Vital dye used to assess the integrity of cornea and conjunctiva. Fluorescein stains the tear film and depending on the tear film layer thickness, more or less green fluorescence will be observed. A cobalt blue filter in the illumination system of the slit lamp biomicroscope is necessary to excite the dye to a green fluorescence. A yellow filter in or in front of the viewing system of the slit lamp biomicroscope will enhance the visibility of any fluorescent staining.
High molecular weight fluorescein dye used to assess static and dynamic lens fit of hydrogel lenses. A cobalt blue excitement filter and a yellow enhancement filter are necessary in the illumination and observation systems respectively. For optimal visibility, the dye should be instilled on the back surface of the contact lens before insertion of the lens. Minimal dosage is of importance because higher amounts of the dye cause stinging and burning which results in excessive tearing and therefore a false appearance of the lens fit will be observed.