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 6 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 μm versus 22.4 ± 2.9 μm, 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 μm versus 10.0 ± 1.1 μm (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 long-term 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.