Trial Information

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].