Ocular surface impression cytology

Impression cytology, either using cellulose acetate strips or the Biopore membrane device, is a simple, noninvasive technique that aids in the diagnosis of several disorders of the ocular surface. These disorders include ocular surface squamous neoplasia, dry eye syndrome, limbal stem-cell deficiency, specific viral infections, vitamin A deficiency, allergic disorders, conjunctival melanosis, and malignant melanoma. Another advantage is the preservation of limbal stem cells, which occur in the basal layer of the limbal epithelium and are responsible for renewal of the corneal epithelium. The Biopore membrane device is particularly user friendly, with little expertise required and adequate specimens obtained in a very high percentage of cases. The most common applications in diagnostic ocular pathology are:(i) primary diagnosis and follow-up of ocular surface squamous neoplasia, including after therapy with topical mitomycin C. The sensitivity is high (78-87%); and (ii) dry eye syndrome where squamous metaplasia and/ or hyperkeratosis are noted. Certain limitations of the technique for diagnosis of squamous neoplasia include the fact that dysplasias are often keratinizing and may yield very few or even no dysplastic cells with impression cytology. Secondly, no definite cytologic criteria reliably distinguish invasive SCC of ocular surface from in situ disease. Other applications include the rapid specific diagnosis of ocular surface infections with herpes simplex, adeno-, and varicella zoster viruses. Impression cytology samples may also be used to obtain mRNA, cells for phenotyping by flow cytometry, and proteins for Western blotting for research studies.