Morphological evaluation of normal human corneal epithelium

Purpose: The human corneal epithelium is usually described as a 50-mu m-thick layer of regular stratified squamous non-keratinized cells with a thickness of 5-7 cells. The purpose of this study is systemically to revisit the histopathological appearance of 100 corneas. Methods: 5-mu m-thick sections of corneas from 100 consecutively selected paraffin-embedded eyes were stained with hematoxylin-eosin and Periodic Acid-Schiff (PAS). All specimens were evaluated by light microscopy. The eyes were enucleated from patients with choroidal melanoma. Corneas were considered to be normal. Results: Ninety of 100 eyes were evaluated. The central epithelial, stromal and total corneal thickness was measured as 36.0 mu m, 618 mu m and 651 mu m, respectively, with a variation coefficient from 0.21 to 0.22. Pathological appearances were found in 27% of corneas, including thickened basement membrane and alterations in Bowman's membrane. No intraepithelial microcysts, as found in Meesmann corneal dystrophy, were observed. Conclusion: The total corneal thickness was higher than reported in in vivo studies and with a wider variation. This may be an effect of uncontrolled swelling and dehydration during preparation. The high number of pathological observations suggests that 'normal' eyes harbour and potentially accumulate considerable pathology.