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Nada H Aldahlawi, Sally Hayes, David O’Brart, Keith Meek, Biophysics Research group; An investigation into corneal enzymatic resistance following epithelium-removed, partial epithelium disruption and epithelium-intact riboflavin/UVA cross-linking procedures. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1134.
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Riboflavin/UVA corneal collagen crosslinking therapy has been shown to successfully halt keratoconus progression by stiffening the corneal stroma and increasing its resistance to enzymatic digestion. The aim of this study was to compare the effectiveness of epithelium-removed, partial epithelial disruption and transepithelial crosslinking protocols, in terms of their ability increase the resistance of the cornea to enzymatic digestion.
Sixty enucleated porcine eyes were examined and randomly divided into ten groups. Groups 1 and 2 had the corneal epithelium removed and 0.1 % riboflavin phosphate/20% dextran eye drops applied for 30 minutes. Groups 3 and 4 had grid pattern partial epithelial disruption followed by 30 minutes of 0.1 % riboflavin phosphate eye drops. All other groups were treated with an intact epithelium. Groups 5 and 6 had 0.25% riboflavin Mediocross transepithelial (TE) eye drops applied for 30 minutes. Groups 7 and 8 underwent iontophoresis for 5 minutes with 0.1 % riboflavin phosphate eye drops, and groups 9 and 10 underwent iontophoresis for 10 minutes with 0.25% riboflavin Mediocross TE. Following the application of riboflavin, groups 2, 4, 6, 8 and 10 were irradiated for 10 minutes with 9 mW UVA light. Daily measurements of corneal diameter were recorded in order to monitor the rate of enzymatic digestion.
Resistance to enzymatic digestion was significantly greater in all cross-linked groups than non-cross-linked groups (p<0.0001). On average, complete digestion of the corneal buttons occurred by day 11 ± 0.5 in the non-irradiated groups and by day 25 ± 9.7 in the cross-linked groups. Epithelium-off cross-linking resulted in a greater increase in enzymatic resistance than partial epithelial disruption crosslinking or epithelium-on cross-linking (p<0.0001). The iontophoresis cross-linking protocol used in Group 10 resulted in a greater resistance to enzymatic digestion than any of the other partial epithelial disruption or trans-epithelial crosslinking protocols tested (Groups 4, 6, 8) (p<0.0001).
Although currently not as effective as epithelium-off cross-linking, the outcome of trans-epithelial cross-linking may be significantly improved through the use of higher concentrations of riboflavin solution and a longer duration of iontophoresis.
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