Transmission Rates of UV-A and Green Light in an ex vivo Corneal Cross-linking Model for Infectious Keratitis

Purpose: To investigate the light transmission (LT) of UV-A and green light through infected corneas saturated with riboflavin or rose bengal in an ex vivo porcine model for infectious keratitis. Setting: University of Zurich and EMPA. Design: Laboratory study. Methods: Ex vivo porcine eyes (n=162) were divided into three groups: control eyes, eyes infected with Staphylococcus aureus , and eyes infected with Pseudomonas aeruginosa . Corneas remained either uninfected, or were infected with S. aureus , and P. aeruginosa , respectively, and were either left untreated, or were instilled with 0.1% riboflavin or 0.1% rose bengal. Corneal buttons were prepared, and corneal LT was measured at 365 nm and 522 nm using a spectrophotometer. LTs were calculated and compared. Transmission electron microscopy (TEM) was used to visualize structural damage and bacteria within infected corneas. Results: Riboflavin-saturated corneas infected by S. aureus or P. aeruginosa (LT = 0.77% [0.41-1.87] and 0.81% [0.23, 1.46]) exhibited 3.18-fold and 3.02-fold lower LTs than uninfected corneas (LT = 2.45% [2.15, 5.89]) (both p -values < 0.001). No LT difference was found between rose bengal-saturated corneas infected by S. aureus or P. aeruginosa and uninfected corneas (all LTs = 0.01% [0.01-0.01]; both p -values = 0.08). TEM showed bacteria on corneal stroma borders and occasionally inside the stroma. Conclusion: Our results indicate that the amount of light arriving at the corneal endothelium is substantially reduced in infected corneas. The total fluence of clinical PACK-CXL protocols can be safely increased substantially while maintaining a low risk of corneal endothelial damage.