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Biomechanical efficacy of corneal cross-linking using hypoosmolar riboflavin solution

Purpose: The use of hypoosmolar riboflavin solution has been suggested for cross-linking thin corneas. The aim of this study was to compare the biomechanical efficacy of corneal cross-linking using hypoosmolar dextran-free riboflavin solution (HCXL) versus isoosmolar standard corneal cross-linking treatment (CXL). Methods: A total of 24 postmortem porcine eyes with debrided corneas were subdivided into three treatment groups: Controls, the isoosmolar group with isoosmolar 0.1% riboflavin-20% dextran solution and the hypoosmolar group with dextran-free, 0.1% riboflavin solution. The samples were irradiated with UVA light of 365 nm wavelength and an irradiance of 3 mW/cm² for 30 min (dose 5.4 J/cm²). For the biomechanical measurements, 400-µm-deep anterior corneal flaps were created using a lamellar rotating microkeratome. Uniaxial stress–strain measurements were performed. Results: In the isoosmolar treatment group, stress and Young’s modulus at 8% strain were significantly increased by 67.97%, respectively, 62.62% versus the controls. In the hypoosmolar treatment group, stress and Young’s modulus at 8% strain were significantly increased by 81.21%, respectively, 51.40% versus the controls. There was no significant difference between the iso- and hypoosmolar groups in biomechanical efficacy. On histology, there was no edema in the anterior 200 µm of the corneas after stromal swelling by the hypoosmolar riboflavin solution. Conclusion: Corneal cross-linking using isoosmolar or hypoosmolar riboflavin solution induces a comparable biomechanical effect. This is explained by the localization of the maximum cross-linking effect in the anterior 200 µm of the cornea which are not affected by the swelling effect of hypoosmolar riboflavin solution.