Exfoliative Cytology
Exfoliative cytology has long been an important tool in differentiating human external ocular diseases after the important findings of Kimura and Thygeson (1955). To obtain cytologic specimens of the conjunctiva one has the option to biopsy the conjunctiva or do a conjunctival scraping. A conjunctival scraping can be done with various instruments as Cytobrush®Plus, Kimura spatula or a scalpel (Evans 2001), after or before the application of an anaesthetic agent. Topical anaesthesia is usually not necessary unless the cornea is scraped (Murphy 1988). The author has found that scraping of the conjunctiva in the canine with a scalpel blade was possible without any evidence of pain after or during the procedure. Debris should be removed from the conjunctival sac before scraping (Murphy 1988, Prasse and Winston 1989). A scraping should be done as early as possible in the course of the disease (Jégou and Liotet 1993-94); the scraped material is to be gently transferred to a microscopic slide. Different stains have been recommended for staining the scrapings as Giemsa (Kimura and Thygeson 1955), Diff-Quick® (Jégou and Liotet 1993-94), Gram (Murphy 1988) or Hemacolor (Evans 2001). If the presence of bacteria is suspected one slide should be stained with Gram's stain (Murphy 1988).
Neurophils predominate in acute and chronic bacterial conjunctivitis (Lavach et al 1977, Severin and Thrall 1981). In the non-diseased human eye neutrophils and lymphocytes are almost always present in the substantia propria or epithelium (Allansmith et al 1978). Ugomori et al (1991) found that "the presence of PMN's was well correlated with existence of rapid growing bacteria in conjunctivitis." In bacterial infection a considerable amount of bacteria may be found on the slide (Jégou and Liotet 1993-94).
The eosinophil is characteristic of an allergic condition (Kimura and Thygeson 1955), and not found in the substantia propria or conjunctival epithelium in normal human eyes (Allansmith et al 1978). The presence of one single eosinophil on the slide indicates allergic inflammation in the canine (Murphy 1988).
Mononuclear cells are predominant in viral conjunctivitis in humans (Kimura and Thygeson 1955). Large multi-nucleated epithelial cells are also seen in viral disease (Kimura and Thygeson 1955), but are not associated with any particular disease in the canine (Lavach et al 1977). In early canine distemper lymphocytes are the most common cell type (Severin and Thrall 1981), which is followed by a mononuclear cells response (Lavach et al 1977). Ernø (1964) found cytoplasmic inclusion bodies on exfoliative cytology of the nictitating membrane in dogs with canine distemper.
A great number of partly or fully keratinised epithelial cells may be found in keratoconjunctivitis sicca (Jégou and Liotet 1993-94), ectropion (Severin and Thrall 1981) or lagophthalmos (Murphy 1988). Care should be taken not to scrape the margin of the eyelids, as the margin normally contains keratinised cells (Severin and Thrall 1981). The squamous cells often contain melanin granules (Prasse and Winston 1989). Increased numbers of goblet cells will be found in chronic conjunctivitis and keratoconjunctivitis sicca (Severin and Thrall 1981). Fungi may be found on exfoliative cytology (Murphy 1988), and identification may be aided by application of Calcoflour or Ink-Postassium Hydroxide (Arffa et al 1985).
This page was authored by T. F. Evans October 2000.
