Wiktionary
n. 4,5,6,7-tetrachloro-2',4',5',7'-tetraiodofluorescein, a stain whose sodium salt is commonly used in eyedrops to stain damaged cells and thereby identify damage.
Wikipedia
Rose bengal (4,5,6,7-tetrachloro-2',4',5',7'-tetraiodofluorescein) is a stain. Its sodium salt is commonly used in eye drops to stain damaged conjunctival and corneal cells and thereby identify damage to the eye. The stain is also used in the preparation of Foraminifera for microscopic analysis, allowing the distinction between forms that were alive or dead at the time of collection.
A form of rose bengal is also being studied as a treatment for certain cancers and skin conditions. The cancer formulation of the drug, known as PV-10, is currently undergoing clinical trials for melanoma and breast cancer. The company also has formulated a drug based on rose bengal for the treatment of eczema and psoriasis; this drug, PH-10, is currently in clinical trials as well.