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Objective Assessment of Contact Lens Wear-Associated Conjunctival Squamous Metaplasia by Linear Measures of Cell Size, Shape and Nucleus-to-Cytoplasm Ratios

Purpose: To objectively assess the cell and nucleus dimensions of human bulbar conjunctival cells in female soft contact lens wearers to illustrate a method for assessment of the nucleus-to-cytoplasm ratio based on simple linear measures. Methods: Impression cytology samples were taken from the nasal side exposed bulbar conjunctiva surface from 12 young adult, white European females with a history of successful daily soft contact lens wear. A Millcell®-CM filter was used after topical anesthesia, which was stained with Giemsa. Color images of portions of the cells, in a monolayer at 200× magnification by light microscopy, were graded by the Nelson scale and then a projection overlay method was used to outline the cell and nucleus borders. The cell longest dimension (LONG), shorter dimension (SHORT), and the longest dimension of the nucleus (NUCLONG) were measured. A nucleus-to-cytoplasm N:C ratio was calculated from (LONG-NUCLONG)/NUCLONG. Results: Cells had appearances consistent with a grade 2 or 3 squamous metaplasia and were moderately enlarged (mean LONG ± SD of 46.0 ± 3.8 microm), only slightly elongated (mean LONG:SHORT ratio of 1.397 ± 0.101) and the nucleus size was consistently greater than normal (man 12.8 ± 1.3 microm). A calculation of N:C showed a relatively wide range of values with average values from 1:2.143 to 1:3.317 (for an overall mean of 2.675 ± 0.371). Conclusions: These studies further indicate that grade 2 to 3 squamous metaplasia of the exposed bulbar conjunctival cells is an expected consequence of soft contact lens wear. The cell enlargement is not associated with a significant change in cell shape (i.e., the LONG:SHORT ratio is little different from grade 0 cells) but is associated in a slight increase in nucleus size. The calculated N:C ratio based on linear measures is no higher than 1:5 and more likely closer to 1:2.5.