Transmission rates of UV-A and green light in an ex vivo corneal crosslinking model for infectious keratitis

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Abstract
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, Zurich, Switzerland, and Empa, St. Gallen, Switzerland. Design: Laboratory study. Methods: Ex vivo porcine eyes (n = 162) were divided into 3 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 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. LT values 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 LT values, respectively, 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 LT values = 0.01% [0.01-0.01]; both P-values = 0.08). TEM showed bacteria on corneal stroma borders and occasionally inside the stroma. Conclusions: The results indicate that the amount of light arriving at the corneal endothelium is substantially reduced in infected corneas. The total fluence of clinical photoactivated chromophore for keratitis corneal crosslinking protocols can be safely increased substantially while maintaining a low risk of corneal endothelial damage.

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