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, and is used therapeutically as a diagnostic aid in corneal injuries and corneal trauma. It has been approved by FDA for use in externally applied drugs and cosmetics. (From Merck Index, 12th ed; American Medical Association Drug Evaluations; 1995, p2275).