Impact of hypothermia on the biomechanical effect of epithelium-off corneal cross-linking

Background:The corneal cross-linking(CXL)photochemical reaction is essentially dependent on oxygen and hypothermia,which usually leads to higher dissolved oxygen levels in tissues,with potentially greater oxygen availability for treatment.Here,we evaluate whether a reduction of corneal temperature during CXL may increase oxygen availability and therefore enhance the CXL biomechanical stiffening effect in ex vivo porcine corneas.Methods:One hundred and twelve porcine corneas had their epithelium manually debrided before being soaked with 0.1%hypo-osmolaric riboflavin.These corneas were equally assigned to one of four groups.Groups 2 and 4 underwent accelerated epithelium-off CXL using 9 mW/cm^(2) irradiance for 10 min,performed either in a cold room temperature(group 2,4℃)or at standard room temperature(group 4,24℃).Groups 1 and 3 served as non-cross-linked,temperature-matched controls.Using a stress-strain extensometer,the elastic moduli of 5-mm wide corneal strips were analyzed as an indicator of corneal stiffness.Results:Accelerated epithelium-off CXL led to significant increases in the elastic modulus between 1%and 5%of strain when compared to non-cross-linked controls(P<0.05),both at 4℃(1.40±0.22 vs.1.23±0.18 N/mm)and 24 C(1.42±0.15 vs.1.19±0.11 N/mm).However,no significant difference was found between control groups(P=0.846)or between groups in which CXL was performed at low or standard room temperature(P=0.969).Conclusions:Although initial oxygen availability should be increased under hypothermic conditions,it does not appear to play a significant role in the biomechanical strengthening effect of accelerated epithelium-off CXL protocols in ex vivo porcine corneas.

Impact of hypothermia on the biomechanical effect of epithelium-off corneal cross-linking

Background:The corneal cross-linking(CXL)photochemical reaction is essentially dependent on oxygen and hypothermia,which usually leads to higher dissolved oxygen levels in tissues,with potentially greater oxygen availability for treatment.Here,we evaluate whether a reduction of corneal temperature during CXL may increase oxygen availability and therefore enhance the CXL biomechanical stiffening effect in ex vivo porcine corneas.Methods:One hundred and twelve porcine corneas had their epithelium manually debrided before being soaked with 0.1%hypo-osmolaric riboflavin.These corneas were equally assigned to one of four groups.Groups 2 and 4 underwent accelerated epithelium-off CXL using 9 mW/cm^(2) irradiance for 10 min,performed either in a cold room temperature(group 2,4℃)or at standard room temperature(group 4,24℃).Groups 1 and 3 served as non-crosslinked,temperature-matched controls.Using a stress-strain extensometer,the elastic moduli of 5-mm wide corneal strips were analyzed as an indicator of corneal stiffness.Results:Accelerated epithelium-off CXL led to significant increases in the elastic modulus between 1 and 5%of strain when compared to non-cross-linked controls(P<0.05),both at 4℃(1.40±0.22 vs 1.23±0.18 N/mm)and 24℃(1.42±0.15 vs 1.19±0.11 N/mm).However,no significant difference was found between control groups(P=0.846)or between groups in which CXL was performed at low or standard room temperature(P=0.969).Conclusions:Although initial oxygen availability should be increased under hypothermic conditions,it does not appear to play a significant role in the biomechanical strengthening effect of epithelium-off CXL accelerated protocols in ex vivo porcine corneas.