2,3,4,5-Tetrachloro-6-(3-hydroxy-2,4,5,7-tetraiodo-6-oxo-xanthen-9-yl)benzoic acid

Tear component comprising of different proteins, such as albumin (although not very common as tear component), lactoferrin, and transferrin, can bind to rose bengal dye and act as diffusion barrier to prevent dye uptake by cells and subsequent cell staining. Lysosymes in tear film can also bind to rose bengal to form precipitates to attenuate cell uptake.

Rose bengal is a staining agent that visualized ocular surfaces of both diseased and dead cells _in vivo_. It has also shown to stain healthy cultured cells, including rabbit corneal epithelial cells, in a rapid, dose-dependent manner. Various studies demonstrate the cytotoxic effects of rose bengal in different cell cultures, including smooth-muscle cells from human intestine, endothelial cells from bovinepulmonary artery, rabbit Tenon fibro-blasts, and rabbit and human corneal epithelial cells. Cellular morphological changes such as detachment, separation, loss of motility and disruption, in addition to swelling, intracytoplasmic vacuole formation and lysis have been manifested with the treatment of rose bengal, indicating that rose Bengal is not a vital dye.

Rose Bengal stains both the nuclei and cell walls of dead or degenerated epithelial cells of the cornea and conjunctiva, and stain the mucus of the precorneal tear film. It is proposed that the staining ability of rose bengal is dependent on the status of tear film protection rather than cell viability, as tear components such as albumin and mucin can block the rose bengal uptake. It induces intrinsic cytotoxic effects by causing cellular morphologic changes, subsequent loss of cellular motility, cell detachment, and cell death. It mediates inhibitory actions on bovine corneal endothelial cells and attenuates cell proliferation.