Objective assessment of squamous metaplasia of conjunctival epithelial cells as associated with soft contact lens wear versus non-lens wearers

Purpose: To objectively assess the morphology of superficial conjunctival surface cells showing squamous metaplasia as seen in contact lens wearers. Methods: Impression cytology samples were taken from interpalpebral bulbar conjunctiva from 23 young adult white European women with an average of ± years of successful daily soft contact lens wear and 23 non-contact-lens-wearing women of the same age. Cell images were graded, and cell and nuclear dimensions and areas were measured by planimetry. Results: The contact lens wearers had a mean squamous metaplasia grade (Nelson) of 2.74 versus 0.35 for the non-lens wearers, with the cell longest dimension (LONG) being 54.4 ± 5.6 mm versus 22.4 6 2.9 mm, respectively (P < 0.001). Similar differences were found for the cell shortest dimension (SHORT) and cell area values (P < 0.001). The cell nuclei in the contact lens wearers, based on measures of cell nuclear length (NUCLONG), were 12.7 ± 1.7 mm versus 10.0 ± 1.1 mm (P < 0.001) with no evidence of pyknotic (shrunken) nuclei. The nucleo-cytoplasmic ratios had mean values of 3.603 versus 1.282 for the cytoplasm-to-nucleus length (CYT/NUC length) ratio, and 0.075 and 0.319 for the NU/CYT length ratio for contact lens wearers and non-wearers, respectively. Conclusions: As squamous metaplasia develops, at least in longterm soft contact lens wearers, the conjunctival surface cells become considerably enlarged, but the nuclear size of these cells also increases, rather than showing signs of pyknosis.