Alternative photosensitizer penetration depth evaluation in ex vivo human eyes for photodynamic antimicrobial therapy

Fungal keratitis has a poor prognosis given deep penetration into the corneal stroma. While Rose Bengal photodynamic antimicrobial therapy (RB-PDAT) is a promising adjunct treatment for refractory cases, poor penetration limits its effectiveness. This study explores the penetration depth of alternative photosensitizers to address this issue. Thirty-five human corneas were soaked for 30 minutes in 0.0075% solution of Rose Bengal disodium (<i>n</i> = 5), Rose Bengal lactone (<i>n</i> = 5), Erythrosin B disodium (<i>n</i> = 5), Erythrosin B lactone (<i>n</i> = 5), Eosin Y disodium (<i>n</i> = 5), Methylene blue (<i>n</i> = 5), or NaCl (control, <i>n</i> = 5). Confocal microscopy was used to assess penetration depth. All photosensitizers penetrated greater into the cornea as compared to control. There was no significant difference in penetration between Rose Bengal lactone and Rose Bengal disodium (RB lactone: 106 ± 11 <b>µm</b> vs RB disodium: 99 ± 13 <b>µm</b>, <i>p</i> &gt; 0.05). The penetration depths of the alternative photosensitizers was significantly greater than either Rose Bengal formulation (Erythrosin Blactone: 192 ± 31 <b>µm</b>, Erythrosin B disodium: 163 ± 13 <b>µm</b>, Eosin Y disodium: 249 ± 31 <b>µm</b>, Methylene Blue: 355 ± 151 <b>µm)</b>. Alternative photosensitizers exhibit superior penetration compared to Rose Bengal. However, antimicrobial efficacy and corneal safety require more robust evaluation before clinical use. This study investigated a new treatment for infections of the eye known as photodynamic antimicrobial therapy. In this treatment, a chemical known as Rose Bengal is activated with a green light which then causes the killing of bacteria in the eye. Unfortunately, Rose Bengal does not go deep enough into the eye to treat more severe infections. Therefore, this study utilized donated human tissue to investigate the penetration depth of other light-sensitive chemicals. The results demonstrated that the penetration depth of these other chemicals was significantly greater than that currently seen with Rose Bengal.