Photochemical activation increases the porcine corneal stiffness and resistance to collagenase digestion

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In this study, we explore the effect of photochemical activation induced corneal cross-linking, utilizing Rose Bengal (RB) and 532 nm green light irradiation (RB-PCL), on porcine corneal biomechanical rigidity and the biochemical resistance against collagenase digestion. A protocol with a wavelength of 532 nm and illumination intensity of 0.4W/cm2 for 250 s to deliver a dose of 100 J/cm2 was chosen. Using confocal microscopy, we demonstrated that the diffusion depth of RB into porcine cornea was approximately 150 μm and mostly localized in anterior stroma 25 min followed by RB application. After photochemical cross-linking, an increase in tensile strength (by average 200%) and Young's modulus (by average 200%) in porcine corneas was observed. The corneal buttons treated by RB-PCL showed doubling of collagenase digestion time from 10.8 ± 3.1 days in the blank group to 19.7 ± 6.2 days in the RB-PCL group, indicating increased resistance to enzymatic digestion. In conclusion, Collagen cross-linking by RB-PCL increased both the biomechanical stiffness and the biochemical resistance against collagenase digestion in porcine corneas, therefore to allow stabilizing and solidifier the cornea. The advantages and disadvantages of RB-PCL versus UVA/riboflavin cross-linking technique (UV-CXL) are fully explored. Due to the nature of minimal penetration of RB into corneal stroma, the RB-PCL method could potentially be used in patients with corneal thickness less than 400 μm where UV-CXL is limited.

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