calceinA chelating agent which fluoresces brightly in the presence of bound Ca2+. The acetomethoxy derivative of calcein is used as a temporary label to test cell viability: once the calcein acetomethoxy complex enters healthy cells, intracellular esterases remove the acetomethoxy group, which fluoresces bright green—apparently in protest—something that dead cells, which lack esterases, cannot do.
A staining agent similar to fluorescein but with a much higher molecular weight (710) and which is less readily absorbed by soft contact lens material. It is used in the fitting of soft or hybrid lenses (e.g. a piggyback lens). It stains a pale yellow-brown. However, it is not recommended for use with high water contact lenses (above 65%).