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

PURPOSE: 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.

METHODS

Thirty-five human corneas were soaked for 30 minutes in 0.0075% solution of Rose Bengal disodium (n = 5), Rose Bengal lactone (n = 5), Erythrosin B disodium (n = 5), Erythrosin B lactone (n = 5), Eosin Y disodium (n = 5), Methylene blue (n = 5), or NaCl (control, n = 5). Confocal microscopy was used to assess penetration depth.

RESULTS

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 µm vs RB disodium: 99 ± 13 µm, p > 0.05). The penetration depths of the alternative photosensitizers was significantly greater than either Rose Bengal formulation (Erythrosin Blactone: 192 ± 31 µm, Erythrosin B disodium: 163 ± 13 µm, Eosin Y disodium: 249 ± 31 µm, Methylene Blue: 355 ± 151 µm).

CONCLUSIONS

Alternative photosensitizers exhibit superior penetration compared to Rose Bengal. However, antimicrobial efficacy and corneal safety require more robust evaluation before clinical use.