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Oxygen diffusion has a central role in the efficiency of corneal cross-linking. Oxygen availability in tissue increases with reduced temperature. The goal of this study was to assess whether a reduction of the corneal temperature during CXL might raise oxygen availability and thus enhance the biomechanical effect of CXL in ex vivo porcine corneas.
One hundred twelve porcine corneas with intact epithelium were divided into 4 groups and analyzed. Prior to corneal soaking with hypo-osmolaric 0.1% riboflavin, the epithelium was removed manually in all groups. Accelerated epithelium-off CXL using 9 mW/cm2 irradiance for 10 minutes was performed either at room temperature (group 1, 24°C) or in a cold room (group3, 4°C). Non-cross-linked corneas (groups 2 and 4) were subjected to the same temperatures and served as controls. The elastic modulus of 5-mm wide corneal strips was analyzed and used to determine corneal biomechanical properties.
Epithelium-off CXL led to significant increases in the elastic modulus determined between 1% and 5% of strain in stress-strain extensometry when compared to non-cross-linked controls, both at 24°C (p<0.001) and 4°C (p=0.006) . However, no significant difference was found between corneas treated with CXL at 24°C and 4°C (p = 0.384).
While oxygen plays a central role in corneal cross-linking, the potentially increased diffusion of oxygen in lower tissue temperatures does not appear to play a significant role in the biomechanical efficiency of epithelium-off CXL accelerated protocols in ex vivo porcine corneas.