Mechanical epithelium removal in CXL may cause more nerve damage then transepithelial approach

This study published in the February issue of the American Journal of Ophthalmology evaluated the early effect of standard and transepithelial collagen cross-linking (CXL) on human corneal nerves in donor eyes. Confocal microscopy demonstrated the absence of subbasal nerves in corneas treated by the standard technique and their preservation in corneas treated by the transepithelial approach. Stromal nerves were visible in both groups, with localized swelling with the standard technique the main difference between the protocols. The authors conclude that subbasal nerve absence in the early phase of treatment appears to be attributable mainly to mechanical scraping of both the epithelium and subbasal nerves rather than ultraviolet light-induced damage.

This is believed to be the first histologic evaluation of corneal nerve response to these two CXL methods. The authors examined eight human eye bank corneal buttons. Ultraviolet A collagen cross-linking was performed postmortem on three corneas with the standard protocol involving epithelial debridement and four corneas by the transepithelial approach. One cornea served as a control.

In addition to confocal microscopy, corneal nerves were evaluated using acetylcholinesterase histology. This revealed that corneas treated by the standard technique experienced 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.

The authors conclude that further research on laboratory animals using different nerve stains is necessary to verify the changes seen in this study over a specified time course without the intervention of postmortem changes.