The use of antibody labeled with fluorescein to localize specific antigens in various tissue preparations was originally described by Coons.1 It has since been used as a laboratory means of rapid diagnosis in a variety of microbiological systems and for the study of disease pathogenesis in a number of conditions in which an antigen-antibody system is involved.2
In 1959 Biegeleisen3 used this technique in differentiating clinically similar skin and mucus lesions due to herpes simplex virus and nonherpetic agents. He demonstrated an excellent correlation between the presence of positive fluoresecent staining and the ability to isolate the herpes virus from the lesions.3 The clinical usefulness of this test as a rapid diagnostic tool in herpetic keratitis has been suggested by the preliminary studies of Kaufman4 and Vozza and Balducci.5
The direct technique of Coons is based on the specificity of the antigen-antibody reaction which