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T. Schilde, E. Spoerl, M. Kohlhaas, L.E. Pillunat; Depth Dependence of Stiffening on Riboflavin/UVA Treated Corneas . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4958.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: It was shown that treatment of keratoconus with riboflavin/UVA is based on a significant stiffening of the cornea (ARVO 2004 Abstr.Nr.2888). Aim of this study was to evaluate how deep the mechanical stabilization after collagen–crosslinking could be shown biochemically. Methods: 10 out of 20 enucleated porcine eyes were treated with riboflavin as photosensitizer and UVA (370nm, 3mW/cm², 30min), the other 10 eyes served as controls. With a microkeratom two flaps of 200µm thickness were cut from each eye and afterwards put into collagenase solution (NaCl + collagenase; 1:1). The surfaces of the flaps were measured digitally and compared daily to characterize the solvent behaviour. Results: The resistance (regarding corneal collagen against enzymatic digestion) of the treated superficial flaps was considerably higher (p=0,001) compared to those which were cut secondly and to the control flaps. But even the flaps from deeper layers showed a significant increase of resistance (p=0,02) in comparison with the untreated flaps. The half–life of the surfaces of the treated superficial flaps was 220 hours, of those cut secondly 80 hours. The both untreated flaps had a half–life of 50 hours. Conclusions: This biochemical study showed that treatment of the cornea with riboflavin/UVA leads to a significant collagen–crosslinking not only in the anterior slice of 200µm but also in the following 200µm. This locally limited crosslinking–effect may be explained by the absorption behaviour for UVA of the riboflavin–treated cornea. 65% of UVA–irradiation is absorbed in the first 200µm and only 25–30% in the next 200µm. Therefore, deeper laying structures and especially the endothelium seem to be not influenced.
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