Rose Bengal Photodynamic Antimicrobial Therapy: A Pilot Safety Study

To evaluate the in vivo corneal changes after Rose Bengal photodynamic antimicrobial therapy (RB-PDAT) treatment in New Zealand White rabbits.

Sixteen rabbits were divided into 5 groups. All groups underwent deepithelialization of an 8 mm diameter area in the central cornea. Group 1: balanced salt solution drops only, group 2: 0.2% RB only, group 3: green light exposure (525 nm, 5.4 J/cm2) only, group 4: 0.1% RB-PDAT, and group 5: 0.1% RB-PDAT. All rabbits were followed clinically. Group 5 rabbits were followed using anterior segment optical coherence tomography (AS-OCT) and clinically. On day 35 after initial treatment, 1 rabbit from group 5 was re-exposed to green light (5.4 J/cm2) to evaluate reactivation of the remaining RB dye, and terminal deoxynucleotyl transferase-mediated UTP-biotin-nick-end labeling assay was performed on corneal cryosections.

Complete reepithelization was observed, and corneas remained clear after treatment in all groups. In group 5, AS-OCT revealed a cross-linking demarcation line. AS-OCT showed RB fluorescence and collagen cross-linking in all treated eyes of group 5 animals after 5 weeks of treatment. Photobleached RB retention in the corneal stroma was corroborated by fluorescence confocal microscopy on frozen sections. There was no evidence of a sustained cytotoxic effect through terminal deoxynucleotyl transferase-mediated UTP-biotin-nick-end labeling at 5 weeks.

RB-PDAT with 0.1% RB is a safe procedure. There was no difference clinically and on histopathology compared with control groups. In eyes where RB dye is retained in the corneal stroma after 1 month of treatment, oxidative stress is not evidenced at long term.