The effect of standard and transepithelial ultraviolet collagen cross-linking on human corneal nerves: an ex vivo study.

PURPOSE: To evaluate the early effect of standard and transepithelial collagen cross-linking on human corneal nerves in donor eyes by ex vivo confocal microscopy and acetylcholinesterase staining.
DESIGN: Experimental laboratory investigation.
METHODS: Eight human eye bank corneal buttons (mean age, 73.6 years) were included. Ultraviolet A collagen cross-linking was performed postmortem on 3 corneas with the standard protocol involving epithelial debridement and 4 corneas by the transepithelial approach. One cornea served as a control. Corneal nerves were evaluated using confocal microscopy and acetylcholinesterase histology.
RESULTS: Confocal microscopy demonstrated the absence of subbasal nerves in corneas treated by the standard technique. These nerves were preserved in corneas treated by the transepithelial approach. Stromal nerves were visible in both groups. Histology of corneas treated by the standard technique revealed localized swellings of the stromal nerves with disruption of axonal membrane and loss of axonal continuity within the treatment zone. These changes were absent in corneas treated by the transepithelial approach.
CONCLUSIONS: This study highlights the immediate effects of collagen cross-linking on the corneal nerves in an ex vivo model. The absence of subbasal nerves in the early phase of treatment appears to be attributable mainly to mechanical removal of epithelium, rather than ultraviolet light-induced damage. Localized swelling of the stromal nerves was the main difference between the 2 treatment protocols. Further research on laboratory animals would be necessary to verify these changes over a specified time course without the super-addition of postmortem changes.