Pilot study on the use of impression cytology specimens for quantitative assessment of the surface area of bulbar conjunctival cells

Purpose. To assess whether impression cytology samples could be used to assess cell conjunctival cell surface areas, and to obtain an estimate of these for normal appearing cells vs. those with squamous metaplasia, Methods. Small sheets of nasal bulbar conjunctival cells (c. 0.03 mm(2)) were obtained from 17 subjects aged 25 to 78 years by manual application of a 0.45 mu m Millipore filter without topical anesthetic. Outlines of cells, visible as a rarefaction of the general cell cytoplasmic staining, were made on an optical overlay and then planimetry was carried out. Results. Reasonable estimates (with +/-2.5%) of the average cell area can be obtained from samples containing contiguous sets of 100 cells. From 14 separate samples of normal cells [subjective assignment of nucleus:cytoplasm (N:C) ratios of 1:1 to 1:2], cell surface area values ranged from 11 to 426 mu m(2), with an overall average value of 108 +/- 43 mu m(2). Samples from individuals with symptoms suggestive of borderline dry eye tended to have slightly higher proportions of larger cells (so increasing the average cell area), and there was a trend for samples from older individuals to contain more smaller cells (so decreasing the average cell area). In marked contrast, cells showing evidence of squamous metaplasia and with N:C ratios of 1:6 or higher were found to have an average area of 543 +/- 76 mu m(2) (range 310 to 1529 mu m(2)). Conclusions. Morphometry of impression cytology specimens is possible. The average cell size in normal individuals is considerably smaller than previously reported (108 vs. 585 mu m(2)), but this is consistent with a range of studies on animal tissue using scanning electron microscopy.