The effect of photodynamic inactivation on experimental herpes simplex keratitis in rabbits was investigated using neutral red as a photosensitizing dye followed by exposure to light at 425 nm. Combined dye application and light exposure early in the disease (two days following infection) reduced to a minimal extent the severity and duration of the acute epithelial infection. The effect on well-established keratitis (three days postinfection) was negligible as evaluated by clinical grading, viral recovery, and histopathological study.
In initial experiments, it was found that the dye and light did not have any observable deleterious effect on intact corneas or cause any noticeable delay in healing of injured corneas. Further, when light or dye were utilized alone, neither changed the severity or duration of the keratitis. In vitro treatment of the virus with light and dye destroys its ability to produce experimental keratitis.
Lahav M, Dueker D, Bhatt PN, Albert DM. Photodynamic Inactivation in Experimental Herpetic Keratitis. Arch Ophthalmol. 1975;93(3):207-214. doi:10.1001/archopht.1975.01010020215010