Light microscopy of control and KC corneas stained with PAS and Mayer's hematoxylin.

<p><b>a.</b> Control corneas showed uniform thickness multilayered epithelium in the central region, with increased stromal thickness towards the limbus. Blood vessels and undulating basal epithelium (asterisks) are only seen in the limbus region. <b>b.</b> In KC buttons, obvious epithelial thinning associated with stromal thinning is seen more centrally. <b>c to h.</b> Representative images at higher magnification show (c) control corneal epithelium and anterior stroma, (d) obvious epithelial thinning in the KC cone compared to the adjacent epithelium. (e, f) Enlarged basal epithelial cells and irregular Bowman’s layer (thinning and breaks, asterisks) are common features in KC specimens. In some KC specimens (g) evidence of incursion of stromal tissue between Bowman’s layer and the epithelium is seen (arrows). (h) A leukocyte is also seen in the KC basal epithelium, where stroma invaded between epithelium and Bowman’s layer (arrows). Epi: epithelium; bv: blood vessel; Adj: adjacent region; BL: Bowman’s layer.