Evaluation of UVA cytotoxicity for human endothelium in an ex vivo vorneal vrosslinking experimental setting
Faculty of Medicine and Health Sciences
Faculty of Pharmaceutical, Biomedical and Veterinary Sciences . Biomedical Sciences
Journal of refractive surgery. - Thorofare, N.J
, p. 41-46
University of Antwerp
PURPOSE: To evaluate endothelial cytotoxicity after exposure of human corneas to ultraviolet-A (UVA) (lambda = 365 nm; 5.4 J/cm(2)) in an experimental ex vivo corneal cross-linking setting. METHODS: Sixteen pairs of human donor corneas were cut into two pieces. One piece of each cornea was treated with 0.025% riboflavin solution prior to UVA irradiation (5 minutes; 18 mW/cm(2)), whereas the other piece was not irradiated but treated with riboflavin (right eye) or preservation medium (left eye). By irradiating from the endothelial side, the UVA dosage applied to endothelial cells exceeded at least eight times the cytotoxic threshold established in animal models (0.65 J/cm2). Endothelial cell counts were performed by two independent investigators after storage (4 to 5 days at 31 degrees C) and staining (trypan blue, alizarin red). Normality (Q-Q plot; Shapiro-Wilk test) and equivalence (mixedeffects modeling with a 10% equivalence threshold) of the endothelial cell counts of the different groups were evaluated. RESULTS: Equivalence of mean endothelial cell density between both groups was observed: 2,237 +/- 208 cells/mm(2) in UVA-irradiated pieces and 2,290 +/- 281 cells/mm(2) in control pieces (mean difference of 53 +/- 240 cells/mm(2) between both groups). CONCLUSIONS: Despite direct irradiation of human donor endothelium using the clinical dosage for cross-linking, equivalence in endothelial cell counts was observed between irradiated tissues and controls. Ex vivo human corneal endothelial cells seem to be far more resistant to riboflavin-enhanced UVA irradiation than previously estimated by animal experiments.