fluorescein Fluorescein: A phthalic indicator dye that appears yellow-green in normal tear film and bright green in a more alkaline medium such as the aqueous humor.. fluorescein (lactone form) : A xanthene dye that is highly fluorescent, detectable even when present in minute quantities. Used forensically to detect traces of blood, in analytical chemistry as an indicator in silver nitrate titrations and in microscopy. | 2.06 | 1 | 0 | 2-benzofurans; gamma-lactone; organic heteropentacyclic compound; oxaspiro compound; polyphenol; xanthene dye | fluorescent dye; radioopaque medium |