Biomechanical efficacy of contact lens-assisted collagen cross-linking in porcine eyes.

Purpose: Contact lens-assisted corneal cross-linking (CACXL) has been proposed for the cross-linking treatment in thin corneas. The aim of this study was to assess the biomechanical efficacy of this treatment.
Methods: Post-mortem porcine eyes were treated with standard cross-linking and with cross-linking placing a contact lens soaked with isoosmolar riboflavin solution on the debrided cornea with or without an adherent precorneal riboflavin film of up to 100 μm thickness. Three soft contact lenses (Air Optix Aqua, SofLens and Galifa) with different degrees of hydrophilic properties were tested. After cross-linking with a surface UVA irradiance of 3 mW/cm² for 30 min (fluence 5.4 J/cm²), a 400 μm deep anterior corneal flap was created using a lamellar rotating microkeratome. Biomechanical stress-strain measurements and thermal shrinkage tests were performed.
Results: In the Air Optix Aqua group (30% hydration) without riboflavin film, Young's modulus and stress at 8% strain were increased significantly versus untreated controls and the effect was 92.4% respectively 86.35% of the standard CXL value. In the SofLens group (59% hydration) without riboflavin film, Young's modulus and stress at 8% strain were increased significantly versus untreated controls and the effect was 67.04% respectively 65.28% of the standard CXL value. In the Galifa group (72% hydration) without riboflavin film, Young's modulus and stress at 8% strain were increased significantly versus untreated controls and the effect was about 68.48% respectively 75.52% of the standard CXL value. In all samples with a precorneal riboflavin film under the contact lens, there was no significant biomechanical effect compared to the untreated controls. Similarly, in the hydrothermal experiments at 70°C, there was a typical mushroom pattern with increased resistance to thermal shrinkage in the anterior stroma after standard CXL, a markedly reduced mushroom effect using a riboflavin-soaked contact lens only and no effect with the use of a riboflavin-soaked contact lens plus a precorneal riboflavin film.
Conclusion: The biomechanical effect of CACXL in porcine corneas is about one-third less than after standard CXL. The efficacy of CACXL might be improved by reducing or omitting the riboflavin film on the contact lens. Further risk assessment studies are necessary.
(© 2018 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.)