Purpose:
To compare the effect of transepithelial delivery of riboflavin through a femtosecond laser-created intrastromal pocket or topical permeability enhancers with ultraviolet A (UVA) to traditional epithelium-off crosslinking on the corneal stromal cellular response and corneal stromal density in rabbits.
Methods:
Thirty-six rabbits underwent study. Animals were divided into three treatment groups and corneas were analyzed at 24 hours and 8 weeks postoperatively. Treatment groups were: 1) standard epithelium off CXR, 2) femtosecond laser pocket riboflavin delivery transepithelial CXR, and 3) permeability enhancer carboxymethylcellulose (CMC)/tetracaine transepithelial CXR. Crosslinking parameters used were 0.1% riboflavin, UVA (370nm) irradiance 3 mW/cm2, 30 minutes (Roisterer, Vienna, Austria). The TUNEL assay was performed to detect stromal cell apoptosis, and immunohistochemistry for the smooth muscle action (SMA) marker for myofibroblasts. Corneal density/haze was quantified using GALILEI Scheimpflug Analyzer (Ziemer, Alton, USA). GALILEI has a diagnostic feature that can measure the relative density from 0 - 100 over two axes (0 least, 100 most).
Results:
At 24 hours, the standard epithelium off CXR and femtosecond pocket transepithelial CXR methods had significantly more stromal cells apoptosis than permeability enhancer CMC/tetracaine transepithelial CXR. 147±8, 140±11, 3±0.5 per 400x power field, respectively (P<0.001). Permeability enhancer CMC/tetracaine transepithelial CXR triggered minimal apoptosis in anterior stroma. Minimal SMA+ myofibroblasts were detected in any group. At 8 weeks after CXR, femtosecond (71±3) and standard CXR (79±4) methods, generated more dense corneas than the permeability enhancer CMC/tetracaine transepithelial CXR method (39±3) and uncrosslinked cornea (26±0.9) (P<0.001, Fig. 1).
Conclusions:
Femtosecond transepithelial CXR triggers less stromal damage but on average an equal amount of corneal density change compared to standard CXL. Permeability enhancer CMC/tetracaine transepithelial CXR is a poor transepithelial permeability enhancer, and triggers minimal apoptosis and no increase in corneal density detected with the GALILEI Scheimpflug Analyzer.
Keywords: keratoconus • photodynamic therapy • cornea: basic science