Assessment of size and nucleo-cytoplasmic characteristics of the squamous cells of the corneal epithelium

Purpose: The aim was to objectively assess size, nucleus and nucleo-cytoplasmic ratio features of squamous cells from the corneal epithelium Methods: The corneas of recent post-mortem sheep eyes were either glutaraldehyde-fixed for transmission electron microscopy or impression cytology samples taken, glutaraldehyde-fixed and stained with Giemsa. From the specimens for impression cytology, a representative region was photographed from 12 different samples taken from the central region and 16 different samples taken from mid-peripheral regions of the corneal epithelium. Images were subjected to morphometry after overlays were generated. Results: Electron microscopy revealed a very distinctive stratified corneal epithelium with several superficial layers, confirming the squamous phenotype. Impression cytology from such superficial layers revealed a cell size of 60.1 ± 4.8μm, nucleus dimension of 12.3 ± 1.5μm, cell area of 2,419 ± 416μm² and nucleus area of 131 ± 31μm². A nucleo-cytoplasmic ratio based on nucleus-to-cell length had a mean of 0.207 ± 0.022, while a cytoplasm-to-nucleus length ratio was 3.975 ± 0.474. Estimates of the nucleo-cytoplasmic ratio based on areas had a mean value of 0.059 ± 0.011. Very similar results were found for mid-peripheral corneal epithelium. Conclusions: The results strongly indicate that the squamous phenotype of the superficial corneal epithelial cells is characterised by a large size, large nucleus and low nucleo-cytoplasmic ratio. These morphological characteristics show a notable resemblance to data obtained from impression cytological studies on human conjunctival epithelial cells showing severe squamous metaplasia.