Background: There is some difference of opinion in the literature about the nature of fluorescein staining of the epithelial surface. Most authors support the view that fluorescein staining is due to drop out of cells and pooling of fluorescein in the footprint. Others believe that fluorescein fills intercellular spaces. Others suggest that cells themselves stain with fluorescein.
Methods: Rabbit corneas were stained with fluorescein and examined with the biomicroscope and later with a higher magnification epifluorescent microscope following excision.
Results: Fluorescein staining was shown to be due to staining of individual cells. No evidence was found to support the contention that fluorescein resides in areas of cell drop out, or that staining was due to filling of intercellular spaces. Micropunctate staining is shown to be due to staining of cells in an optimum manner, which is referred to as hyperfluorescence.
Conclusions: The recognition that fluorescein stains cells, even in the case of epithelial abrasion, allows reinterpretation of many staining phenomena, including "salt and pepper" staining.