UV-A Crosslinking Induces Linear Stiffness Increase in Donated Human Corneas  

Riboflavin-based UV-A crosslinking (CXL) induces an immediate response of a linear stiffness increase in human donor corneas, according to a study published in Cornea. There were no significant short-term delayed biomechanical changes after CXL therapy in these corneas, according to the report. 

Keratoconus leads to visual deterioration due to irregular astigmatism and corneal thinning,” the study authors explain. “Riboflavin-based corneal UV-A CXL induces novel intramolecular and intermolecular links resulting in corneal tissue stiffening, thereby halting disease progression.”

Researchers evaluated the immediate and delayed biomechanical responses to riboflavin-based UV-A crosslinking in 20 corneas (mean age, 75.4 years) from 15 human donors.

CXL treatment was performed based on the Dresden protocol to corneas not suitable for transplantation. Biomechanical properties were monitored via measuring the Young modulus utilizing nanoindentation.

The immediate response indicates a linear stiffness increase by means of linear mixed model.

The immediate tissue response was confirmed after 0, 1, 15, and 30 minutes of irradiation. Delayed biomechanical effects were evaluated with follow-up measurements immediately and 1, 3, and 7 days following UV-A CXL.

Young’s modulus showed a linear trend in direct response to increasing irradiation times (mean values: 61.31 kPa [SD 25.53] in total, 48.82 kPa [SD 19.73] at 0 minutes, 53.44 kPa [SD 25.95] after 1 minute, 63.56 kPa [SD 20.99] after 15 minutes, and 76.76 kPa [SD 24.92] after 30 minutes). The linear mixed model for the elastic response of corneal tissue was 49.82 kPa + (0.91 kPa/min · time [minutes]); P <.001, the report shows. 

The follow-up measurements demonstrated no significant delayed changes in the Young modulus (mean values: 55.28 kPa [SD 15.95] in total, 56.83 kPa [SD 18.74] immediately after UV-A crosslinking, 50.28 kPa [SD 14.15] at day 1, 57.08 kPa [SD 14.98] at day 3, and 56.83 kPa [SD 15.07] at day 7).

“The immediate response indicates a linear stiffness increase by means of linear mixed model,” according to the study authors. “The study provides no evidence of delayed biomechanical changes.”

Study limitations include that the availability of tissue samples was limited, the donor’s age and the time between explanation and start of the experiment varied, and possibility of alteration of the swelling properties of the cornea. 


Ross AKM, Schlunck G, Böhringer D, et al. Characterization of the immediate and delayed biomechanical response to UV-A crosslinking of human corneas. Cornea. Published online June 19, 2023. doi:10.1097/ICO.0000000000003336