Interlamellar cohesion after corneal crosslinking using riboflavin and ultraviolet A light.

Aims: Collagen crosslinking treatment of progressive keratoconus using the photosensitiser riboflavin and ultraviolet A light of 370 nm wavelength has been shown to increase significantly the tensile strength of corneal collagen by about 300%. In keratoconus, interlamellar and interfibrillar slippage have been proposed as pathogenetic mechanisms. Therefore, the aim of this study was to assess the impact of collagen crosslinking on the interlamellar cohesive force. Methods: 72 post mortem porcine eyes were divided into six different treatment groups: the untreated control group, the standard crosslinking group, the hypo-osmolar crosslinking group, the stromal swelling group, the formaldehyde group and the α-amylase group. An anterior 9X4 mm strip of 400 μm thickness was prepared using a lamellar rotating microkeratome. For interlamellar cohesive force measurements a splitting plane was created at 50% depth. Force-distance profiles were recorded using a microcomputer-controlled biomaterial testing machine. Results: The mean interlamellar cohesive force was 0.24 N/mm in the untreated control group, 0.26 N/mm in the standard crosslinking group, 0.25 N/mm in the hypoosmolar crosslinking group, 0.23 N/mm in hydrated corneas, 0.27 N/mm in the formaldehyde group without statistically significant difference. Only the values of the α-amylase group were statistically significantly lowered by 31.5% to 0.16 N/mm. Conclusions: Surprisingly, corneal crosslinking does not increase the interlamellar cohesive force. In the α-amylase group the cohesive force was mainly decreased because of the digestion of proteoglycans. Crosslinking seems to stabilise only inter- and intrafibrillar, but not interlamellar cohesion.