Biomechanical property analysis after corneal collagen cross-linking in relation to ultraviolet A irradiation time.

Purpose: To study the biomechanical effect of riboflavin-ultraviolet A irradiation (UVA)-induced collagen cross-linking (CXL) in porcine corneas using two different exposure times of 30 and 60 min.

Methods: Seventeen enucleated porcine eyes were divided into three groups: group A, six eyes without any treatment, group B, six eyes treated by UVA CXL for 30 min, and group C, five eyes treated by UVA CXL for 60 min. Riboflavin (vitamin B2) was used as a photosensitizer in both groups of treatment. Then, the stress-strain behavior of all the specimens was measured to compare the corneal biomechanical properties among the three groups. The Young's modulus E of the mean curve of each group shows the stiffness of treated and untreated tissue. The stress data necessary for stretches of 6, 8, and 12% were used to perform the statistical analysis of the values.

Results: Group B (riboflavin-UVA-CXL, 30 min, E = 46 MPa) showed a stiffer behavior than group A (control, E = 29 MPa) . Group C (60 min CXL, E = 28 MPa) showed lower stiffness than group B and a similar mechanical behavior than group A. The statistical analysis of the stress-strain curves showed significant differences in the corneal response between group B and the control at the three values of stretch considered, 6, 8, and 12% (p = 0.025, p = 0.025 and p = 0.037, respectively) and between group B and group C (p = 0.028, p = 0.028, and p = 0.028). No statistically significant difference was found between group C and control (p = 0.855, p = 0.715, and p = 0.584).

Conclusions: The application of 30-min UVA CXL treatment with riboflavin increased stiffness of the porcine corneal tissue. A 60-min UVA-radiated tissue presents lower stiffness than the 30-min treated tissue, showing a similar biomechanical behavior than the untreated corneas. A prolongation of the UVA irradiation time may cause structural weakening of the porcine corneas.