Biopsy of conjunctival goblet cells may be carried out by pressing a piece of Millipore filter on the conjunctival surface. This can then be stained with PAS and hematoxylin and observed under the microscope after the filter has been cleared with oil. Either spots of mucous corresponding to the openings of the goblet cells are seen, or the filter adheres to the surface and pulls off one or more layers of epithelial cells and goblet cells. The procedure can be carried out on the unanesthetized eye and does not cause discomfort.