Determining the Relationship Between Corneal Stiffening and Tissue Dehydration After Corneal Cross-Linking

Area of Science:

• Ophthalmology
• Biomechanical Engineering
• Tissue Engineering

Background:

• Corneal cross-linking (CXL) is a standard procedure to strengthen the cornea and halt progressive keratoconus.
• Accurate assessment of CXL-induced stiffening is crucial for understanding treatment efficacy.
• Tissue hydration is a known factor influencing corneal biomechanics.

Purpose of the Study:

• To quantify corneal cross-linking (CXL)-induced stiffening using mechanical testing.
• To estimate the impact of hydration levels (H) on measured corneal stiffness.
• To evaluate depth-dependent tissue hydration changes after CXL.

Main Methods:

• Eighty-three porcine corneas underwent standard CXL (S-CXL), accelerated CXL (A-CXL), or served as controls.
• Hydration levels were modulated, and dynamic mechanical analyzer compression tests measured Young's modulus (E).
• Biphasic material modeling and confocal reflection microscopy (CRM) were used to analyze tissue properties.

Main Results:

• Young's modulus increased significantly after S-CXL and A-CXL compared to controls.
• Corneal hydration (H) decreased post-CXL, with lower values in S-CXL than A-CXL.
• After accounting for hydration and using biphasic modeling, the solid tissue network modulus showed a smaller increase post-CXL.

Conclusions:

• Corneal tissue hydration significantly impacts measured stiffness after CXL.
• Failure to account for hydration leads to a major overestimation of CXL's stiffening effect.
• Depth-dependent hydration changes are influenced by the integrity of the corneal tissue.