A simple, non-invasive means of studying cells on the conjunctiva. It is carried out by pressing a small piece of special filter paper against the anaesthetized bulbar conjunctiva for a few seconds, after which it is removed. The operation is usually repeated two or three times over the same area. The filter paper is then fixed to a glass slide, stained and examined under a microscope. Mucin, goblet cells and many epithelial cells which stain in different colours, depending on the dyes used, can be assessed and facilitate the diagnosis of many external eye diseases, such as keratoconjunctivitis sicca and xerophthalmia. See Gram stain.