved at different time intervals after death and examined by EVCM. Five regions were examined in each eye: central, superior, inferior, temporal and nasal. In each region, corneal nerve images were categorised according to their anatomical location in the cornea into sub-basal, stromal and limbal nerves. Five nerve parameters were measured: density, orientation, diameter, numbers and branching pattern.

Exvivo confocal scanning of a motionless eye allows high quality imaging and tracking of corneal and limbal nerves. Stromal nerves from the sub-Bowman's plexus perforate the Bowman's zone and terminate in bulb-like structures, from each of which a leash of sub-basal nerves arises. Following death, sub-basal nerve parameters showed significant changes. The density decreased from 9.23+/-4.48 to 0.45+/-0.07 mm/mm(2), the diameter from 4.01+/-0.81 to 2.08+/-0.20 microm, the numbers from 8.3 to 1.0 and branching pattern from 39.38% to 0% (p<0.05) from day 1 to day 5 postmortem. Stromal and limbal nerves showed no significant changes in their density and diameter.

This study establishes a direct link between sub-basal nerves and the sub-Bowman's nerves via distinct terminal bulbs. Limbal nerves are the thickest, are seen in all quadrants and can be traced to the corneal centre. The sub-basal nerve plexus rapidly degenerates after death but stromal and limbal nerves survive during the first five days after death.