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.
