Rose bengal photosensitized crosslinking stiffens the cornea efficiently, with and without the presence of oxygen, Harvard Medical School researchers report.

Since rose bengal photosensitized protein crosslinking has been proposed for several applications in the eye, investigators hoped to identify oxygen-dependent and oxygen-independent mechanistic pathways in the cornea to enhance its efficiency for ocular treatments.

Researchers stained ex vivo rabbit corneas with 1mM rose bengal and irradiated at 532nm. They then performed rose bengal photobleaching with and without oxygen present. The study examined the effects of sodium azide, D₂O, arginine and ascorbate to discriminate between mechanisms involving energy transfer (forming singlet oxygen) and electron transfer (forming radical ions).

The study reported rose bengal photobleaching was greater in the presence than in the absence of oxygen, enhanced by D₂O and partially inhibited by azide, indicating a singlet oxygen pathway. Photobleaching without oxygen was enhanced by arginine and ascorbate and accompanied by a shift in the absorption to shorter wavelengths, suggesting that electron transfer initiates rose bengal photodecomposition, researchers noted. Additionally, the investigation reported rose bengal-photosensitized tensile strength increase in air was enhanced by D₂O and inhibited by azide.

Rose bengal photosensitized crosslinking of the cornea in the absence of oxygen can be enhanced by arginine to produce the same level of stiffness exhibited in the presence of oxygen. The findings may expand the treatment’s range of clinical applications in the cornea and other tissues, the researchers note.