Mechanical damage to corneal stromal cells by epithelial scraping.

OBJECTIVE: Corneal epithelial scraping, a common clinical procedure, triggers a loss of underlying keratocytes. This study was conducted to examine whether the physical impact of epithelial scrape injury plays any role in the death of these cells.
METHODS: Epithelial debridement was carried out on the cornea of a freshly killed mouse either by mechanical scraping with a blunt spatula, as in the clinical scraping, or lifting by repeated touching with a gelatin-coated slide. Subsequently, nuclei, nuclear envelope, microtubules, microfilaments, and plasma membranes were examined with specific probes. Some corneas were fixed with alcohol before scrape injury. Fate of keratocytes after epithelial injury was investigated with isolated eyes ex vivo and living mice in vivo. Some of the procedures were performed with human donor corneas.
RESULTS: Within seconds of, or possibly simultaneous to, mechanical epithelial scraping, nuclei of underlying keratocytes became grossly deformed to assume extremely stretched morphology, accompanied by destruction of microfilaments and microtubules as well as compromised plasma membranes. These cells deteriorated gradually over several hours both ex vivo and in vivo. Nuclear deformation was observed even when the cornea was fixed with alcohol before epithelial scraping. When the epithelium was removed by gentle lifting, nuclei remained mostly intact. Similar results were obtained with human donor corneas.
CONCLUSION: Mechanical epithelial scraping can cause immediate damage to underlying anterior keratocytes by a physical impact, which appears to lead to degeneration of these cells.