Using Impression Cytology to Observe the Cytological Changes of Ocular Surface Cells in Various Ocular Surface Disorders

Impression cytology is a simple, noninvasive technique that has been widely used to aid in the diagnosis of several disorders of the ocular surface. The first use of impression cytology specimens for diagnosis of ocular surface squamous neoplasia was reported in France in 1954 by Larmande and Timsit. [1] In the English language literature, Egbert et al [2] in 1977 documented the use of cellulose acetate filters to detect goblet cell density in patients with the dry eye syndrome. Traditionally, the cytology specimens were obtained by pressing cellulose acetate (Millipore) filters onto the surface of the globe, then air-dried and stained with PAS. [2] The procedure is usually painless even without anesthesia. The filters remove 1 to 3 superficial cell layers of conjunctiva and cornea.

Since its first applications in ocular surface squamous neoplasia and dry eye syndrome, [1,2] the use of impression cytology has expanded to include the staging of conjunctival squamous metaplasia, [3,4] diagnosis of ocular surface squamous neoplasia, [5-11] and follow-up of ocular surface squamous neoplasia after topical mitomycin-C, [10] limbal stem-cell deficiency, [12,13] specific viral infections, [14-16] vitamin A deficiency, [17,18] epithelial cell storage disorders, [19] allergic disorders, [19] conjunctival melanosis and malignant melanoma, [20] and psoriasis [21]. The technique has the additional advantage of preserving limbal stem cells, which occur in the basal layer of the limbal epithelium and are responsible for renewal of the corneal epithelium throughout life. Since ocular surface squamous neoplasia preferentially involves the limbus, limbal stem cells are potentially reduced in number with each surgical biopsy. The progressive loss of limbal stem cells results in limbal stem-cell deficiency, conjunctivalization of the cornea with corneal opacity. Thus, impression cytology offers a safer alternative to diagnosis than repeated biopsies.

With impression cytology, the morphology of the corneal and conjunctival epithelial cells, their staining behavior, and nuclear/cytoplasmic ratio could be observed in detail. Other important characteristics such as goblet cell density, the degree of keratinization of the epithelial cells, the quality of the cell-to-cell cohesion, and the condensation of the nuclear chromatin could also be detected through proper specimens. [3, 22-26] Furthermore, with the improvement of immunocytochemical staining and confocal microscopy, specimens of impression cytology can be further analyzed for complicated ocular disorder such as cytokeratins 3 and 19 are useful in classification of limbal stem cell deficiency [27] and mucin secretion of goblet cells can be evaluated by confocal microscopy [28].