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

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 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.